interesting article

[bjanes]

bjanes,

I've reproduced the two lines of data for easy reference.

[attachment=507:attachment]


4. The huge discrepancy I see, comparing  these figures, is in the actual quantity of data numbers (DN) available to describe or quantify the signal during A/D conversion.

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I did not answer your final quesiton. Conversion from numbers of electrons to camera data number involves the camera gain, which is expressed in electrons/12 bit data number. For ISO 100, the gain of the EOS 1D MII is 13.02 electrons/DN and for ISO 1600 the gain is 0.81 electrons/DN. Gain reported in CCD imaging is actually inverse amplification; that is why it decreases with increasing ISO.

[a href=\"http://www.photomet.com/library_enc_gain.shtml]http://www.photomet.com/library_enc_gain.shtml[/url]


Spending a bit of time reading Roger's post and his references is time very well spent.

[BJL]

BJL,
As I suspected, you are really suggesting a procedural approach for achieving the optimum combination of shutter speed, aperture and ISO, consistent with ETTR.

That sounds right: I am trying to adopt the digital reality of being able to easily use all three exposure parameters (aperture, shutter speed and "gain/sensitivity" (ISO speed)).

I therefore did a series of tests [with a D60] to determine just how much benefit to image quality and tonality was achieved by using a higher ISO setting, as opposed to using the same exposure at ISO 100 and in effect underexposing the image.

To my surprise, there was essentially none, or very little at best. The deepest shadows showed marginally better detail and tonality, but such shadows are usually black on a print.

That makes sense to me; common or garden variety JPEG's from DSLR's at low to moderate ISO settings typically have about an eight stop DR, a couple of stops more than prints can reveal. So this ETTR and ISO setting fiddling is mainly relevant when dealing with a scene of high subject brightness range (over 8 stops), so that one needs to compress that range for printing, including bringing deep shadows up several stops.

[Ray]

For ISO 100, the gain of the EOS 1D MII is 13.02 electrons/DN and for ISO 1600 the gain is 0.81 electrons/DN. Gain reported in CCD imaging is actually inverse amplification; that is why it decreases with increasing ISO.

I'm not implying that there is an error in these figures. I'm stating that as a consequence of preamplification there are more data numbers available to describe each level (voltage variance, however you want to describe it) for each photosite. It is clearly better to have more than one DN for each electron than less than one DN. One DN for 13 electrons seems clearly inadequate and seems more likely to be the cause of the greater noise in the ISO 100 image than increased read noise.

The problem I have with your assertion (admittedly because you believe more qualified people have made that assertion) that there is no additional noise reduction taking place at higher ISOs and that the greater noise readily apparent in the ISO 100 image is due primarily to additional read noise, is that it raises the question, 'why have Canon not implemented 16 bit A/D conversion?'

A 16 bit A/D converter for a fully exposed image might well be overkill, but it would certainly seem that it could help the underexposed image (or underexposed part of the image) at ISO 100.

It would seem to me, if you are right, that all Canon has to do to dramatically improve dynamic range is reduce readout noise at ISO 100 to the same level it is at ISO 1600 and then use 16 bit A/D conversion. Since the nature of the CMOS chip is that it can accommodate additional processors at the photosite, that does not seem, on the face of it, an insurmountable problem.

If you are right (and actually I'd prefer you to be right) we can look forward to a future DSLR which will be as noise-free in the deepest shadows at ISO 100 as the 1D2 and 5D currently are at ISO 1600 (with the same photon count).

bjanes, I read the explanation of gain in the link you provided. I've read similar stuff years ago. There's nothing new there for me. What is new is the concept that it's possible for a camera system to produce images that are dramatically less noisy at a given ISO setting and similar pixel size (or pitch) without having employed additional noise reduction.

There is clearly something different between the preamplification of a signal in the earlier D60 and the preamplification of the same signal in the 20D. If it doesn't involve noise reduction, or noise cancellation of some sort, then what does it involve?

[Ray]

That sounds right: I am trying to adopt the digital reality of being able to easily use all three exposure parameters (aperture, shutter speed and "gain/sensitivity" (ISO speed)).

[a href=\"index.php?act=findpost&pid=63685\"][{POST_SNAPBACK}][/a]

Now that cameras like the 20D and 5D show such a marked improvement at higher than base ISO, underexposure at ISO 100 suddenly seems a disadvantage in relative terms. With the D60 is wasn't.

