Extreme vignetting with OAG on guider image

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astrofrank
Posts: 5
Joined: Thu Dec 13, 2018 2:50 pm

Extreme vignetting with OAG on guider image

Post by astrofrank » Tue Apr 07, 2020 3:25 pm

I just received my ZWO OAG and attached it to my Celestron Edge11 . Main cam is 1600MM and guider is ASI 174. See attached guider image. The pinhole in the OAG prism stalk is too small to allow a full image to get through, and this is a problem. I need as wide a view as possible with the guider to be able to find a guide star. Can you supply an accessory prism stalk with a larger hole, or can mine be drilled or modified to open it up? Other than that, I am very pleased with the design and quality of the OAG. Thanks, Frank
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CCD Image 40guider.jpg

astrofrank
Posts: 5
Joined: Thu Dec 13, 2018 2:50 pm

Re: Extreme vignetting with OAG on guider image

Post by astrofrank » Wed Apr 08, 2020 12:53 pm

Looks like other OAG don't have this issue. Here is a comment from my post on Cloudy Nights:

"I use the ASI 174 with my Edge 8, and I use the Celestron OAG. It has a large enough prism to make full use of the 174 sensor. Having that larger field of view for guiding makes a big difference in the number of guide stars you have to choose from. With a smaller chip, or a smaller prism (like in the ZWO), it can often be difficult to find a star."

I think the ZWO OAG needs an update.

Frank

Moson
Posts: 205
Joined: Wed Apr 01, 2020 8:28 am

Re: Extreme vignetting with OAG on guider image

Post by Moson » Fri Apr 17, 2020 7:11 am

It is normal for 174+OAG, because 174 sensor is larger than the aperture of OAG. And we recommend you to do the focus of main camera and guide camera in the daytime, it will help you find the star easier.Also, I will convey your feedback to our devs and they will consider this.

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