night shots and noise

[Nate Klueter]

I've read that longer exposure times increase noise and so does higher iso ratings. So which combonation should give the lowest noise (high iso/short exposure, low iso/long exposure, something in between)?

 

[robertwsimpson]

low iso long exposure. but why not just try it yourself?

 

[bigtwinky]

I try and find a balance between the two.

I aim for low ISO. So when doing night shots, at ISO 100, if my shutter is getting too high (say 30 secs), I'll up the ISO to 200 to get it down lower. But thats about the only time I don't shoot at ISO 100.

The long exposure shouldn't matter as you should be doing long exposures on a tripod.

Light noise from long exposures are dependant on the lighting conditions and other factors present at a specific scene and may not happen in a different scene with similar settings.

Noise from high ISO will happen more often. As in I know my camera sucks at ISO 1600, so I don't shoot at that ISO. Some scenes seem to be better than others though.

 

[robertwsimpson]

noise lives in the dark bits of photos. That means if you take a picture at night at ISO 1600, you're going to have noise all over. If you take a properly expose picture in broad daylight, ISO 1600 might be an option, although it will still be noisy (especially with my XTi)

I've taken tons of 30 second exposures at ISO100 with little to no noise. Just try and let your camera rest in between photos.

 

[Garbz]

Quite simply the lowest noise is always the lowest iso for the same exposure. The effect of noise due to longer is marginal compared to ISO. Consider this you shoot at 1/100th at ISO 1600, or at 1/6th at ISO100, take a guess at which has lower noise. The effects are drawn out further but still the relationship holds. A clear example of this can quite easily be shown:

The below images in order are 4min at ISO100, 2min at ISO200, 1min at ISO400 and 30seconds at ISO800.
The shots were RAW. Lightroom had the following settings:
Exposure +3
Blacks 0
Brightness 150
Contrast 25
Noise reduction 0 for both luminance and colour, everything else is default.
Shot on a D200:

4min@ISO100

2min@ISO200

1min@ISO400

30sec@ISO800

The noise increases almost exponentially with ISO, but noise does not increase exponentially with shutter time. Though it does increase and here I have dramatically brightened the image to show it, at 10min and beyond the difference between ISO100 and 200 become really apparent, the differences between ISO100 and 400 or higher start becoming keep vs throwaway.

 

[musicaleCA]

Garbz, I've read your remarks often about layering shorter exposures to cut down on noise (thermal noise, yes?). How do you go about doing this exactly (the layering part; I'm reasonably certain we all know how to take 30s exposures with our cameras here...).

 

[Garbz]

Normally I used ImageStacker but this isn't a free program. Recently I found DeepSkyStacker - Free which is a free program which appears to do the same thing and possibly more.

It was recommended to me by someone who does this properly with a tracking telescope to take pictures of things like supernovas and galaxies, however I haven't used it at all yet.

Funny timing you mention though. I have had the program installed for 6 months, and on Friday I'm driving 500km into the bush so I'll actually be trying this program for the first time early next week