SGP vs. BYE image quality not the same


Good evening,

Finally getting the hang of SGP and have the sequencing and tracking working great. The issue I am having is with the image quality of SGP not being on par with BYE.

Camera: Modified Canon T6i
OTA: Celestron EdgeHD 11" no reducer

As you can see in the attachedments, both the unstretched and streched images do not look the same. The left hand image is the capture obtained via SGP. The right image was captured via BYE. Both files are 120 sec. exposures as ISO800. Both were captured as RAW format. Some on Cloudy Nights have suggested the ISO is actually capturing at 100 instead of 800.

Question: What additional setting(s) am I missing that may be causing these poor images/incorrect ISO in SGP?

If additional information is needed, please ask.

Thanks in advance for any assistance provided.


If you’re capturing as RAW it should be pretty easy to look at the EXIF data and see what the camera set between the two.

Are you using mirror lockup? My guess would be that it is not enabled in SGP and you’re only capturing the lockup time. I think the difference between 100 and 800 ISO (while certainly noticeable) would not be this dramatic.




Thanks for the EXIF tip, looks like it is exposure time and not ISO (see attached image). You mention mirror lock. I do not see anything with “mirror lock up” or the like in SGP. Are you recommending disabling it in the camera itself? I may try that tonight to see if it makes any difference.


The option for mirror lockup is in the Canon Settings dialog:

SGP does not enable the mirror lock up in the camera. So if you have a non-zero value set here you need to have mirror lock up enabled in the camera. My guess is that you have it disabled in the camera but possibly enabled in SGP.



yep - been there, done that ! When the EOS has mirror lock up enabled in its menu system, it expects two trigger events. The first flips the mirror, the second does the exposure. I didn’t realise and had the SGP dialog as Jared shows. In this case there is only one trigger and I wasted an entire night before I realized what I had been doing. Also note that some acquisitions programs display a color image and others do not. The default color debayer algorithm used by photographic RAW converters is not necessarily ideal for astro work. I normally save as a FITS file and then carefully select a debayer algorithm (like VNG) that improves the appearance in the image processing software.


Much appreciated. Issue has been resolved. Thanks Jared. I had the “Mirror Settle Time” set to 1 sec. in SGP but had “Mirror Lock” disabled. As a result the shutter was only staying open for the 1 sec. settle time. I set the “Mirror Settle Time” to 0 sec. and everything is capturing as expected during tonight’s session (still ongoing.) Will attempt to enable the mirror lock in the camera and the mirror settle time during the next session.


Hello All,

Just to be clear, if I want to use the mirror lock up function on my EOS then I need to enter a value higher than zero (0) on the “Mirror Settle Time” box and also enable this function on my camera, correct?



That is correct, check the information on your EOS. If I remember correctly, the T6 series was the first to have a configurable “Mirror Lock” which has carried over into the T7 series. I believe earlier models do not have this option.

Steps I have tested that work:

1 - Enable “Mirror Lock” in the EOS menu.
2 - Set the “Mirror Settle Time” in SGP to something greater than 0. The value is in seconds.


1 - Disable “Mirror Lock” in the EOS menu
2 - Set the “Mirror Settle Time” in SGP to 0.

Good luck gomezdb and clear skies.


Ryan, I saw your thread on CN. Glad you got this resolved! Interesting to know about the mirror lock feature/side effects here. Will have to remember that for future reference.


Hi Ryan,

Thanks for the information!


Camera shutter will only stay open for 2-3 seconds