I am now wondering if the next step in a future Canon DSLR will be another 'priority' mode. In addition to AV and TV priority, I would find advantageous a combined AV & TV priority mode in relation to ISO. In other words, the user selects the aperture and shutter speed, as in manual mode, and the camera automatically selects the approprate ISO for the metered reading. It would save time. Getting the aperture and shutter speed right for a particular shot is critical for a sharp image with a desired DoF. In situations where one is trying to capture the moment, AV can let one down by producing a shutter speed that's too slow. TV can result in a DoF which is too shallow, and full manual mode can cause one to waste time  trying to select an approprite ISO, which could mean missing the shot.

[bjanes]

I'm not implying that there is an error in these figures. I'm stating that as a consequence of preamplification there are more data numbers available to describe each level (voltage variance, however you want to describe it) for each photosite. It is clearly better to have more than one DN for each electron than less than one DN. One DN for 13 electrons seems clearly inadequate and seems more likely to be the cause of the greater noise in the ISO 100 image than increased read noise.

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It really does not make sense to have the camera gain set to less than less than the readout noise. For an explanation see the link below. For example, the the EOS 1D Mark II at ISO 100 has a gain of 13 electrons/12 bit DN and a read noise of 16 electrons. If you had a 16 bit AD converter, you could set the gain to 1 electron/DN and not have overflow at the full well electron count, but you would be resolving mainly noise.

[a href=\"http://spiff.rit.edu/classes/phys559/lectures/gain/gain.html]http://spiff.rit.edu/classes/phys559/lectures/gain/gain.html[/url]

The problem I have with your assertion (admittedly because you believe more qualified people have made that assertion) that there is no additional noise reduction taking place at higher ISOs and that the greater noise readily apparent in the ISO 100 image is due primarily to additional read noise, is that it raises the question, 'why have Canon not implemented 16 bit A/D conversion?'

[a href=\"index.php?act=findpost&pid=63689\"][{POST_SNAPBACK}][/a]

Probably for the above reason. Why increase the raw file size merely to record noise? Ron Parr and others have not denied that the Canon employs additional noise reduction at ISO 1600, but merely that they see no evidence of it. Why do not bring your observations to Ron's attention? He is a regular visitor on the DPReview forums. Since he shoots Canon, you might try the Canon forums.

bjanes, I read the explanation of gain in the link you provided. I've read similar stuff years ago. There's nothing new there for me. What is new is the concept that it's possible for a camera system to produce images that are dramatically less noisy at a given ISO setting and similar pixel size (or pitch) without having employed additional noise reduction.


[a href=\"index.php?act=findpost&pid=63689\"][{POST_SNAPBACK}][/a]

Well, Ray, if you do not know that standard deviations are not additive and that it makes little sense to have the camera gain set to less than the readout noise, then you probably should do a bit more reading.  

[Ray]

Well, Ray, if you do not know that standard deviations are not additive and that it makes little sense to have the camera gain set to less than the readout noise, then you probably should do a bit more reading. 
[a href=\"index.php?act=findpost&pid=63712\"][{POST_SNAPBACK}][/a]

bjanes,
There are not enough hours in the day to do the reading required to know all the things that even I think I should know, never mind what you think I should know.

I read what interests me and I'm fast losing interest in this topic. Let's call it quits.

[Mark D Segal]

I've been following this thread with my mouth shut (i.e. fingers off the keyboard) because I agree with expose to the right, but I'm in learning mode about the relationship between ISO settings and visible noise. I was always told and read, until I started seeing the material on this thread, that lower ISO settings produce less noise than higher ones - in general. So in just about every camera review one reads, one is told the camera is fine at ISO 100, and then depending on the model they get increasingly noisy as you progress up beyond say 400, etc. Those observations seem contrary to views in this thread that shooting at high ISO produces LESS visible noise than shooting at low ISO (and I assume that whether we use low or high ISO we are keeping the histogram to the right without clipping, hence shutter speed/and or aperture adjusts accordingly). Or have I not understood correctly what is being said here? Can someone explain in simple English why shooting at high ISO produces less visible noise than shooting at low ISO, assuming one obeys the histogram to the right principle, and of course one is using the same camera?

Ray - not time to quit yet. Let's see if "civil clarity" emerges on this point.  

[Ray]

So in just about every camera review one reads, one is told the camera is fine at ISO 100, and then depending on the model they get increasingly noisy as you progress up beyond say 400, etc. Those observations seem contrary to views in this thread that shooting at high ISO produces LESS visible noise than shooting at low ISO (and I assume that whether we use low or high ISO we are keeping the histogram to the right without clipping, hence shutter speed/and or aperture adjusts accordingly).

