Mount vs Exposure time vs Guiding vs Star trails?

[RikM]

So to oversimplify you could conclude a heq5 or greater mount gives the hit rate and the guiding gives the quality and therefore a guided lesser mount could approach/equal the result from a better mount if you accepted the low hit rate and were a very patient person with plenty of hair?

That sounds about right to me

[nmoushon]

So to oversimplify you could conclude a heq5 or greater mount gives the hit rate and the guiding gives the quality and therefore a guided lesser mount could approach/equal the result from a better mount if you accepted the low hit rate and were a very patient person with plenty of hair?

LOL You could look at it that way. Only other thing is to make sure the mount can support the total weight of your imaging set up. If it cant it will just add to the amount of subs you'll have to toss as well as limit the exposure length even more.

[ollypenrice]

Thanks,

What would be a good target to demonstrate the difference between short (say 90s) and longer subs (say 10mins) if the total exposure time was the same? I assume it will be something with very fine detail?

Inevitably it's a bit more complicated than that! You need a dark site to be able to exploit long subs to the full. I live and work from a very dark site, SQM often 21.7, so long subs make a big difference. An example would be the tidal tail from the Hamburger galaxy in the Leo Triplet or the Integrated Flux around M81/82. It's the faint stuff just above the read noise that is hard to tease out and having lots of integration for one dose of read noise helps. However, post process sharpening can also be pushed further from a deep dataset. On M45 or M42 long subs will deliver the faint dusty background as well as the more obvious brighter nebulosity.

I doubt I'd be able to get any of this faint stuff if I stuck to short subs but the dark site plays a role in the equation. The browns in M42 here are not Ha but RGB, though there is Ha in the image. The RGB subs were 10 minutes at a fast F3.9. Ha, being faint, is something else that absolutely must be shot in long subs. I never use less than 15 minutes for these.

Olly

[jimjam11]

Inevitably it's a bit more complicated than that! You need a dark site to be able to exploit long subs to the full. I live and work from a very dark site, SQM often 21.7, so long subs make a big difference. An example would be the tidal tail from the Hamburger galaxy in the Leo Triplet or the Integrated Flux around M81/82. It's the faint stuff just above the read noise that is hard to tease out and having lots of integration for one dose of read noise helps. However, post process sharpening can also be pushed further from a deep dataset. On M45 or M42 long subs will deliver the faint dusty background as well as the more obvious brighter nebulosity.

I doubt I'd be able to get any of this faint stuff if I stuck to short subs but the dark site plays a role in the equation. The browns in M42 here are not Ha but RGB, though there is Ha in the image. The RGB subs were 10 minutes at a fast F3.9. Ha, being faint, is something else that absolutely must be shot in long subs. I never use less than 15 minutes for these.

Olly

Those are spectacular images!

[dph1nm]

I would agree with you on that but you also got to take in effect the focal length to. PE will be noticeable first at shorter FL while I think mis-polar alignment would be more noticeable first at longer FL.

Well it's really pixel scale not focal length which is important - although the two are related of course. PE ceases to be an issue if your pixel size is larger than the PE - which I guess can can happen at very short focal lengths (e.g. camera lenses), but polar mis-alignment will still get you eventually.

NigelM

[Ags]

"Well it's really pixel scale not focal length which is important - although the two are related of course."

Lucky I use a 12MP 1100D and not an 18MP something else :-)