Hi All

I have a mount controller that has the ability for me to enter a
custom tracking rate for tracking comets. Could somebody tell me what
is the best way to calculate the information given to me by TheSky6
into the format required for my controller.

TheSky6 RA rate (arcsec/sec) -0.1690
TheSky6 Dec rate (arcsec/sec) 0.0546

My controller requires the format of

RA = Min - Sec - 1/100 sec per minute of time
DEC = Deg - Min - sec/minute of time

Hope somebody can help

Regards
-Paul

Out of curiosity, which controller are you using?

Seconds in sidereal day = ~86164.

Here's an example of how to set the Temma's custom tracking rates via the
command protocols and my driver.  It may help you figure out what you need.



      1.      From TheSKy6, click Edit > Find.

2.      Enter desired object in the Find text box, and then click the Find
button.

3.      On the Object Information dialog box report note the RA Rate
(arcseconds/sec) and the Dec Rate (arcseconds/sec). For this example ra =
-0.1690 and dec = 0.0546

4.      Compute the RA adjustment using the following equation: (TheSky6's RA
Rate * (86164/15)) * -1. For this example, the value is ~970.

5.      Compute the Dec adjustment using the following equation: (TheSky6's Dec
Rate * (86164/60)) * -1. For this example, the value is ~-78.

6.      Enter both values, then click Set.



Regards,
Chuck Faranda
http://ccdastro.com


   ----- Original Message -----
   From: paul_lx200gps
   To: ccd-newastro@yahoogroups.com
   Sent: Sunday, March 01, 2009 6:44 AM
   Subject: [ccd-newastro] Custom Tracking Rates


   Hi All

   I have a mount controller that has the ability for me to enter a
   custom tracking rate for tracking comets. Could somebody tell me what
   is the best way to calculate the information given to me by TheSky6
   into the format required for my controller.

   TheSky6 RA rate (arcsec/sec) -0.1690
   TheSky6 Dec rate (arcsec/sec) 0.0546

   My controller requires the format of

   RA = Min - Sec - 1/100 sec per minute of time
   DEC = Deg - Min - sec/minute of time

   Hope somebody can help

   Regards
   -Paul




[Non-text portions of this message have been removed]

Hi

The controller is the Pulsar controller for the G41/G42 mounts.

-Paul

Can a good quality T-shirt flat be taken at the following conditions:

1) During the day pointed at the clear sky?
2) During the day pointed at solid cloud cover?
3) Same as above but at dusk?
4) During the day pointed at the ground?
5) Since I am using a dew shield the cloth is wrapped around the end
of the dew shield, do I need another made-up dew shield out side the
T-shirt to avoid light gradients hitting the t-shirt?

Just trying to produce best results...

Also, while I have Ron's books and they provide lots of good info, is
there a good summarized workflow proceedure that details the process
from taking the images to final image processing sequence?

Thanks!

--- In ccd-newastro@yahoogroups.com, "sc02492" <sc02492@...> wrote:
>
> Hi- be careful of the units.  Gain is typically expressed in units
of
> electrons per ADU.  So for a full well of 50,000 electrons, and
gain
> of 0.8 electrons/ADU in your example, this means 50,000/0.8 = 62500
> ADU at saturation (i.e., divide, not multiply).  30% of 62500 would
> be 18,750 ADU.  Always start from knowing the full well capacity
(in
> electrons) and the gain, and you can figure it out.  Don't assume
> that the max ADU of your brightest star (65535) represents true
> saturation (it may be close, but will usually represent
> oversaturation, depending upon the full well and gain).  In other
> words, you could easily be at saturation with an ADU of 45,000,
> depending upon your camera specs.
>
> Steve
>
> Steve Cannistra
> http://www.starrywonders.com
>
> --- In ccd-newastro@yahoogroups.com, "Robert Malinowski"
> <robt.wndy@> wrote:
> >
> > Ok, let me see if I have this right....
> >
> > I measure the max pixel value of the brightest star..lets say
it's
> > 65535..this would mean ( at 30% ) a flat adu of 19660 ..(max
times
> > 30%)
> >
> > Now, suppose my camera's spec's say it has a 50000e- Full Well,
and
> a
> > Gain of 0.8 unbinned...1.6 binned.....
> >
> > These would work out to:(at 30%)..
> >
> > Saturation Level: Full Well*Gain
> > Flat adu (at 30%): Saturation Level * 0.3
> >
> > thus
> >
> > 50000*0.8 * 0.3 = 12000adu for Unbinned
> >         and
> > 50000*1.6 * 0.3 = 24000adu for Binned
> >
> > Right?
> >
> > Robert
> >
> >
> >
> >
> > --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@>
> > wrote:
> > >
> > > Rick's advice on ADU for 2x2 was correct. The idea behind the
ADU
> > for
> > > for any flat isn't a specific number; it's some proportion of
the
> > > saturation value (or the non-linear value for ABG chips).
> > >
> > > So the first thing to determine is the saturation level. You
can
> > > calculate it (full-well capacity times the gain - this is not
> > always
> > > known for bin modes, however), but that is only going to close.
> The
> > > actual saturation value will vary a little from one camera to
the
> > next.
> > > If you look at the brightness value of saturated pixels (e.g.,
> > bright
> > > stars), this will give you a more accurate (but still slightly
> > fuzzy,
> > > because it will vary a little from pixel to pixel) saturation
> value.
> > >
> > > Depending on a variety of choices, you want to have an average
> flat
> > > value in the 30% to 75% of saturation range. For chips with
very
> > linear
> > > response, you can go up to 75% of saturation to improve your
flat
> > S/N.
> > > For anti-blooming chips with average non-linear response (non-
> > linear
> > > because anti-blooming doesn't wait until saturation to start
> > draining
> > > excess charge; it starts long before that), you want 30-50% of
> > > saturation. (You would need to take a series of exposures of
the
> > same
> > > star to determine where the non-linear point clicks in; if you
> > aren't
> > > doing this, then your choice of ADU becomes less well
determined.
> > > However, anything in the 30-50% range is likely to work
> reasonably
> > well
> > > unless you have critical requirements.)
> > >
> > > The concept of 'imaging with the CCD vertical' doesn't really
> > exist. The
> > > chip is read out exactly the same way every time. The rotation
of
> > the
> > > image has no effect whatsoever on how the chip is read.
> > >
> > > Since the chip is read the same way every time, there is
nothing
> > for you
> > > to worry about with respect to this aspect.
> > >
> > > If you do rotate the camera, however, sometimes vignetting may
> > change.
> > > Some telescopes will give you very similar flats no matter how
> the
> > > camera is rotated; some will not. The only way to know is to
take
> > flats
> > > at different rotation angles and compare them (e.g., subtract
one
> > from
> > > the other and see what's left over).
> > >
> > > It's nice to prepare in advance, but there are many things you
> > won't
> > > know until you try them both ways. <G>
> > >
> > > Ron Wodaski
> > >
> > >
> > >
> > > Robert Malinowski wrote:
> > > > Thanks Rick...I saw recent talk relating to this, thanks for
> your
> > > > explanation...
> > > > Still, what about The ADU setting for 2x2 flats?? same as
1x1 ??
> > > > Also, if imaging with the ccd vertical, will my image
> processing
> > > > program (maximdl), orient the darks and flats automatically
> > during
> > > > calibration(reduction)??
> > > > Robert
> > > >
> > > >
> > > > --- In ccd-newastro@yahoogroups.com, "Rick Wiggins"
> > <rickwiggins@>
> > > > wrote:
> > > >
> > > >> Hi,
> > > >> Seems this question comes up often lately.
> > > >>
> > > >> Darks: Darks should be taken for each different binning,
> > > >>
> > > > temperature
> > > >
> > > >> and time. Darks for a given binning can be scaled for time
and
> > to
> > > >> some extent can be scaled for temperature; however, this
does
> > not
> > > >> work as well as for time as it is not as linear. It is
always
> > > >>
> > > > better
> > > >
> > > >> to take darks longer and scale down than the reserse. Best
> case
> > is
> > > >> to take them at teh exact temp and time.
> > > >>
> > > >> Flats: Flats can be scaled for binnning. Yesterday, Stan
Moore
> > > >> pointed out that scaling the binning of flats is not perfect
> as
> > it
> > > >> does not model well the pixel to pixel variation of the
chip,
> > but
> > > >> this is a minor effect in my experience. I take my flats at
> the
> > > >>
> > > > same
> > > >
> > > >> temperature as my darks, but this is probably not necessary.
> If
> > you
> > > >> flats are long in duration, you may want to make custom
darks
> > for
> > > >> the flats and dark subtract the flats. I prefer my flats at
25-
> > 50%
> > > >> of full well ADU.
> > > >>
> > > >> Bias: Take these at the same temperature as the darks
> (probably
> > not
> > > >> critical, but I do it anyway) and do not try to scale the
> > binning
> > > >> for your bias files.
> > > >>
> > > >> Ron Wodaski has a nice discussion of these principles in his
> > book.
> > > >> Stan Moore has posted many useful tips on the SBIG Group
over
> > the
> > > >> years and he has some good stuff in the CCDStack help files.
> > > >>
> > > >> Hope this helps,
> > > >> Rick
> > > >>
> > > >>
> > > >>
> > > >
> > > >
> > > >
> > > >
> > > > ------------------------------------
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
>

