Imaging with a CMOS device

[Terrierist]

Hello All.

Please could I ask for some advice and information?

I'm imaging in Bortle 8 skies with a Zenithstar 71 and ASI 178 MC OSC which is uncooled. I'm saving for a cooled camera, but that won't be for a while.

My question. What sort of exposure times should I be looking at with this camera/scope? My mount is a tuned EQ5 which is taking images of two-minutes without guiding, polar alignment is via a Pole master.

I've been reading various reports/pieces that state shorter images and lots of exposures is the way to go with this, would someone advise if this is correct?

Thank you for any help.

 

Kev

[vlaiv]

Simple fact is that smaller number of longer exposures always wins vs larger number of shorter exposures. Important point is that both need to add up to same total imaging time.

This will hold true until someone invents camera with 0 read noise.

Big issue with above statement is that depending on read noise and other factors this difference in quality of less longer subs vs more shorter subs can be either large enough to be noticeable in finished image, or small enough to give same results for all intents and purposes.

Shorter subs have many benefits over longer subs that are not related to final SNR. Looser guiding requirements. Less total imaging time lost due to unforeseen circumstances like wind gusts, earthquakes (even if caused by passing heavy vehicle or similar), sudden small cloud passing, cable snag, anything than can ruin one or more subs - with shorter exposure less total imaging time will be wasted (you can either loose single 1 minute sub due to sudden strong wind gust, or you can loose 10 minute sub for same reason - I prefer option 1 ). Since you are using non cooled camera - shorter subs might have edge there as well - less total heat accumulates in one sub (this actually depends on camera design, so don't take it to hold 100% true). Pixel well depth plays a part as well - in shorter subs less chance of saturated stars, and bright parts of target (important for proper color rendition).

For your particular case, you should just check if there is noticeable difference. I suspect that you will find that 30s to 1m work quite good as well. You are in Bortle 8 skies - so a lot of LP - dominant noise source will be LP, read noise will be less important.

Drawback of shorter subs is of course amount of data that you need to store and process.