Are other peoples iOptron GEM45's this good? because I'm blown away!

[Chris]

2 hours ago, vlaiv said:

What is average FWHM, star eccentricity and number of frames that did not make it into the stack?

I was using a stand alone Fuji XT1 so no PC hook up for FWHM info. I stacked 90% but all subs had round stars when I zoomed so I probably could have stacked 100%. 

The whole thing feels supernatural some how! 

 

[vlaiv]

6 minutes ago, Chris said:

I was using a stand alone Fuji XT1 so no PC hook up for FWHM info. I stacked 90% but all subs had round stars when I zoomed so I probably could have stacked 100%. 

The whole thing feels supernatural some how! 

You can check FWHM of the stack as well as roundness of the stars.

Roundness of the stars coupled with sampling rate (arc seconds per pixel) will show to some extent periodic error drift over duration of exposure.

Total FWHM will show what was the seeing like. Poor seeing can mask star elongation, and if stars have high FWHM - we can't know if it is down to seeing (missing guiding info since you did not guide) or mount precision.

[Chris]

2 hours ago, vlaiv said:

You can check FWHM of the stack as well as roundness of the stars.

Roundness of the stars coupled with sampling rate (arc seconds per pixel) will show to some extent periodic error drift over duration of exposure.

Total FWHM will show what was the seeing like. Poor seeing can mask star elongation, and if stars have high FWHM - we can't know if it is down to seeing (missing guiding info since you did not guide) or mount precision.

I've used CCD inspector to chart the FWHM over the course of the night. As you can see it gets pretty bad later on, but not using a dew strap could have caused this due to lens haze.

Also, CCD inspector doesn't open the Fuji Raw files so this is based on Jpegs (I have the camera set to RAW plus jpeg) and I know you're supposed to use RAW for this. 

For reference the setup gives a pixel scale of 2.29"/pixel.

The mean average FWHM was around 6" which isn't great. 

For what it's worth:

Here is the actual real world difference between sub 6 (the best FWHM because sub 1 was me focusing on a star :D) and sub 23 (the worst)

 

When I've recovered from the dreaded lurgy and have another clear night I will repeat the above (but on another target) and see how it compares. 

Edited December 20, 2021 by Chris

[vlaiv]

40 minutes ago, Chris said:

The mean average FWHM was around 6" which isn't great. 

Yes, that is very high.

I've blown up a bit image so it can be seen easily - these stars are in fact elongated by pixel or two in horizontal. Given that your pixel scale is ~2.3"/px, that sort of matches <7" p2p periodic error claimed by iOptron.

This mount can be used at this sampling rate without guiding (and stars won't be perfect but close) - but someone doing a bit higher resolution work won't think the same.

[Chris]

Is that from the centre Vlaiv? I crop zoomed the centre of the image and the stars were round (well square because of compression)

I'll show you when I've figured out how to upload a super cropped image that doesn't appear tiny  

Edited December 20, 2021 by Chris

[vlaiv]

4 minutes ago, Chris said:

s that from the centre Vlaiv? I crop zoomed the centre of the image and the stars were round (well square because of compression)

I'll show you when I've figured out how to upload a super cropped image that doesn't appear tiny  

Yes, that was from center - just to make sure there are no edge aberration issues.

[Chris]

Just now, vlaiv said:

Yes, that was from center - just to make sure there are no edge aberration issues.

I'm not sure why mine looks different to yours in that case? I'll try zooming in even further. 

[Chris]

Jpegs were to blame. 400% zoom on a RAW saved as png:

 

[Chris]

23 minutes ago, vlaiv said:

 

This mount can be used at this sampling rate without guiding (and stars won't be perfect but close) - but someone doing a bit higher resolution work won't think the same.

I agree with your assessment Vlaiv, expecially on an individual frame basis.

I thought it would be interesting to see a 400% zoom crop of the stacked and processed image. I'm thinking the final image may be what counts for many and there is a difference, the elongation appears to be a little less obvious after stacking and processing. 

 

[vlaiv]

1 minute ago, Chris said:

400% zoom crop

For some reason - that does not look like 100% zoom - it looks more like 100% zoom?

Here is what I get when zooming in to 400% on one of subs you attached above:

That is quite a bit of difference in zoom level.

[Chris]

1 minute ago, vlaiv said:

For some reason - that does not look like 100% zoom - it looks more like 100% zoom?

Here is what I get when zooming in to 400% on one of subs you attached above:

That is quite a bit of difference in zoom level.

Maybe software? I'm zooming to 400% in GIMP and cropping to the field of view before exporting. 

[Chris]

This is 800% according to GIMP. Probably in the ball park of your 400% but we're really pixel peeping now  

 

Edited December 20, 2021 by Chris

[vlaiv]

20 minutes ago, Chris said:

This is 800% according to GIMP. Probably in the ball park of your 400% but we're really pixel peeping now  

Not sure what is happening - but whenever you attach a crop - it is always very small and not zoomed in

 

[Chris]

2 minutes ago, vlaiv said:

Not sure what is happening - but whenever you attach a crop - it is always very small and not zoomed in

 

I'll leave it there I think. I won't subject you to the size of the 1600% crop!