Hi Hilary -- Yes, I was asking the question to find the most time
efficient way to collect the data if in fact it makes no difference in
the final quality of the combined data.  It seems to me that with "A",
one is throwing out some data just to equalize the filter differences.
  "B" looks like the best in order to make life easier with the dark
library. I usually use one of the statistical combining methods like
SD Mask or sigma clip.  Using method "B" with one of these, would the
combine ratio be 1:1:1?

Joe

--- In ccd-newastro@yahoogroups.com, "Hilary Jones" <hilaryyahoo3@...>
wrote:
>
> If you use dark frame scaling, all three options work well enough.
> But if you want to use darks that are exactly the same length as your
> exposures, then options A and B certainly are easier.
>
> Options B and C tend to equalize the amount of shot noise in all
> three channels, so I would probably not use option A.  (Actually
> truth be known, I use option A all the time because it's easier on my
> brain!)
>
> With option C, you equalize the read noise better than option B.  My
> gut feeling is that read noise isn't an issue, but your mileage might
> vary.
>
> With option B, you have to be careful how you combine the images.  If
> you average them, then the weights will be 1.2:1: 1.8, but if you sum
> them, then the weights will be 1:1:1.
>
> There's a caveat that you probably only have a certain amount of time
> available to do your exposures; so if the total time is 300 minutes,
> option C would actually use 9, 7.5, and 13.5 minute exposures, while
> option B might require 9, 8, and 13 exposures, depending on how you
> want to round the numbers.  I haven't figured out if this has any
> real bearing on the question you asked, but I thought I would mention
> it anyhow.
>
> Hilary
>
> --- In ccd-newastro@yahoogroups.com, "Joe Morris" <joemorris@>
> wrote:
> >
> > If you have a set of RGB filters that a G2V star calibration gave
> you
> > the following weights,R= 1.2, G=1, B=1.8, which of the following
> would
> > be the preferred senerio for data collection and stacking?   Maybe
> it
> > makes no difference which senerio is chosen although it would be
> easier
> > to maintain a  dark calibration library with senerio A or B.
> >
> > A.  Take 10  ten minute images of each R,G,B and combine them
> using
> >   the 1.2:1: 1.8 weights
> >
> > B.  Take 12 ten minute R images, 10 ten minute G images, and 18 ten
> B
> >  images and combine them using 1:1:1 weights
> >
> > C.  Take 10 twelve minute R images, 10 ten minute G images, and 10
> > eighteen G images and combine them using 1:1:1 weights
> >
> > Joe
> >
>

I have tried many of these techniques over the years and have come to
the conclusion that the very best and cost-effective flats are still
sky flats obtained at either dusk or dawn.  The trick is to know
where to point the scope at dusk or dawn to minimize the gradient
caused by the setting or rising sun, respectively.  This is
automatically calculated for you, and the scope is pointed at this
optimal location, using automation software like CCDAutopilot or CCD
Commander.  The benefit of using such software, in addition to being
able to sleep, is that it will point your scope to the optimal
position and then continually adjust the exposure time to maintain a
constant target ADU value for your flats.

If you're interested in a nice paper that approaches the problem of
sky flats quantitatively, you might check this one out:

http://adsabs.harvard.edu/abs/1996PASP..108..944C

As I do not have much experience with the T shirt method, beyond not
being as impressed with it compared to sky flats, will let others
chime in...

