ISO ratings with digital cameras

[b2hbm]

Ok folks, I realise this is probably a dumb question, but here goes....

I know how ISO ratings affect the quality with that quaint old plastic film stuff but I've just made my first venture into the DSLR world and am faced with ISO ratings at what sounds like crazy numbers to me. Although I've had digital cameras before they're usually the happy-snappy point'n'shoot ones where you just set everything to auto and leave it alone.

So the question is, how relevant is the ISO number to digital photography ? The camera manual says above 3200 starts to lose quality, but how do you go on with say ISO 1000 or thereabouts ?

I've viewed shots between taken 100 & 1000 and quite honestly can't see a lot of difference on my monitor, so how does an ISO 1000 shot print out at say 10x8 ? (camera is a very budget Nikon 3100 set to "Fine")

Brian

[realjv]

The simple answer is noise. The higher the ISO the more noise there will be. However many cameras carry out automatic noise reduction as they process every image and on how agressive this is will have an effect on the finished photo often leading to a little softness when particularly agressive.

[tim-b]

Higher ISO definitely will result in more grain - at very high ISO (like 3200) the grain should be very obvious, especially when zoomed in (even at ISO 400 you should see a difference at 100% zoom). At very high ISO the image will also have less contrast - I think this is something to do with lower dynamic range; as I understand it the effects of using a higher ISO are similar to underexposing the image then 'boosting' the levels to make everything brighter, just like push-processing in film-speak, so the range of data captured is much smaller than a correctly exposed/lower ISO image.

How it looks printed, or on screen, will really depend on the shot. I always try to use as low ISO as I can, whilst maintaining a high enough shutter speed (although the modern noise control is getting so good this is less of an issue than it used to be). Having said that, it's more important to worry about shutter speeds than ISO, I'd rather have a grainy image than a blurry one!

[tuscman]

Also depends a lot on the camera. A decent modern DSLR will produce photo's with no noticeable graining up to ISO 1600, although I don't tend to go above 800. Your camera manual and/or reviews should give you an idea of what your camera is capable of but obviously best to test for yourself and compare low and high ISO shots at a good size.

[GetCarter]

b2hbm said:

So the question is, how relevant is the ISO number to digital photography ?

It's one of the best things about digital, compared to film.

With film you could only balance aperture and speed to control depth of field. With a digital camera you have a third and frankly brilliant way to control your shot. By upping the ISO, you can 'gain' as many as 5 or 6 stops. I wish I'd had that in my film days!

As for quality, the full frame sensors on the more expensive camera (starting at about £1500) are much better at coping with 'noise'. I shot a wedding recently and left my camera at 4000 ISO - so indoors, no need for a flash or a tripod!

[K12beano]

b2hbm said:

Ok folks, I realise this is probably a dumb question, but here goes....

No such thing - every question relevant!

b2hbm said:

So the question is, how relevant is the ISO number to digital photography ?

Just as relevant as the speed of a film would be - instead of bigger clumps of silver you've got more electrical amplification as you go up the scale. In the same way lower ISO should be fundamentally "better" in terms of achieving high quality. Which would you use Pan F, FP4 or HP5?

b2hbm said:

The camera manual says above 3200 starts to lose quality, but how do you go on with say ISO 1000 or thereabouts ?

Try it out and see what it does - given your expected output. It's a gradual process, not really like falling off a cliff, and different subjects and circumstances can "tolerate" different noise levels.

b2hbm said:

I've viewed shots between taken 100 & 1000 and quite honestly can't see a lot of difference on my monitor, so how does an ISO 1000 shot print out at say 10x8 ? (camera is a very budget Nikon 3100 set to "Fine")

Probably pretty well. Where you'll notice it is in the shadow detail when you're pushing up the ISO and your exposure is not at the optimum. Then the case is what does the camera do about it (or what you instruct the camera to do in terms of how aggressive the NR is set or turned off - More Noise Reduction = Less Detail).