Mark,
Sorry for the confusion here. We've introduced a comparison which is not normally made; an exposure that is correct for ETTR at ISO 1600 compared with the same exposure at ISO 100, or to put it another way a fully exposed shot at ISO 1600 compared with a shot at ISO 100 that is underexposed by 4 stops.

The purpose of doing this seems of more academic interest than of practical value, but the results are very surprising for me. They really put into graphic terms just how much cleaner high ISO image now are in Canon's latest DSLRs, yet images at base ISO do not seem to have got any better, whether they are underexposed or exposed to the right. A 5D image at ISO 100 is just as noisy in the shadows as my old D60.

The conclusion I would draw from this is that at base ISO (100), it is now even more important to expose to the right because there is more to lose by not doing so. That's is, there's a higher ISO alternative which really does reduce noise at the same exposure.

Has this clarified anything?  

ps. I mentioned earlier in the thread that I felt quite relaxed about not exposing to the right at ISO 100 and endangering highlight detail loss. Having thought this through, I'm now not so relaxed. With my D60, a stop underexposed at ISO 100 was really no different to a fully exposed shot at ISO 200. If I needed a particular shutter speed and aperture that resulted in a stop of underexposure at ISO 100, then so be it. Of course I'm talking about RAW images and hand-held shots and situations where it's inconvenient to change ISO.

[Mark D Segal]

Yes and no. It raises a further question about whether these comparisons are of analytic value - by which I mean are we isolating one variable at a time and seeing the effect. From what I've been reading, it seems that one should expect less noise with lower ISO, and less noise the further to the right the image sits on the histogram. If that is the case, when you crank the ISO to 1600 you introduce noise, but then when you crank down the ISO to 100, you introduce noise because of under-exposure. So then the issue becomes whether under-exposure at a "clean" ISO produces more or less noise than correct exposure at a "less clean" ISO. May-be of some interest to some shooting situations, but I guess I was thinking more in terms of "best practice" in general. It still seems to be, after all this discussion - that best practice consists of using the lowest ISO achievable with ETTR conditions, where "achievable" means a shutter speed and aperture that makes photographic sense relative to the subject matter. Is this correct?

[Ray]

It still seems to be, after all this discussion - that best practice consists of using the lowest ISO achievable with ETTR conditions, where "achievable" means a shutter speed and aperture that makes photographic sense relative to the subject matter. Is this correct?
[a href=\"index.php?act=findpost&pid=63748\"][{POST_SNAPBACK}][/a]

Basically, yes, with a qualification that I added in the postcript in my previous thread. But I'm struggling to understand why Canon are not improving noise at base ISO yet are achieving such spectacular results at high ISO.

[bjanes]

Yes and no. It raises a further question about whether these comparisons are of analytic value - by which I mean are we isolating one variable at a time and seeing the effect. From what I've been reading, it seems that one should expect less noise with lower ISO, and less noise the further to the right the image sits on the histogram. If that is the case, when you crank the ISO to 1600 you introduce noise, but then when you crank down the ISO to 100, you introduce noise because of under-exposure. So then the issue becomes whether under-exposure at a "clean" ISO produces more or less noise than correct exposure at a "less clean" ISO. May-be of some interest to some shooting situations, but I guess I was thinking more in terms of "best practice" in general. It still seems to be, after all this discussion - that best practice consists of using the lowest ISO achievable with ETTR conditions, where "achievable" means a shutter speed and aperture that makes photographic sense relative to the subject matter. Is this correct?
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Mark,

I think your summary is right on.

You might want to look at another thread on the Nikonians forum by Bill Claff, who seems quite knowledgable. He finds that for the Nikon D70, noise is the same for ISO 100 and ISO 1600, provided that the exposure is the same and the same number of electrons are collected by the sensor:

[a href=\"http://home.comcast.net/~TomatoMan/Mirror/Cached/86_4938.htm]http://home.comcast.net/~TomatoMan/Mirror/Cached/86_4938.htm[/url]

I did a quick test with my Nikon D200, exposing a scene at ISO 100 and 1600, using the same shuttter speed and aperture. My results more or less confirm Bill's and I don't see much difference in noise. The ISO 1600 is mislabeled as ISO 16000. The  NEFs were processed in ACR with exposure +4EV for the ISO 100 shot. These results are unlike Ray's and require explanation--I don't have the answer. Perhaps Canon is doing some NR.