Steve

Steve Cannistra
http://www.starrywonders.com



--- In ccd-newastro@yahoogroups.com, "kurt102602" <kurt1026@...>
wrote:
>
> Can a good quality T-shirt flat be taken at the following
conditions:
>
> 1) During the day pointed at the clear sky?
> 2) During the day pointed at solid cloud cover?
> 3) Same as above but at dusk?
> 4) During the day pointed at the ground?
> 5) Since I am using a dew shield the cloth is wrapped around the
end
> of the dew shield, do I need another made-up dew shield out side
the
> T-shirt to avoid light gradients hitting the t-shirt?
>
> Just trying to produce best results...
>
> Also, while I have Ron's books and they provide lots of good info,
is
> there a good summarized workflow proceedure that details the
process
> from taking the images to final image processing sequence?
>
> Thanks!
>
> --- In ccd-newastro@yahoogroups.com, "sc02492" <sc02492@> wrote:
> >
> > Hi- be careful of the units.  Gain is typically expressed in
units
> of
> > electrons per ADU.  So for a full well of 50,000 electrons, and
> gain
> > of 0.8 electrons/ADU in your example, this means 50,000/0.8 =
62500
> > ADU at saturation (i.e., divide, not multiply).  30% of 62500
would
> > be 18,750 ADU.  Always start from knowing the full well capacity
> (in
> > electrons) and the gain, and you can figure it out.  Don't assume
> > that the max ADU of your brightest star (65535) represents true
> > saturation (it may be close, but will usually represent
> > oversaturation, depending upon the full well and gain).  In other
> > words, you could easily be at saturation with an ADU of 45,000,
> > depending upon your camera specs.
> >
> > Steve
> >
> > Steve Cannistra
> > http://www.starrywonders.com
> >
> > --- In ccd-newastro@yahoogroups.com, "Robert Malinowski"
> > <robt.wndy@> wrote:
> > >
> > > Ok, let me see if I have this right....
> > >
> > > I measure the max pixel value of the brightest star..lets say
> it's
> > > 65535..this would mean ( at 30% ) a flat adu of 19660 ..(max
> times
> > > 30%)
> > >
> > > Now, suppose my camera's spec's say it has a 50000e- Full Well,
> and
> > a
> > > Gain of 0.8 unbinned...1.6 binned.....
> > >
> > > These would work out to:(at 30%)..
> > >
> > > Saturation Level: Full Well*Gain
> > > Flat adu (at 30%): Saturation Level * 0.3
> > >
> > > thus
> > >
> > > 50000*0.8 * 0.3 = 12000adu for Unbinned
> > >         and
> > > 50000*1.6 * 0.3 = 24000adu for Binned
> > >
> > > Right?
> > >
> > > Robert
> > >
> > >
> > >
> > >
> > > --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@>
> > > wrote:
> > > >
> > > > Rick's advice on ADU for 2x2 was correct. The idea behind the
> ADU
> > > for
> > > > for any flat isn't a specific number; it's some proportion of
> the
> > > > saturation value (or the non-linear value for ABG chips).
> > > >
> > > > So the first thing to determine is the saturation level. You
> can
> > > > calculate it (full-well capacity times the gain - this is not
> > > always
> > > > known for bin modes, however), but that is only going to
close.
> > The
> > > > actual saturation value will vary a little from one camera to
> the
> > > next.
> > > > If you look at the brightness value of saturated pixels
(e.g.,
> > > bright
> > > > stars), this will give you a more accurate (but still
slightly
> > > fuzzy,
> > > > because it will vary a little from pixel to pixel) saturation
> > value.
> > > >
> > > > Depending on a variety of choices, you want to have an
average
> > flat
> > > > value in the 30% to 75% of saturation range. For chips with
> very
> > > linear
> > > > response, you can go up to 75% of saturation to improve your
> flat
> > > S/N.
> > > > For anti-blooming chips with average non-linear response (non-
> > > linear
> > > > because anti-blooming doesn't wait until saturation to start
> > > draining
> > > > excess charge; it starts long before that), you want 30-50%
of
> > > > saturation. (You would need to take a series of exposures of
> the
> > > same
> > > > star to determine where the non-linear point clicks in; if
you
> > > aren't
> > > > doing this, then your choice of ADU becomes less well
> determined.
> > > > However, anything in the 30-50% range is likely to work
> > reasonably
> > > well
> > > > unless you have critical requirements.)
> > > >
> > > > The concept of 'imaging with the CCD vertical' doesn't really
> > > exist. The
> > > > chip is read out exactly the same way every time. The
rotation
> of
> > > the
> > > > image has no effect whatsoever on how the chip is read.
> > > >
> > > > Since the chip is read the same way every time, there is
> nothing
> > > for you
> > > > to worry about with respect to this aspect.
> > > >
> > > > If you do rotate the camera, however, sometimes vignetting
may
> > > change.
> > > > Some telescopes will give you very similar flats no matter
how
> > the
> > > > camera is rotated; some will not. The only way to know is to
> take
> > > flats
> > > > at different rotation angles and compare them (e.g., subtract
> one
> > > from
> > > > the other and see what's left over).
> > > >
> > > > It's nice to prepare in advance, but there are many things
you
> > > won't
> > > > know until you try them both ways. <G>
> > > >
> > > > Ron Wodaski
> > > >
> > > >
> > > >
> > > > Robert Malinowski wrote:
> > > > > Thanks Rick...I saw recent talk relating to this, thanks
for
> > your
> > > > > explanation...
> > > > > Still, what about The ADU setting for 2x2 flats?? same as
> 1x1 ??
> > > > > Also, if imaging with the ccd vertical, will my image
> > processing
> > > > > program (maximdl), orient the darks and flats automatically
> > > during
> > > > > calibration(reduction)??
> > > > > Robert
> > > > >
> > > > >
> > > > > --- In ccd-newastro@yahoogroups.com, "Rick Wiggins"
> > > <rickwiggins@>
> > > > > wrote:
> > > > >
> > > > >> Hi,
> > > > >> Seems this question comes up often lately.
> > > > >>
> > > > >> Darks: Darks should be taken for each different binning,
> > > > >>
> > > > > temperature
> > > > >
> > > > >> and time. Darks for a given binning can be scaled for time
> and
> > > to
> > > > >> some extent can be scaled for temperature; however, this
> does
> > > not
> > > > >> work as well as for time as it is not as linear. It is
> always
> > > > >>
> > > > > better
> > > > >
> > > > >> to take darks longer and scale down than the reserse. Best
> > case
> > > is
> > > > >> to take them at teh exact temp and time.
> > > > >>
> > > > >> Flats: Flats can be scaled for binnning. Yesterday, Stan
> Moore
> > > > >> pointed out that scaling the binning of flats is not
perfect
> > as
> > > it
> > > > >> does not model well the pixel to pixel variation of the
> chip,
> > > but
> > > > >> this is a minor effect in my experience. I take my flats
at
> > the
> > > > >>
> > > > > same
> > > > >
> > > > >> temperature as my darks, but this is probably not
necessary.
> > If
> > > you
> > > > >> flats are long in duration, you may want to make custom
> darks
> > > for
> > > > >> the flats and dark subtract the flats. I prefer my flats
at
> 25-
> > > 50%
> > > > >> of full well ADU.
> > > > >>
> > > > >> Bias: Take these at the same temperature as the darks
> > (probably
> > > not
> > > > >> critical, but I do it anyway) and do not try to scale the
> > > binning
> > > > >> for your bias files.
> > > > >>
> > > > >> Ron Wodaski has a nice discussion of these principles in
his
> > > book.
> > > > >> Stan Moore has posted many useful tips on the SBIG Group
> over
> > > the
> > > > >> years and he has some good stuff in the CCDStack help
files.
> > > > >>
> > > > >> Hope this helps,
> > > > >> Rick
> > > > >>
> > > > >>
> > > > >>
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > ------------------------------------
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > > [Non-text portions of this message have been removed]
> > > >
> > >
> >
>

SD Mask and sigma clipping are just fancy ways of doing averages,  so
the weights should be 1.2:1: 1.8.

