Bright subs

[hornedreaper33]

Hey all,

After losing my mojo for a time, I am finally back in the game. My kit has been evolving over the last few years and with the addition of the Jackery Explorer 300 battery, I'm finally all set. Anywho, I have been tackling M51. I'm having issues with my guiding, I think Windows 10 has finally evolved beyond my old laptop and I am getting intermittent connection issues with my guide camera as the computer struggles with life. Because of this, I am only managing 3 min subs. However, my subs seem very bright. See pictures below (example of a 2 min and a 3 min sub from my location. Bonus look at my first attempt at processing a DSO). I have the Optolong L-Pro installed as I am shooting from North Vancouver which is Bortle class 8. The longer the sub the brighter the background gets. I'm guessing this is because of the light pollution?? I'm not fully understanding how this filter is/isn't working.

It seems like people are suggesting 10 min subs on this guy but, looks like I would wipe out all detail if I tried that from this location. 

Any help/advice, greatly appreciated. 

[vlaiv]

As long as you don't saturate your target - bright background is really not important - you remove it by setting black level in processing (or in case of gradients - with gradient removal tool).

However, bright background is telling you that you really don't need to use longer exposures.

Exposure length should be set to whatever exposure length is enough for LP noise to swamp read noise. Cameras with higher read noise - benefit from longer subs. As long as you use same total exposure length, once any other noise source (be that thermal, or LP noise) swamps the read noise - you don't need to use longer subs - results will be roughly the same (very small difference that won't be seen in final image).

In above example - you won't be able to tell the difference between 30 x 120s stack versus 20 x 180s stack (same total imaging time - but 120s is already swamping the read noise so there is not much point in going longer).