I have read Alan's original post over and over again and something a bit left-of-field comes to mind that has not been explored: the characteristic of the lens. A lens (uncorrected) with known chromatic aberration will also have a relationship to image sharpness. I would imagine that the Mamiya lens is maybe not a highly corrected optic and it would have some definite chroma or a fairly nondescript refraction index (which would be further deranged by the use of a deep aperture)? So if a coloured filter is introduced, is that exaggerating the amount of chromatic aberration and thus resulting in a perceived greater loss of image sharpness? Colour theory and lens technology was explored in my uni days: the subject of aspherical, apochromatic and polyapochromatic theory and design. I have not for many years used an orange, blue or yellow filter on any of my lenses, most of which are apochromatic, but I do use red on my fairly bog-standard design 67 lenses (red, predominantly with ACROS 100) with absolutely no derangement of sharpness anywhere. So is the problem mechanical? Has the scene(s) been shot with another camera loaded with the same film, lens and filter? What was the result of the parallel test: unsharp or completely different in characteristics?
I'll have to shoot the same scenes with and without the filter to see the difference, if any. Thanks everyone for your ideas.
Au contraire, Poisson :)
Originally Posted by Poisson Du Jour
When a lens has chromatic aberration, that means it is not focusing all colors at the same plane. Removing one or more of these colors (especially if you remove the one that is the most out-of-focus) actually improves the sharpness.
Usually it is blue that is the culprit (hence the blue color of many fringes on non-apo lenses) and using a red or orange filter would fix it right up...
That was brought up earlier. Almost all modern lenses are "achromatic", if not officially "apochromatic" (which in an official sense is more strictly defined for process lenses than general taking lenses). Some older lenses, prior to the 1960's were not always corrected with respect to the blue, so would benefit in black and white work from truncating the blue with a yellow, orange, or red filter. This was differentiated from "color" lenses, like the Commercial Ektars, which were expected to handle the full spectrum reasonably well. Nowadays we just take it for granted that
all lenses are fine for either color or black and white work. But older lenses still have certain qualities that some desire, or maybe you just got
ahold of one cheap.
Exactly right! Real world photography trumps results from optical bench tests.
Originally Posted by DREW WILEY
I've got decades of real world photography, plus bench tests. So that trumps both. But it's all about intelligent decisions. I even use things like
blue filters once in awhile, and even flare itself for creative purposes. I wouldn't mind owning an old totally uncoated lens or two for my 8x10.
But there are times to use them, and times not to. Using tools wisely is just part of the craft. But the whole point is what you make with those
tools, not the gadgets for their own sake.