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Ready to give up on AP

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#1 Orion64

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Posted 19 January 2013 - 10:37 AM

Hi folks, I know this seems a bit drastic, but I am really tired of struggling with the same issue for over a year. I have now spent almost 6000USD on my equipment upgrade. Since then it was only trouble.
My system actually only has one flaw, but this makes it impossible to take photos.
I have a carbon fiber 10inch f/4 newtonian. I purchased the ASA korr reducer/ corrector. My spacing is perfect, although I tried a lot of spacings. Stars in all corners are perfect, EXCEPT one. The one corner is drastically out of focus with lots coma.
I dont think its the ccd. When rotating, the corner gets better but others get worse.
The only answer I get is orthogonality. but I have changed everything in my system now. Nothing gets the problem better.
I have calculated my correct offset of secondary and used how glatters tools in combo with Jason Khadder's colimation steps to colimate my system. No difference. Should I maybe colimate without offset???????
I must add that I have some focusser sag, but I have tried improving it to see the effect and no change to my problem.

The only solution I have to continue my hobby is to do mosaics. This way I can overlay the good part of my 2nd image over my bad part of the 1st image.

#2 vpcirc

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Posted 19 January 2013 - 11:10 AM

Newts are very sensitive to collmanation. The faster the optics the more flaws will show. I wonder if you have a defect in a mirror?

#3 fetoma

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Posted 19 January 2013 - 01:32 PM

If you have focuser sag, try imaging with the focuser on top of the tube.

#4 guyroch

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Posted 19 January 2013 - 01:38 PM

If you have focuser sag, try imaging with the focuser on top of the tube.


I have to agree. How much weight do you have from hanging on the focuser?

I have the same issue right now with my AT8RC. I put the same gear/weight on my AT6RC and all is fine. But on the AT8RC I can't seem to fix it. I understand your frustration first hand.

Guylain

#5 Orion64

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Posted 19 January 2013 - 01:42 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.

#6 jjongmans

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Posted 19 January 2013 - 01:42 PM

Are you sure that the sensor is correctly mounted in the camera housing?

#7 SANDRO78

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Posted 19 January 2013 - 02:29 PM

Effectively, there is a problem on the set up, but I hope that you will arrive has to solve your concern(marigold)??
You have ask advice has ASA or to the manufacturer of the CCD?

Go courage!! :crazy:

#8 Orion64

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Posted 19 January 2013 - 03:22 PM

I cannot confirm that there is no fault with the sensor, however,as I stated when I rotate the camera, the unfocussed corners shift to another spot.

#9 zerro1

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Posted 19 January 2013 - 03:40 PM

I cannot confirm that there is no fault with the sensor, however,as I stated when I rotate the camera, the unfocussed corners shift to another spot.


I take that to mean that the defocussed location does not rotate with the camera...

Do you have this problem without the reducer/corrector?

#10 Orion64

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Posted 19 January 2013 - 04:47 PM

Could not test this because I only have the one reducer. Wouldnt I have horrible coma all over when testing without a reducer?

#11 jmasin

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Posted 19 January 2013 - 04:50 PM

Brett,

Others gave good advice and it seems you have something to try. Don't give up, I have known that level of frustration before, so can relate. It is worth it when you get it right.

Jon

#12 zerro1

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Posted 19 January 2013 - 05:29 PM

Could not test this because I only have the one reducer. Wouldnt I have horrible coma all over when testing without a reducer?


I would think it should be fairly uniform with well focused good looking stars in the center region and increasing coma radiating to the edge of field. If it looks like a normal uncorrected field then it's possible the reducer/corrector is introducing the distortion

You may want to consider just a coma corrector without the focal reduction...

Edit:: I'm pretty sure that moonlite sells a really nice focuser assembly that would solve sag without buying a whole new "APO" scope, for somewhere in the $300 dollar range. :grin:

#13 mmalik

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Posted 19 January 2013 - 09:15 PM

Ready to give up on AP


Don't; here are some thoughts/suggestions, I am afraid you'll have to spend just a bit longer.

1. Ditch your Newtonian; buy or test your setup on an APO if you have access to one. That will rule out the scope. Personally, I am for APOs when it comes to AP; rest are just half measures in my opinion.

2. To rule out it’s not the scope, try a DSLR on the same setup if you have access to one. May borrow one if you can or just buy a good one that you may also keep using alongside the CCD.

3. You seem to have too much weight for your focuser; changing scope with an APO may bring a solid focuser into the picture.

4. Orthogonality of the sensor, if true, will require fixing or swapping your existing CCD with a different one. One of the above should help to confirm/reject that conjecture.

5. Last, but not least; start salvaging your entire setup in favor of starting fresh and recouping some of your losses. Weakest link in your setup are your scope/focuser in my opinion.


Some useful links in light of the above:

•APO consideration...

•DSLR consideration...

•DSLR image processing instructions...

•Other CCD alternatives...

