Question regarding ISO 50 on 5D III

[TrumpetPower!]

I see lots of confusion here.

Except for the EXIF flag indicating exposure, the RAW file you'll get with ISO50 @ f/8 @ 1/400 will be exactly the same as the one you'll get at ISO100 @ f/8 @ 1/400. The only difference is that, if the camera's meter tells you that the proper exposure is ISO100 @ f/8 @ 1/400, it'll tell you that you should be exposing the ISO50 shot at f/8 @ 1/200. And, of course, the RAW developers are programmed to invisibly apply a stop of digital pull to the ISO50 shot.

There will be a difference between ISO50 @ f/8 @ 1/200 and ISO100 @ f/8 @ 1/400 -- and it's that difference that people almost always compare.

BUT!

There won't be a difference between ISO50 @ f/8 @ 1/200 and ISO100 @ f/8 @ 1/200.

And, of course, there will be a difference in the RAW files between ISO100 @ f/8 @ 1/400 and ISO200 @ f/8 @ 1/400.

Hope that helps clear things up....

Cheers,

b&

P.S. A very similar thing happens with highlight tone priority, except in the opposite direction. The RAW files for a given shutter and aperture will be identical between ISO100 and ISO200 + HTP, but the meter will be different. b&

[3kramd5]

I see lots of confusion here.

Except for the EXIF flag indicating exposure, the RAW file you'll get with ISO50 @ f/8 @ 1/400 will be exactly the same as the one you'll get at ISO100 @ f/8 @ 1/400. The only difference is that, if the camera's meter tells you that the proper exposure is ISO100 @ f/8 @ 1/400, it'll tell you that you should be exposing the ISO50 shot at f/8 @ 1/200. And, of course, the RAW developers are programmed to invisibly apply a stop of digital pull to the ISO50 shot.

There will be a difference between ISO50 @ f/8 @ 1/200 and ISO100 @ f/8 @ 1/400 -- and it's that difference that people almost always compare.

BUT!

There won't be a difference between ISO50 @ f/8 @ 1/200 and ISO100 @ f/8 @ 1/200.

And, of course, there will be a difference in the RAW files between ISO100 @ f/8 @ 1/400 and ISO200 @ f/8 @ 1/400.

Hope that helps clear things up....

Cheers,

b&

P.S. A very similar thing happens with highlight tone priority, except in the opposite direction. The RAW files for a given shutter and aperture will be identical between ISO100 and ISO200 + HTP, but the meter will be different. b&

So basically you're saying the ISO50 setting only affects metering, not sensitivity?

If I set up at ISO100, meter dead center, take a photo, and then drop to ISO50 with all else being equal, I'll see the meter move one stop to the left, but the actual picture will be the same?

[neuroanatomist]

So basically you're saying the ISO50 setting only affects metering, not sensitivity?

If I set up at ISO100, meter dead center, take a photo, and then drop to ISO50 with all else being equal, I'll see the meter move one stop to the left, but the actual picture will be the same?

Metering and the ISO value recorded in the metadata.  Assuming you're in manual mode (since in an AE mode, the change from ISO 100 to ISO 50 will result in a compensatory change in aperture or shutter speed to maintain metered exposure), the RAW data file will be the same - an ISO 100 exposure.  The jpg file will be pulled down a stop, and when you open the ISO 50 RAW file in an editor, it will display darker than the ISO 100 file, because the RAW editor/converter will pull the exposure down based on the ISO value in the metadata.

[3kramd5]

So basically you're saying the ISO50 setting only affects metering, not sensitivity?

If I set up at ISO100, meter dead center, take a photo, and then drop to ISO50 with all else being equal, I'll see the meter move one stop to the left, but the actual picture will be the same?

Metering and the ISO value recorded in the metadata.  Assuming you're in manual mode (since in an AE mode, the change from ISO 100 to ISO 50 will result in a compensatory change in aperture or shutter speed to maintain metered exposure), the RAW data file will be the same - an ISO 100 exposure.  The jpg file will be pulled down a stop, and when you open the ISO 50 RAW file in an editor, it will display darker than the ISO 100 file, because the RAW editor/converter will pull the exposure down based on the ISO value in the metadata.

Seems silly/pointless for manual/raw (how I shoot). Good to know.

[TrumpetPower!]

If I set up at ISO100, meter dead center, take a photo, and then drop to ISO50 with all else being equal, I'll see the meter move one stop to the left, but the actual picture will be the same?

By George, I think he's got it!

Yes. If you ignore the meter, two exposures at the same shutter and aperture but with the one at ISO50 and the other at ISO100 will be identical save for the metadata (and therefore subsequent default processing). So, if you shoot manual and RAW, ISO50 is pointless.

But for those who use autoexposure, and especially for those who shoot JPEG, it can be a very handy tool to have in the toolchest as a quick way to get the benefits of ETTR (at, of course the expense of a stop of headroom) either straight out of the camera or with fewer steps in post-processing.

Cheers,

b&

[Pi]

I see lots of confusion here.

I do not.

[Skirball]

So basically you're saying the ISO50 setting only affects metering, not sensitivity?

If I set up at ISO100, meter dead center, take a photo, and then drop to ISO50 with all else being equal, I'll see the meter move one stop to the left, but the actual picture will be the same?

Metering and the ISO value recorded in the metadata.  Assuming you're in manual mode (since in an AE mode, the change from ISO 100 to ISO 50 will result in a compensatory change in aperture or shutter speed to maintain metered exposure), the RAW data file will be the same - an ISO 100 exposure.  The jpg file will be pulled down a stop, and when you open the ISO 50 RAW file in an editor, it will display darker than the ISO 100 file, because the RAW editor/converter will pull the exposure down based on the ISO value in the metadata.

Seems silly/pointless for manual/raw (how I shoot). Good to know.

Indeed, thanks NA.

So, I haven't played with my camera above 25.6k, but I'd assume it's the same situation going above there as well?

[neuroanatomist]

So, I haven't played with my camera above 25.6k, but I'd assume it's the same situation going above there as well?

Just like the L expansion is a digital pull, the H expansion settings are digital pushes, yes.

[TrumpetPower!]

So, I haven't played with my camera above 25.6k, but I'd assume it's the same situation going above there as well?

Just like the L expansion is a digital pull, the H expansion settings are digital pushes, yes.

And, to follow up on neuro's point, because I know somebody will wonder and / or ask...yes, they're equally useless for knowledgeable photographers shooting RAW in manual mode, but they can be useful for those shooting in an autoexposure mode and especially useful for JPEG shooters.

The utility for JPEG shooters is especially pertinent because the 5DIII has such an awesome onboard RAW processor.

If you shoot JPEG in low light, you'd be a bit silly to not enable the H modes. If you shoot RAW and manually expose, there's no point to them.

Cheers,

b&