Tuesday, 16 March 2010

On comparisons

So the latest from Luminous Landscape is this short piece on making comparisons, in response to the minor debacle that was the comment on dynamic range comparisons. I'm kind of glad the later response went up, gives some balance and avoids me posting a rant against the original.

I agree that in print there are likely (I've not seen so can't say from experience) visible, visceral differences in output from DLSRs and Digital Medium Format (DMF). Large prints are almost certain to make that more apparent. Just as I can clearly see differences in the formats I shoot regularly once print size passes some threshold. All well and good.

Thing is, that goes no way to dispelling the myth propounded in the first piece that DMF has a larger dynamic range than DSLR. Unfortunately for LL, this is a measurable quantity and it doesn't matter what constraints you put on the range (such as the base signal to noise ratio), it is still directly measurable. And as comparisons over at DXOMark will show, there is precious little difference in modern DSLRs and DMF.

Another problem I had is that LL was using DR as a proxy for usable detail, although it is nothing of the sort. DXOMark has a separate measure for this (and the merits of that could be argued) in its tonal range measure. Again, objectively measurable. The one problem here is that when doing print comparisons, they re-base to a shrunk print - the lowest common denominator. It would be useful to see that also done for larger size (but then that would mean up-scaling lower resolutions, with attendant problems).

The biggest problem I had with the LL position is that they are using the subjective stuff, and ropey assessment of measurable values, to debunk the science as it doesn't agree with their conclusion. Unfortunately it doesn't work like that. Just because you don't agree with the measurements doesn't make them wrong. But likewise (to the chagrin of the measurebators) the numbers don't make the subjective preferences (opinions) wrong either.


  1. We see the same song and dance in the audio field. Ultimately you have to let your ears decide since there 'are' differences and you have to decide if you're willing to pay for that difference.

    I think something similar here. Let your eyes decide. (and use your brain as well!). It also depends on what you are using 'To Let your eyes decide'). Small prints, Big prints, 100% on Screen, etc.

    As well, sometimes hard to correlate what you see with what you measure in all aspects.

  2. Kjell H Andersen16 March 2010 at 21:07

    I'm really with on this one Martin. I am in no position to say if they are right or wrong since I don't own a MF back, but the way they argue doesn't make any sense.

    The first issue I have is that I think they downplay the dynamic range of a DSLR a bit. 6-7 stops seems a bit on the low side in my reality, but give the subjective arguing, they probably have higher standards than me.

    The serious issue, and the one that makes me wonder if they know what the heck they're talking about, is the fact that they say most MF backs can capture 12-13 stops. Given that a DSLR with a measured dynamic range of 10-11stops can capture significantly less than that, it beats me how a MF back can capture a step or two more than the measured dynamic range (PhaseOne P65 max at 11.5 stops at DxoMark).

    Unless all the MF back measurements at DxoMark is wrong, there is no way the MF backs can have a higher practical dynamic range than the one measured. It may be higher than a DSLR, but no way it is 12-13 stops.

  3. Interesting to read the interview with the Pentax product planner for the 645D. About 2/3 down the page, he says that Kodak specifies the 40MP sensor delivered to that camera to have a 11.5stop dynamic range. And that is the physical property of the sensor alone. The dynamic range for the total camera system is bound to be less.

    OK, this is Pentax, and not PhaseOne, but the sensors aren't that different.


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