DLSR imaging question

[Lee_P]

I'm trying to figure out the most efficient settings for DSLR imaging of DSOs. Currently I can get 90-second exposures without trailing using my ED80 (I'm tracking but not guiding), and ISO 400 gets me decent results. Would it be better to crank the ISO up to 1600 (for example) and have reduced exposure times but more shots in total to stack? There's too much light pollution to put the ISO much higher at 90-seconds. Dark, bias and flats would all be thrown into the mix. Any thoughts would be appreciated!

[VigdisVZ]

Yeah go ahead. I've been imaging at ISO 3200/30sec subs with "ok" results. I want to bring my ISO down now however, to get more star color.

[jambouk]

People will say turning up the ISO doesn't increase the "sensitivity" of the sensor, it just makes EVERYTHING brighter, including all the noise and other artefacts.

There are threads about which talk of what the optimum ISO is for the various dslr's. Usually 400-800 if memory serves me correctly.

I'd say you should experiment. Do a run at various ISOs, stack, compare. You might find ISO 1600 works for your set up.

Else Light pollution filters; but you'd need to increase the duration of exposures and run the risk of trailing; again people do unguided subs in the region of 5+ minutes apparently.

The image below is on my c11, iso 1600 (i think), 30 second subs, 270 of them, with a light pollution filter; canon 5d, lights and darks applied. I'm not after publication quality images, just something to satisfy myself.

James

[VikN46]

I am still very much a beginner but depending on my conditions (nr Leicester city centre) with my 600D I tend to use 800 ISO but I drop down to 400 ISO if needed, any higher and I find the images start to become too noisy when processed. My subs tend to be around 300s but again I am guiding, but whatever length if a sub I try to take as many as I can fit into a session. I use Backyard EOS and also keep an eye on the histogram and adjust accordingly too.

[Leveye]

You must experiment. I even get different color ranges using higher ISO's so it's a trade off. It also depends what the DSO is. For faint nebula work ISO 1600 works for great for me. For star clusters 400-800 range. For Andromeda i layer mask 3 different ranges of ISO so not to blow out the core. Gradient Xterminator and HLVG will take care of the LP later in post.

[Lee_P]

Thanks for all the replies. I'll try upping the ISO and seeing how that works out.

[oldpink]

depending where I'm pointing I use different ISO's
if I'm pointing away from the streetlamps I go to 1600 ISO
but if I'm close to the light glare from the streetlights in front of me I can drop as low as 400ISO

[Aeseir]

Simple rule regarding ISO settings.

Higher the ISO, lower the time needed to expose as the objects become brighter and not as defined.

Lower the ISO, higher the exposure time needed but the objects become sharp and clear.

Then you need to muck around with processing.

Sometimes a combination of HIgh ISO and Low ISO is required for some images.

All depends on the object you are capturing.

[Pete Presland]

the higher the ISO the lower the dynamic range is, so 800 would probably be good compromise.

[dph1nm]

Simple rule regarding ISO settings.

Higher the ISO, lower the time needed to expose as the objects become brighter and not as defined.

Lower the ISO, higher the exposure time needed but the objects become sharp and clear.

Changing ISO does not change the required total exposure length. As as result you can't really use it to compensate for bad tracking. You can lower ISO to get less saturation in a given sub length though, but if you go too low (below where 1 photon gives one count on the camera) you will get quantisation problems (which means losing some of those precious photons).

NIgelM