Sharpness and filters

[Ian C]

If you increased the exposure for the filtered shot by opening the aperture, then the depth of field is reduced.

If you forgot about the aperture change, the reduction in depth of field might be interpreted as a “loss of sharpness” and wrongly blamed on the filter.

 

[Richard S. (rich815)]

Richard,

Let me qualify

I'm talking about optimizing resolution and contrast here, nothing more. There's really no question that modern computer-aided designs and multi-coatings coupled with more stringent quality control and assembly procedures have resulted in a general improvement in these parameters when compared with single or uncoated lenses that were hand assembled and designed "on paper." Whether you like that or not or whether you call that "quality," is another issue.

The OP's question was about whether a particular color of filter would degrade contrast and sharpness more than another. That is what I was addressing, not aesthetic issues.

FWIW, there were/are a lot of older lenses that don't fit this generality; I love my Ektars and there are those who swear by the Red-dot Artars, etc. etc.

Best,

Doremus

I hear ya.

And understand your point. I just take issue with the blanket statement that "modern" lens are "superior" to older ones. In many cases sharper and more contrasty? Yes. But that does not make them necessarily superior in my book.

 

[Maris]

The sharpness challenge taken to the limit should recognise that a perfect lens working with a perfect dark red filter can deliver only about half the resolution of that same lens with a perfect dark blue filter. The longer the wavelength the lower the theoretical diffraction limited resolution.

 

[DREW WILEY]

Let me give an example of when being nitpicky helps. Most of my time I'm lugging around at least a 4x5, and often an 8x10, and the effect on
perceived sharpness with any high-quality modern glass coated filter is going to be largely undetectable. But now that Quickload and Readyload film sleeves are no longer available, and I'm getting to be a bit of a geezer, I sometimes prefer to carry 6x9 roll film backs for my 4x5 on long backpacking trips. If I put a film like Ektar in that (color) or maybe ACROS (black and white), I might be able to squeeze out a 16x20 print that pretends to look like I shot it in large format, if everything is optimized, including the quality of any filters. That's like trying to get a chiuahua to bite like a rottweiler. Needs some good sharp teeth. But again, how many filters does a person really need to carry?
Unless you're talking very large sized ones, good multicoated ones don't cost all that much more than so-so varieties.

 

[DREW WILEY]

Maris - in the real world, you've got it backwards. Blue light is more easily scattered by the atmosphere. That's why the sky looks blue, and why, outdoors, shots with blue filters (over a distance) will come out softer than red filter shots, often dramatically so. This fact will overcome
the characteristics of the lens itself, at least with modern lenses and panchromatic films. Doesn't mean you shouldn't use a blue filter for a
deliberately atmospheric effect, creatively. Just means distant details will be much less contrasty, maybe to the point of being undetectable.

 

[Poisson Du Jour]

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?

 

[Alan Klein]

I'll have to shoot the same scenes with and without the filter to see the difference, if any. Thanks everyone for your ideas.

 

[Doremus Scudder]

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?

Au contraire, Poisson

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...

Best,

Doremus

 

[DREW WILEY]

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.

 

[Maris]

Maris - in the real world, you've got it backwards. Blue light is more easily scattered by the atmosphere. That's why the sky looks blue, and why, outdoors, shots with blue filters (over a distance) will come out softer than red filter shots, often dramatically so. This fact will overcome
the characteristics of the lens itself, at least with modern lenses and panchromatic films. Doesn't mean you shouldn't use a blue filter for a
deliberately atmospheric effect, creatively. Just means distant details will be much less contrasty, maybe to the point of being undetectable.

Exactly right! Real world photography trumps results from optical bench tests.

 

[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.