Hilary

  --- In ccd-newastro@yahoogroups.com, "Joe Morris" <joemorris@...>
wrote:
>
> Hi Hilary -- Yes, I was asking the question to find the most time
> efficient way to collect the data if in fact it makes no difference
in
> the final quality of the combined data.  It seems to me that
with "A",
> one is throwing out some data just to equalize the filter
differences.
>  "B" looks like the best in order to make life easier with the dark
> library. I usually use one of the statistical combining methods like
> SD Mask or sigma clip.  Using method "B" with one of these, would
the
> combine ratio be 1:1:1?
>
> Joe
>
> --- In ccd-newastro@yahoogroups.com, "Hilary Jones" <hilaryyahoo3@>
> wrote:
> >
> > If you use dark frame scaling, all three options work well
enough.
> > But if you want to use darks that are exactly the same length as
your
> > exposures, then options A and B certainly are easier.
> >
> > Options B and C tend to equalize the amount of shot noise in all
> > three channels, so I would probably not use option A.  (Actually
> > truth be known, I use option A all the time because it's easier
on my
> > brain!)
> >
> > With option C, you equalize the read noise better than option B.
My
> > gut feeling is that read noise isn't an issue, but your mileage
might
> > vary.
> >
> > With option B, you have to be careful how you combine the
images.  If
> > you average them, then the weights will be 1.2:1: 1.8, but if you
sum
> > them, then the weights will be 1:1:1.
> >
> > There's a caveat that you probably only have a certain amount of
time
> > available to do your exposures; so if the total time is 300
minutes,
> > option C would actually use 9, 7.5, and 13.5 minute exposures,
while
> > option B might require 9, 8, and 13 exposures, depending on how
you
> > want to round the numbers.  I haven't figured out if this has any
> > real bearing on the question you asked, but I thought I would
mention
> > it anyhow.
> >
> > Hilary
> >
>

Ron/et. al.--What is the small yellow circle that shows up around a
bright star or small galaxy during AutomapperII runs?  I see it in
all/most of the CCDSoft5 images during the mapping runs.  Just curious
as I do not recall seeing it before?

Thanks,
David
www.cherrymountainobservatory.com

I'm not 100% sure, but I think that the circle is used to indicate
moving objects like asteroids.

Ron Wodaski



David Plesko wrote:
> Ron/et. al.--What is the small yellow circle that shows up around a
> bright star or small galaxy during AutomapperII runs?  I see it in
> all/most of the CCDSoft5 images during the mapping runs.  Just curious
> as I do not recall seeing it before?
>
> Thanks,
> David
> www.cherrymountainobservatory.com
>
>
>
>
> ------------------------------------
>
>
>
>
>


[Non-text portions of this message have been removed]

I'd enjoy hearing from people who have used the Meade DSI Pro II and
the Meade software that utilizes Drizzle.  What worked, what didn't,
and what tips might you offer?

Regards, Red

Would someone please take a look at this photo
<http://astronomy.mdodd.com/files/offset_diffraction_rings.jpg> and
offer an opinion about it?

I'm trying to check the collimation of my TMB-130SS APO 910mm FL f/7).
Seeing tonight was terrible, so I didn't attempt any adjustments --
just took some diffraction-ring photos.

The photo illustrates what I saw visually in a 3.5mm eyepiece.
Starting with an in-focus star (Elnath, nearly straight up in the sky)
I slowly moved the Feather Touch electric focuser outward to defocus
the star. As the star went out of focus, the diffraction rings began
to form, but they were not concentric with the star -- they formed off
to one side, as seen in the photo.

The bright spot at the 4:00 position is the star, and the bright halo
surrounds the outermost diffraction rings.

I'm very puzzled by this behavior, and wonder if it represents a
defective telescope or if something in my technique caused the offset
pattern. The star was very well centered in the eyepiece (there was
enough moon glow to easily see the eyepiece FOV). The camera was
securely mounted on a bracket attached to the eyepiece, so it didn't move.

I always thought diffraction rings form concentrically around the
star. Seeing was too poor to even see the inner diffraction rings, so
I don't know what they look like. What do the experts say about the
offset rings? Thanks in advance.

Mike
-----

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com

Mike, offset diffraction rings usually indicate miscollimation. If
the image appeared stable and the center hot spot didn't move around
due to poor seeing, this would indicate a collimation error.

I'm not so sure that your image actually shows difraction rings --
possibly just some reflections or distortions due to seeing/tube
currents.

Here's a shot of another F/7 refractor defocused star (with some
admittedly dusty camera!):

http://pk.darkhorizons.org/tmp/refractor.jpg

Regards,

       -Paul

--- In ccd-newastro@yahoogroups.com, "Mike Dodd" <mike@...> wrote:
>
> Would someone please take a look at this photo
> <http://astronomy.mdodd.com/files/offset_diffraction_rings.jpg> and
> offer an opinion about it?
>
> I'm trying to check the collimation of my TMB-130SS APO 910mm FL
f/7).
> Seeing tonight was terrible, so I didn't attempt any adjustments --
> just took some diffraction-ring photos.
>
> The photo illustrates what I saw visually in a 3.5mm eyepiece.
> Starting with an in-focus star (Elnath, nearly straight up in the
sky)
> I slowly moved the Feather Touch electric focuser outward to
defocus
> the star. As the star went out of focus, the diffraction rings
began
> to form, but they were not concentric with the star -- they formed
off
> to one side, as seen in the photo.
>
> The bright spot at the 4:00 position is the star, and the bright
halo
> surrounds the outermost diffraction rings.
>
> I'm very puzzled by this behavior, and wonder if it represents a
> defective telescope or if something in my technique caused the
offset
> pattern. The star was very well centered in the eyepiece (there was
> enough moon glow to easily see the eyepiece FOV). The camera was
> securely mounted on a bracket attached to the eyepiece, so it
didn't move.
>
> I always thought diffraction rings form concentrically around the
> star. Seeing was too poor to even see the inner diffraction rings,
so
> I don't know what they look like. What do the experts say about the
> offset rings? Thanks in advance.
>
> Mike
> -----
>
> Mike Dodd
> Montpelier, VA USA
> http://astronomy.mdodd.com
>

Paul K wrote:
> Mike, offset diffraction rings usually indicate miscollimation. If
> the image appeared stable and the center hot spot didn't move around
> due to poor seeing, this would indicate a collimation error.

It didn't move around. The star was rock-steady (except for some
seeing-induced "swimming"), and the rings formed off-center.

>
> I'm not so sure that your image actually shows difraction rings --
> possibly just some reflections or distortions due to seeing/tube
> currents.

I seriously doubt if the image represents reflections, and tube currents
seem unlikely, since the telescope spent the day in a 30°F observatory
and had plenty of time to cool down to the 20°F ambient temperature
before I made these test observations.

Visually, the diffraction rings were quite distinct as they formed. They
don't show up in the photo because the long exposure time coupled with
poor seeing blurred them.

