Some Thoughts on ISO 50

My recently acquired DP1s and DP2s have the so-called 'extended ISO'. Sigma warns about less headroom but also states "ISO50 can provide an exceptional result with fine details and lower noise."

So I tried some shots and checked both the raw histograms and the SPP review images. They showed that, not surprising, the selection of ISO 50 alters the metering so that, for 0.0 EV, you have to set double the exposure than for ISO 100. All well and good. Just as ISO 200 forces half the exposure than for ISO 100.

There is a subtle difference in SPP, though. The review image for a ISO 50 shot is twice as bright as an ISO 100 shot. But an ISO 100 shot is not twice as bright as an ISO 200 shot.

I see eyes glazing over

To me, I see absolutely no difference between shooting a scene at ISO 50 and shooting at ISO 100 + 1 EV both done with appropriate exposure compensation needed by that scene. Both methods produce the same raw histogram (more or less).

So I'm wondering where "an exceptional result with fine details and lower noise" comes from.

Does anyone here habitually use ISO 50 where possible and do they find it noticeably better?

Caveat: I'm talking about non-AFE models here.

xpatUSA wrote:

Does anyone here habitually use ISO 50 where possible and do they find it noticeably better?

Yes.

SigmaChrome wrote:

Yes.

Ta.

maceoQ wrote:

xpatUSA wrote:

To me, I see absolutely no difference between shooting a scene at ISO 50 and shooting at ISO 100 + 1 EV both done with appropriate exposure compensation needed by that scene. Both methods produce the same raw histogram (more or less).

So I'm wondering where "an exceptional result with fine details and lower noise" comes from.

As you say, you can overexpose ISO 100 by one stop, or use ISO 50. Both produce cleaner files compared to ISO 100 without exposure correction. And cleaner files means more detailed files.

Ah, I see. Less noise by means of "pushing" the exposure resulting in a) brighter shadows and b) more tones or levels in the shot. And, I suppose, less NR in post then leads to more detail or micro-contrast.

Because there is no AFE (analog front end) in the older SDs and DPs, the iso setting is software driven (i.e. SPP reads the iso setting and adjusts the exposure on your monitor accordingly). AFE was added in the SD15 and later DPs resulting in the iso setting telling the camera to actually amplify the RAW signal before recording to the SD card. This had the effect of slightly lowering the noise at higher ISOs but at the expense of lowering the overall DR, a tradeoff not everyone was happy about.

And to further add to the confusion the Merrills don't have AFE and the Quattros do.

IMHO, the SD14 at iso 50 produces the most noise free skies of any Sigma camera. And if you can get the color balance correct, can produce better looking images than the SD15.

http://www.pbase.com/mikeearussi/sd14_iso_50

mike earussi wrote:

Because there is no AFE (analog front end) in the older SDs and DPs, the ISO setting is software driven (i.e. SPP reads the ISO setting and adjusts the exposure on your monitor accordingly).

One difference I found is that, ISO 50 shots do not have their exposure on the monitor adjusted - as I tried to explain in the OP. In other words, the adjustment factor for ISO 100 is 1, for 200 is 2, etc but, for ISO 50, the adjustment factor remains at 1, not 0.5 which one might have expected.

AFE was added in the SD15 and later DPs resulting in the ISO setting telling the camera to actually amplify the [sensor] signal before recording to the SD card. This had the effect of slightly lowering the noise at higher ISOs but at the expense of lowering the overall DR, a trade-off that not everyone was happy about.

And to further add to the confusion, the Merrills don't have AFE and the Quattros do.

IMHO, the SD14 at iso 50 produces the most noise free skies of any Sigma camera. And if you can get the color balance correct, can produce better looking images than the SD15.

http://www.pbase.com/mikeearussi/sd14_iso_50

Excellent shots there, of course . . . I blame the photographer, not the camera settings

xpatUSA wrote:

mike earussi wrote:

Because there is no AFE (analog front end) in the older SDs and DPs, the ISO setting is software driven (i.e. SPP reads the ISO setting and adjusts the exposure on your monitor accordingly).

One difference I found is that, ISO 50 shots do not have their exposure on the monitor adjusted - as I tried to explain in the OP. In other words, the adjustment factor for ISO 100 is 1, for 200 is 2, etc but, for ISO 50, the adjustment factor remains at 1, not 0.5 which one might have expected.

AFE was added in the SD15 and later DPs resulting in the ISO setting telling the camera to actually amplify the [sensor] signal before recording to the SD card. This had the effect of slightly lowering the noise at higher ISOs but at the expense of lowering the overall DR, a trade-off that not everyone was happy about.

And to further add to the confusion, the Merrills don't have AFE and the Quattros do.

