The FOV of view on my C14 is consistent from night to night. I have the
mirror locked, so the focuser always is at the same location for a given
temperature.

Ron Wodaski
author of The New CCD Astronomy
http://www.newastro.com


-----Original Message-----
From: Paul Luckas [mailto:luckas@...]
Sent: Friday, January 31, 2003 10:47 PM
To: ccd-newastro@yahoogroups.com
Subject: [ccd-newastro] FOV Question


With a dual focuser system (e.g. LX200 with NGF-S) does the field of view
change slightly if you find fine focus at different positions from night to
night (presumably from changes to the course focuser) ?   I seem to recall
discussions regarding focal length variations with SCTs that use movement of
the primary mirror as the course focussing mechanism, and am trying to wrap
my mind around how this may subtlety affect the field of view. Any comments
?  Ron ?


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


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Sorry Arnie, the only comment I can come up with is : GREAT SHOT!
Congratulations....
Bert

Bert Katzung
katzung1@...
www.astronomy-images.com

----- Original Message -----
From: <arnie@...>
To: <ccd-newastro@yahoogroups.com>
Sent: Friday, January 31, 2003 10:11 PM
Subject: [ccd-newastro] Comet Neat in color


> http://www.arnierosner.com/ccd/AREO/comet_neat.htm
>
> Comments are welcome.
>
> Arnie
>
>

Thanks!



Arnie
949-283-2801 Cell

http://www.arnierosner.com



-----Original Message-----
From: Bert Katzung [mailto:katzung1@...]
Sent: Friday, January 31, 2003 11:08 PM
To: ccd-newastro@yahoogroups.com
Subject: Re: [ccd-newastro] Comet Neat in color



Sorry Arnie, the only comment I can come up with is : GREAT SHOT!
Congratulations....
Bert

Bert Katzung
katzung1@...
www.astronomy-images.com

----- Original Message -----
From: <arnie@...>
To: <ccd-newastro@yahoogroups.com>
Sent: Friday, January 31, 2003 10:11 PM
Subject: [ccd-newastro] Comet Neat in color


> http://www.arnierosner.com/ccd/AREO/comet_neat.htm
>
> Comments are welcome.
>
> Arnie
>
>




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

Hi Ron,
you said: >> I take all darks at 10 minutes length.< . So you are
always working with "REDUCTION" what, if I understand it right,
is calculating the right dark-exposure length by the bias.

What if your light-exposure is longer than 10 minutes?

Would it make a difference to the image-quality taking always the
exect dark-exposure like the light? (And therefore no bias <SBIG-camera>)

Rolf
morrinho@...



> -----Ursprüngliche Nachricht-----
> Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> Gesendet: Mittwoch, 29. Januar 2003 20:52
> An: ccd-newastro@yahoogroups.com
> Betreff: RE: [ccd-newastro] A Dark Question
>
>
> I take all darks at 10 minutes length. I typically take about 16 darks and
> bias frames at the end of any given night of imaging, and add them to the
> library. Most of my bias and dark frames at this point have between 16 and
> 64 individual frames in them. Having lots of frames makes scaling work
> _much_ better (lower noise).
>
> I take bias/dark frames every 5 degrees, and always cool the camera to the
> best available temperature: -15, -20, -25, and -30 are my targets and they
> pretty much cover the year.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com

The library darks are of exceptional quality (64 frames is my goal; the most
commonly used temps are already at that level). They scale extremely well
and cleanly. They even scale remarkably well up to 15 minutes, but if
someone using the system is going to routinely take longer images like that
I'd simply take the longer darks required.

It's just my opinion, but I think that you get better results from building
a huge library of standardized exposures times and temperature than you do
from have smaller numbers of recent frames. Since changing to library
frames, I am getting much, much cleaner images. I used to hate having to
image at, say, -20 degrees because the darks seemed to add noise to the
image. With 64 darks and bias frames, my images are cleaner than they have
ever been after calibration/reduction.

In other words, the reduction in total noise in the master dark frame is
larger than if you take a limited number of darks at the same
time/temperature on the same night.

In part, I think this stems from the fact that, over even a few minutes, you
can see significant variations in dark current. By averaging very large
numbers of darks, you get a cleaner result, especially if the combined darks
are from multiple nights. My first inkling that this might be true can from
making darks from 3 separate nights. Taking 8 darks on three nights gave
cleaner results than taking 24 darks on a single night.

Also, consider that a 10-minute dark applied to a 3- or 5-minute light frame
will add less noise when properly scaled. Longer exposure times lead to less
noise in darks just like they do in light frames.

Ron Wodaski
author of The New CCD Astronomy
http://www.newastro.com


-----Original Message-----
From: morrinho@... [mailto:morrinho@...]
Sent: Saturday, February 01, 2003 2:05 AM
To: ccd-newastro@yahoogroups.com
Subject: [ccd-newastro] Further Dark Question


Hi Ron,
you said: >> I take all darks at 10 minutes length.< . So you are
always working with "REDUCTION" what, if I understand it right,
is calculating the right dark-exposure length by the bias.

What if your light-exposure is longer than 10 minutes?

Would it make a difference to the image-quality taking always the
exect dark-exposure like the light? (And therefore no bias <SBIG-camera>)

Rolf
morrinho@...



> -----Ursprüngliche Nachricht-----
> Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> Gesendet: Mittwoch, 29. Januar 2003 20:52
> An: ccd-newastro@yahoogroups.com
> Betreff: RE: [ccd-newastro] A Dark Question
>
>
> I take all darks at 10 minutes length. I typically take about 16 darks and
> bias frames at the end of any given night of imaging, and add them to the
> library. Most of my bias and dark frames at this point have between 16 and
> 64 individual frames in them. Having lots of frames makes scaling work
> _much_ better (lower noise).
>
> I take bias/dark frames every 5 degrees, and always cool the camera to the
> best available temperature: -15, -20, -25, and -30 are my targets and they
> pretty much cover the year.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com


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Hi Ron,

I'm sorry to say that I think that you are completely wrong on this
point :-) The pixel structure of the Sony devices includes a very
thin 'P type' surface layer, which isolates the thermal electron
generating surface layer (where nearly all thermal charge
originates) from the electron storage well beneath. Almost 100% of
photons pass through this layer, as it is virtually transparent, and
do not generate photoelectrons until they are deep within the well,
at which point they are trapped by the potential barrier at the 'P'
layer junction. Absolutely no leakage of these electrons occurs,
unless the well is nearly full and the ABG has started to take
effect.

You might argue that the P layer must scavenge some photons, but
this would affect the blue and UV end of the spectrum more than the
red, as red photons have a high penetration into silicon and blue is
absorbed at shallow depths. However, the high blue response of the
Sony chips shows that this is NOT the case.

For comparison, the Kodak chips achieve a relatively low dark
current by creating an even thicker surface barrier layer over their
pixels, which is generated by a 'doping' of the substrate to give a
charge 'inversion' to sweep off the thermal electrons. This has a
greater blue light absorbing effect than that in the Sony chip, so
that their blue response 'droops' more than the Sony devices. If
your comments were correct, then the Kodaks would be worse than the
Sonys for the charge loss effect in faint regions.

I stand by the statement that the SXV-H9 has a better sensitivity
than the ST7E-NABG and has much less thermal noise. There is no
reason why an SXV would give worse results on a faint region of
nebulosity, and, in practise, it gives much better results.

Regards,

Terry

--- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo Groups"
<yahoo@w...> wrote:
> No, these are two different things. ABG works by "topping off" the
wells -
> when the pixel accumulates a certain amount of electrons, often
about half
> the full well, the ABG circuits bleed off electrons. This involves
pixels in
> very bright areas of the chip.
>
> The thing I am talking about is what happens in very dim areas.
Thermal
> electrons are removed from the pixels to limit noise. Inevitably,
there is
> no difference between very low signal and thermal noise as far as
these
> circuits are concerned.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com
>
>
> -----Original Message-----
> From: Paul K <pkane2001@h...> [mailto:pkane2001@h...]
> Sent: Friday, January 31, 2003 6:51 PM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Re: SXV-H9 or ST-7XE
>
>
> Ron,
>
> My understanding is that the "sucking away" of electrons is done as
> part of the ABG process on Sony chips, not to reduce the dark
> current. If this somehow does reduce the signal, it can be turned
off
> with a simple on-camera adjustment on the HX916 and very likely on
> the SXV-H9.
>
> The full-well capacity I believe is another place where the two
chips
> differ, with ST-7E NABG having a larger well.
>
> Regards,
>
>      -Paul
>       http://pk.darkhorizons.org
>
>
> --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo Groups"
> <yahoo@w...> wrote:
> >
> > * I have a  different opinion about the low dark current in the
> Sony (and
> > some other) chips. The low dark current exists because the chip
> design
> > "sucks away" unwanted electrons from the pixels. However, if you
are
> > recording very dim subjects, some of your signal can get sucked
out
> as well.
> > Thus the low-dark-current cameras tend to have low noise overall
> but to have
> > poor performance with very dim subjects (e.g., extended
nebulosity,
> outer
> > areas of galaxies, etc.).
>
>

Hi Ron,

I'm sorry to say that I think that you are completely wrong on this
point :-) The pixel structure of the Sony devices includes a very
thin 'P type' surface layer, which isolates the thermal electron
generating surface layer (where nearly all thermal charge
originates) from the electron storage well beneath. Almost 100% of
photons pass through this layer, as it is virtually transparent, and
do not generate photoelectrons until they are deep within the well,
at which point they are trapped by the potential barrier at the 'P'
layer junction. Absolutely no leakage of these electrons occurs,
unless the well is nearly full and the ABG has started to take
effect.

You might argue that the P layer must scavenge some photons, but
this would affect the blue and UV end of the spectrum more than the
red, as red photons have a high penetration into silicon and blue is
absorbed at shallow depths. However, the high blue response of the
Sony chips shows that this is NOT the case.

For comparison, the Kodak chips achieve a relatively low dark
current by creating an even thicker surface barrier layer over their
pixels, which is generated by a 'doping' of the substrate to give a
charge 'inversion' to sweep off the thermal electrons. This has a
greater blue light absorbing effect than that in the Sony chip, so
that their blue response 'droops' more than the Sony devices. If
your comments were correct, then the Kodaks would be worse than the
Sonys for the charge loss effect in faint regions.

I stand by the statement that the SXV-H9 has a better sensitivity
than the ST7E-NABG and has much less thermal noise. There is no
reason why an SXV would give worse results on a faint region of
nebulosity, and, in practise, it gives much better results.

Regards,

Terry

--- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo Groups"
<yahoo@w...> wrote:
> No, these are two different things. ABG works by "topping off" the
wells -
> when the pixel accumulates a certain amount of electrons, often
about half
> the full well, the ABG circuits bleed off electrons. This involves
pixels in
> very bright areas of the chip.
>
> The thing I am talking about is what happens in very dim areas.
Thermal
> electrons are removed from the pixels to limit noise. Inevitably,
there is
> no difference between very low signal and thermal noise as far as
these
> circuits are concerned.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com
>
>
> -----Original Message-----
> From: Paul K <pkane2001@h...> [mailto:pkane2001@h...]
> Sent: Friday, January 31, 2003 6:51 PM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Re: SXV-H9 or ST-7XE
>
>
> Ron,
>
> My understanding is that the "sucking away" of electrons is done as
> part of the ABG process on Sony chips, not to reduce the dark
> current. If this somehow does reduce the signal, it can be turned
off
> with a simple on-camera adjustment on the HX916 and very likely on
> the SXV-H9.
>
> The full-well capacity I believe is another place where the two
chips
> differ, with ST-7E NABG having a larger well.
>
> Regards,
>
>      -Paul
>       http://pk.darkhorizons.org
>
>
> --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo Groups"
> <yahoo@w...> wrote:
> >
> > * I have a  different opinion about the low dark current in the
> Sony (and
> > some other) chips. The low dark current exists because the chip
> design
> > "sucks away" unwanted electrons from the pixels. However, if you
are
> > recording very dim subjects, some of your signal can get sucked
out
> as well.
> > Thus the low-dark-current cameras tend to have low noise overall
> but to have
> > poor performance with very dim subjects (e.g., extended
nebulosity,
> outer
> > areas of galaxies, etc.).
>
>

