Testing 8 minute unguided subs with the GEM45

[Chris]

A week or two back I attempted 5 minute unguided subs with the following rig - StellaMira 90 EDT with 0.8 Reducer Flattener, working at 432mm focal length, 2.29"/seconds with the Fuji XT1 onboard the iOptron GEM45 mount.

I marvelled that I could get 5 minute unguided subs, however after discussion with Vlaiv and others I plugged the subs into CCDInspector to check the FWHM readings and it turned out that there was a around 1-2 pixel width of wobble on the exposures because the FWHM was reading 5-6"/pixel. Still remarkable and the picture of the California nebula looked detailed to my eyes. 

This week I thought I would take this one step further and I ended up taking 8 x 8 minute unguided subs on the Monkey head Nebula in Orion. Again I was working at 2.29"/seconds and plugging the subs into CCD inspector revealed a very similar 6"/seconds average which matches iOptrons <7"/second claim for this mount.

With 8 minute exposures we must have completed at least one rotation of the mounts worm gear so in theory you could expose as long as you want with a short apo as long as you can accept 6"/seconds. To be fair the image looks detailed enough for social media to my eyes but you probably wouldn't get away with blowing it up for a print. 

Here is the FWHM chart for the 8 minute subs, plus a PNG of the Monkey Head nebula, and a short video documenting the night. 

 

    

 

Edited January 8, 2022 by Chris

[Jerry Barnes]

Impressed that you can push the mount that far.  Nice image.

I'm loosing faith with my mount and considering either a GEM45 or an EQ6R Pro as a replacement so a useful post, thank you.