IMHO, the SD14 at iso 50 produces the most noise free skies of any Sigma camera. And if you can get the color balance correct, can produce better looking images than the SD15.

http://www.pbase.com/mikeearussi/sd14_iso_50

Nice shots there, of course. I blame the photographer, not the camera settings

The shots aren't meant to be artistic, of course, but they do demonstrate the noise free skies the SD14 is capable of producing at iso 50.

mike earussi wrote:

xpatUSA wrote:

mike earussi wrote:

Because there is no AFE (analog front end) in the older SDs and DPs, the ISO setting is software driven (i.e. SPP reads the ISO setting and adjusts the exposure on your monitor accordingly).

One difference I found is that, ISO 50 shots do not have their exposure on the monitor adjusted - as I tried to explain in the OP. In other words, the adjustment factor for ISO 100 is 1, for 200 is 2, etc but, for ISO 50, the adjustment factor remains at 1, not 0.5 which one might have expected.

AFE was added in the SD15 and later DPs resulting in the ISO setting telling the camera to actually amplify the [sensor] signal before recording to the SD card. This had the effect of slightly lowering the noise at higher ISOs but at the expense of lowering the overall DR, a trade-off that not everyone was happy about.

And to further add to the confusion, the Merrills don't have AFE and the Quattros do.

IMHO, the SD14 at iso 50 produces the most noise free skies of any Sigma camera. And if you can get the color balance correct, can produce better looking images than the SD15.

http://www.pbase.com/mikeearussi/sd14_iso_50

Nice shots there, of course. I blame the photographer, not the camera settings

The shots aren't meant to be artistic, of course, but they do demonstrate the noise free skies the SD14 is capable of producing at iso 50.

Yes, did notice the skies, Mike. I do like the SD14 in spite of what "they" say. Sold my first one as fast as I could (was going to shoot JPEGs with it at the time). But they do grow on you.

mike earussi wrote:

xpatUSA wrote:

mike earussi wrote:

Because there is no AFE (analog front end) in the older SDs and DPs, the ISO setting is software driven (i.e. SPP reads the ISO setting and adjusts the exposure on your monitor accordingly).

One difference I found is that, ISO 50 shots do not have their exposure on the monitor adjusted - as I tried to explain in the OP. In other words, the adjustment factor for ISO 100 is 1, for 200 is 2, etc but, for ISO 50, the adjustment factor remains at 1, not 0.5 which one might have expected.

AFE was added in the SD15 and later DPs resulting in the ISO setting telling the camera to actually amplify the [sensor] signal before recording to the SD card. This had the effect of slightly lowering the noise at higher ISOs but at the expense of lowering the overall DR, a trade-off that not everyone was happy about.

And to further add to the confusion, the Merrills don't have AFE and the Quattros do.

IMHO, the SD14 at iso 50 produces the most noise free skies of any Sigma camera. And if you can get the color balance correct, can produce better looking images than the SD15.

http://www.pbase.com/mikeearussi/sd14_iso_50

Nice shots there, of course. I blame the photographer, not the camera settings

The shots aren't meant to be artistic, of course, but they do demonstrate the noise free skies the SD14 is capable of producing at iso 50.

Yes, did notice the skies, Mike. I do like the SD14 in spite of what "they" say. Sold my first one as fast as I could (was going to shoot JPEGs with it at the time). But they do grow on you.

Longer shutter times for capturing motion along with low noise.
Waterfalls, leaf motion blur etc.
--
Barry Byrd
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http://www.pbase.com/sigmadslr

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1952-2008

The ISO 50 is amazing I've used it many times on my previous SD14 and after on the SD15.

BarrytheB wrote:

Longer shutter times for capturing motion along with low noise.
Waterfalls, leaf motion blur etc.

Yes, but the same longer shutter time can be set in ISO 100 and the resulting image is the same for a given scene and lighting.

I do see the point, though, if one's procedure is to simply adjust the ISO and then shoot with the same metering, e.g. zero on the meter with the same compensation.

The oft-mentioned low noise comes from the higher exposure, does it not? The same as claimed for ETTR?

xpatUSA wrote:

BarrytheB wrote:

Longer shutter times for capturing motion along with low noise.
Waterfalls, leaf motion blur etc.

Yes, but the same longer shutter time can be set in ISO 100 and the resulting image is the same for a given scene and lighting.

For the SD14, since it does not have the AFE, that's correct.

I do see the point, though, if one's procedure is to simply adjust the ISO and then shoot with the same metering, e.g. zero on the meter with the same compensation.

The oft-mentioned low noise comes from the higher exposure, does it not? The same as claimed for ETTR?

Yes, the greater the signal the lower the noise.

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