--- In roddier@yahoogroups.com, "zeissnut" <grzincic@...> wrote:
>
> Hi Mick,
> I'm still here lurking in the shadows.  Maybe I'll have more
> time for it in coming weeks.  I don't have any insights
> yet to the apparent contradictory results -- will take me
> some time to dig through the postings.  But I agree it is
> important to figure it out.  Or at least understand the
> scenarios where it works well, or has issues.
> - John B.
>

Dr. Biretta  -  it's wonderful to hear from you again and know you are still
around. We can surmise what's been happening in your world since the Hubble
repair.

There is certainly no question of hurry here; wading through all my blather will
be hard enough. If I can be of any further help, just let me know. I would be
more than glad to send DVDs with copies of the original videos (from which the
intra/extra images were derived) if that becomes necessary; at >300 MB each,
they are too big to post and/or E-mail, and there is a slug of them.

Hopefully we can still eventually arrive at some constructive
answers/conclusions.

Thanks again for all your help.

Mick Hollimon
21 Nov 09
9:21 AM PST USA

Chris,
I made some efforts along the lines of your item (1) some years
ago using Aberrator.  The primary issue is that Aberrator does
not seem to have linear output.  I am not quite sure of the details
just now, but it scales the output images to something like gamma=0.5
(i.e. ouput brightness = square root[input brightness])
so that the fainter features are preserved and not lost.
Apparently it is trying to match what Dick Suiter did in
his book on Star Testing -- IIRC the images in his book
are scaled to gamma=0.5.  Anyway, the point is that you cannot
take the output fom Aberrator and run it directly into
Roddier without somehow correcting for this.  There is a
"gamma" adjustment in Aberrator on the "Monitor Calibrate"
window, but I was never able to convince myself of what it did.
Probably a solution would be to get the source code for
Aberrator (or the code Suiter used) and make it output
with a linear brightness scale.
- John B.


--- In roddier@yahoogroups.com, "Chris" <chrisn999@...> wrote:
>
> Yes, still here, thinking about, but no results on the following:
>
> 1)Testing Roddier with computer generated data, an extended Aberrator of some
kind. Still working out the maths. Apparently some report Aberrator doesn't work
with Roddier?
>
> 2)Moving to a Hartmann screen test, anybody tried it?  Should be less
dependent on image intensity and camera response. Hard to do on smaller
telescope (<10 inches diameter), should work great on bigger Dobsonians.
>
> Interested in comments on number 2)
>
> -Chris
>
> --- In roddier@yahoogroups.com, "Marshall" <mhholl@> wrote:
> >
> > Group  -  with the exception of a single item on 1 Sept 09, I am the only
person to post anything to this forum since 12 June 09, a span of slightly over
5 months. Are any group members still monitoring here? Any of the active core
from a year or so ago still around? Anyone still interested in the somewhat
contradictory results of a fair amount of investigation into Roddier and its
operation? Anyone still interested in trying to improve Roddier?
> >
> > Is anybody out there?
> >
> > Mick Hollimon
> > 16 Nov 09
> > 1:50 PM PST USA
> >
>

Hi Mick,
I'm still here lurking in the shadows.  Maybe I'll have more
time for it in coming weeks.  I don't have any insights
yet to the apparent contradictory results -- will take me
some time to dig through the postings.  But I agree it is
important to figure it out.  Or at least understand the
scenarios where it works well, or has issues.
- John B.

--- In roddier@yahoogroups.com, "Marshall" <mhholl@...> wrote:
>
> Group  -  with the exception of a single item on 1 Sept 09, I am the only
person to post anything to this forum since 12 June 09, a span of slightly over
5 months. Are any group members still monitoring here? Any of the active core
from a year or so ago still around? Anyone still interested in the somewhat
contradictory results of a fair amount of investigation into Roddier and its
operation? Anyone still interested in trying to improve Roddier?
>
> Is anybody out there?
>
> Mick Hollimon
> 16 Nov 09
> 1:50 PM PST USA
>

Yes, still here, thinking about, but no results on the following:

1)Testing Roddier with computer generated data, an extended Aberrator of some
kind. Still working out the maths. Apparently some report Aberrator doesn't work
with Roddier?