This is what I saw when I defocused the star further:
<http://astronomy.mdodd.com/files/diffraction_rings.jpg> The outer rings
appear concentric. The seeing was so bad I couldn't see the inner rings,
even visually.

However, look at this photo
<http://astronomy.mdodd.com/files/airy_12mm.jpg>  Taken several nights
ago through a 12mm illuminated reticle eyepiece. This appears to show
distinct diffraction rings around a bright spot in the same area as the
going-out-of-focus photo taken tonight.

I'm very puzzled.

Mike
-----

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com

--- In ccd-newastro@yahoogroups.com, Mike Dodd <mike@...> wrote:
> However, look at this photo
> <http://astronomy.mdodd.com/files/airy_12mm.jpg>  Taken several
nights
> ago through a 12mm illuminated reticle eyepiece. This appears to
show
> distinct diffraction rings around a bright spot in the same area as
the
> going-out-of-focus photo taken tonight.
>
> I'm very puzzled.

That image is very strange, Mike. There appear to be two airy discs in
the image, one at the center, where it should be, and one of to the
right and slightly lower. There are very obvious diffraction rings
about both points. The larger diffraction rings appear well-centered
around the real center, and the smaller diffraction rings are located
around the second airy disc to the right. Two things I can think of
that can cause this:

1. A close double
2. A defect in the lens and/or optical window of the camera, possibly
a reflective speck or a water droplet?

You shared another image with me previously, where there was an
obvious distortion off-center in the defocused star image. That one
also showed some diffraction rings around the off-center spot. Was
that image taken on the same night/same star, or on a different night?
If that was a different star on a different night, I would recommend
checking the optics carefully, under a bright light for any chips or
surface artifacts.

Regards,

     -Paul

>> <http://astronomy.mdodd.com/files/airy_12mm.jpg>

> That image is very strange, Mike. [...] Two things I can think of
> that can cause this:
>
> 1. A close double

The star was probably Elnath, but could have been Bellatrix; I don't
remember for sure. It definitely was one or the other. Tonight's star
was Elnath.

> 2. A defect in the lens and/or optical window of the camera, possibly
> a reflective speck or a water droplet?

I haven't seen anything on the objective lens; I'll check with a bright
light tomorrow. The camera is not a factor because I observed the offset
diffraction rings form while looking into the 3.5mm eyepiece as the star
moved out of focus.

--
Mike

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com

Mike, you did tell me it was Bellatrix for that other image, which
is not a double. This leaves something point-like in the optical
path causing diffraction rings. This is the other image you sent me,
showing the same off-center rings:

http://astronomy.mdodd.com/files/collimation_1.jpg

To me, this appears to be exactly the same size and distance from
the center as the defect in that other image (I flipped your image
and resized it):

http://pk.darkhorizons.org/tmp/defect.jpg

Regards,

       -Paul

--- In ccd-newastro@yahoogroups.com, Mike Dodd <mike@...> wrote:
>
> >> <http://astronomy.mdodd.com/files/airy_12mm.jpg>
>
> > That image is very strange, Mike. [...] Two things I can think
of
> > that can cause this:
> >
> > 1. A close double
>
> The star was probably Elnath, but could have been Bellatrix; I
don't
> remember for sure. It definitely was one or the other. Tonight's
star
> was Elnath.
>
> > 2. A defect in the lens and/or optical window of the camera,
possibly
> > a reflective speck or a water droplet?
>
> I haven't seen anything on the objective lens; I'll check with a
bright
> light tomorrow. The camera is not a factor because I observed the
offset
> diffraction rings form while looking into the 3.5mm eyepiece as
the star
> moved out of focus.
>
> --
> Mike
>
> Mike Dodd
> Montpelier, VA USA
> http://astronomy.mdodd.com
>

I would highly recommend using the dimmer stars in a slightly unfocused
image for photographic assessment of collimation. (CCDInspector
essentially does this and adds metrics.)

You want to see an even distribution of light around stars at the center
of the image, and it's reasonable to see offsets away from the center,
symmetrical about the center.


Ron Wodaski



Mike Dodd wrote:
>>> <http://astronomy.mdodd.com/files/airy_12mm.jpg>
>>>
>
>
>> That image is very strange, Mike. [...] Two things I can think of
>> that can cause this:
>>
>> 1. A close double
>>
>
> The star was probably Elnath, but could have been Bellatrix; I don't
> remember for sure. It definitely was one or the other. Tonight's star
> was Elnath.
>
>
>> 2. A defect in the lens and/or optical window of the camera, possibly
>> a reflective speck or a water droplet?
>>
>
> I haven't seen anything on the objective lens; I'll check with a bright
> light tomorrow. The camera is not a factor because I observed the offset
> diffraction rings form while looking into the 3.5mm eyepiece as the star
> moved out of focus.
>
>


[Non-text portions of this message have been removed]

I would tend to agree that there is some dirt or _something_ involved
here. Diffraction rings don't lie. <G>

Ron Wodaski



Paul K wrote:
> Mike, you did tell me it was Bellatrix for that other image, which
> is not a double. This leaves something point-like in the optical
> path causing diffraction rings. This is the other image you sent me,
> showing the same off-center rings:
>
> http://astronomy.mdodd.com/files/collimation_1.jpg
>
> To me, this appears to be exactly the same size and distance from
> the center as the defect in that other image (I flipped your image
> and resized it):
>
> http://pk.darkhorizons.org/tmp/defect.jpg
>
> Regards,
>
>       -Paul
>
> --- In ccd-newastro@yahoogroups.com, Mike Dodd <mike@...> wrote:
>
>>>> <http://astronomy.mdodd.com/files/airy_12mm.jpg>
>>>>
>>> That image is very strange, Mike. [...] Two things I can think
>>>
> of
>
>>> that can cause this:
>>>
>>> 1. A close double
>>>
>> The star was probably Elnath, but could have been Bellatrix; I
>>
> don't
>
>> remember for sure. It definitely was one or the other. Tonight's
>>
> star
>
>> was Elnath.
>>
>>
>>> 2. A defect in the lens and/or optical window of the camera,
>>>
> possibly
>
>>> a reflective speck or a water droplet?
>>>
>> I haven't seen anything on the objective lens; I'll check with a
>>
> bright
>
>> light tomorrow. The camera is not a factor because I observed the
>>
> offset
>
>> diffraction rings form while looking into the 3.5mm eyepiece as
>>
> the star
>
>> moved out of focus.
>>
>> --
>> Mike
>>
>> Mike Dodd
>> Montpelier, VA USA
>> http://astronomy.mdodd.com
>>
>>
>
>
>
>
> ------------------------------------
>
>
>
>
>


[Non-text portions of this message have been removed]

Paul K wrote:
> [...]This is the other image you sent me,
> showing the same off-center rings:
>
> http://astronomy.mdodd.com/files/collimation_1.jpg
>
> To me, this appears to be exactly the same size and distance from
> the center as the defect in that other image (I flipped your image
> and resized it):
>
> http://pk.darkhorizons.org/tmp/defect.jpg

Yes, I noticed that myself. I'll try adjusting the collimation screws
when the seeing is more stable, hopefully tomorrow night.