Another beauty Arnie.  I love the number of galaxies that you have captured
in this image.  You certainly are an imaging machine <g>.

Clear skies,
Kevin Dixon
ksbtk@...


From: <arnie@...>


> http://www.arnierosner.com/ccd/AREO/ngc4216.htm

Ron - that is absolutely stunning.  I love the color and detail that you
have captured in the galaxy.  The foreground stars add a beautiful dimension
to the picture.

Thank goodness for the images from you and Arnie as the clouds continue here
in the Northeast.

Clear skies,
Kevin Dixon
ksbtk@...

From: "Wodaski Yahoo Groups" <yahoo@...>


> This image is the work of bits and pieces captured on a half-dozen nights.
I
> took the luminance about a week ago, but did not have time to get any
color
> shots. I've been taking 1-2 RGB sets on the last few nights as I've been
> setting up the remote scope for users. I finally had enough color data to
> take a swing at the processing.
>
> http://www.newastro.com/remote/images/NGC1055_LRGB3.jpg
>
> The foreground stars have a very intense color, sort of like candy to my
> eye. I'm continuing to get rich star colors in the dim stars as well - I
> wish I could tell you what I was doing differently; star colors just seem
to
> be richer with this setup for some reason.
>
> The overall structure of the galaxy strikes me as interesting. It's got a
> prominent dust lane, and a large general glowing mass of stars as well.
Not
> nearly as prominent as Centaurus A, but more scattered stars than most
> spirals. A little reminiscent of NGC 253, maybe. See what I mean? I can't
> classify it! <g>
>
> 30 minutes of luminance (6x5minutes) and 25:25:25 minutes of RGB exposures
> (also 5min/exposure), some binned 2x2 and some 1x1 (don't ask).

If you have 2x2 binned RGB and unbinned L images do you,
1. first calibrate the binned and unbinned images
2. then resize the binned images to the unbinned images size
3. then put both the resized binned and unbinned images into one
folder for alignment
4. then separate the aligned images into separate LRGB folders for
combination into master LRGB images?

--- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo Groups"
<yahoo@w...> wrote:
> Here's the routine I follow:
>
> * Calibrate all images in CCDSoft. Output goes all in one folder,
even if
> they are different color filters.
> * Align all images at one time. Output again goes into a single
folder. I've
> occasionally had problems with CCDSoft not aligning some images,
but lately
> I've had 100% alignment success.
>
> At this point, all images are aligned - you won't need to align
anything
> again.
>
> Now go to Sigma, and create master L, R, G, and B images. The input
images
> are aligned, so the masters will be aligned.
>
> Combine however you prefer to combine to create RGB or LRGB. The
images are
> already aligned, so no work to do on that.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com
>
>
> -----Original Message-----
> From: vmat9 <vmat9@a...> [mailto:vmat9@a...]
> Sent: Friday, January 31, 2003 11:54 AM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Problem aligning color images combined with
> Sigma
>
>
> I had a problem aligning color images that were combined with the
> Sigma program.
>
> I combined two sets of color images(RGB and LRGB). The
> individual colors were calibrated and aligned in CCDSoft before I
> combined them using the Sigma program. The resulting images were
very
> clean and looked great.
>
> I ran into a problem, however, when I tried to align these image in
> CCDSoft. Although CCDSoft appeared to process the images
> without a problem, the output was badly misaligned.
>
> The Red in the RGB was rotated clockwise 90 degrees with respect to
> the green and the Blue was rotated about 30 degees. CCDSoft would
not
> align and rejected the green image in the LRGB image set, and the
LRB
> images that it did process were slightly misaligned.
>
> I went back and median combined the images in CCDSoft and the images
> aligned properly without a problem.
>
> Has anyone else had this problem? Any suggestions for curing it?
>
> Thanks,
>
> Vic
>
>
> To unsubscribe from this group, send an email to:
> ccd-newastro-unsubscribe@egroups.com
>
>
>
> Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/

Hi Kevin,



You are too kind.  Thank you.  I'm glad you like the image.



Arnie
949-283-2801 Cell

http://www.arnierosner.com



-----Original Message-----
From: ksbtk@... [mailto:ksbtk@...]
Sent: Saturday, February 01, 2003 3:57 AM
To: ccd-newastro@yahoogroups.com
Subject: Re: [ccd-newastro] NGC4216 From Rent-a-scope



Another beauty Arnie.  I love the number of galaxies that you have
captured
in this image.  You certainly are an imaging machine <g>.

Clear skies,
Kevin Dixon
ksbtk@...


From: <arnie@...>


> http://www.arnierosner.com/ccd/AREO/ngc4216.htm



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

That is a GREAT picture!

Very Cool!

Michael
astroden

-----Original Message-----
From: Arnie Rosner <arnie@...>
[mailto:arnie@...]
Sent: Saturday, February 01, 2003 1:12 AM
To: ccd-newastro@yahoogroups.com
Subject: [ccd-newastro] Comet Neat in color

http://www.arnierosner.com/ccd/AREO/comet_neat.htm

Comments are welcome.