Also here is a detailed noise analysis of the D200 at ISOs 100 and 1600 according to Roger Clark's methods. As is shown, the ISO 100 images have much better S/N. I see no advantage exposing with unorthodox methods.

[BJL]

best practice consists of using the lowest ISO achievable with ETTR conditions, where "achievable" means a shutter speed and aperture that makes photographic sense relative to the subject matter. Is this correct?
[a href=\"index.php?act=findpost&pid=63748\"][{POST_SNAPBACK}][/a]

This discussion might be simplified of we put our imaginary cameras in full manual exposure setting mode, instead of the aperture priority mode that seems to be silently assumed in many comparisons. That is, we should not assume that shutter speed and ISO speed are tied together.

Then the first key to minimizing noise is using the lowest possible shutter speed. If you are using aperture priority mode with no exposure compensation, this is the same as using the lowest possible ISO speed, but it is slightly misleading to attribute the low noise to the low ISO; the basic physical origin of the low noise (high S/N ratio) is the fact that a lower shutter speed gathers more light from the subject (at a given aperture.)

However, at a given shutter speed (and aperture), manual exposure setting allows more than one choice of ISO speed. For example we could choose between
(-2) f/2.8 1/250s ISO 100, with the meter saying we are two stops underexposed, probably requiring compensating up by two stops in post-processing.
(-1) f/2.8 1/250s ISO 200, with the meter saying one stop underexposed
(0) f/2.8 1/250s ISO 400, with the meter saying correct exposure
(+1) f/2.8 1/250s ISO 800, with the meter saying one stop overexposed
(+2) f/2.8 1/250s ISO 1600, with the meter saying two stops overexposed
Now, increasing ISO here will in general improve the S/N ratio, by reducing the impact of read noise and quantization noise in the A/D converter. I think that we are all agreed that option (-2) is probably a bad idea, (-1) is likely to be better, (0) to be better still.

But why stop at (0)? Why not keep going to (+1) or (+2) or so on?
Answer: at some point, the extra pre-amplification of the higher ISO speeds will cause highlight values to exceed the limits of the amplifier ("clipping"), or to exceed the input level that the A/D convertor can handle: let me call either of these problems "clipping".

But if you stop short of clipping, so that the highlights are pre-amplified to about the maximum level that the pre-amp can handle and the maximum input level of the A/D converter, producing near maximum output levels (about 4096 with 12-bit A/D), the results are probably optimal. This is likely to be far better than with one fourth the ISO speed, when the signal to the A/D converter is two stops lower so that the brightest highlights come out at only about level 1024 out of 4096 in 12-bit A/D output.

Most often, option (0) will be best, but for a scene no highlights much brighter than the metered mid-tones and with interesting detail in deep shadows, option (+1) might be better. And if the metered is dominated by a subject at low reflectivity (say 10%) and there are a few highlights at close to 100% reflectivity, over three stops brighter than the metered mid-tones, option (0) might cause highlight clipping, so that "under-amplification" like option (-1) might be better.

In other words, choose

a shutter speed and aperture that makes photographic sense relative to the subject matter
[a href=\"index.php?act=findpost&pid=63748\"][{POST_SNAPBACK}][/a]

and then decide whether to use the normal "matching" ISO speed or a different one.

Ray has the same idea as I have speculated about: an "ATv" auto exposure mode where one specifies shutter speed, aperture and maybe exposure compensation, from which the AE system chooses the ISO speed. Better yet, if the light metering could effectively scan all photo-sites to find the brightest highlights, it could choose an ISO speed just from shutter speed and aperture n order to have the brightest highlights come out at "level 4096".


P. S. But as Ray and I seem to agree, probably only in rare cases do deep shadows need this much care and feeding.

[bjanes]

Most often, option (0) will be best, but for a scene no highlights much brighter than the metered mid-tones and with interesting detail in deep shadows, option (+1) might be better. And if the metered is dominated by a subject at low reflectivity (say 10%) and there are a few highlights at close to 100% reflectivity, over three stops brighter than the metered mid-tones, option (0) might cause highlight clipping, so that "under-amplification" like option (-1) might be better.

[a href=\"index.php?act=findpost&pid=63788\"][{POST_SNAPBACK}][/a]

Look at Jeff Schewe's comments earlier in this thread. If you are metering from the midtones, you really are not exposing properly for digital--you should be metering and exposing for the highlights. Until such time as the camera system can scan all the photosites and find the brightest highlights as you mention, you will have to do this yourself. Also, the automated system might not be able to exclude specular highlights. With high dynamic range subjects, it would not know whether to preserve highlights or shadows.