Mike
-----

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com

Mike, a few weeks ago a discussion came up on the PlaneWave group about
collimation.  Someone reference the AstroGeeks 'MetaGuide' web site.  You
might want to look into MetaGuide, images on this page shows patterns of out
of collimation and Seeing induced distortion.   You might have both.

I don't know if you want to get this involved and I haven't used MetaGuide
myself, but when I get my 12.5" Hyperion I plan upon giving it try.  Its
Free and looks quite comprehensive  HTH...joe  :)

http://www.astrogeeks.com/Bliss/MetaGuide/index.html


"May You Go Among The Imperishable Stars"
Joe Mize  www.cav-sfo.com
Chiefland Astronomy Village, Fla.

----- Original Message -----
From: "Mike Dodd" <mike@...>
To: <ccd-newastro@yahoogroups.com>
Sent: Monday, March 02, 2009 9:08 PM
Subject: [ccd-newastro] Collimation diffraction ring question


> Would someone please take a look at this photo
> <http://astronomy.mdodd.com/files/offset_diffraction_rings.jpg> and
> offer an opinion about it?
>
> I'm trying to check the collimation of my TMB-130SS APO 910mm FL f/7).
> Seeing tonight was terrible, so I didn't attempt any adjustments --
> just took some diffraction-ring photos.
>
> The photo illustrates what I saw visually in a 3.5mm eyepiece.
> Starting with an in-focus star (Elnath, nearly straight up in the sky)
> I slowly moved the Feather Touch electric focuser outward to defocus
> the star. As the star went out of focus, the diffraction rings began
> to form, but they were not concentric with the star -- they formed off
> to one side, as seen in the photo.
>
> The bright spot at the 4:00 position is the star, and the bright halo
> surrounds the outermost diffraction rings.
>
> I'm very puzzled by this behavior, and wonder if it represents a
> defective telescope or if something in my technique caused the offset
> pattern. The star was very well centered in the eyepiece (there was
> enough moon glow to easily see the eyepiece FOV). The camera was
> securely mounted on a bracket attached to the eyepiece, so it didn't move.
>
> I always thought diffraction rings form concentrically around the
> star. Seeing was too poor to even see the inner diffraction rings, so
> I don't know what they look like. What do the experts say about the
> offset rings? Thanks in advance.
>
> Mike
> -----
>
> Mike Dodd
> Montpelier, VA USA
> http://astronomy.mdodd.com
>
>
>
>
>
> ------------------------------------
>
>
>
>
>

May I also suggest that you also take a good quality flat? This will
show anything in the optical path that should not be there.

Regards,

        -Paul

--- In ccd-newastro@yahoogroups.com, Mike Dodd <mike@...> wrote:
>
> Paul K wrote:
> > [...]This is the other image you sent me,
> > showing the same off-center rings:
> >
> > http://astronomy.mdodd.com/files/collimation_1.jpg
> >
> > To me, this appears to be exactly the same size and distance
from
> > the center as the defect in that other image (I flipped your
image
> > and resized it):
> >
> > http://pk.darkhorizons.org/tmp/defect.jpg
>
> Yes, I noticed that myself. I'll try adjusting the collimation
screws
> when the seeing is more stable, hopefully tomorrow night.
>
> Mike
> -----
>
> Mike Dodd
> Montpelier, VA USA
> http://astronomy.mdodd.com
>

--- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@...> wrote:
>
> I would tend to agree that there is some dirt or _something_ involved
> here. Diffraction rings don't lie. <G>


How large a piece of dirt are we talking about? Here's a photo of the
objective lens taken this morning
<http://astronomy.mdodd.com/files/lens_dust_03-03-2009.jpg>. There are
a couple of tiny dust specks (which I removed later). Do you see
anything suspicious?

Mike
-----

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com

Mike
Dust specks on the front objective lens should not produce the kind of
spots that you would see on flats. The images you present do seem to
indicate some kind of collimation problem. The image with the two
diffraction patterns is very strange. If not caused by a double star, then
it might be caused by a reflection from an optical surface in your reticule
eyepiece. Do you get the same pattern if you use a different, non-reticule
eyepiece?

Richard



At 04:37 PM 3/3/2009 +0000, you wrote:

>--- In
><mailto:ccd-newastro%40yahoogroups.com>ccd-newastro@yahoogroups.com, Yahoo
>- Wodaski <yahoo@...> wrote:
> >
> > I would tend to agree that there is some dirt or _something_ involved
> > here. Diffraction rings don't lie. <G>
>
>How large a piece of dirt are we talking about? Here's a photo of the
>objective lens taken this morning
><<http://astronomy.mdodd.com/files/lens_dust_03-03-2009.jpg>http://astronomy.md\
odd.com/files/lens_dust_03-03-2009.jpg>.
>There are
>a couple of tiny dust specks (which I removed later). Do you see
>anything suspicious?
>
>Mike
>-----
>
>Mike Dodd
>Montpelier, VA USA
><http://astronomy.mdodd.com>http://astronomy.mdodd.com
>
>
>
>
>__________ Information from ESET Smart Security, version of virus
>signature database 3905 (20090303) __________
>
>The message was checked by ESET Smart Security.
>
><http://www.eset.com>http://www.eset.com


[Non-text portions of this message have been removed]

Richard Seavey wrote:
> Mike
> Do you get the same pattern if you use a different, non-reticle
> eyepiece?

This photo
<http://astronomy.mdodd.com/files/offset_diffraction_rings.jpg> and this
one <http://astronomy.mdodd.com/files/diffraction_rings.jpg> were made
with a brand new 2.5mm Vixen eyepiece. The first photo shows how the
diffraction rings formed just after the star had gone out of focus. The
bright spot in the 3:30 area is the star, and the rings formed offset in
the opposite direction.

The second photo shows the diffraction rings with the star more out of
focus. Notice how the 3:30 area is brighter. This is the same area where
the bright star was in the first image.

I checked the objective lens this morning and found no giant dust spots.
There were one or two specks, but that's all. I brushed them away.

I just came in from the observatory. The seeing tonight was just as bad
as last night, so I have no new information. Hopefully one of these
nights the atmosphere will calm down.

Mike
-----

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com

I'm thinking of purchasing an Orion ShortTube 80 telescope and Orion StarShoot
AutoGuider camera for deep sky object tracking.  My setup is as follows:

Celestron CGE 800 SCT
Orion StarShoot Pro (imaging camera)
Celestron GEM mount
GPS

Questions:
1) Does anyone have experience with the ShortTube 80 and AutoGuider?
2) Is this appropriate equipment for tracking (overkill, underkill, etc.)?
3) Is the focuser supplied with the ShortTube (rack and pinion) sufficient for
this task (tracking)?

After modest success with sky flats, due to lack of experience and to continuous
bad weather in central Europe, I use now an electrofluorescent sheet to produce
my flats: this a flexible, reliable and reproduceable method.
 