2)Moving to a Hartmann screen test, anybody tried it?  Should be less dependent
on image intensity and camera response. Hard to do on smaller telescope (<10
inches diameter), should work great on bigger Dobsonians.

Interested in comments on number 2)

-Chris

--- In roddier@yahoogroups.com, "Marshall" <mhholl@...> wrote:
>
> Group  -  with the exception of a single item on 1 Sept 09, I am the only
person to post anything to this forum since 12 June 09, a span of slightly over
5 months. Are any group members still monitoring here? Any of the active core
from a year or so ago still around? Anyone still interested in the somewhat
contradictory results of a fair amount of investigation into Roddier and its
operation? Anyone still interested in trying to improve Roddier?
>
> Is anybody out there?
>
> Mick Hollimon
> 16 Nov 09
> 1:50 PM PST USA
>

--- In roddier@yahoogroups.com, "bron gervais" <bgervais@...> wrote:
>
> If my rusty trigonometry is correct, that focuser runout gives an >error in
spot location on the primary of 0.83mm at 1524mm (60").  I >thought that errors
of only a few mm were significant for fast >Newts. Is that error still dominated
by what seems to be secondary >shift with ALT change?
>
> Bron
>

Bron  -  the 0.001 inch runout I measured on my focuser (JMI NGF-DX2) was
reasonably linear and progressive, meaning that the sideways motion over an 8 mm
segment of the 45.7 mm travel would be roughly 8/45.7 of the 0.001 inch runout,
or 0.000175 inch, a negligible shift of the image in the focal plane.

As for shift of the focuser aim, i.e., spot movement on the primary mirror, I
would estimate it to be under 0.05 inch for the full 45.7 mm travel, which
compares well with the above 0.83 mm, 0.0327 inch. This magnitude of aiming
error will have almost no detectable effect on image quality in my 10 inch f/6
Newt. Further, during Roddier image acquisition the shift will be only 8/45.7 of
these magnitudes.

Seems like shifts due to focuser travel errors can't account for much problem in
this scope.

As far as shifts produced by altitude change (OTA far from vertical), the latter
Roddier test results were obtained from images taken after collimation was
fine-adjusted while rotating the camera in the focuser to reduce radial motion
of the star image, all done on Vega when it was within 15-20 degrees of the
zenith. This should effectively compensate for any equivalent secondary motion.
In fact, secondary motion in the test scope is essentially undetectable,
verified by a lot of testing with a laser collimator in the focuser and moving
the OTA to many angles very far from vertical while observing the spot on the
primary.

I hope the above addresses your thoughts on the optical system. Keep thinking,
maybe something further will turn up.

Mick Hollimon
17 Nov 09
11:05 AM PST USA

--- In roddier@yahoogroups.com, "bron gervais" <bgervais@...> wrote:
>
> Mick,
>
> I have been following and find this all very interesting.  However, I'm
convinced this is over my head and my needs at this juncture in my amateur
astronomical endeavors.  I joined in May 2008, hoping to find an affordable and
accessible way to quantify the performance of my telescope.  What I learned here
is that it would take a lot of time for me to learn how to use this method with
confidence.
>
> I wish there were more members who are at a level to maintain this dialog with
you, as I do find I have learned many things in following the discussions here. 
I have been amazed at your persistence and the care and diligence with which you
conduct your work.
>
> Best,
>
> Bron
>

Bron  -  thanks much for the kind words and encouragement.

I joined this group for exactly the same reason as you, and am still hopeful of
that endeavor. As you probably observed, the path converged to include attempts
to reconcile Roddier with Bath interferometry, so far not fully successful. Sure
is a nice dream, though.

