another reason to toss DoF calculations

[ho_co]

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New LuLa Mark Dubovoy article emphasizes once again why digital and analog don't behave the same way in regard to depth of field.

 

An Open Letter To The Major Camera Manufacturers

 

 

Overall, I've got problems with DxO's techniques, and I question not their results but the meaning they assign to the results.

 

But I think the point that digital pixel wells lie at the bottom of tubes and don't get the side-striking rays as film did goes a long way toward explaining why the old calculations regarding depth of field aren't borne out with digital.

 

I don't know why CMOS is singled out in the article (in what way does a CCD sensor differ in terms of physical location of the photosites?) and would like to see similar comparisons with both CCD sensors and with the Foveon design, which throws a new architecture into the mix.

 

 

 

OOPS. I intended to post this in Digital Forum, not M8 Forum.

 

Please look there.

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[SJP]

Sorry I do not agree at all with the analysis in this article or at least I do not see how it impacts on DoF. The article is about transmission/light intensity which might be a valid point but DoF is only about "acceptable resolution/sharpness" and it is a purely geometric argument. Acceptable DoF or sharpness has changed somewhat with digital imaging as one tends to print larger, view on large screens etc. and that leads to ca. 1 stop correction compared to the historical criteria, M8 sensor crop adds an additional factor again ca. 1 stop. However it is totally misleading in the article that digital sensors would eliminate the need for fast lenses. This might be true if you want "sharp" across the board (basically P&S) but there is no substitute for fast lenses in their ability for 3D isolation i.e. summilux & noctilux type images cannot be replicated with a f/4 lens.

[lct]

Am i the only one to use the DoF markings of my lenses the same way as i've always done with film? (I mean with FF cams of course.)

[pgk]

Sorry I do not agree at all with the analysis in this article..... there is no substitute for fast lenses in their ability for 3D isolation i.e. summilux & noctilux type images cannot be replicated with a f/4 lens.

Absolutely. The conclusions drawn make enormous assumptions and, as far as I am aware from my own experience, do not mirror reality. I use wide aperture lenses to isolate or at least emphasise subject matter and I see vast differences in say f/1.4 and f/2 on both film (when I used it) and digital. Looks like a triumph of ill thought out theory over actuality to me!

[lct]

As far as DoF is concerned i don't significant difference between theory and practice personally. OoF doesn't look exactly the same with film & digital for sure but what is blurred with film is blurred with digital at same crop factor, focal length, aperture, subject distance and acceptable sharpness IMHO. Now some photogs practice pixel peeping so much that their level of acceptable sharpness does not remain the same perhaps, i don't know.

[mjh]

Looks like a triumph of ill thought out theory over actuality to me!

Actually the theory (if it even warrants that label) doesn’t hold much water and the tests haven’t yet been carried out by DxO. The issue with light loss is a real one but everything else is conjecture at best.

[blakley]

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Paul, are you talking about results with an M8 or M9? Reichmann points out that the Kodak CCD sensors in these cameras are designed differently from the CMOS sensors represented in the DXO tests, so the claims he makes about light loss and depth of field presumably do not apply (at least in the same way) to these cameras. Results on a digital M are simply irrelevant to his claim.

 

Stephen, it's pretty clear that Reichmann agrees with you that DoF is a strictly geometric argument, which is why he takes pains to point out that oblique rays get absorbed by the walls of the CMOS sensors' pixel wells. He's making a geometric argument, but I agree with you that it may not be a correct one - for his argument to be correct it would be necessary to assume that "out of focus" rays are always more oblique than "in focus rays", and a few simple drawings suggest that this really can't be the case.