Just my 2 cents.
 
Ad

--- On Sun, 3/1/09, sc02492 <sc02492@...> wrote:


From: sc02492 <sc02492@...>
Subject: [ccd-newastro] Re: Darks, Flats, Camera rotation, and binning 2x2
To: ccd-newastro@yahoogroups.com
Date: Sunday, March 1, 2009, 5:16 PM






I have tried many of these techniques over the years and have come to
the conclusion that the very best and cost-effective flats are still
sky flats obtained at either dusk or dawn. The trick is to know
where to point the scope at dusk or dawn to minimize the gradient
caused by the setting or rising sun, respectively. This is
automatically calculated for you, and the scope is pointed at this
optimal location, using automation software like CCDAutopilot or CCD
Commander. The benefit of using such software, in addition to being
able to sleep, is that it will point your scope to the optimal
position and then continually adjust the exposure time to maintain a
constant target ADU value for your flats.

If you're interested in a nice paper that approaches the problem of
sky flats quantitatively, you might check this one out:

http://adsabs. harvard.edu/ abs/1996PASP. .108..944C

As I do not have much experience with the T shirt method, beyond not
being as impressed with it compared to sky flats, will let others
chime in...

Steve

Steve Cannistra
http://www.starrywo nders.com

--- In ccd-newastro@ yahoogroups. com, "kurt102602" <kurt1026@.. .>
wrote:
>
> Can a good quality T-shirt flat be taken at the following
conditions:
>
> 1) During the day pointed at the clear sky?
> 2) During the day pointed at solid cloud cover?
> 3) Same as above but at dusk?
> 4) During the day pointed at the ground?
> 5) Since I am using a dew shield the cloth is wrapped around the
end
> of the dew shield, do I need another made-up dew shield out side
the
> T-shirt to avoid light gradients hitting the t-shirt?
>
> Just trying to produce best results...
>
> Also, while I have Ron's books and they provide lots of good info,
is
> there a good summarized workflow proceedure that details the
process
> from taking the images to final image processing sequence?
>
> Thanks!
>
> --- In ccd-newastro@ yahoogroups. com, "sc02492" <sc02492@> wrote:
> >
> > Hi- be careful of the units. Gain is typically expressed in
units
> of
> > electrons per ADU. So for a full well of 50,000 electrons, and
> gain
> > of 0.8 electrons/ADU in your example, this means 50,000/0.8 =
62500
> > ADU at saturation (i.e., divide, not multiply). 30% of 62500
would
> > be 18,750 ADU. Always start from knowing the full well capacity
> (in
> > electrons) and the gain, and you can figure it out. Don't assume
> > that the max ADU of your brightest star (65535) represents true
> > saturation (it may be close, but will usually represent
> > oversaturation, depending upon the full well and gain). In other
> > words, you could easily be at saturation with an ADU of 45,000,
> > depending upon your camera specs.
> >
> > Steve
> >
> > Steve Cannistra
> > http://www.starrywo nders.com
> >
> > --- In ccd-newastro@ yahoogroups. com, "Robert Malinowski"
> > <robt.wndy@> wrote:
> > >
> > > Ok, let me see if I have this right....
> > >
> > > I measure the max pixel value of the brightest star..lets say
> it's
> > > 65535..this would mean ( at 30% ) a flat adu of 19660 ..(max
> times
> > > 30%)
> > >
> > > Now, suppose my camera's spec's say it has a 50000e- Full Well,
> and
> > a
> > > Gain of 0.8 unbinned...1. 6 binned.....
> > >
> > > These would work out to:(at 30%)..
> > >
> > > Saturation Level: Full Well*Gain
> > > Flat adu (at 30%): Saturation Level * 0.3
> > >
> > > thus
> > >
> > > 50000*0.8 * 0.3 = 12000adu for Unbinned
> > > and
> > > 50000*1.6 * 0.3 = 24000adu for Binned
> > >
> > > Right?
> > >
> > > Robert
> > >
> > >
> > >
> > >
> > > --- In ccd-newastro@ yahoogroups. com, Yahoo - Wodaski <yahoo@>
> > > wrote:
> > > >
> > > > Rick's advice on ADU for 2x2 was correct. The idea behind the
> ADU
> > > for
> > > > for any flat isn't a specific number; it's some proportion of
> the
> > > > saturation value (or the non-linear value for ABG chips).
> > > >
> > > > So the first thing to determine is the saturation level. You
> can
> > > > calculate it (full-well capacity times the gain - this is not
> > > always
> > > > known for bin modes, however), but that is only going to
close.
> > The
> > > > actual saturation value will vary a little from one camera to
> the
> > > next.
> > > > If you look at the brightness value of saturated pixels
(e.g.,
> > > bright
> > > > stars), this will give you a more accurate (but still
slightly
> > > fuzzy,
> > > > because it will vary a little from pixel to pixel) saturation
> > value.
> > > >
> > > > Depending on a variety of choices, you want to have an
average
> > flat
> > > > value in the 30% to 75% of saturation range. For chips with
> very
> > > linear
> > > > response, you can go up to 75% of saturation to improve your
> flat
> > > S/N.
> > > > For anti-blooming chips with average non-linear response (non-
> > > linear
> > > > because anti-blooming doesn't wait until saturation to start
> > > draining
> > > > excess charge; it starts long before that), you want 30-50%
of
> > > > saturation. (You would need to take a series of exposures of
> the
> > > same
> > > > star to determine where the non-linear point clicks in; if
you
> > > aren't
> > > > doing this, then your choice of ADU becomes less well
> determined.
> > > > However, anything in the 30-50% range is likely to work
> > reasonably
> > > well
> > > > unless you have critical requirements. )
> > > >
> > > > The concept of 'imaging with the CCD vertical' doesn't really
> > > exist. The
> > > > chip is read out exactly the same way every time. The
rotation
> of
> > > the
> > > > image has no effect whatsoever on how the chip is read.
> > > >
> > > > Since the chip is read the same way every time, there is
> nothing
> > > for you
> > > > to worry about with respect to this aspect.
> > > >
> > > > If you do rotate the camera, however, sometimes vignetting
may
> > > change.
> > > > Some telescopes will give you very similar flats no matter
how
> > the
> > > > camera is rotated; some will not. The only way to know is to
> take
> > > flats
> > > > at different rotation angles and compare them (e.g., subtract
> one
> > > from
> > > > the other and see what's left over).
> > > >
> > > > It's nice to prepare in advance, but there are many things
you
> > > won't
> > > > know until you try them both ways. <G>
> > > >
> > > > Ron Wodaski
> > > >
> > > >
> > > >
> > > > Robert Malinowski wrote:
> > > > > Thanks Rick...I saw recent talk relating to this, thanks
for
> > your
> > > > > explanation. ..
> > > > > Still, what about The ADU setting for 2x2 flats?? same as
> 1x1 ??
> > > > > Also, if imaging with the ccd vertical, will my image
> > processing
> > > > > program (maximdl), orient the darks and flats automatically
> > > during
> > > > > calibration( reduction) ??
> > > > > Robert
> > > > >
> > > > >
> > > > > --- In ccd-newastro@ yahoogroups. com, "Rick Wiggins"
> > > <rickwiggins@ >
> > > > > wrote:
> > > > >
> > > > >> Hi,
> > > > >> Seems this question comes up often lately.
> > > > >>
> > > > >> Darks: Darks should be taken for each different binning,
> > > > >>
> > > > > temperature
> > > > >
> > > > >> and time. Darks for a given binning can be scaled for time
> and
> > > to
> > > > >> some extent can be scaled for temperature; however, this
> does
> > > not
> > > > >> work as well as for time as it is not as linear. It is
> always
> > > > >>
> > > > > better
> > > > >
> > > > >> to take darks longer and scale down than the reserse. Best
> > case
> > > is
> > > > >> to take them at teh exact temp and time.
> > > > >>
> > > > >> Flats: Flats can be scaled for binnning. Yesterday, Stan
> Moore
> > > > >> pointed out that scaling the binning of flats is not
perfect
> > as
> > > it
> > > > >> does not model well the pixel to pixel variation of the
> chip,
> > > but
> > > > >> this is a minor effect in my experience. I take my flats
at
> > the
> > > > >>
> > > > > same
> > > > >
> > > > >> temperature as my darks, but this is probably not
necessary.
> > If
> > > you
> > > > >> flats are long in duration, you may want to make custom
> darks
> > > for
> > > > >> the flats and dark subtract the flats. I prefer my flats
at
> 25-
> > > 50%
> > > > >> of full well ADU.
> > > > >>
> > > > >> Bias: Take these at the same temperature as the darks
> > (probably
> > > not
> > > > >> critical, but I do it anyway) and do not try to scale the
> > > binning
> > > > >> for your bias files.
> > > > >>
> > > > >> Ron Wodaski has a nice discussion of these principles in
his
> > > book.
> > > > >> Stan Moore has posted many useful tips on the SBIG Group
> over
> > > the
> > > > >> years and he has some good stuff in the CCDStack help
files.
> > > > >>
> > > > >> Hope this helps,
> > > > >> Rick
> > > > >>
> > > > >>
> > > > >>
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > ------------ --------- --------- ------
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > > [Non-text portions of this message have been removed]
> > > >
> > >
> >
>



