Be clear on an important point: my observations would indicate that Roddier
testing is relatively straitforward to apply to refractors; it appears to be
much trickier to apply to obstructed systems such as Newtonians and SCTs, for
reasons that at least to me are not well understood as of now. If your scope
mentioned above is a refractor, by all means give Roddier a try and feel
reasonably confident about the result.

Again, thanks for the input.

Mick Hollimon
16 Nov 09
3:42 PM PST USA

--- In roddier@yahoogroups.com, "bron gervais" <bgervais@...> wrote:
>
> Mick,
>
> Is it possible that the way you judge the holding of collimation might be
improved?  Have you removed focuser slop and laser internal misalignment for the
picture?   I was just reading about Nils Olaf Carlin's Barlowed laser alignment
method.
>
> Excuse me if you're already aware of Carlin's method.  I have no experience
with Roddier, so I can't speak to that.
>
> Bron
>
> Collimation with a Barlowed Laser, by Nils Olaf Carlin
> http://www.cameraconcepts.com/barlowed%20laser%20collimation.pdf
>
> Rear View Barlowed Laser Collimation, By Steve Smallcombe,
> http://www.smartavtweaks.com/RVBL.html
>
Bron  -  thanks for the suggestions.

As explained in the documents mentioned in my last post, I carefully checked the
motion of the focuser drawtube using a dial indicator and found the maximum
side-side shift to be 0.001 inch (0.025 mm) over its full travel range (1.8
inch, 45.7 mm), essentially negligible for the 8 mm travel used when taking
Roddier image pairs.

The laser collimator has been placed in a ball-bearing fixture which allows
rotation on axis, and adjusted until there is no discernable wobble in the beam
dot at a distance of 5 feet, 1.5 meters. This indicates very high alignment of
the beam with the axis of the collimator body and thus of the drawtube.

I am aware of Carlin's barlowed laser technique but have not yet tried it; maybe
that will be a good project for this winter.

Mick Hollimon
16 Nov 09
3:29 PM PST USA

--- In roddier@yahoogroups.com, Sander Pool <sander_pool@...> wrote:
>
>
> Hi Mick,
>
> I'm here but just lurking.
>
> Sander
>

Sander  -  good to see you here and glad you're at least lurking; if you have
any thoughts/opinions on some of the stuff in my latter posts I would be very
grateful for same.

Mick Hollimon
16 Nov 09
3:15 PM PST USA

Hi Mick,

I'm here but just lurking.

Sander

Marshall wrote:
>
> Group - with the exception of a single item on 1 Sept 09, I am the
> only person to post anything to this forum since 12 June 09, a span of
> slightly over 5 months. Are any group members still monitoring here?
> Any of the active core from a year or so ago still around? Anyone
> still interested in the somewhat contradictory results of a fair
> amount of investigation into Roddier and its operation? Anyone still
> interested in trying to improve Roddier?
>
> Is anybody out there?
>
> Mick Hollimon
> 16 Nov 09
> 1:50 PM PST USA
>
>

Group  -  with the exception of a single item on 1 Sept 09, I am the only person
to post anything to this forum since 12 June 09, a span of slightly over 5
months. Are any group members still monitoring here? Any of the active core from
a year or so ago still around? Anyone still interested in the somewhat
contradictory results of a fair amount of investigation into Roddier and its
operation? Anyone still interested in trying to improve Roddier?

Is anybody out there?

Mick Hollimon
16 Nov 09
1:50 PM PST USA

Group  -  in post #680 I raised two questions about the interaction between
camera sensor chip orientation and Roddier analysis results. I have so far found
no way to systematically measure and/or control camera chip tilt (WRT the
optical axis), but in an attempt to investigate effects due to camera chip
decentering, I performed a short study involving both telescope physical/optical
properties and software effects.