I've had three digital SLRs - each newer one has been a jump, not big between the first two, but what would have been 640 in a 2003 design is bettered by 6400 in a 2012 one. And that's before trying to address noise either in-camera or in post-processing. Also, for many years we all agreed that Nikon's noise - when it appears - managed to be quite "film-grain-like" and could be quite acceptable. All down to personal taste.

If you read too many reviews - or critiques of photos - you could be forgiven for thinking that noise is a terrible, terrible blight on society - like chicken pox - and should be avoided at all costs. That's just rubbish, just as more pixels doesn't mean a better final image.

[b2hbm]

Wow, that's an excellent response, thanks to all who have contributed. As you might guess I'm from the days when ISO 400 was considered the ultimate, so seeing the camera auto select ISO 900 or whatever was a bit off-putting. (the PanF, FP4, HP4 comment was exactly what went through my mind when I saw the ISO setting)

So thanks for the info from all concerned. I hadn't realised that the effects would be more noticeable on some tones more than others, or that it would affect contrast, so I guess my next step is to check again at my shots. At the moment it's a very steep learning curve so all advice is appreciated !

Brian

Edited by b2hbm on Friday 15th June 16:55

[sneaky schnell]

I don't have much to add to the good responses above. Below is a link to DP Review's review of the Nikon 3100. They are usually very comprehensive and will show the varying levels of performance your camera will offer at different ISO ratings.

http://www.dpreview.com/reviews/nikond3100/

[b2hbm]

Thanks for that link, I guess I should have read that before posting !

On balance I think that's a fair review of the camera. As I said before it's my first DSLR and for what I need at this point I think it's excellent. I still can't get over being able to use such high ISO values though, and reading that review it looks like I leave this on Auto with a maximum range of 1600 without worrying too much.

Again, thanks to all who pitched in to help and explain.

[davepoth]

b2hbm said:

Wow, that's an excellent response, thanks to all who have contributed. As you might guess I'm from the days when ISO 400 was considered the ultimate, so seeing the camera auto select ISO 900 or whatever was a bit off-putting. (the PanF, FP4, HP4 comment was exactly what went through my mind when I saw the ISO setting)

So thanks for the info from all concerned. I hadn't realised that the effects would be more noticeable on some tones more than others, or that it would affect contrast, so I guess my next step is to check again at my shots. At the moment it's a very steep learning curve so all advice is appreciated !

Brian

Edited by b2hbm on Friday 15th June 16:55

ISO 400 the ultimate for film? Pah!

http://www.ilfordphoto.com/products/product.asp?n=...

And I usually have to get it pushed too. Great fun.

[Simpo Two]

ASA 1000 was new in about 1984 as I recall. I promptly went out around a streetlit Nottingham!

[checkmate91]

davepoth said:

ISO 400 the ultimate for film? Pah!

http://www.ilfordphoto.com/products/product.asp?n=...

And I usually have to get it pushed too. Great fun.

But it's B/W!

[davepoth]

checkmate91 said:

davepoth said:

ISO 400 the ultimate for film? Pah!

http://www.ilfordphoto.com/products/product.asp?n=...

And I usually have to get it pushed too. Great fun.

But it's B/W!

Colour is overrated.

[K12beano]

davepoth said:

ISO 400 the ultimate for film? Pah!

http://www.ilfordphoto.com/products/product.asp?n=...

And I usually have to get it pushed too. Great fun.

Or, pushable to 12,800? http://www.kodak.com/global/en/professional/produc...

[RobDickinson]

ISO on digital is achieved (to a point) through analogue gain applied to the signal coming from the photosites on the sensor.

No gain = base ISO.
Then gain (amplification) is applied in steps to its top proper ISO.
After that point the camera 'under exposes' and pushes in post (internally) via tweaking the digital values. This can be done better in photoshop et al later anyhow.

Typically each stop of ISO you add (gain or digital) reduces the dynamic range the image can have and increases the noise.