[Non-text portions of this message have been removed]

The Short tube 80 and SSAG are a good match. I've used this combo with PHD and
MaximDL with good success. You will have no trouble finding guide stars with
this setup. You will need an extension tube or diagonal to reach focus with the
st80/ssag. The focuser on the st80 is pretty weak, but it's not that critical
for guiding.

Robin Uffer

--- In ccd-newastro@yahoogroups.com, "jayres11" <jayres11@...> wrote:
>
> I'm thinking of purchasing an Orion ShortTube 80 telescope and Orion StarShoot
AutoGuider camera for deep sky object tracking.  My setup is as follows:
>
> Celestron CGE 800 SCT
> Orion StarShoot Pro (imaging camera)
> Celestron GEM mount
> GPS
>
> Questions:
> 1) Does anyone have experience with the ShortTube 80 and AutoGuider?
> 2) Is this appropriate equipment for tracking (overkill, underkill, etc.)?
> 3) Is the focuser supplied with the ShortTube (rack and pinion) sufficient for
this task (tracking)?
>

To answer your questions:
1. Yes. I use the ST80 and a QHY5 ( similar I think to the Orion) on my ED80
and the 10" LX200 ( was using the ED80 as the guide on the LX200)
2. Yes. It's very good. I use PHD software and never have a problem.
3. No. I replaced the focuser with a 2" Crayford. Not mandatory, but
certainly an improvement.
The ST80 is MUCH lighter than the ED80 and makes balancing easier.

--
"Very funny Scotty... now beam down our clothes!"


[Non-text portions of this message have been removed]

Hello,
I am also considering external guiding scope for my C14. I already have SBIG
external guiding camera and ST9XE on C14.

But i would also want to do wide field imaging with the refractor..so what
do you guys suggest for a not so expensive scope which i can use for both
guiding and imaging.

Regards,

Umair Asim
www.umairasim.com


On Wed, Mar 4, 2009 at 7:30 PM, Ken Harrison <kenm.harrison@...>wrote:

>   To answer your questions:
> 1. Yes. I use the ST80 and a QHY5 ( similar I think to the Orion) on my
> ED80
> and the 10" LX200 ( was using the ED80 as the guide on the LX200)
> 2. Yes. It's very good. I use PHD software and never have a problem.
> 3. No. I replaced the focuser with a 2" Crayford. Not mandatory, but
> certainly an improvement.
> The ST80 is MUCH lighter than the ED80 and makes balancing easier.
>
> --
> "Very funny Scotty... now beam down our clothes!"
>
> [Non-text portions of this message have been removed]
>
>
>


[Non-text portions of this message have been removed]

Hi Mike,

Your photos show a classic Out-Of-Colimation condition.  The overall shape of
the diffraction rings should be round, unless there is astigmatism (which you
probably do not have).  The off center star image is the key that it is not
colimated.  Look at Covington's book "Astrophotography for the Amateur" page 172
for diagrams.  Only perfect colimation will show perfect concentricity of the
star image and difraction pattern.

Hope this helps,
Don

--- In ccd-newastro@yahoogroups.com, "Mike Dodd" <mike@...> wrote:
>
> Would someone please take a look at this photo
> <http://astronomy.mdodd.com/files/offset_diffraction_rings.jpg> and
> offer an opinion about it?
>
> I'm trying to check the collimation of my TMB-130SS APO 910mm FL f/7).
> Seeing tonight was terrible, so I didn't attempt any adjustments --
> just took some diffraction-ring photos.
>
> The photo illustrates what I saw visually in a 3.5mm eyepiece.
> Starting with an in-focus star (Elnath, nearly straight up in the sky)
> I slowly moved the Feather Touch electric focuser outward to defocus
> the star. As the star went out of focus, the diffraction rings began
> to form, but they were not concentric with the star -- they formed off
> to one side, as seen in the photo.
>
> The bright spot at the 4:00 position is the star, and the bright halo
> surrounds the outermost diffraction rings.
>
> I'm very puzzled by this behavior, and wonder if it represents a
> defective telescope or if something in my technique caused the offset
> pattern. The star was very well centered in the eyepiece (there was
> enough moon glow to easily see the eyepiece FOV). The camera was
> securely mounted on a bracket attached to the eyepiece, so it didn't move.
>
> I always thought diffraction rings form concentrically around the
> star. Seeing was too poor to even see the inner diffraction rings, so
> I don't know what they look like. What do the experts say about the
> offset rings? Thanks in advance.
>
> Mike
> -----
>
> Mike Dodd
> Montpelier, VA USA
> http://astronomy.mdodd.com
>