Question about Neutral Density filters

[Alex]

Can Neutral Density affect coloration of the picture because a more wide open f-stop uses more of the lens, and theoretically more of the lens coatings than a higher f-stop, or is that a wrong assumption to make?

Does a picture with less depth of field affect the film chemistry differently as the light hits the film versus shooting at a greater depth of field?

[Actor]

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I think f 5.6 is the sweet spot on most lenses.
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This idea that f/5.6 somehow represents some kind of golden mean is a concept that I never heard of prior to my exposure to the internet. I could be wrong but IN MY HUMBLE OPINION it is an old wives' tale. The laws of physics and chemistry simply come together in such a way that, for realizable films, camera and lens designs will wind up having f/5.6 somewhere in the middle of the range. There is a tendency in human nature to regard extremes as suspect and thus the legend of the f/5.6 "sweet spot" evolves.

Actually the effects of all lens aberrations (spherical, chromatic or whatever) are reduced by stopping down the lens. To reduce the effects of lens aberrations as much as possible you should, in theory, stop down the lens as much a possible and obtain the correct exposure by whatever other means are available, i.e., shutter angle, film speed or lighting.

I cannot resist a brief aside here. The immortal Ansel Adams once stated that his favorite shutter speed was 1/8 second. He was also a member of the "32 ?lub", a group that favored f/32. That Adams favored these two settings is not surprising when you consider his favorite subjects were outdoor landscapes. Using ASA 100 film most midday sunlight will make f/32 and shutter speed of 1/8 second quite compatible. A Playboy photographer shooting centerfolds is unlikely to share Adam's bias.

As a practical matter, stopping down as much as possibe to minimize lens aberrations is overkill. Although no lens is absolutely free of aberrations, a well made lens has them under control. In Super8 many aberrations will get lost in the grain.

Ideally as a cinematographer I would want to stop my camere down to f/32, use ASA 50 film, a shutter angle of 144 (1/60 sec @ 24fps) and control the exposure by adjusting the lights. That's the hard way to do it and quite impractical on my budget.
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Can Neutral Density affect coloration of the picture because a more wide open f-stop uses more of the lens, and theoretically more of the lens coatings than a higher f-stop, or is that a wrong assumption to make?
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It's the wrong assumption. What you are discussing here is chromatic aberration and to minimize it you want to stop down the lens, not open it up. I.e., you want to use the center of he lens and that's where the coatings are thinnest.
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Does a picture with less depth of field affect the film chemistry differently as the light hits the film versus shooting at a greater depth of field?
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No. The film reacts to how much light strikes it and where it strikes it. It does not matter how the light got there.

[Actor]

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should I buy several....an ND 8 to use in strong bright sunlight, and an ND6 to use in more moderate sun?
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Personally I would buy two: a 0.3ND and a 0.6ND. the former gives me 1 stop, the latter 2 stops and stacking them together gives 3 stops, enough for most situations. If you want more then get a 0.1ND and a O.2ND. With these four you can get anything from 0.1ND to 1.2ND is 0.1ND steps.

0.1ND = O.1ND
0.2ND = 0.2ND
0.3ND = 0.3ND0.4ND = 0.3ND + 0.1ND
0.5ND = 0.3ND + 0.2ND
0.6ND = 0.6ND
0.7ND = 0.6ND + 0.1ND
0.8ND = 0.6ND + 0.2ND
0.9ND = 0.6ND + 0.3ND
1.0ND = 0.6ND + 0.3ND + 0.1ND
1.1ND = 0.6ND + 0.3ND + 0.2ND
1.2ND = 0.6ND + 0.3ND + 0.2ND + 0.1ND

If you want to get a fifth it should be a 1.2ND

[cameraguy]

In regards to stacking filters, some camera lens only allow 1 filter before it gets into the picture at wide angle.

[Actor]

Good point, however I've never run into that problem. And only one filter seems to be kind of a severe limitation.

There are various work-arounds, such as using large square filters and a matte box.

I've been known to gaffer tape filters in front of the lens.

[Alex]

Ansell Adams may not be a good example for our purposes, (although that was very interesting info about his shooting philosophy) because his primary goal was perfectly sharp, scenic wide shots. Sort of like consumer video (everything's in muddy focus), but masterfully done on film, and crystal clear...

Becasue Ansell Adams produced such sharp imagery for master shots, he needed as high an f-stop as possible, AND the slower shutter speed would allow for such a high f-stop.

Film does have an exposure characteristic (I think it's called either latency or repricosity) to it that changes slightly as the shutter time varies.

That's why I was wondering if depth of field can affect film chemistry. If more of the light hitting the film plane is out of focus versus in focus, the silver in the film could react differently.

[Actor]

I think Adams is a good example for the point I was trying to make (and apparently failed) which was that one's shooting philosophy depends on what one is trying to accomplish. You seem to be making the same point.

Reciprocity failure generally does not set in until exposure time exceeds one second. You have to correct for it and not believe the light meter. The correction cannot be built into the light meter because it is different for different films. Kodak prints the correction on the inside of the box. Reciprocity failure is a function of shutter speed alone and has nothing to do with focus. Since it does not set in until shutter speed exceeds one second cinematographers generally do not have to deal with it.

[Alex]

Ansell Adams is a great example of how someone develops a style of shooting as it relates to film stocks and what they are trying to accomplish.

But I don't think what Ansell Adams did is applicable to the f 5.6 "sweet-spot" discussion. I do have a techy assoicate who may have a take on this issue, I'll ask his opinion as to if there is "sweet-spot" as it relates to lens performance.

It could be that f 5.6 is just the most popular mainstream setting because of the look of the depth of field in most cases.

[cameraguy]

Its probably not a huge problem expect for wide angle and large apertures on some cameras. I know I have read a few manuals that warn against stacking filters.

[TA152]

<font color="#a62a2a" size="1">[ August 28, 2003 11:07 PM: Message edited by: S8 Booster ]</font>