#14 blueman

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Posted 19 January 2013 - 10:16 PM

I had my years of frustration with reflectors. Flexure, coma, field curvature all of the problems that you can face, I wrestled with in spades.

I finally went to a good APO refrator and never had to deal with these issues again.

Am I saying reflectors are bad? No. I am saying they can be very difficult to deal with and life is too short.
Blueman

#15 vpcirc

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Posted 19 January 2013 - 10:34 PM

I'd ditch the CGEM before anything else!

#16 JWalk

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Posted 19 January 2013 - 11:49 PM

I'd ditch the CGEM before anything else!


Don't knock the CGEM!!! It is capable. Couldn't resist Mikey

#17 elbee

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Posted 20 January 2013 - 01:46 AM

Don't knock the CGEM!!! It is capable.

uhhh, Paramount? is that the consequence of a close relationship with a CGEM :roflmao:

#18 Orion64

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Posted 20 January 2013 - 07:46 AM

Thanks for the replies guys. I have access to an apo refractor. I will try my setup on this in the mean while

#19 vpcirc

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Posted 20 January 2013 - 09:15 AM

Don't knock the CGEM!!! It is capable.

uhhh, Paramount? is that the consequence of a close relationship with a CGEM :roflmao:


Yea I started with one those &$$@@%~} mounts. Jimmy is giving me a hard time because he shot beautiful images on one. (He got a good one)
I hadn't read Wodaski's book when I started telling me most of money should be in the platform. I was also doing a typical beginner mistake and going for the most aperture I could afford, then reality set in! Once I bought my first AP, I'd never go back to a low end mount. I'd image with a 15 year old APO and a 5 year old camera before I'd image with a poor platform!
Jimmy why don't you send that AP1600 with encoders back and put that new RC 16" on a CGEM deluxe? Lol In all fairness, CGEMs have gotten better since I owned one 4 years ago.

#20 JWalk

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Posted 20 January 2013 - 09:41 AM

I wouldn't put much on top of the CGEM. I think my FSQ was about at the limit of one.

#21 orion69

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Posted 20 January 2013 - 10:14 AM

Do you use OAG? If you don't then you can expect all kinds of funny things with newton telescope. I would never try to image with any telescope whose backfocus don't allow use of OAG, especially newton.
I'm considering to buy Veloce RH200 sometime this year and there is ongoing debate if RH200 can use OAG. RH200 is probably far better constructed compared to any newton but I will not buy it if there is not enough backfocus to support OAG, filter wheel and camera.
Of course you can get good images without OAG but you can never be sure that some flexure wouldn't appear.
With use of OAG you solve flexure problem for sure.

Also, I don't think that CGEM can handle 10" newton for AP. If it's perfectly balanced, maybe.

#22 Orion64

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Posted 20 January 2013 - 01:20 PM

Helo Knez, Luckily I have the carbon fiber version. It is very light with only about 10kg to it. Yes I am using an off axis guider with about 10mm left for other spacers and so on

#23 quantumac

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Posted 20 January 2013 - 04:28 PM

With this hobby we typically image objects thousands to billions of light years away, incredibly vast yet unimaginably faint, and we're doing so with relatively inexpensive commercial-grade equipment which must be calibrated to extremely tight tolerances, sometimes to the micron level.

Somebody needs to write "Zen and the Art of Deep Sky Astrophotography." The first two words should be "Patience, grasshopper."

#24 Bill W.

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Posted 20 January 2013 - 11:26 PM

Getting a f/2.8 reflector collimated can be very, very trying. F/4 is bad enough. I'd seriously consider getting a coma corrector (Baader, Astro-Tech, Paracorr) and using your scope at is native focal ratio if that's possible. The other thing you might want to think about is just selling the newt and getting a refractor especially if your setup isn't mounted in an observatory. The last thing you might consider is replacing the focuser. I use a Moonlite with the high precision encoder on my AT8IN. It's great to be able to focus without going out to my scope. In the very least I'd rotate the focuser so it's on top or bottom.

-Bill

#25 jmasin

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Posted 21 January 2013 - 11:06 AM

I had my years of frustration with reflectors. Flexure, coma, field curvature all of the problems that you can face, I wrestled with in spades.

I finally went to a good APO refrator and never had to deal with these issues again.

Am I saying reflectors are bad? No. I am saying they can be very difficult to deal with and life is too short.
Blueman


I do not wish to start a refl/refr war... but I too went through this. While F/4 or faster might be nice, I cannot begin to express the joy of putting a scope in the dovetail and having it just work. There's enough things to go wrong without me fiddling with the optics themselves.

Other than very long FL work that hope to do some day when I have a more permanent setup, I do not see myself going reflector again. I know this doesn't help your current situation, but I did want to add to what Blueman said.

I guess if it does get to the point where one isn't enjoying the hobby anymore (and I've been there), sometimes a change of direction is required. That's what I went through, it was a hard and not cheap decision, but it reinvigorated me and I spend a lot less time cursing in the dark and more time imaging.

Just food for thought... whatever form it takes, don't give up!






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