[Class A]

Yes I had thought at that time that each stop increase in your iso decreased your DR by a stop. I just recently got corrected on that.

Do you remember where you received that "correction"?

I don't see how they could have a point.

Of course, the actual sensor DR never changes, as neither the sensitivity or the full-well capacity of the sensor is affected by the ISO setting.

However, in almost every camera, increasing the ISO setting results in higher numbers being stored in the RAW file. This in turn means, that even if the sensor DR has not been exhausted, the actual numbers stored in the RAW file will represent clipped highlights.

For instance, say at ISO 100, a certain light level results in 8191 being stored in the RAW file. This means that at ISO 400, a 32764 would have to be stored, which is not possible, given the maximum of 16383 using a 14-bit format. Since the initial exposure had a stop of headroom to the maximum value and we are now over one stop of the maximum value, you can see that we lost two stops of dynamic range at ISO 400, compared to ISO 100.

Long story short, with almost all cameras one does lose effective dynamic range when increasing the ISO setting.

The only way around this issue would be to let the camera always record the ISO 100 - equivalent RAW numbers and use metadata to tell the software how many stops the image needs to be pushed (according to the actually chosen ISO setting). Cameras like the Fuji GFX 50S use this approach starting with ISO 1600. They rely on companies like Adobe to play along and observe the respective metadata.

[GUB]

Do you remember where you received that "correction"?

I don't see how they could have a point.

Of course, the actual sensor DR never changes, as neither the sensitivity or the full-well capacity of the sensor is affected by the ISO setting.

However, in almost every camera, increasing the ISO setting results in higher numbers being stored in the RAW file. This in turn means, that even if the sensor DR has not been exhausted, the actual numbers stored in the RAW file will represent clipped highlights.

For instance, say at ISO 100, a certain light level results in 8191 being stored in the RAW file. This means that at ISO 400, a 32764 would have to be stored, which is not possible, given the maximum of 16383 using a 14-bit format. Since the initial exposure had a stop of headroom to the maximum value and we are now over one stop of the maximum value, you can see that we lost two stops of dynamic range at ISO 400, compared to ISO 100.

Long story short, with almost all cameras one does lose effective dynamic range when increasing the ISO setting.

The only way around this issue would be to let the camera always record the ISO 100 - equivalent RAW numbers and use metadata to tell the software how many stops the image needs to be pushed (according to the actually chosen ISO setting). Cameras like the Fuji GFX 50S use this approach starting with ISO 1600. They rely on companies like Adobe to play along and observe the respective metadata.

Yeah here.
Vintage lenses on digital cameras. How good are they in reality compared to modern - Page 3 - PentaxForums.com

I ended up as usual confused with ISF.

[Class A]

Yeah here.

OK, thanks, I had a look.

The apparent disagreement stems from using "dynamic range" in a somewhat imprecise and hence ambiguous way.

The graphs show the "camera's dynamic range", i.e., the potentially available dynamic range.

Ian Stuart Forsyth was talking about the "image's dynamic range", i.e. the dynamic range capture by the image.
He of course correctly observes that any given image whose dynamic range fits within the range available during capture, would not have profited if any additional headroom had been available.

Say the image needs the number range 1024-4096 to be captured at base ISO (i.e. there are no darker nor lighter tones available in the scene, given the capture parameters of shutter speed and aperture). Then you can capture that image at ISO 100, ISO 200, etc. up to ISO 400, without clipping highlights, i.e., without losing dynamic range. Ian Stuart Forsyth's point is that even by increasing the ISO setting to ISO 400, you are not getting an image with less dynamic range, compared to an image of the same scene with the ISO setting at ISO 100.

At the same time, however, the potential of the camera to capture more dynamic range is considerably smaller at ISO 400 than it was at ISO 100. So in my view, the graphs are not misleading, they simply show the loss of exposure range / loss of headroom for capturing highlights.

So both views are correct, they just reference two different ideas: dynamic range potential (camera dynamic range) and dynamic range captured (image dynamic range).

Hope that makes sense.

BTW, it is definitely not true that the "...the lower iso shot has a higher dynamic range which you can harvest via the curve tool creating more tonal control in the image" as long as the higher ISO setting image does not contain any clipped highlights. In this latter case, both captures contain the same dynamic range to play with in post-processing.

However, using lower ISO settings than indicated by the metering system is still useful in order to insure oneself against blown highlights. The "same dynamic range" argument only applies if the higher ISO image still fit into the (reduced) potential dynamic range, a likelihood which gets significantly diminished, the higher up the ISO range you go.

[GUB]

I am very much about the practical application of this stuff.
Was it a solid concept I had that if the DR dropped with +iso then two identical and correctly exposed images, one low iso -one high would have a different footprint on the camera histogram.? I think the high iso would have the larger footprint.
It is so hard to get my head around this. And for instance does the histo on the K-1 constantly represent 14 odd stops or does it rescale for say iso changes.?

