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Ready to give up on AP

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#26 John Wunderlin

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Posted 21 January 2013 - 03:48 PM

Have you considered pinched optics? The clamps that hold reflector mirrors in place can very easily mess up your optics if one is too tight...

#27 Chrishem57

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Posted 25 January 2013 - 05:46 PM

I've got a C14HD that changes drifts through the night, The autoguider shows that it is dead on. After a lot of investigation, I determined that the mirror was moving with rotation. The mirror clamps that are on the back do little to help. Solved that with off axis guiding. Still the focus is very sensitive to temp and requires a few checks through the night.
By the sounds of your issues, I think you have (at least) two; culmination, ccd imager not being square to focal plane and some mirror movement. With your mirror movement, culmination will be tough since it will move out of culmination when you rotate to your target. Try without the reducer/corrector, look at using a smaller chip (surrender). Figure out some way to keep the mirror from moving.

#28 Jared

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Posted 26 January 2013 - 11:20 AM

Lots of good ideas for problems other than what you are describing, but you already identified the problem yourself. Differences in focus in different corners are due to orthogonality. Collimation won't do it. Pinched optics won't. Virtually all optical defects in the mirror or reducer would affect the entire image. It's an orthogonality issue, and you already mentioned you have some focuser sag. No need to look elsewhere for the cause.

What to do about it... I assume you are already setting your scope up so the camera is either on top or on the bottom, not hanging out the side as you would set it up for visual, yes? If not, that's the first step. Obviously, the tube rotation will be different for different parts of the sky. the idea is to minimize the effects of gravity so you minimize sag. I see lots of people with imaging Newtonians putting their cameras on the bottom rather than the top--perhaps having gravity pulling the camera "out" rather than pushing "in" produces less flex? Worth a shot if you aren't already doing it. Next, make sure the focuser itself is adjusted to minimize flex. Can't tell you the specific steps to take since I am not familiar with your particular focuser.

After these two ideas, things get a little harder. The adapter you are buying will let you make an adjustment, and if you have a true orthogonality problem rather than just focuser sag it will work perfectly. I have a similar device on my AT10 and it works great. If, however, this is really just focuser sag it isn't going to help any since the adjustments required will be different for each part of the sky. If it's really focuser sag and you can't adjust the focuser enough to fix it, your only choices are to contact the manufacturer (ASA?) for ideas or to reduce the weight of your camera and OAG. Obviously, that last option isn't very appealing. If you are already using a DSLR rather than a large, heavy CCD you've really got nowhere to go.

Have you talked to ASA yet about the focuser sag? You simply can't have focuser sag in a fast optical system--too wide a field of view.

#29 Jared

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Posted 26 January 2013 - 11:35 AM

By the way, one test you can do to determine whether the problem is focuser sag or a more "permanent orthogonality issue is to choose a target near the meridian and take a sub exposure with the scope on either side of the mount (do a meridian flip). If the corner stays the same (after you orient the images the same way, since the meridian flip will flip the images), then it's focuser sag and your shimming adapter won't help. If the corner changes (again, after you flip the second image to have the same orientation as the first), then the shimming adapter should fix the problem permanently.

I think I got that test the right way around. :) It's hard to think these things through straight in one's head. Please someone correct me if I've got it backwards. I think the meridian flip and the change in gravity would offset, so the corner would stay the same.

#30 SL63 AMG

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Posted 26 January 2013 - 03:21 PM

If you are using an ASA 10" Newtonian you should not have issues with mirror flop when slewing. If you are, then you need to adjust the three nylon screws that hold your mirror in place.

I have an ASA 10" Newtonian and I had a similar problem with mirror movement. I also had issues with collimation and I solved all of these issues.

This is how I solved them.

To elliminate all mirror shift, remove the primary mirror from the telescope, loosen the three nylon screws and then place a sheet of standard printer paper between the side of the mirror and the nylon scew. Tighten the nylon screws until they place some pressure just enough against the paper that you can't pull it out. Then back off the nylon scew just a fraction or until a slight tug allows you to pull the sheet of paper away from the mirror. Do this same procedure for all three nylon scews. This will leave the nylon screws in a position to where they barely are touching the edge of the mirror, enough to prevent mirror movement while not placing unecessary pressure against the mirror.

