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Where does the tilt come from?

TS-Optics PHOTON 150mm/6" f/4 Newtonian ZWO ASI533MC Pro ZWO AM3 Tilt Troubleshooting
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Maksim Selivanov avatar
Maksim Selivanov avatar
Hello,
Recently bought used TS 6F4 and trying to start AP with it. My setup is ZWO AM3, TS 6F4, Sharpstar 0.95 CC, ASI 533MC Pro, Gemini EAF. On the first captured images i saw a tilt, ASTAP measured it in about 15-20%. I've moved camera and CC to my main scope (SW 130PDS) and checked - there is no tilt at all. So i think tilt is coming from TS telescope.
I've put some tape into TS focuser (like on SW), so CC does not move and sag. Also i add ZWO tilter to the camera and it helped - i can adjust tilt with it up to 3-5%.
But how can i find which part of TS telscope make this tilt? Maybe it can be fixed without tilter.
Helpful Engaging
andrea tasselli avatar
andrea tasselli avatar
Focuser.
Maksim Selivanov avatar
Maksim Selivanov avatar
andrea tasselli:
Focuser.

Thanks. Do you mean that the focuser is not centered? It is not adjustable like SW focusers, so if yes, i have to use tilter and forget about it)
Ruediger avatar
Ruediger avatar
99% sure the focuser. Really good focuser are rare and expansive. Usually the weakest part in the chain and often neglected by vendors.
Haakon Rasmussen avatar
Haakon Rasmussen avatar
Hallo Maksim,

in my experience the tilt is caused by miscollimation, most often of the secondary mirror not being perpendicular to the main mirror. Are you absolutely sure that your telescope is well collimated? On my telescope, if i get i well collimated, the tilt disappears.   

CS Haakon
Helpful Concise
Maksim Selivanov avatar
Maksim Selivanov avatar
Haakon Rasmussen:
Hallo Maksim,

in my experience the tilt is caused by miscollimation, most often of the secondary mirror not being perpendicular to the main mirror. Are you absolutely sure that your telescope is well collimated? On my telescope, if i get i well collimated, the tilt disappears.   

CS Haakon

Thanks, i'm sure that it's collimated as well as possible, this is not my first experience with collimation)
Dark Matters Astrophotography avatar
Dark Matters Astrophotography avatar
Tilt causes a change in focus across the field. If you posted a sample frame, people would be able to weigh in more.
Well Written Insightful Respectful Concise
andrea tasselli avatar
andrea tasselli avatar
Maksim Selivanov:
Thanks. Do you mean that the focuser is not centered? It is not adjustable like SW focusers, so if yes, i have to use tilter and forget about it)


*On mine there is silght tilt and the only way you can correct for it is by using a tilter. Tilt, not offset.
Maksim Selivanov avatar
Maksim Selivanov avatar
Dark Matters Astrophotography:
Tilt causes a change in focus across the field. If you posted a sample frame, people would be able to weigh in more.

Here are some examples captured without guiding in city center:
before tilt adjustment


after tilt adjustment


Now i prepared this telescope for guiding and waiting for the weather to do more tests and do fine adjustment.
Maksim Selivanov avatar
Maksim Selivanov avatar
Haakon Rasmussen:
Hallo Maksim,

in my experience the tilt is caused by miscollimation, most often of the secondary mirror not being perpendicular to the main mirror. Are you absolutely sure that your telescope is well collimated? On my telescope, if i get i well collimated, the tilt disappears.   

CS Haakon

You was absolutely right! I tried to think logically - what part of telescope forms light cone to focuser? Ofcourse it is the secondary mirror.. What if try to adjust it under the stars, not by chinese collimator? Yesturday i tried slightly move screws and see what happens with tilt in astap, and it works! Thank you very much, finally i can remove the tilter and see good stars in each corner.
So if that laser collimator is enough for my 130PDS (F5), for F4 i need adjust secondary mirror much more carefully. Hope that will helps someone.
Supportive
Maxim avatar
Maxim avatar
Worth mentioning that laser colimators also require collimation
Haakon Rasmussen avatar
Haakon Rasmussen avatar
Glad to be of help!
David Serquera avatar
David Serquera avatar
You will need an autocollimator and cat's eye collimation method. You can use a laser only for the first approximation to center the secondary but then you forget about it and you collimate with cta's eye method and then with a star following Nawratil's guide: https://data.tommynawratil.com/Astro/pdf/Photonewton_Collimation_Primer_EN.pdf
Your sensor is small so I do not think you will have much problems when the secondary will deviate with time.
Maksim Selivanov avatar
Maksim Selivanov avatar
David Serquera:
You will need an autocollimator and cat's eye collimation method. You can use a laser only for the first approximation to center the secondary but then you forget about it and you collimate with cta's eye method and then with a star following Nawratil's guide: https://data.tommynawratil.com/Astro/pdf/Photonewton_Collimation_Primer_EN.pdf
Your sensor is small so I do not think you will have much problems when the secondary will deviate with time.

As newbie i didn't hear about autocollimators yet. Read some information, it's seems to be that i need. But the price for cat's eye is the same as the price of my Photon 6F4) Will try to find one with good delivery price to my city. Maybe i'll find another AC with the same features..
Anyway, thank you!
David Serquera avatar
David Serquera avatar
Maksim Selivanov:
David Serquera:
You will need an autocollimator and cat's eye collimation method. You can use a laser only for the first approximation to center the secondary but then you forget about it and you collimate with cta's eye method and then with a star following Nawratil's guide: https://data.tommynawratil.com/Astro/pdf/Photonewton_Collimation_Primer_EN.pdf
Your sensor is small so I do not think you will have much problems when the secondary will deviate with time.

As newbie i didn't hear about autocollimators yet. Read some information, it's seems to be that i need. But the price for cat's eye is the same as the price of my Photon 6F4) Will try to find one with good delivery price to my city. Maybe i'll find another AC with the same features..
Anyway, thank you!

*** Hi, check the one of Farpoint Astro ***
Maksim Selivanov avatar
Maksim Selivanov avatar
Hello Experts!
Don't want to create another post and will ask new question here. After carefully adjustment and first tests i found another problem that i can't explain. On the fits image i see pretty round stars, but after initial stretch in ghs they looks like a small crosses. It happens only wigh middle-bright stars on the whole image, not in the corners. If i use bxt to reduce their size they looks like sharp crosses) I didn't see that before with another telescopes. What can it be - pinched optics, astigmatism or something else? Bright stars looks good..
fits.jpg
pi_ghs.jpg
pi_bxt.jpg
David Serquera avatar
David Serquera avatar
Hello. It is difficult to say. Looks like undersample but I think you have 1.36 arsec/px. What I would do is to drizzle 1x or 2x and see if there is an improvement.
Maksim Selivanov avatar
Maksim Selivanov avatar
David Serquera:
Hello. It is difficult to say. Looks like undersample but I think you have 1.36 arsec/px. What I would do is to drizzle 1x or 2x and see if there is an improvement.

Hi, thanks for that idea. I've compared two same stretched images - without drizzle and with 1x, and last looks a little bit better. So this pixel scale is not enough for good seeing, right? And solution for me is only with postprocessing by PI?
David Serquera avatar
David Serquera avatar
I think your images are fine anyway. It depends on what do you want to show, if small stars or large nebula gradients or fine structures. I personally always try to do drizzle 2x to gain from deconvolution with BxT but that it is up to you.
Maksim Selivanov avatar
Maksim Selivanov avatar
After all it was a pinched mirror. Here is crop of processed picture (without drizzle) after releasing the mirror clips - stars looks round and pretty good.
David Serquera avatar
David Serquera avatar
excelent
Tony Gondola avatar
Tony Gondola avatar
This is a good example of understanding and applying the basics first.