Imaging setup help

[tramsden]

New to imaging and just setting up a system, I have a skywatcher esprit 100 with Zwo 60mm guidescope & Zwo asi120mm guide cam + asiair - At this moment I’m going to use a Nikon d7100 as imaging camera until I can afford a dedicated Zwo cam. Mount wise I have an old first gen ( black) Heq5 pro. I think that it’s probably at the limit load weight wise but will I be able to nebula images with this setup. 

I read about tracking errors etc but I’m confused- doesn’t guiding help to override these errors and keep the image Centered. 

Btw is there anything else thats essential I should get to add to this setup. 

So many questions. 

Thanks for any help

Tony

[Phillyo]

You should be able to get nebula images yes, what you might find is that longer exposures are harder to do. If you stick to shorter exposures (1-2min?) and a higher ISO you should be fine.

[rickwayne]

The devil is in the details with deep-sky. Guiding does help keep the image centered, but "centered" is a relative term. For your scope and camera, a pixel represents about 2 arcseconds. Let's be generous and say that anything under two pixels' error would be undetectable in the image. (Try processing an astro image with a blur filter set to two pixels -- I bet you can tell the difference pretty easily.)

So that's four seconds of arc, one nine-hundredth of a degree. Which means that a displacement sufficient to move the end of your scope 0.005 millimeters -- five microns -- will be visible on the image.

Guiding definitely helps with this. Unfortunately, guiding only corrects for errors, it doesn't prevent them. Since seeing -- the fluctuation of the image due to the atmosphere, about which we can basically do nothing -- happens at a fairly high frequency, and since stars aren't all that bright, usually the exposure time on a guide camera is 1 second or more. Doesn't take much slop or imperfection in the gears to produce a 5-micron swing over 1-3 seconds, and guiding can only sense and correct it after it occurs.