Results and discussions of this study are presented in the Files section,
Newtonian 10 inch folder, Camera_Chip_Decentering_Study subfolder,in following
documents:

RoddAnalTable1.pdf              table of numerical results of Roddier analyses
performed on image pairs from various versions of Registax and using various
processing techniques in Registax

RoddAnalTable1Discussion.txt          discussion of the results in Table 1

MechOptIssues.txt                          discussion of focuser drawtube motion
errors and image centering errors

WinRoddAnalSteps.txt                     precise steps used in WinRoddier2.2-eng
to process images; all images with results in Table 1 were processed identically
in  WinRoddier2.2-eng using these steps

Telescope mechnical/optical properties investigated were:

1. Focuser drawtube run-out (sideways/lateral shift)  -   this was found to be
0.001 inch (25.4 um), or about 4.5 camera pixels, over the 1.8 inch travel range
of the drawtube; for the approx. 8 mm travel range involved in Roddier image
defocussing, the shift is about 0.8 pixel; negligible effect on Roddier results.

2. Camera sensor chip decentering  -  for a distant object centered in a 12.5 mm
reticle eyepiece, direct substitution of the camera (with its 1.25 inch focuser
adaptor) showed the object to be approx.
48 pixels off center on the camera chip. A camera centering adaptor (to replace
the focuser 2-1.25 inch eyepiece adaptor) was machined; this device allows 0.18
inch sideways shift (from center) of the camera in any direction when in the
focuser. Using this adaptor, image shift between eyepiece and camera was reduced
to 13 pixels, a 3.5/1 improvement.

3. Even after centering the camera, rotating the camera in the centered position
still showed a small residual image shift, attributed to slight collimation
error. Using successive camera rotations, followed by fine collimation
adjustments, this rotational shift was reduced to about 6.4 pixels on the camera
chip.

Roddier image files were taken after steps 2 (Test 12) and 3 (Test 13) above.
These were processed as per above, and the results are presented in Table 1 and
compared with Roddier analyses of selected older image pairs, and with some
results from interferometry.

Some condensed observations from results:

A. An early test from Test 4 produced the best performance result yet obtained
for this scope; this test was performed well before the improvements of steps 2
and 3 above were done.

B. The last test (T9) before improvement indicates anomalously high amounts of
Spherical Aberration and Cosine Secondary Coma.

C. Test 13, with both improved camera centering and improved collimation, might
be expected to show reduced Sec Coma; instead, SA appears to have been reduced,
contrary to conventional optical wisdom.

D. Roddier results appear to be influenced by both the version of Registax used
to process the image sequences and by the settings within Registax used in the
processing. Classic quality estimation done on 500-1000 frames seems to produce
the best results.

Some condensed conclusions:

E. Extreme stringency in scope alignment and collimation appears to improve
Roddier analysis results. It is doubtful if this degree of alignment and
collimation is required for best visual or photographic images. Roddier analysis
appears to be ultimately demanding in these regards.

F. The amount of SA reported by Roddier appears to be affected by the above
adjustment precision, and in some analyses is well above the amount resulting
from interferometry analysis. Conventionally, SA cannot be introduced into an
optical system by alignment/collimation errors. It looks unfortunately like
Roddier can confuse some other system defects for SA, at least in Newtonian
reflectors (or other obstructed optical systems). It may also possibly
exaggerate the
amount of SA actually present.

G. Equally unfortunately, if Roddier can be confused about SA, it might also be
confused about Sec Coma in Newts, etc.

F. Variations in Roddier results versus scope alignment and image processing
variables may mean that a careful calibration of Roddier will be necessary
against an independent analysis technique such as interferometry if consistent
"correct" results are to be obtained. "Uncalibrated" Roddier analysis may be
questionable tool in analyzing obstructed systems (Newts at least).

This small study is certainly not a comprehensive investigation but it may have
indicated some important effects; examination of the posted documents would be
greatly appreciated. Comments/questions/criticisms/etc. are cordially suggested.
Interested members are also
encouraged to check these points independently, hopefully using different image
pairs. If any wish to double check using my image pairs, I will be glad to post
them; I have not done so up to now in a
spirit of being careful with forum storage allotments.

Any assistance with investigating the points discussed here will be most
welcome.

Mick Hollimon
15 Sept 09
6:12 PM PDT USA