M13

I've not had a lot of time of late to invest in astronomy but I did get some time to test out the SN-10 on my new mount (EQ6). Tracking is pretty good but the SN10's optics still need work* and I haven't yet been able to play with the SPC900 as an autoguiding camera. I'm using an iterative approach to finding optimal focus.

With the camera automation script I wrote I managed to get fifty shots of reasonably good quality, the image linked below is a stack of eleven 30sec exposures taken at ISO 800. Anything over 30 seconds introduced a lot of light pollution. The artefact in the star shape is lamentable but should be fixable.

tinyurl.com/mohq9xe

I didn't take any darks or flats as this was just a test run but I'm hopeful that with a little more time I can create a library of darks at the very least.

Any and all advice/criticism is gladly accepted.


*I need to run a roddier test to determine the optimal corrector plate rotation in relation to the mirror and build a new mirror cell as the existing one is pants.

Martinus

You said "Anything over 30 seconds introduced a lot of light pollution".
I don't follow, surely a stack of n * t exposures will capture exactly the same amount of light pollution as, say, half that number of frames at twice the original exposure.

Is there some other effect you are mitigating against?

Mark C.

I think this describes the nature of the problem pretty well:

"If your single one minute shots are in light polluted conditions with fast optics, then photon noise from the brighter skies can swamp out camera read noise to the point where it's very much insignificant. Therefore, a stack would be roughly equivalent in SNR to the single long shot. This is why you generally stop your individual exposures when that limit is reached because going longer on the subs offers no further SNR benefits than if you just started stacking images of that same length."

cs.astronomy.com/asy/astro_imaging/f/45/t/49285.aspx


I'm sure the relatively high ambient temperature doesn't help either. I would expect the sensor noise to be quite high but I'm living near a few floodlit areas (security lights) so I'm stuck with high light pollution.

I have the same problems with an SN10. Very difficult to get anything decent with it. I keep reverting to the 80ED.

The DSLR struggles with in-focus too.

I have only recently started to use my SN10 again for visual, and even more recently trying imaging. But its bugging me that much Im looking at getting an alternative "big scope".

Mine has a Revelation focuser so there's no issue getting focus, I had to buy a couple of extension tubes but that's not a big deal IMHO.

I stick with it because I've seen the quality of the images I can get. Whilst my site may not be ideal I'm aiming to travel a bit further afield in the near future when I have a bit more time. Alas, I have to get a PhD polished off.