Arnie


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

How do you scale a dark in terms of time and temp?
Thanks
Joe

On Saturday, February 1, 2003, at 05:44  AM, Wodaski Yahoo Groups wrote:

> The library darks are of exceptional quality (64 frames is my goal;
> the most
> commonly used temps are already at that level). They scale extremely
> well
> and cleanly. They even scale remarkably well up to 15 minutes, but if
> someone using the system is going to routinely take longer images like
> that
> I'd simply take the longer darks required.
>
> It's just my opinion, but I think that you get better results from
> building
> a huge library of standardized exposures times and temperature than
> you do
> from have smaller numbers of recent frames. Since changing to library
> frames, I am getting much, much cleaner images. I used to hate having
> to
> image at, say, -20 degrees because the darks seemed to add noise to the
> image. With 64 darks and bias frames, my images are cleaner than they
> have
> ever been after calibration/reduction.
>
> In other words, the reduction in total noise in the master dark frame
> is
> larger than if you take a limited number of darks at the same
> time/temperature on the same night.
>
> In part, I think this stems from the fact that, over even a few
> minutes, you
> can see significant variations in dark current. By averaging very large
> numbers of darks, you get a cleaner result, especially if the combined
> darks
> are from multiple nights. My first inkling that this might be true can
> from
> making darks from 3 separate nights. Taking 8 darks on three nights
> gave
> cleaner results than taking 24 darks on a single night.
>
> Also, consider that a 10-minute dark applied to a 3- or 5-minute light
> frame
> will add less noise when properly scaled. Longer exposure times lead
> to less
> noise in darks just like they do in light frames.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com
>
>
> -----Original Message-----
> From: morrinho@... [mailto:morrinho@...]
> Sent: Saturday, February 01, 2003 2:05 AM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Further Dark Question
>
>
> Hi Ron,
> you said: >> I take all darks at 10 minutes length.< . So you are
> always working with "REDUCTION" what, if I understand it right,
> is calculating the right dark-exposure length by the bias.
>
> What if your light-exposure is longer than 10 minutes?
>
> Would it make a difference to the image-quality taking always the
> exect dark-exposure like the light? (And therefore no bias
> <SBIG-camera>)
>
> Rolf
> morrinho@...
>
>
>
> > -----Ursprüngliche Nachricht-----
> > Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> > Gesendet: Mittwoch, 29. Januar 2003 20:52
> > An: ccd-newastro@yahoogroups.com
> > Betreff: RE: [ccd-newastro] A Dark Question
> >
> >
> > I take all darks at 10 minutes length. I typically take about 16
> darks and
> > bias frames at the end of any given night of imaging, and add them
> to the
> > library. Most of my bias and dark frames at this point have between
> 16 and
> > 64 individual frames in them. Having lots of frames makes scaling
> work
> > _much_ better (lower noise).
> >
> > I take bias/dark frames every 5 degrees, and always cool the camera
> to the
> > best available temperature: -15, -20, -25, and -30 are my targets
> and they
> > pretty much cover the year.
> >
> > Ron Wodaski
> > author of The New CCD Astronomy
> > http://www.newastro.com
>
>
> To unsubscribe from this group, send an email to:
> ccd-newastro-unsubscribe@egroups.com
>
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
>
>
> To unsubscribe from this group, send an email to:
> ccd-newastro-unsubscribe@egroups.com
>
>
>
> Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.

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

I had my first imaging sessions on the ART telescope this week. I
imaged a total of sixteen hours over four nights. It was a great
experience.

First, you should know that I'm new to CCD imaging. I have owned
an
ST–8E for about six months. I use it with an 8 inch Meade LX 200
in
light polluted, mostly cloudy skies of Chicago. Imaging is a struggle.

The ART Software is clean and simple and very easy to use. If I had
any questions or problems during an imaging session (very few and
inevitably due to my inexperience, not due to the ART equipment or
software) I would immediately call Ron in Seattle and he would
quickly correct the problem.

The following morning all my images were available in a zip file for
downloading. Ron provides Master Darks, Flats, and Biases that work
beautifully.

My images are in the users group site in the vmat file folder.
Please keep in mind that I am new to all of this. I plan to reprocess
most of them now that Ron has taught me how to use Sigma. Critiques
and suggestions would be appreciated.

Some of the many advantages of ART include:
· Dark Skies
· 7000 foot elevation
· State of the art equipment
· No maintenance
· No set up, just log on when you are ready to image
· No tear down, just log off. If the clouds roll in and it
starts to storm in New Mexico, just one click and go to bed. This
week I was imaging during snowstorms and cloudy subzero weather in my
warm and cozy home in Chicago.
· The polar alignment, focusing, and calibration frames are
done for you by the best.
· If you have a problem, just pick up the phone and call Ron.

I am looking forward to many more hours of imaging on this wonderful
system. I highly recommend ART to everyone.

Vic

Ron, there is a real insight in that post and one that I'm very pleased to know
about. The implications for me is that I can pretty much automate my dark frame
acquisition then not have to worry about doing darks with each image. I can take
my dark frames on cloudy nights, too. A method of managing a dark frame library
is something I always wanted to see included in CCDSoft (the reduction groups
goes part way towards it). However, when I read that darks taken 'on the night'
were subjectively better, I gave up on that idea and stopped bugging the
Bisques. Actually, I'm not convinced they really understood what I was waffling
on about, anyway ;-)

Some further questions, if you don't mind:
Do you think it is important to capture the bias frames at the same time as the
darks, or can they be done separately (on different nights, say). Do you throw
away the bias frames when they get old and capture new ones, like the dark
frames, or do you just keep the same bias frames?

