What ISO?

[DanLXIX]

I've been shooting at IOS800, but the default in BAckYardNikon is ISO1600. I suppose this might be a hangover of taking normal photos, where I always try to go for the lowest possible ISO, but should I be going higher on the ISO?

[happy-kat]

Other factors help with choice. Aim for the light histogram totally clear of the left hand edge say around a third towards the right hand side.

[Alien 13]

If its the Nikon D7100 that you are using then the best ISO for AP is 200 or 400 at a push.

Alan

[vlaiv]

Depends on sensor. It is good to understand what ISO represents and what are benefits and drawbacks for each setting.

DSLRs have limited bit range to represent captured levels - like 12bit or 14bit - each of these can be used to represent certain number of levels - 4096 or 16384 for those two. Most DSLRs are capable of capturing more light than there are levels - that depends on full well capacity. Let's say full well is 40000e. This means that captured signal has 40000 levels - but you can't read that much levels - so you need to decide if you are going to read lower, middle or high part of it.

It there is plenty of light you want to go for high part - as you are not interested in very small variations of light - this would be low ISO. If there is not enough light - pixels will not fill up to high levels - no point in reading off high levels, you are better of reading low levels - high iso.

There are other things to consider - amount of certain noise (read noise) depends on where you put window - go too low and you increase read noise. This is not to be confused with low light performance in regular photography where high ISO gives you more noise. High ISO gives you more noise in regular photography because it gives you finer representation of your signal - lower levels where "fine grained" differences are - it is not more noisy - it just reveals that light is intrinsically noisy if you look at it more carefully.

So it is the balance of above things - you want to capture precise enough levels (lower parts) but avoid saturation (you can control this by other means than ISO) and you also want to avoid more read noise than you need. All of this depends on camera model - how big full well capacity is, how much read noise there is and how it varies with ISO, etc ...

So you will find different recommendations for this. Most cameras have best values of ISO in 400-800 range for AP purposes.

[DanLXIX]

Thanks for all the responses.

This is the image that has got me thinking about the ISO and it does have quite a lot of noise in it so am I better backing off to say ISO400? Then is the compensation more light frames (this picture was (57x60sec), because I'm not guided at the moment so I'm probably not going to get much more than 60 second exposures without some trailing starting?

[Alien 13]

I would certainly try at a lower ISO setting because a lot of Nikon cameras are effectively ISO-less, this is the link to camera ISO settings for both Canon and Nikon.

http://dslr-astrophotography.com/iso-values-nikon-cameras/

Alan

[DanLXIX]

21 minutes ago, Alien 13 said:

I would certainly try at a lower ISO setting because a lot of Nikon cameras are effectively ISO-less, this is the link to camera ISO settings for both Canon and Nikon.

http://dslr-astrophotography.com/iso-values-nikon-cameras/

Alan

That's really useful, thank you. Going on that info I've been way too high on ISO.

[wxsatuser]

The general rule is to get the histogram to separate from the left hand side, anywhere upto 25% should do it.

[Alien 13]

12 minutes ago, DanLXIX said:

That's really useful, thank you. Going on that info I've been way too high on ISO.

The info is certainly counter intuitive, I found that my Canon 80D is also supposedly best at ISO 200.

This article expains what ISOless or ISO invariance means.

https://photographylife.com/iso-invariance-explained

Alan