To ensure excellent collimation with this telescope I recommend three important steps.

1) replace the secondary mirror screws with socket head screws. This will enable you to have more precision control over adjusting collimation of the secondary mirror.

2) re-center spot your mirror with a radiation symbol instead of the triangle. This will provide more precision alignment when using the CatsEye Inifinity autocollimator in the final step of collimation.

3) Use the CatsEye Blackcat XL and Inifinity Autocollimator to collimate this scope.

And NEVER use a star to collimate your ASA Newtonian telescope. When you are perfectly collimated, a star will ALWAYS appear out of round.

The ASA N10 Newtonian astrograph is an excellent telescope. I use mine with their DDM85 mount and I can take images at F/2.8, F/3.6 and F/6.3 up to 30 minutes without guiding. I have no need for an OAG for this system.

#31 guyroch

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Posted 26 January 2013 - 04:10 PM

I found an adapter that adjusts any tilt that one has in the optical path. So I wihl place my order on monday and try this out. Its not expensive, so its definitely worth giving a go.

Tonight is one of those clear wind still nights, however my equipment stays in doors until my adapter arrives.


Have you received your tilt camera adapter yet? 'm curious to see the results.

Guylain

#32 alpal

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Posted 26 January 2013 - 07:28 PM

If you are using an ASA 10" Newtonian you should not have issues with mirror flop when slewing. If you are, then you need to adjust the three nylon screws that hold your mirror in place.

I have an ASA 10" Newtonian and I had a similar problem with mirror movement. I also had issues with collimation and I solved all of these issues.

This is how I solved them.

To elliminate all mirror shift, remove the primary mirror from the telescope, loosen the three nylon screws and then place a sheet of standard printer paper between the side of the mirror and the nylon scew. Tighten the nylon screws until they place some pressure just enough against the paper that you can't pull it out. Then back off the nylon scew just a fraction or until a slight tug allows you to pull the sheet of paper away from the mirror. Do this same procedure for all three nylon scews. This will leave the nylon screws in a position to where they barely are touching the edge of the mirror, enough to prevent mirror movement while not placing unecessary pressure against the mirror.

To ensure excellent collimation with this telescope I recommend three important steps.

1) replace the secondary mirror screws with socket head screws. This will enable you to have more precision control over adjusting collimation of the secondary mirror.

2) re-center spot your mirror with a radiation symbol instead of the triangle. This will provide more precision alignment when using the CatsEye Inifinity autocollimator in the final step of collimation.

3) Use the CatsEye Blackcat XL and Inifinity Autocollimator to collimate this scope.

And NEVER use a star to collimate your ASA Newtonian telescope. When you are perfectly collimated, a star will ALWAYS appear out of round.

The ASA N10 Newtonian astrograph is an excellent telescope. I use mine with their DDM85 mount and I can take images at F/2.8, F/3.6 and F/6.3 up to 30 minutes without guiding. I have no need for an OAG for this system.



Pity they don't say all that in their adverts:

http://www.optcorp.c....aspx?pid=10553

I can understand the frustration of Brett.
I had a lot of experience before buying my setup &
knew about the problems of short focal length Newts.
That is why I went for an 8" f6 Newt.
All the short FL Newts. require an advanced imager to set up.

When I take my flats I can see that my secondary is not centred -
it's also covered in dust but I'm loathed to play around with it in case I make it worse.
I seem to get a nice flat field just by collimating with a
$120 laser collimator using a black paper re-enforcement circle on the centre of the mirror.

All of the above problems make me hesitate to buy a short FL scope.
RC scopes are of interest to me at the moment but that's once again a whole new ball game.