--Tim





-----Original Message-----
From: Wodaski Yahoo Groups [mailto:yahoo@...]
Sent: Saturday 01 February 2003 10:44
To: ccd-newastro@yahoogroups.com
Subject: RE: [ccd-newastro] Further Dark Question


The library darks are of exceptional quality (64 frames is my goal; the most
commonly used temps are already at that level). They scale extremely well
and cleanly. They even scale remarkably well up to 15 minutes, but if
someone using the system is going to routinely take longer images like that
I'd simply take the longer darks required.

It's just my opinion, but I think that you get better results from building
a huge library of standardized exposures times and temperature than you do
from have smaller numbers of recent frames. Since changing to library
frames, I am getting much, much cleaner images. I used to hate having to
image at, say, -20 degrees because the darks seemed to add noise to the
image. With 64 darks and bias frames, my images are cleaner than they have
ever been after calibration/reduction.

In other words, the reduction in total noise in the master dark frame is
larger than if you take a limited number of darks at the same
time/temperature on the same night.

In part, I think this stems from the fact that, over even a few minutes, you
can see significant variations in dark current. By averaging very large
numbers of darks, you get a cleaner result, especially if the combined darks
are from multiple nights. My first inkling that this might be true can from
making darks from 3 separate nights. Taking 8 darks on three nights gave
cleaner results than taking 24 darks on a single night.

Also, consider that a 10-minute dark applied to a 3- or 5-minute light frame
will add less noise when properly scaled. Longer exposure times lead to less
noise in darks just like they do in light frames.

Ron Wodaski
author of The New CCD Astronomy
http://www.newastro.com


-----Original Message-----
From: morrinho@... [mailto:morrinho@...]
Sent: Saturday, February 01, 2003 2:05 AM
To: ccd-newastro@yahoogroups.com
Subject: [ccd-newastro] Further Dark Question


Hi Ron,
you said: >> I take all darks at 10 minutes length.< . So you are
always working with "REDUCTION" what, if I understand it right,
is calculating the right dark-exposure length by the bias.

What if your light-exposure is longer than 10 minutes?

Would it make a difference to the image-quality taking always the
exect dark-exposure like the light? (And therefore no bias <SBIG-camera>)

Rolf
morrinho@...



> -----Ursprüngliche Nachricht-----
> Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> Gesendet: Mittwoch, 29. Januar 2003 20:52
> An: ccd-newastro@yahoogroups.com
> Betreff: RE: [ccd-newastro] A Dark Question
>
>
> I take all darks at 10 minutes length. I typically take about 16 darks and
> bias frames at the end of any given night of imaging, and add them to the
> library. Most of my bias and dark frames at this point have between 16 and
> 64 individual frames in them. Having lots of frames makes scaling work
> _much_ better (lower noise).
>
> I take bias/dark frames every 5 degrees, and always cool the camera to the
> best available temperature: -15, -20, -25, and -30 are my targets and they
> pretty much cover the year.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com


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ccd-newastro-unsubscribe@egroups.com



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

I think darks are only scaled for time. The bias frames need to be taken at the
same temperature as the darks.

--Tim





-----Original Message-----
From: Joe Marietta [mailto:jmarietta@...]
Sent: Saturday 01 February 2003 12:27
To: ccd-newastro@yahoogroups.com
Subject: Re: [ccd-newastro] Further Dark Question


How do you scale a dark in terms of time and temp?
Thanks
Joe

On Saturday, February 1, 2003, at 05:44  AM, Wodaski Yahoo Groups wrote:

> The library darks are of exceptional quality (64 frames is my goal;
> the most
> commonly used temps are already at that level). They scale extremely
> well
> and cleanly. They even scale remarkably well up to 15 minutes, but if
> someone using the system is going to routinely take longer images like
> that
> I'd simply take the longer darks required.
>
> It's just my opinion, but I think that you get better results from
> building
> a huge library of standardized exposures times and temperature than
> you do
> from have smaller numbers of recent frames. Since changing to library
> frames, I am getting much, much cleaner images. I used to hate having
> to
> image at, say, -20 degrees because the darks seemed to add noise to the
> image. With 64 darks and bias frames, my images are cleaner than they
> have
> ever been after calibration/reduction.
>
> In other words, the reduction in total noise in the master dark frame
> is
> larger than if you take a limited number of darks at the same
> time/temperature on the same night.
>
> In part, I think this stems from the fact that, over even a few
> minutes, you
> can see significant variations in dark current. By averaging very large
> numbers of darks, you get a cleaner result, especially if the combined
> darks
> are from multiple nights. My first inkling that this might be true can
> from
> making darks from 3 separate nights. Taking 8 darks on three nights
> gave
> cleaner results than taking 24 darks on a single night.
>
> Also, consider that a 10-minute dark applied to a 3- or 5-minute light
> frame
> will add less noise when properly scaled. Longer exposure times lead
> to less
> noise in darks just like they do in light frames.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com
>
>
> -----Original Message-----
> From: morrinho@... [mailto:morrinho@...]
> Sent: Saturday, February 01, 2003 2:05 AM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Further Dark Question
>
>
> Hi Ron,
> you said: >> I take all darks at 10 minutes length.< . So you are
> always working with "REDUCTION" what, if I understand it right,
> is calculating the right dark-exposure length by the bias.
>
> What if your light-exposure is longer than 10 minutes?
>
> Would it make a difference to the image-quality taking always the
> exect dark-exposure like the light? (And therefore no bias
> <SBIG-camera>)
>
> Rolf
> morrinho@...
>
>
>
> > -----Ursprüngliche Nachricht-----
> > Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> > Gesendet: Mittwoch, 29. Januar 2003 20:52
> > An: ccd-newastro@yahoogroups.com
> > Betreff: RE: [ccd-newastro] A Dark Question
> >
> >
> > I take all darks at 10 minutes length. I typically take about 16
> darks and
> > bias frames at the end of any given night of imaging, and add them
> to the
> > library. Most of my bias and dark frames at this point have between
> 16 and
> > 64 individual frames in them. Having lots of frames makes scaling
> work
> > _much_ better (lower noise).
> >
> > I take bias/dark frames every 5 degrees, and always cool the camera
> to the
> > best available temperature: -15, -20, -25, and -30 are my targets
> and they
> > pretty much cover the year.
> >
> > Ron Wodaski
> > author of The New CCD Astronomy
> > http://www.newastro.com
>
>
> To unsubscribe from this group, send an email to:
> ccd-newastro-unsubscribe@egroups.com
>
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
>
>
> To unsubscribe from this group, send an email to:
> ccd-newastro-unsubscribe@egroups.com
>
>
>
> Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.

