low low ISO

[robert lamont]

Just wondering if anyone has had a lot of experience shooting at ISO's lower than 100. I have just upgraded my camera and the new one goes down to ISO 80. I did take a few shots at this speed and they turned out incredibly sharp. I don't know if this was coincidence, i think the camera was set on Av (f8) and shutter was about1/125 sec @ 150mm. Reasonable light, about 3.00 pm clear blue sky, shooting in and around trees but it was still fairly open. If this is how low ISO shots turn out then why doesn't everyone use it? Obviously not all situations will allow it but i don't see ISO below 100 very often in EXIF.

[OsmosisStudios]

It's not likely a result of your ISO. Those are pretty ideal conditions.

There arent many cameras that can go below 100iso. Off the top of my head, I think the Canon 5DmkII can.

[Niresangwa]

Pentax k-5 goes down to ISO 80. Biggest advantage is detail preservation in the shadows, so improved DR overall.

I'd say Os is right about the settings. Not a direct result of the ISO, just good technique and appropriate settings.

[Jim Bryant]

I think the extended ISO for the MKII's go down to 50 ISO and run up to 3200. I have used the lower ISO when conditions warrant such a low ISO.

[BCampbell]

ISO 50 on the 5D/5DMkII is software, not a native ISO. In fact, only the multiples of 100 are native ISOs on those cameras (100/200/400/800 etc), so for example ISO 320 is interpolated, and you can actually get better signal-to-noise by shooting 400 and pulling or 200 and pushing (this is true for photos only, not video on the MkII).

Anyway.

ISO 50 on the 5D series does essentially the same thing as you shooting in ISO 100 and pulling by one stop in post. The problem here is that you'll lose some dynamic range, in particular clipping the extreme highlights and shadows. You will get less apparent noise, just as you get less apparent noise from pulling any exposure.

It's handy if you shoot in Av/Tv; the main reason you would want to shoot in ISO 50 is to hit whatever shutter speed/aperture combo you're looking for without having to do any math. It's possible that something is so bright that you couldn't get under the 1/8000 sec maximum at ISO 100, & your chosen aperture, I guess. If you shoot in manual you are probably better off overexposing and pulling yourself. You can experiment with it on your own simply by switching to manual, shooting one exposure at ISO 50, then switching to ISO 100 and doubling your shutter speed. Try both pushing the ISO 50 shot one stop and pulling the ISO 100.

[sk66]

My understanding is that there is only one "native ISO" for any camera. For most cameras it's 100 (Canon) or 200 (Nikon). This is the ISO around which the camera was designed for best performance....any step away from the native ISO requires additional "electronics" (amplification/ fuzzy math) to capture the desired results and will result in image degradation (** may not be noticeable by you).

What is listed as the "native ISO range" for a camera is the range in which the designers/company/marketers feel the camera gives good results with acceptable degradation.

[BCampbell]

You're right, I used the term "native" loosely.

There is a single "native" absolute ISO. This is where there is no gain applied to the analog input. To use the 5D as an example, that is ISO 100.

As I understand, beyond that you have two different types of gain to achieve different ISO ratings. Remember our cameras have an analog to digital converter; one type of gain is applied to the analog signal itself. This is what I was referring to as "native" ISOs, I'm not sure what a better term would be (natively amplified?). Again, on the 5D, 200, 400, 800, and 1600 are ISO levels where gain is applied only to the analog signal.

Then, there is gain applied to to the digital signal after it is converted from analog. Again, on the 5D, these are the intermediary and extended ISOs, 50 (Lo), 3200 (Hi), 320, etc. This is roughly equivalent to simply adjusting exposure in post, and in many cases has a negative effect on the signal-to-noise ratio. For example, on the 5D, ISO 320 has a lower StN than ISO 400 even though it's technically a lower ISO. That is, if you shot at ISO 400 and pulled by 1/3 stop in post, you'll have less noise than ISO 320.

Lo and Hi extended ISO functions the same but the larger impact is on dynamic range. As far as I know, using intermediate ISO within the standard range doesn't affect dynamic range.

Again this is to my knowledge, off the top of my head. You'll probably want to do more research.

[sk66]

Does that mean "native range" with only analogue gain is applied is full stops? That would kind of make sense...And since "digital" is really just "fuzzy math" I can see where that would cause potential issues....

Maybe I should set my ISO steps to 1?

[BCampbell]

Originally Posted by sk66

Does that mean "native range" with only analogue gain is applied is full stops? That would kind of make sense

In the example of the 5D, yes. I used it because it's what I'm familiar with, I've done some tests, and I've seen charts confirming it (can't find them at the moment but if I do I'll link). I can't speak for any other cameras though I think all of the Canon APS-C and 5D cameras work the same though some have a higher maximum level of analog gain than others.

As for Nikon, as you said I've also heard that ISO 200 is the native ISO, I don't know the details beyond that.

But, for the 5D and I assume most other other Canons, any ISO setting that is not a full stop is a digital signal gain, and there is degradation there, especially at the very high ISO end.

Maybe I should set my ISO steps to 1?

Yes, I never use any of the 1/3 stop ISO settings unless I'm in a rush and don't notice. Practically speaking it doesn't often make a difference, but there are the 1 in 10 or 20 or 50 or whatever photos where it does, especially if I need to push in post. But if you're getting good images, I wouldn't worry about it too much. If aint' broken, don't fix it, and if you can't fix it, don't break it

And again don't totally take my word for it! But this should give a good place to start further research.

[SwissJon]

I just put some Ilfords PanF Plus 50 black and white film in my film camera.. No idea what the results will be like, but I have to keep my tripod nearby!