The differences in read noise at various ISOs are relatively insiginificant in most situations (as shown by Dr. Clark's analysis), but are of interest to astronomers. If you really need good SN in the shadows, you should really strive to expose as near to full well capacity of the sensor as possible, and expose maximally to the right. A half stop or so of blown highlights can usually be recovered in ACR.

[Ray]

I did a quick test with my Nikon D200, exposing a scene at ISO 100 and 1600, using the same shuttter speed and aperture. My results more or less confirm Bill's and I don't see much difference in noise. [a href=\"index.php?act=findpost&pid=63754\"][{POST_SNAPBACK}][/a]

I think you might have just opened a can of worms with this latest comparison, bjanes. I'm surprised BJL has not commented.

Since I don't own any Nikon equipment, I tend not to spend much time reading Nikon reviews, but there's a very clear demonstration at dpreview of the effect of turning on and off the in-camera noise reduction of the D200, at high ISOs. I gather the D200's NR feature is very analagous to the software NR of programs like Neat Image, ie. there's usually a trade-off with regard to fine detail.

I don't know whether or not some users prefer to leave the camera's NR off and do their own noise reduction with Noise Ninja or Neat Image, but it wouldn't surprise me.

One final comment, and perhaps just another way of making the same point that BJL has already made, the ETTR principle is not always of much practical value in certain situations when one is battling to achieve a minimum shutter speed, depending upon the design of the camera.

I'll give a specific example. The ISO setting of 3200 on the 5D, by all accounts, does not provide better image quality than the same exposure would at ISO 1600 (which would be one stop underexposed by the meter).

The noise levels are generally so good on the 5D at high ISOs, one can wander around at night in any city and take candid shots without an obtrusive flash that draws attention to oneself. (In any case, the 5D does not sport a built-in flash).

When doing this, and I've done it, there's a tendency to set the camera on ISO 3200 (actually 'H') and be careful one is exposing fully to the right. One makes a judgement as to what minimum shutter speed would be acceptable. With the Canon 24-105 IS, I consider 1/25th as a minimum speed. 1/13th is too risky.

However, accepting that ISO 3200 provides no benefit over ISO 1600, noise-wise, the above procedure or practice does not seem the best. In that situation described above, not exposing to the right at a lower ISO is a better procedure.

There actually are advantages in not exposing to the right.

What are they? If the 5D is set on ISO 1600, the shutter speed 1/25th and the aperture maximum, yet exposure is 1 stop under, one should take the shot. Moving up to ISO 3200 to achieve ETTR will not improve image quality, will not improve the noise situation in the shadows, but will risk blowing out highlight detail in street lights and objects close to the lights. There will also be a risk of 'missing the moment' because it does take time to change ISO. There will also be an additional risk of missing the moment in the next shot, should lighting conditions improve slightly so that ETTR can be achieved by moving back to ISO 1600.

[Chris_T]

That makes sense to me; common or garden variety JPEG's from DSLR's at low to moderate ISO settings typically have about an eight stop DR, a couple of stops more than prints can reveal. So this ETTR and ISO setting fiddling is mainly relevant when dealing with a scene of high subject brightness range (over 8 stops), so that one needs to compress that range for printing, including bringing deep shadows up several stops.
[a href=\"index.php?act=findpost&pid=63685\"][{POST_SNAPBACK}][/a]

Are you suggesting that DSLRs can capture a DR range equal to negative film and greater than transparencies? Is this specific for DSLRs only, or all digital cameras? My understanding is that digital cameras' DR range (before any editing in RAW or PS) is similar to transparencies', i.e. about five stops.

Print compression occurs on both film and digital captures. But with PS (and RAW), some tricks can be applied to alleviate the print compression.

[Chris_T]

If you are metering from the midtones, you really are not exposing properly for digital--you should be metering and exposing for the highlights.
[a href=\"index.php?act=findpost&pid=63803\"][{POST_SNAPBACK}][/a]

Metering from the midtones (or auto metering modes) can be problematic for some images, on *both* film and digital cameras. I think that those who have mastered proper metering (actaully all aspects of photo techniques) on film have some advantage when crossing over to digital. It is quite amusing to find topics like composition, etc. being extensively covered in *digital* photography books, as if these are *digital* specific.

[bjanes]

I think you might have just opened a can of worms with this latest comparison, bjanes. I'm surprised BJL has not commented.