[GUB]

BTW, it is definitely not true that the "...the lower iso shot has a higher dynamic range which you can harvest via the curve tool creating more tonal control in the image" as long as the higher ISO setting image does not contain any clipped highlights. In this latter case, both captures contain the same dynamic range to play with in post-processing.

I think this happens a lot more than you think - having a nicely exposed set of clouds along with your landscape is a modern day luxury. In the film days we managed a bit of tonal range in the sky but very marginal.(unless we were dodging and burning.)

[Class A]

Was it a solid concept I had that if the DR dropped with +iso then two identical and correctly exposed images, one low iso -one high would have a different footprint on the camera histogram.?

The high-ISO image will show a wider histogram on the camera back LCD, but it is produced from the same data that is captured in the low-ISO image.

When you compare the two histograms with each other, you'll see the same underlying data but in the high-ISO image, all numbers have been multiplied (with a factor that is determined by the ISO setting).

You can create the same histogram, though, by taking the low-ISO image and pushing it in post-production (we are ignoring different tone-curves, etc. between in-camera JPEG development and out-of-camera post-processing).

With an ISO-invariant camera, changing the ISO setting just means pulling the digital multiplication of the RAW numbers forward in the chain, i.e., let the camera do it rather than the RAW editor.

So, again, as long as the ISO-shot does not feature blown-out highlights, you are not gaining anything, in terms of image dynamic range, by using a lower ISO setting.

There is still a practical advantage to using a lower ISO setting, though, which is to have better insurance against blowing out highlights during shooting.

And for instance does the histo on the K-1 constantly represent 14 odd stops or does it rescale for say iso changes.?

It should always show the full range from 100% black to 100% white. I cannot imagine that it wouldn't do that, nor what the basis for any rescaling would be (since the K-1 actually stores the multiplied RAW data, including blown highlights, if the ISO setting happened to be too high).

[Class A]

I think this happens a lot more than you think...

I'm not sure what you mean.

I was just stating a fact. I didn't mean to imply any frequency of occurrence.

FWIW, I do think there is a practical advantage in maximising both shutter speed and aperture and somewhat underexposing via the ISO setting since that way you are

1. maximising the number of photons reaching the sensor, i.e., minimising the noise (technically rather maximising SNR), and
2. less likely to blow out highlights.

Pentax cameras tend to be rather conservative regarding exposure anyhow, so by using TAv mode you should be pretty much OK most of the time. Using a bit of negative exposure compensation will further decrease the likelihood of ending up with blown highlights. Remember that seeing highlights blown in the histogram on the back of the camera does not necessarily mean that the actual RAW data hit the roof. It will depend on your in-camera JPEG settings how much of a false warning you'll get.

In the film days we managed a bit of tonal range in the sky but very marginal.

OK, but you know that film is different to digital sensors. Film with a higher ISO rating actually is more sensitive. Having said that, there were a number of films sold suggesting ISO ratings like ISO 3200 which actually weren't that sensitive. These were designed to be push-processed by the lab to effectively achieve the marketed sensitivity, much like pushing an underexposed digital image in post-processing.

[Transit]

,..... so by using TAv mode you should be pretty much OK most of the time. ....

Gubs camera is on M Mate ;-)

[Class A]

Gubs camera is on M Mate ;-)

As it should!

[GUB]

Gubs camera is on M Mate ;-)

Rusted there.
EDIT Iso wheel too!
wish I could rust up the custom image button and WB button too. Sick of being bent over upside down over a log etc to get a closeup shot and having to reset these functions coz I bumped them.

[GUB]

I'm not sure what you mean.

I was just stating a fact. I didn't mean to imply any frequency of occurrence.

Yeah I was more philosophising about what I gained in reality. Otherwise there is no point to utilising Iso invariance.
There are times when I boost the iso because there is no contrast challenge in the subject but most of the time there is something to control.

[Transit]

Rusted there.
EDIT Iso wheel too!
wish I could rust up the custom image button and WB button too. Sick of being bent over upside down over a log etc to get a closeup shot and having to reset these functions coz I bumped them.

hotglue !

[Class A]

wish I could rust up the custom image button and WB button too.

Just toggle them to move your AF point instead.

I'm sure you are using MF, so you wouldn't be affected if the AF point selection gets bumped.
Or choose centre-point AF, so pressing any of those four-way buttons won't do anything anymore.

[GUB]

Just toggle them to move your AF point instead.

I'm sure you are using MF, so you wouldn't be affected if the AF point selection gets bumped.
Or choose centre-point AF, so pressing any of those four-way buttons won't do anything anymore.

Good try.
But doesn't work with MF lenses coz you are stuck on spot mode.

[richandfleur]

Few pics from Kapiti Island and Taranaki: