Focusing on a star

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skullandbones
Posts: 6
Joined: Fri Aug 03, 2018 10:24 pm

Focusing on a star

Post by skullandbones » Mon Jun 08, 2020 4:42 pm

I have my asiair pro attached to a asi120mc-s on my Meade 12 SCT. I tried focusing on a star and got a surprise. When I got close to the focal plane, I could see donuts on both side of fine focus but when zeroing in I could not attain a pin point. Instead I got a disc about the size of the donut hole. Is there a setting like exp or gain that would create this result? My image train is made up of an EP adapter on the visual back with a diagonal attached to that and then the camera. From the VB to the approximate camera sensor plane is about 120mm. So my question is: do I have an image train issue or a setting adjustment problem (user error)?

Thank you,

WEK

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ASIAIR@ZWO
Posts: 487
Joined: Tue May 29, 2018 3:29 am

Re: Focusing on a star

Post by ASIAIR@ZWO » Mon Jun 29, 2020 7:12 am

skullandbones wrote:
Mon Jun 08, 2020 4:42 pm
I have my asiair pro attached to a asi120mc-s on my Meade 12 SCT. I tried focusing on a star and got a surprise. When I got close to the focal plane, I could see donuts on both side of fine focus but when zeroing in I could not attain a pin point. Instead I got a disc about the size of the donut hole. Is there a setting like exp or gain that would create this result? My image train is made up of an EP adapter on the visual back with a diagonal attached to that and then the camera. From the VB to the approximate camera sensor plane is about 120mm. So my question is: do I have an image train issue or a setting adjustment problem (user error)?

Thank you,

WEK
Hey WEK, could you please send us some images of your setup to asiair@zwoptical.com? It seems like an optical issue.
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skullandbones
Posts: 6
Joined: Fri Aug 03, 2018 10:24 pm

Re: Focusing on a star

Post by skullandbones » Tue Jun 30, 2020 7:41 pm

Yes. I think it is a optical problem after reading more and getting some advice from other users. with this slow (f10) scope and camera with tiny sensor, I may be trying to achieve results which are not worth the trouble. I will eventually acquire another zwo camera with adequate sensor and characteristics I need for success. I used my asiair pro with the same asi120mc-s camera but on a Celestron 8 with Hyperstar lens. so with a focal length of 390 as opposed to the 3048 of the Meade, I had much better results at capturing at least a star image. I used a alt-az mount and a short snap shot for Alberio. f1.9 is much better than f10. I still have pointing problems so I am also switching over to my new SW eq6r-pro. i should have much better results with this setup after getting a good PA.

Thank you for your concern but we can call this issue closed.

skullandbones
Posts: 6
Joined: Fri Aug 03, 2018 10:24 pm

Re: Focusing on a star

Post by skullandbones » Thu Jul 02, 2020 11:54 pm

Just to follow up: I have changed my rig to something a little easier for this camera to handle. I installed a Hyperstar lens on my Celestron 8 with the asi120mc-s. I also am using my new asiair pro. So immediately, the very fast f1.9 Schmidt camera makes all the difference in the world. Finding and focusing on a star is easy now. I'm not even using a Bahtenov mask yet. I am now sure the setup using the Meade 12 was just not fair for the camera and it's tiny sensor. I will stick to dslr 40d Cannon on the big scope. With the Hyperstar/C8 combo there is no problem focusing with this camera. I can't imagine how good it will be with a better camera with large sensor will be like.

Thank you,

WEK

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