The dangers of pixel peeping

[DarkPenguin]

That's interesting.  Mine are all defined by opportunity.  If I had different camera gear with me at the time they would have come out about the same.

[Robert Roaldi]

Several of the ones on my walls were shot with an Olympus Stylus Epic (fixed 35mm lens), using some Fuji 100 ISO film or other (who remembers) and printed at a local lab, who did good work without much trial and error hassle.

[Ray]

The significance is that obviously pixel peeping -- analysing the technological aspects of our gear: lens resolution, diffraction limitation, dynamic range, color accuracy, noise/grain -- seem to have little to do with producing our favorite (and ergo by inference, best) images

I should have also asked when you started doing photography seriously...
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Jack,
I do not think that's true in my case, although I would agree that all pixel peeping is not necessarily productive. I have spoiled shots as a result of the camera's auto metering overexposing highlights, spoiled shots as a result of not exposing to the right, resulting in excessive noise in the shadows, spoiled shots by not using a fast enough shutter speed and spoiled shots as a result of not using f16 or f22 because of reports that resolution begins to fall off at f11 and is seriously diffraction limited at f16.

A bit of pixel peeping is often necessary to get 'much talked about' differences into perspective in one's own mind. Just how significant, for example, is resolution fall-off at f16 in relation to a desired increase in sharpness in the foreground. With some lenses, the fall-off in resolution at the point of focus might be effectively zilch at f16. It appears to be with my Canon 24-105. With other lenses, such as a 100-400/1.4x extender combination, f22 might produce best results, and yet other lenses, top rate primes for example, might show obvious softening at f16.

I started doing photography 'more seriously' when the desktop computer darkroom became an option and I bought my first scanner, the Nikon LS2000. But I've taken photos now and again (off and on) for many years, since I was a kid, and many of them have sentimental value. My first and only published images were a series of shots of Angkor Wat that appeared in a mazazine called 'Look East' around 1970. I remember we had a lot of trouble getting the magazine printers to get the colors right and everything in register.

[dwdallam]

Remeber you can also increase ppi in photoshop, and interpolation is getting better every day.

The point also is that these SQF tests you refer to were carried out in the 1970's before Photoshop and digital cameras for the general public were available. That does not mean of course that the 'subjective quality factor' is no longer valid. However, the methods of achieving that SQF have progressed and that factor may now no longer be so dependent upon lens contrast at low frequencies.

In the example of the yellow cars in your first link showing the lower resolution image appearing to be sharper than the higher resolution image, the higher resolution, slightly blurry looking car can be made to 'appear' as sharp as the more contrasty car by simply applying a bit of sharpening. (I tried it, using a blur width of 3 pixels in Focus Magic at 100%).

The real question here is, in what ways can a contrasty lens produce an appearance of sharpness that cannot be created or imitated in Photoshop with an appropriate amount and type of sharpening, including edge sharpening and local contrast enhancement?

The bottom line might well be, no amount of processing can create detail where none existed, but processing can create an appearance of additional sharpness or accutance (SQF) to compensate for a lack of contrast of the lens at low frequencies.

It would be interesting to see some comparisons between a first rate prime and a first rate zoom, (or 2nd rate prime), with the image from the less contrasty lens processed more to mimic that appearance of greater accutance.

Also, it's always been the case that the smaller the print, the lower the image resolution required because the eye cannot discern (apparently) a greater resolution than 4 to 6 lp/mm from a 'normal' viewing distance. I recall somewhere, you quoted a very precise figure of 6.7 lp/mm. However, if we take the figure at the top of the range, 6 lp/mm, and do a bit of simple maths, then we cannot avoid a conclusion that no current Canon camera, except possibly the 1Ds2, is able to take an image of sufficiently high resolution that would meet this very high standard on an 8x12" print.

For example, 6 lp/mm across the width of a vertically oriented 8x12' print requires a print resolution of 6x200=1200 line pairs.

The 20D and 30D have a maximum resolution of around 60 lp/mm. 15x60=900 line pairs. That's a big shortfall. According to Dpreview, the 5D has a 'total picture height' number of lines that varies in the vertical and horizontal direction. Why this should be so, I have no idea, but the higher figure of 2300 lines does not quite meet the standard of 1200 line pairs, but that's close enough for me. The lower figure of 2000 lines is a bit too far off.

My general view is, I do not always know when a shot I take might look impressive blown up larger at a later date, for a customer perhaps or just because I might later be able to afford a larger printer. There's no disadvantage in capturing an image which has higher resolution for one's immediate purposes, but the reverse  certainly does have some disadvantages, with the possible exception of DoF appearances on print, the smaller print producing greater DoF, which might not be the desired effect.
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