I think Brett will have to follow your advice & see where it takes him.
The rewards could be excellent in theory.

cheers
Allan

#33 shams42

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Posted 26 January 2013 - 10:26 PM

I've imaged with a variety of fast Newts -- "fast" being a relative term. I had a lot of frustration with an f/4 Newt that I ran at f/4.6 due to the Paracorr. Even tiny little shifts in collimation due to structural sag or temperature shift would cause me to get bad corners.

I think somewhere around f/5 is the "sweet spot" for Newts. I recently bought a 10" f/4.7 that runs at f/5.4 with Paracorr and so far it's been really sweet and easy to deal with.

My experience at f/4.6 makes me extremely hesitant to try anything faster. The tolerances are just too tight IMO.

Good luck.

#34 SL63 AMG

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Posted 27 January 2013 - 02:15 AM

I don't have any issues with collimation at F/3.6. I have a focusing issue with the corrector for F/2.8. It hangs aoccasionally when trying to home. Haven't played with it enough yet to try to correct it.

By the way, I am not an advanced imager. I would categorize myself as beginner to intermediate.

I started imaging 2 1/2 years ago with a CPC1100 on a wedge, with a refractor for guiding and it was a disaster.

I bought the ASA system just about 2 years ago and have learned literally everything I know in that time. I have had tons of help, did lots of research and reading and experimented alot before figuring out these things I have learned about imaging with a fast newtonian.

I can say this. I feel I have mastered all of these problems and I believe anyone can do it with time, patience and some help from people like myself that have experienced these issues.

In the end, I wouldn't trade my ASA 10" Newtonian Astrograph for anything. I love it. The images are spectacular and thanks to some help processing from YuriyT, my LBN438 image was published in January 2013 Astronomy Magazine.

LBN438 taken with ASA 10" Newtonian Astrograph

Don't give up. You have a wonderful imaging telescope. Learn to master it and you won't be dissapointed.

Let me know if you need more help. I am happy to share the knoweledge I have gained about this telescope.

By the way, I also image with an AstroTech AT12RC. I had mirror issues, collimation issues, tilt issues, focuser sag issues and more.

I have solved all of them with help from more experienced people and now I have an excellent 2432mm FL RC.

M51 taken with AT12RC

I think all imaging telescopes present their own unique set of challenges. You can overcome them all with perseverence, patience and sometimes a little money.

My RC is a $4000 telescope and I have about $10K hanging off the back of it and that's not including the MOAG and ST402 I just ordered for guiding.

AT12RC Rear Cell with Pyxis Rotator, Atlas Focuser, CFW and Camera

Again, let me know if you need additional assistance getting your ASA performing. I am sure I can help you.

#35 SL63 AMG

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Posted 27 January 2013 - 02:25 AM

Pity they don't say all that in their adverts:

http://www.optcorp.c....aspx?pid=10553

cheers
Allan


What is there to say? Adjusting the tension on the mirror is not something worthy of advertising on a sales page.

Nor is telling the owner which type of collimation tools they should use. It's really a matter of preference. I am merely stating what worked best for me.

Recenter spotting the mirror was another personal preference. I feel that a more precision final autocollimation can be performed bringing together two radiation symbols which make a perfect circle rather than two intersecting triangles making the star of david.

I also felt like I had more precision control of the collimation of the secondary using socket head allen screws rather than the indented ones.

These are all personal modifications that I made to my astrograph in order to make it simpler and quicker for me to make a precision collimation of my scope.

Others have successfully collimated their ASA astrographs with no modifications.

I don't really think it is necessary for a reseller or manufacturer to put this information in their sales literature, however, it may be wise of ASA to look at my mods and implement them.

#36 morten

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Posted 28 January 2013 - 11:55 AM

I have the same problem with f/4.8 and the ASA reducer.
Goes away with the paracorr, but the system gets slower.
I'll work some more, but are more inclined to accept f/5.5.
If tilt is the culprit shouldn't we see defocused stars rather than the oblong ones? The acceptable tolerance for the ASA reducer, as coma corrector, is around 1 mm, which is way, way above the 3-4 micron focus tolerance. 1mm corersponds to 250 steps in my focuser, and that gives you out-of focus stars where you can see the central obstruction, and where the spikes are absent.
Can anyone explain why slight tilt should give you coma in one corner?