Since I don't own any Nikon equipment, I tend not to spend much time reading Nikon reviews, but there's a very clear demonstration at dpreview of the effect of turning on and off the in-camera noise reduction of the D200, at high ISOs. I gather the D200's NR feature is very analagous to the software NR of programs like Neat Image, ie. there's usually a trade-off with regard to fine detail.

I don't know whether or not some users prefer to leave the camera's NR off and do their own noise reduction with Noise Ninja or Neat Image, but it wouldn't surprise me.

[a href=\"index.php?act=findpost&pid=63812\"][{POST_SNAPBACK}][/a]

Ray,

Yes, one has to be quite careful when reading noise tests on the D200 (and other Nikon cameras) since these are often done with JPEGs, where the in camera NR is automatically applied at ISO above 800 and can't be turned off. Noise may look good, but detail suffers, since as you state, the Nikon NR is a filtering process applied across pixels. Also, many cameras reduce sharpening with high ISO so as to avoid accentuating the noise. However, ACR ignores NR and sharpening settings that are tagged to the RAW file, and no NR is performed except for what is specified in the ACR detail tab. I usually use the default of 0 for luminance and 25 for color and no ACR sharpening. I then use Noise Ninja in PP.

The D200 does have quite a bit more read noise than the EOS 1DS Mark II--9.87 electrons vs  3.90 for the Canon for ISO 1600, so the methods you and BJL suggest for the Canon should work even better for the Nikons. However, Bill Claff and I have observed little difference.

Ron Parr has said that the Canon on chip NR at high ISO is consistent with the correlated double sampling that he thinks Canon does on chip and does not affect detail since it is not applied across pixels and is more like true NR and not simply filtering. In any event, methods to reduce shadow noise need to take the characteristics of the camera into account.

[madmanchan]

Are you suggesting that DSLRs can capture a DR range equal to negative film and greater than transparencies? Is this specific for DSLRs only, or all digital cameras? My understanding is that digital cameras' DR range (before any editing in RAW or PS) is similar to transparencies', i.e. about five stops.

Print compression occurs on both film and digital captures. But with PS (and RAW), some tricks can be applied to alleviate the print compression.
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See here (first table)  as an example for the 30D:

[a href=\"http://www.dpreview.com/reviews/canoneos30d/page21.asp]http://www.dpreview.com/reviews/canoneos30d/page21.asp[/url]

According to Phil's measurements, the usable DR is about 8.4 EV until ISO 1600, where it drops to about 8 EV.  At 3200 it's about a stop less, 7.3 EV.  If you'd like more specifics, take a closer look at Phil's description of how he measures DR.

These measurements are for JPEGs.  The bottom tables on that page are for RAW.

Eric

[bjanes]

Are you suggesting that DSLRs can capture a DR range equal to negative film and greater than transparencies? Is this specific for DSLRs only, or all digital cameras? My understanding is that digital cameras' DR range (before any editing in RAW or PS) is similar to transparencies', i.e. about five stops.

Print compression occurs on both film and digital captures. But with PS (and RAW), some tricks can be applied to alleviate the print compression.
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Roger Clark has done some testing with the Canon EOS1 D Mark II in comparison to Velvia and Kodak Gold 200 print film. Like most serious photographers, he is of course using raw. His conclusions are that the Canon has 10.6 stops of dynamic range, Velvia 5 stops, and Kodak Gold 7 stops. The digital is considerably better than film. The floor is DR is determined by noise, and there can be some argument as to when image detail is overwhelmed by noise in the shadows, so there is some ambuguity to the figures.

With digital, DR is defined as full well electron capacity / read noise by CCD manufacturers, but many photographers determine the noise floor visually. In any event, with digital there is much less DR at high ISO due to the small number of electrons collected by the sensor. P&S cameras have small sensors and small full well capacities, so their DR is limited.

[a href=\"http://www.clarkvision.com/imagedetail/dynamicrange2/index.html]http://www.clarkvision.com/imagedetail/dyn...nge2/index.html[/url]

[bjanes]

Metering from the midtones (or auto metering modes) can be problematic for some images, on *both* film and digital cameras. I think that those who have mastered proper metering (actaully all aspects of photo techniques) on film have some advantage when crossing over to digital. It is quite amusing to find topics like composition, etc. being extensively covered in *digital* photography books, as if these are *digital* specific.
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I agree entirely. I don't think Ansel Adams would have any trouble exposing for digital. He would merely place Zone X at the highest DN of the raw file. In his later books, he recommended against using an averaging meter, but used a 1 degree spot meter to determine dynamic range and place the tones properly. Similarly, chrome users are accustomed to exposing for the highlights.