Minimum f-stop?

[Bob Salomon]

"IMHO it's usually a no-brainer because insufficient depth of field (arising from using too wide an aperture because of worries about diffraction) in a photograph where everything is supposed to be sharp is usually far more noticeable and distressing than are the effects of diffraction with LF film and even a large (say 20x30) print. "

That assumes that the camera was properly focused so the near and far points will fall into the DOF at the largest useable aperture for those two points.

Too many people that we talk to over the years focus on the far point and then stop down until the near point appears sharp. And that ends up with apertures that are beyond the optimal ones for the lens design.

Also, the DOF attained is also effected by the magnification one wants for the print. Assuming you are using a 4x loupe and are checking the DOF at shooting aperture on 4x5 then you are seeing the DOF on a 16 x 20"print. If you then make a larger print you will no longer appear sharp at the same near and far points.

It is not just a matter of f64 and be dammed.

[Ken Lee]

I have been contemplating the recovery of detail in an image through sharpening or contrast enhancement and the notion that some sharpening or contrast enhancement can recover resolving power at very low MTF contrast values. In fact I can do this by upping the contrast in an image to an extreme degree. This, in effect, takes a slice of the film dynamic range and dramatically ups the resolution of fine detail at that particular density by dropping out the low contrast parts of the detail robbing high frequency components. The disadvantage is that limiting the film density to such a narrow range eliminates the information at other densities above and below the slice chosen. The result is a very high contrast image which provides high resolution of features at the chosen density but destroys structures above and below that density. Sharpening does something similar in that it increases contrast at an edge of a structure by increasing the high frequency components at a step in density.

I just find there are tradeoffs between the contrast enhancement technique and sharpening which introduce artifacts from sharpening or eliminate density details during contrast enhancement. OTOH I'll use both techniques with a modicum of restraint to achieve a particular effect. In deference to Bernices' comments (I think) above, I've found that in fact one can certainly enhance detail that was truly muddy or soft in the original film but obviously additional detail cannot be found. If fine detail is what you are after then you'd better get it on the film, and the diffraction limits are important.

Nate Potter, Austin TX.

One reason I like 5x7 over 4x5 is that less sharpening is required, and there is less demand on my humble scanner. With less sharpening, many of my images have a more natural appearance.

I can't demonstrate this theoretically, but I routinely see it practice. I presume it relates to your observations above. Sharpening may seem to take place only at a local level, but it can affect the tonality of an entire image. That's one reason I sharpen different parts of the tonal scale, separately.

[Drew Wiley]

Contact printers can get away with lot in terms of diffraction. But once you start enlarging signifcantly it can spoil critical sharpness. I never stop down 4x5 more than f/32. With 8x10 black and white I'll go down to f/64 because I don't intend to print it larger than 20x24, but for any color work intended to be printed up to 30x40, I prefer to stay within f/45. I was printing some 6x9 Ektar work last nite up to what I consider utter madness for a subminature format like this (20X24 high gloss prints); but the lenses were top notch and I think I had exposed at f/22, so the results were impressive anyway. Don't
know if I'd risk that degree of enlargment of 6x9 if I'd used f/32, but will have to test that theory some day.

[Mark Sawyer]

Contact printers can get away with lot in terms of diffraction...

That's the key. The little bit you lose to diffraction is nothing unless the image is greatly enlarged, but significant out-of-focus is obvious in any print big enough to view. Remember that Edward Weston used pinhole apertures in his lens (and all-day exposures) to get enough depth of field for his still lifes. No one ever says his 8x10 contact prints of peppers and nautilus shells aren't sharp enough. But for Ansel Adams, who'd push a 4x5 negative to a 20x24 print, it was a different story...

[Drew Wiley]

What Edward also routinely got away with was wide apertures, as in those classic Point Lobos shots with crisp waves splashing due to short shutter speeds. If any of these so-called "f/64" style shots were actually enlarged to 16x20, I think the results would be atrocious. The whole point is to understand your end result. There's no way to make one shoe size fit
everybody, or every situation.

[unixrevolution]

Short version: I have used everything up to and including F/64 for extreme situations where DoF is necessary, but generally I shoot most work at f/16 and f/22.

Long version: on 4x5 I typically have enough DoF wide open for landscapes that I don't need to worry too much. On occasions where I need to get right up to the camera sharp, a little tilt and f/22 works wonders. I do wide-open portraits on 4x5 all the time, cause I like the look. Typically those are with a 210 and seated a bit away from me. With polaroid backs handheld, my super graphic is frequently used with its 135mm lens wide open at f/4.7 due to light. I shoot a lot in fairly dark places so I make more use of the wide end of the aperture scale than most do.

On 8x10, which i've been shooting for a little under a week, I find that even with seated portraits, f/16 and f/22 produce a nicely blurred background. Any wider, and you don't get the whole subject in focus. In practice on landscapes i"ve used F/64 once, and f/22-f/32 for most of the remainder. I could see getting away with wide open on 8x10 if your perched somewhere high, such that you don't have anything close to the camera in shot.

[Drew Wiley]

With sheet film, shooting at large apertures can have the distinct disadvantage of not giving enough depth on an uneven
film plane. This is especially a problem if the camera is pointed down. Film sags in the holder unless you are using some kind of vacuum or adhesive holder. Maybe for soft focus work like certain portraiture projects you can get away with this,
but I think not, because I personally like at least some point in the subject, like the eyes, to be crisply focussed. Shallow
depth of field and sloppy depth of field are not synonymous. Fortunately, some black and white sheet films are fairly stiff.
Most color films are not.