#37 Orion64

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Posted 28 January 2013 - 02:44 PM

Thank you everyone for the posts and replies.
I think that the manufacturers could pay a little more attention to their manuals. I would suggest that they give a little more info on issues that have a major effect on especially these fast systems. I agree that everyone has their own preferences but maybe just go in depth on the more popular methods eg Howie Glatter AND catseye.

For my collimation in the end, I am spot on. I used Jason Khadder's procedure. I modified his template for my newtonian and by just using the glatter laser and the holographic attachment, I was able to get dead accurate offset, secondary and primary colimation. I must add that, at f2.8, collimation is very sensitive to slight errors. I saw this one night when I realized my stars were looking very bad. I checked my colimation and there it was, my primary was just a tad out. when I got this fixed, everything was working. Luckily, my colimation technique is rock solid by now and it only took about two minutes.

My tilt adjuster arrived. In short, I think that it might have done the job! But, I do not want to count my chickens before they hatch. There were quite a few tricks for this simple but efficient tool. If everything works out as hoped, I will post a review of my experience on CN. My biggest challenge however was that I could not reach the adjustment screws for the tilt adjuster due to my filter wheel blocking the way.
Anyway, It looks like my stars are now round and in focus right into the corners. I tested this with a bahtinov mask as well.
Unfortuneately, high winds caused the skies to be very unsteady, yielding very soft stars. This is why I am not 100% sure that my setup is working now.

BTW Dave, I followed your advice and made a few mods to the scope example the secondary colimation scews. Works much better now! Thanks

#38 Orion64

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Posted 28 January 2013 - 02:53 PM

I have the same question that Morten asked. I do not quite know the answer, but I have seen a lot of strange things happen when there is tilt in the system. Above a certain (actually quite small with the ASA reducer) tolerance level, stars can actually became elongated double stars...

#39 Orion64

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Posted 28 January 2013 - 03:11 PM

This is my star test of flatness of field posted in flickr. If someone would like to use ccd inspector and give me the results, that would be great. I do not think that the field is perfect, but it looks like the system is now working. It also looks like a BIG improvement on what I had.

Apologies for the hot column. The TEC was off when I tested the camera.

http://www.flickr.co...in/photostream/

#40 SANDRO78

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Posted 28 January 2013 - 03:18 PM

Hy Orion64
What is that it would not be bound has a probleme of USB or an alimentation??
@lex

#41 Orion64

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Posted 28 January 2013 - 03:27 PM

Hi alex, I think it is just a hot column caused by the tec which was turned off. When I uploaded the image onto flickr, it seemed to make the problem much worse (dont know why).

#42 SANDRO78

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Posted 28 January 2013 - 03:57 PM

Your problem is strange !!
Good luck !!
@lex

#43 neptun2

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Posted 28 January 2013 - 04:30 PM

Well the image looks ok now. I don't see any problem in one of the corners. Most probably it was really orthogonality problem. A friend of mine had similar problem - prolonged stars in one of the corners and in his case it was caused by sensor shift after the modification of his DSLR. When this was fixed everything was ok. in your case the focuser alignment that you did obviously fixed the problem.

#44 shams42

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Posted 28 January 2013 - 06:57 PM

Have you tried test exposures on both sides of the meridian, etc, to make sure that the problem isn't fixed only in one orientation?

#45 Orion64

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Posted 29 January 2013 - 05:58 AM

Have you tried test exposures on both sides of the meridian, etc, to make sure that the problem isn't fixed only in one orientation?


This is a good point. I will test this tonight.

#46 morten

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Posted 30 January 2013 - 02:08 PM

What is the difference bewteen using a tilt aduster in the path between the reducer and the cam, and adjusting the tilt of the focuser. I guess new collimation is necessary for the latter?

#47 Gray

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Posted 01 February 2013 - 11:22 AM

Looks like you may have it figured out Brett. With $6K involved you shouldn't even think give up. Never give up. I hope all of your work pays off soon. CS






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