Alan Edward Klein
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So should I use the filter manufacturer's suggested factor? That's what I do. The rest is too speculative.
So should I use the filter manufacturer's suggested factor? That's what I do. The rest is too speculative.Musings about filter factors:
The logical "standard" for a factor for a given filter would be the extra exposure needed to render a mid-tone neutral gray the same density on the film with and without the filter. Other colors would have more or less density on the negative depending on the degree to which they are transmitted (blocked) by the filter. E.g., a red filter, which transmits mostly red light, would need enough extra exposure to transmit enough of the red in the neutral gray to achieve the same density in the negative as there would be without a filter. Other colors would fall where they may.
This factor, of necessity, would vary to differing degrees from film to film, depending on the spectral response of the films, as well from meter to meter, for the same reason. Furthermore, the color content of the light source would make a significant difference in determining factors. (Black-and-white films used to come with tech sheets giving factors for both daylight and tungsten, for example).
So, already, it seems apparent that you can only have an accurate filter factor for a given meter, film and light source. Now take into account the reality of metering in the field. Sure, we can take a gray card with us and use that, but many don't and it would often be impractical. So, we end up metering things that aren't neutral (i.e., don't have an even spectral reflectance). That can easily wreak havoc with filter factors; just try metering that deep blue shadow in an alpine scene to base your exposure on and then add a red filter and the published filter factor. You've just based your exposure on mostly blue light and then blocked all of that out with the red filter and only given an extra three stops to retain some detail in the shadow. Featureless, disappointing shadows are sure to be the result. Or vice-versa; take a reading off that red barn illuminated by the setting sun and then add your red filter. Oops, overexposure! (Which, however, isn't so bad as underexposure).
And, even if we can arrive at a factor that renders spectral-neutral objects at the desired density on the film, determining how much densities from colored objects will be affected is a crap shoot. Usually, we're just guessing: "darker" blue sky (how much darker?). Lighter foliage? How much? (and do we even take into account that although leaves often appear green, that there is a lot of red in there too?)
It would be technically possible to make a meter that had the same spectral response as a given film. Then a simple reading through the filter would suffice for both determining exposure and knowing how colored objects would be rendered. That was the idea behind Zone VI modified meters. I don't think it worked that well though, for whatever reason (I've had two Zone VI modified meters over the years and simply reading through the filters, especially the stronger ones, didn't work as advertised.)
Add to all this the fact that film emulsions react to different colors of light with varying sensitivity and contrast and the plot thickens even more. A deep red filter might end up making one film contrastier and another less contrasty when developed to "normal."
Published filter factors are the manufacturers' best recommendation for getting good results, but they are, of necessity, approximations based on general conditions and (hopefully) a safety factor. One can do all the necessary tests to arrive at better filter factors for the conditions, equipment and materials they use regularly. Many do this (I have). However, the results of such tests are also just guidelines/approximations/educated guesses for compensation, even if more refined.
The best we can do is understand how filters work and how the system reacts to them and be aware of what conditions might require modifying the factor (and how much in which way). We can go down that rabbit hole as far as we like. We can also bracket in questionable situations, not only exposure, but using different filters too. This is especially important when learning in order to gain the experience in using filters that will help us to refine our filter choice and to modify the factors we use.
Best,
Doremus
It was an attempt at humor, that apparently fell flat.
I'm glad at least a couple of people did. Sometimes the forum seems a bit too, um, SiriusI thought it was funny.
I'm glad at least a couple of people did. Sometimes the forum seems a bit too, um, Sirius
So should I use the filter manufacturer's suggested factor? That's what I do. The rest is too speculative.
So should I use the filter manufacturer's suggested factor? That's what I do. The rest is too speculative.
Good point. I also forgot that some film data sheets provide filter factors for their film which you ought to follow. Also note that the factors are different for tungston lighting from sunlight.Using the manufacturer's filter factor is as speculative, as you then assume the manufacturer just had the same idea in mind concerning colour reproduction as you intend when they established that factor.
I am not certain, but unless a filter has a Wratten number, specific colors and tints for black and white are determined by the filter manufacturer and might vary, so a film spec sheet is a starting point.Good point. I also forgot that some film data sheets provide filter factors for their film which you ought to follow. Also note that the factors are different for tungston lighting from sunlight.
I am not certain, but unless a filter has a Wratten number, specific colors and tints for black and white are determined by the filter manufacturer and might vary, so a film spec sheet is a starting point.
Is there any relationship between reciprocity failure and color of light? I mean, is it possible that reciprocity failure can happen for a specific film earlier or later depending the color of light?
Using the manufacturer's filter factor is as speculative, as you then assume the manufacturer just had the same idea in mind concerning colour reproduction as you intend when they established that factor.
Don't sweat it too much. There are too many variables + unknowns to be precise about it. ...
I already hinted at this before. But as I also hinted at, to apply the filter factor only makes sense if one wants to render a neutral grey the same after applying the filter. But this is not necessarily the case, as rendering a certain colour the same as before may be a prerequisite in filter application.As I mentioned before, manufacturers' factors are calculated to render a neutral gray card the same density both with and without the filter.
I got it. Was grocery shopping so could read the post while the deli person fed me baloney and cut the cheese. When I use a dark red filter I automatically have a beard and a big view camera!
Don't sweat it too much. There are too many variables + unknowns to be precise about it.
Use the suggested factor from the filter or film manufacturer (depending on the type of filter) and some judgment which comes from experience. When in doubt give a little extra exposure and bracket.
A basic understanding of light/colour is of course helpful.
I already hinted at this before. But as I also hinted at, to apply the filter factor only makes sense if one wants to render a neutral grey the same after applying the filter. But this is not necessarily the case, as rendering a certain colour the same as before may be a prerequisite in filter application.
Not understanding this I see as the main fault in considering filter application.
Of course that only goes by approximation. Let's say, a red object will be rendered "about" the same with a red filter as without. If one aims at such one would leave aside the filter factor given for that filter.
I would think something is astray.Of course that only goes by approximation. Let's say, a red object will be rendered "about" the same with a red filter as without. If one aims at such one would leave aside the filter factor given for that filter.
That is why I left the conversation days ago.I would think something is astray.
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