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


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<http://docs.yahoo.com/info/terms/> .




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

Check the news, the space shuttle that was scheduled to land some mins
ago is missing from radar

Michael
astroden


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

Shuttle is down over Dallas...

I just saw some video of it burning up coming in.

It don't look good!

God Bless those 7 crew members.

Michael
astroden

-----Original Message-----
From: Jay Stanley [mailto:jaystanley@...]
Sent: Saturday, February 01, 2003 9:37 AM
To: ccd-newastro@yahoogroups.com
Subject: Re: [ccd-newastro] Missing Shuttle

Shuttle is down over Dallas...


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

My deepest sympathy to the families.

:(

Bob
----- Original Message -----
From: "Michael Downing" <michael@...>
> Check the news, the space shuttle that was scheduled to land some mins
> ago is missing from radar

Hello all

I took 3 x 30 minute integrations of the Rosette Nebula last night,
took 3 flat fields (median combine) 3 bias and 3 dark frames (all
median combined).  Yet I was very disappointed to see so much "dirt"
in the image.  Almost like lots and lots of cool pixels but all
irregular shapes.  In fact, it took me the best part of an hour to
clean the image up in Photoshop.

Immediately prior to this, I dusted off the filters on the CFW8 but
I would of thought that the flat would have got rid of this.

I have posted a sample here
(http://groups.yahoo.com/group/UncensoredTakGroup/files/Rosette.jpg)
...could anyone tell me if these artefacts are normal in images and
if not, where I should be looking to clear it up.

thanks

Martin

Sorry all...I put the image accidentally into another newsgroup.

Here is the link to the file for this group:

http://groups.yahoo.com/group/ccd-newastro/files/Rosette.jpg

VMT

Martin

--- In ccd-newastro@yahoogroups.com, "mpastro2001 <martin-
pugh@t...>" <martin-pugh@t...> wrote:
> Sorry all...I put the image accidentally into another newsgroup.
>
> Here is the link to the file for this group:
>
> http://groups.yahoo.com/group/ccd-newastro/files/Rosette.jpg
>
> VMT
>
>

      Martin I have the same problem from time to time and I find the
dirt on the camera window. Bill

Martin

Objects probably too small to be on the window. Almost looks like
cosmic ray hits...

Tom






--- In ccd-newastro@yahoogroups.com, "Bill Perry <wperry38@n...>"
<wperry38@n...> wrote:
> --- In ccd-newastro@yahoogroups.com, "mpastro2001 <martin-
> pugh@t...>" <martin-pugh@t...> wrote:
> > Sorry all...I put the image accidentally into another newsgroup.
> >
> > Here is the link to the file for this group:
> >
> > http://groups.yahoo.com/group/ccd-newastro/files/Rosette.jpg
> >
> > VMT
> >
> >
>
>      Martin I have the same problem from time to time and I find
the
> dirt on the camera window. Bill
>
> Martin

You can't scale (at least not easily) in temp, just in time. CCDSoft, Mira,
MaxIm DL - they all offer a way to do this, and with various options.

The basic idea is this: the master bias is subtracted from the master dark.
The master dark is scaled for time. Then the bias is added back into the
master dark, and it is applied to the light frame.

The bias doesn't change with time, which is why it must be subtracted before
scaling, then added back in.

You can scale for time because the increase in dark current is linear with
time, or very nearly so. The changes with temperature are non-linear. You
would need a huge number of frames, documenting how each pixel changes over
temperature, in order to scale by temperature. You couldn't make any
assumptions about how things change from one temperature to the next.

Ron Wodaski
author of The New CCD Astronomy
http://www.newastro.com


-----Original Message-----
From: Joe Marietta [mailto:jmarietta@...]
Sent: Saturday, February 01, 2003 4:27 AM
To: ccd-newastro@yahoogroups.com
Subject: Re: [ccd-newastro] Further Dark Question


How do you scale a dark in terms of time and temp?
Thanks
Joe

On Saturday, February 1, 2003, at 05:44  AM, Wodaski Yahoo Groups wrote:

> The library darks are of exceptional quality (64 frames is my goal;
> the most
> commonly used temps are already at that level). They scale extremely
> well
> and cleanly. They even scale remarkably well up to 15 minutes, but if
> someone using the system is going to routinely take longer images like
> that
> I'd simply take the longer darks required.
>
> It's just my opinion, but I think that you get better results from
> building
> a huge library of standardized exposures times and temperature than
> you do
> from have smaller numbers of recent frames. Since changing to library
> frames, I am getting much, much cleaner images. I used to hate having
> to
> image at, say, -20 degrees because the darks seemed to add noise to the
> image. With 64 darks and bias frames, my images are cleaner than they
> have
> ever been after calibration/reduction.
>
> In other words, the reduction in total noise in the master dark frame
> is
> larger than if you take a limited number of darks at the same
> time/temperature on the same night.
>
> In part, I think this stems from the fact that, over even a few
> minutes, you
> can see significant variations in dark current. By averaging very large
> numbers of darks, you get a cleaner result, especially if the combined
> darks
> are from multiple nights. My first inkling that this might be true can
> from
> making darks from 3 separate nights. Taking 8 darks on three nights
> gave
> cleaner results than taking 24 darks on a single night.
>
> Also, consider that a 10-minute dark applied to a 3- or 5-minute light
> frame
> will add less noise when properly scaled. Longer exposure times lead
> to less
> noise in darks just like they do in light frames.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com
>
>
> -----Original Message-----
> From: morrinho@... [mailto:morrinho@...]
> Sent: Saturday, February 01, 2003 2:05 AM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Further Dark Question
>
>
> Hi Ron,
> you said: >> I take all darks at 10 minutes length.< . So you are
> always working with "REDUCTION" what, if I understand it right,
> is calculating the right dark-exposure length by the bias.
>
> What if your light-exposure is longer than 10 minutes?
>
> Would it make a difference to the image-quality taking always the
> exect dark-exposure like the light? (And therefore no bias
> <SBIG-camera>)
>
> Rolf
> morrinho@...
>
>
>
> > -----Ursprüngliche Nachricht-----
> > Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> > Gesendet: Mittwoch, 29. Januar 2003 20:52
> > An: ccd-newastro@yahoogroups.com
> > Betreff: RE: [ccd-newastro] A Dark Question
> >
> >
> > I take all darks at 10 minutes length. I typically take about 16
> darks and
> > bias frames at the end of any given night of imaging, and add them
> to the
> > library. Most of my bias and dark frames at this point have between
> 16 and
> > 64 individual frames in them. Having lots of frames makes scaling
> work
> > _much_ better (lower noise).
> >
> > I take bias/dark frames every 5 degrees, and always cool the camera
> to the
> > best available temperature: -15, -20, -25, and -30 are my targets
> and they
> > pretty much cover the year.
> >
> > Ron Wodaski
> > author of The New CCD Astronomy
> > http://www.newastro.com
>
>
> To unsubscribe from this group, send an email to:
> ccd-newastro-unsubscribe@egroups.com
>
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
>
>
> To unsubscribe from this group, send an email to:
> ccd-newastro-unsubscribe@egroups.com
>
>
>
> Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.

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


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I don't worry about same night, but as a matter of convenience it usually
winds up that I take the bias first, because it goes so fast, and then the
darks. I'll typically take 16 of each on a given night, then 16 more of each
on another night, etc.

Library darks with such large numbers of frames last a long time, months
probably. I rotate all the frames with fresh ones.

Ron Wodaski
author of The New CCD Astronomy
http://www.newastro.com


-----Original Message-----
From: Tim Long [mailto:Tim@...]
Sent: Saturday, February 01, 2003 5:46 AM
To: ccd-newastro@yahoogroups.com
Subject: RE: [ccd-newastro] Further Dark Question


Ron, there is a real insight in that post and one that I'm very pleased to
know about. The implications for me is that I can pretty much automate my
dark frame acquisition then not have to worry about doing darks with each
image. I can take my dark frames on cloudy nights, too. A method of managing
a dark frame library is something I always wanted to see included in CCDSoft
(the reduction groups goes part way towards it). However, when I read that
darks taken 'on the night' were subjectively better, I gave up on that idea
and stopped bugging the Bisques. Actually, I'm not convinced they really
understood what I was waffling on about, anyway ;-)

Some further questions, if you don't mind:
Do you think it is important to capture the bias frames at the same time as
the darks, or can they be done separately (on different nights, say). Do you
throw away the bias frames when they get old and capture new ones, like the
dark frames, or do you just keep the same bias frames?

--Tim





-----Original Message-----
From: Wodaski Yahoo Groups [mailto:yahoo@...]
Sent: Saturday 01 February 2003 10:44
To: ccd-newastro@yahoogroups.com
Subject: RE: [ccd-newastro] Further Dark Question


The library darks are of exceptional quality (64 frames is my goal; the most
commonly used temps are already at that level). They scale extremely well
and cleanly. They even scale remarkably well up to 15 minutes, but if
someone using the system is going to routinely take longer images like that
I'd simply take the longer darks required.

It's just my opinion, but I think that you get better results from building
a huge library of standardized exposures times and temperature than you do
from have smaller numbers of recent frames. Since changing to library
frames, I am getting much, much cleaner images. I used to hate having to
image at, say, -20 degrees because the darks seemed to add noise to the
image. With 64 darks and bias frames, my images are cleaner than they have
ever been after calibration/reduction.

In other words, the reduction in total noise in the master dark frame is
larger than if you take a limited number of darks at the same
time/temperature on the same night.

In part, I think this stems from the fact that, over even a few minutes, you
can see significant variations in dark current. By averaging very large
numbers of darks, you get a cleaner result, especially if the combined darks
are from multiple nights. My first inkling that this might be true can from
making darks from 3 separate nights. Taking 8 darks on three nights gave
cleaner results than taking 24 darks on a single night.

Also, consider that a 10-minute dark applied to a 3- or 5-minute light frame
will add less noise when properly scaled. Longer exposure times lead to less
noise in darks just like they do in light frames.

Ron Wodaski
author of The New CCD Astronomy
http://www.newastro.com


-----Original Message-----
From: morrinho@... [mailto:morrinho@...]
Sent: Saturday, February 01, 2003 2:05 AM
To: ccd-newastro@yahoogroups.com
Subject: [ccd-newastro] Further Dark Question


Hi Ron,
you said: >> I take all darks at 10 minutes length.< . So you are
always working with "REDUCTION" what, if I understand it right,
is calculating the right dark-exposure length by the bias.

What if your light-exposure is longer than 10 minutes?

Would it make a difference to the image-quality taking always the
exect dark-exposure like the light? (And therefore no bias <SBIG-camera>)

Rolf
morrinho@...



