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Full Version: St4i 4.0d Image Scale Grade issue
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In the Target Selection tab I have several targets that Sti4 displays the Image Scale Grade as "---" even though it displays the Image Size as several hundred pixels. This is confusing to me. It should display the grade as "A", 'B", etc.

See the attached screenshot with M101 highlighted and the Image Scale Grade listed as "---".

Greg Jones
Hi Greg J.,

Could the issue be related to Surface Brightness of the objects with the '---' entries? I looked at the Messier target list provided with ST4i and M101 has the lowest surface brightness and is the only Messier object with the '---' in the image scale column. The Sh 2-216 has no listed magnitude as does IC 63 and IC 342 has lower surface brightness than M101. Perhaps the code that calculates the scale factor has a cutoff for low surface brightness objects.

Phil S.

I found a couple of bugs that could cause the scale rating to fail. An update will be out soon with a fix.
Thank You, Greg.

I will look forward to the fix.

Greg Jones
I just installed St4i 4.0e and it looks like this issue is fixed.

All targets in the Target Selection tab that have a specific image size listed now also have a specific letter grade for the image scale.

Thank you,
Greg Jones
Thanks for reporting the problem!
Hi Greg C.,

I just tested the Image Scale fix in ST4.0e Imaging using two of my photography based Imaging Systems and there still looks like there's something wrong with Grade. I've attached some screenshots that demonstrate the issue. Galaxies, planetary nebulae and emission nebulae look fixed, but star clusters (open and globular) can show the dashes instead of the expected Grade letter. The lens focal length and camera sensor size both affect the behavior of the Grade letter. For the full frame DSLR camera (5D4) using a lens 200mm or shorter the star clusters have dashes while for the 400mm lens all objects on the Target List receive a Grade letter as expected. For a crop sensor camera (7D2) the cutoff is between 135mm (dashes) and 200mm (correct function). An imaging system using a 1m focal length OTA as the imaging objective also works correctly for both DSLR cameras.

Since I don't have any Imaging Systems that use conventional astro cameras, I didn't check them. I also didn't check the behavior of the iTelescope systems, although I can if you like.

Let me know if you need more information,

Phil S.
Thanks. I'll look into it.