> -----Ursprüngliche Nachricht-----
> Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> Gesendet: Mittwoch, 29. Januar 2003 20:52
> An: ccd-newastro@yahoogroups.com
> Betreff: RE: [ccd-newastro] A Dark Question
>
>
> I take all darks at 10 minutes length. I typically take about 16 darks and
> bias frames at the end of any given night of imaging, and add them to the
> library. Most of my bias and dark frames at this point have between 16 and
> 64 individual frames in them. Having lots of frames makes scaling work
> _much_ better (lower noise).
>
> I take bias/dark frames every 5 degrees, and always cool the camera to the
> best available temperature: -15, -20, -25, and -30 are my targets and they
> pretty much cover the year.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com


To unsubscribe from this group, send an email to:
ccd-newastro-unsubscribe@egroups.com



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<http://docs.yahoo.com/info/terms/> .




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


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Those are cosmic ray hits in your dark frame. You should try taking
additional darks and using a median combine (or Ray Gralak's Sigma program)
to remove the cosmic ray hits. You have a heavier-than-usual dose of them in
that image, but if you are imaging at elevation then you will often see
that. You'll need a minimum of four darks to have reasonable cleanup; I use
64 (!) darks to get really clean results.

Ron Wodaski
author of The New CCD Astronomy
http://www.newastro.com


-----Original Message-----
From: mpastro2001 <martin-pugh@...>
[mailto:martin-pugh@...]
Sent: Saturday, February 01, 2003 7:00 AM
To: ccd-newastro@yahoogroups.com
Subject: [ccd-newastro] Dirty Images


Sorry all...I put the image accidentally into another newsgroup.

Here is the link to the file for this group:

http://groups.yahoo.com/group/ccd-newastro/files/Rosette.jpg

VMT

Martin


To unsubscribe from this group, send an email to:
ccd-newastro-unsubscribe@egroups.com



Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

Dutch news broadcast confirms the disaster. Colombia was lost 68 km high.
Pieces of it are allready found in Tx.
The astronauts , 6 Americans and 1 Israeli , could not have survived this.
My condolenses to their families. Makes me sad .

Max

So Ron,

Let me see if I understand. Tonight while I am sitting here at my
computer with clouds in the SKY. I could turn on my camera which is in
my dome and start Shooting Darks that I could use next time I image?


See if I am getting this right.


1. Pick round convenient temps that will would work year round
2. Take 64 frames and bias at each temp
3. Make a master Dark and bias with each 64 frames for each temp
4. If I shoot most of my images at 10 minutes, I could use these master
frames for shorter exposures provided I scale them and up to 15 minutes
if I wanted to.
5. Then after several months start rotating frames with newer ones.

Are you using SIGMA to make these master Dark and Bias frames.... ?  or
do you load all 64 frames into CCDsoft and do a reduction group?

Thanks
Joe


On Saturday, February 1, 2003, at 05:44  AM, Wodaski Yahoo Groups wrote:

> The library darks are of exceptional quality (64 frames is my goal;
> the most
> commonly used temps are already at that level). They scale extremely
> well
> and cleanly. They even scale remarkably well up to 15 minutes, but if
> someone using the system is going to routinely take longer images like
> that
> I'd simply take the longer darks required.
>
> It's just my opinion, but I think that you get better results from
> building
> a huge library of standardized exposures times and temperature than
> you do
> from have smaller numbers of recent frames. Since changing to library
> frames, I am getting much, much cleaner images. I used to hate having
> to
> image at, say, -20 degrees because the darks seemed to add noise to the
> image. With 64 darks and bias frames, my images are cleaner than they
> have
> ever been after calibration/reduction.
>
> In other words, the reduction in total noise in the master dark frame
> is
> larger than if you take a limited number of darks at the same
> time/temperature on the same night.
>
> In part, I think this stems from the fact that, over even a few
> minutes, you
> can see significant variations in dark current. By averaging very large
> numbers of darks, you get a cleaner result, especially if the combined
> darks
> are from multiple nights. My first inkling that this might be true can
> from
> making darks from 3 separate nights. Taking 8 darks on three nights
> gave
> cleaner results than taking 24 darks on a single night.
>
> Also, consider that a 10-minute dark applied to a 3- or 5-minute light
> frame
> will add less noise when properly scaled. Longer exposure times lead
> to less
> noise in darks just like they do in light frames.
>
> Ron Wodaski
> author of The New CCD Astronomy
> http://www.newastro.com
>
>
> -----Original Message-----
> From: morrinho@... [mailto:morrinho@...]
> Sent: Saturday, February 01, 2003 2:05 AM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Further Dark Question
>
>
> Hi Ron,
> you said: >> I take all darks at 10 minutes length.< . So you are
> always working with "REDUCTION" what, if I understand it right,
> is calculating the right dark-exposure length by the bias.
>
> What if your light-exposure is longer than 10 minutes?
>
> Would it make a difference to the image-quality taking always the
> exect dark-exposure like the light? (And therefore no bias
> <SBIG-camera>)
>
> Rolf
> morrinho@...
>
>
>
> > -----Ursprüngliche Nachricht-----
> > Von: Wodaski Yahoo Groups [mailto:yahoo@...]
> > Gesendet: Mittwoch, 29. Januar 2003 20:52
> > An: ccd-newastro@yahoogroups.com
> > Betreff: RE: [ccd-newastro] A Dark Question
> >
> >
> > I take all darks at 10 minutes length. I typically take about 16
> darks and
> > bias frames at the end of any given night of imaging, and add them
> to the
> > library. Most of my bias and dark frames at this point have between
> 16 and
> > 64 individual frames in them. Having lots of frames makes scaling
> work
> > _much_ better (lower noise).
> >
> > I take bias/dark frames every 5 degrees, and always cool the camera
> to the
> > best available temperature: -15, -20, -25, and -30 are my targets
> and they
> > pretty much cover the year.
> >
> > Ron Wodaski
> > author of The New CCD Astronomy
> > http://www.newastro.com
>
>
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