exposure with filter and spotmeter

[neil poulsen]

I've written a bit here and on APUG about how I use my Pentax spotmeters to read directly through filters. I'll elaborate a bit later, but first, here's a quote from the manual that comes with the Pentax digital spotmeter:

"By mounting different filters in front of the objective lens of the Pentax Spotmeter and comparing the readings taken of the various colored areas with each filter, it will be easy to determine which on provides the best contrast for black and white film."

So, obviously the manufacturer thinks metering through the filter a viable option. . . .

Respectifully, I tend to be skeptical about these kinds of manufacturers' statements. For one thing, it's out of context, since it refers to conventional exposure determination, which is fundamentally flawed, versus Zone Systems exposure determination (for the shadows). Also, one doesn't know whether it might be quasi-advertising, representing more aspirational thinking, versus realistic thinking.

There are two reasons for using a meter that are worthwhile to bear in mind. One is to get an idea of how one area of the scene will compare with another in the final black and white photograph.

A second is to determine exposure (exposing for the shadows) and to determine development (through metering highlights). I have both an analog Pentax V modified meter (where I can at least estimate tenths of stops for film texting and calibration), and a Pentax Digital modified meter for use in the field. I tend to think that modified meters are more useful for the former reason (above), where one is compariing how different colors will appear in the final black and white photograph. If one is using a color filter, then one can make these comparisons by metering through the color filter.

In contrast, by evaluating shadows and highlights, one is metering areas in the scene that are relatively colorless. I think that using a non-modified meter in these cases is acceptable. If one is using a color filter, then one can compensate the meter reading by applying a filter factor.

When I'm in the field, it might be nice to compare how different areas in the scene will copare in the final black and white photograph, with or without a filter. But, my primary purpose is to determine both exposure and what development time that I'll be using. After these have been determined for the negative, it's pretty much job-done.

Chris Burkett is a master color photographer, especially when the method of capture is via color transparency. And I've had the good fortune to have twice participated in guided tours of his studeo. Its interesting to note that he used a Pentax modified meter to estimate exposure in the field. Just in case, he also maintained a second Pentax Zone VI modified meter as a backup.

[Drew Wiley]

If Chris Burkett has his reasons for using a modified Pentax meter, I have equally good reasons for using using the un-modified version. And one of those is the fact that modified meters contain internal filters which fade or degrade over time, and need a specialized kind of service, whereas factory meters are all calibrated to an industry standard which can easily be compared one to another to see if adjustment is due. The functional debate one style over the other, has been known to occur even with Hollywood cinematographers working in color exclusively. But all the modified ones are getting old by now, and I sure wouldn't buy one personally. But other than that arcane debate, Pentax and similar Minolta spotmeters are a well-known precise products known to be consistent for a number of decades now. I've have four of them, one so mauled from hundreds of trips the mountains that it's held together with masking tape, the others in fine condition - but all still read the same over the full range, given a minor recalibration tuneup about once per decade.

[neil poulsen]

Just as an aside, I was speaking in past tense to the time of the tours. (Probably 15 years ago.)

I just had both my meters calibrated by Richard Ritter; I'll check with him on this. I know that both meters are currently reading corrrectly after calibration.

[Robert Opheim]

I just keep a notation of the filter factor in each filter case.

[Jim Noel]

The Zone VI modified meters are supposed to be accurate when you take a reading through the filters. The regular non-modified meters are not calibrated for that use.

I have 2 of the modified meters, and they work through filters.

[Doremus Scudder]

I have 2 of the modified meters, and they work through filters.

I've got two modified and one unmodified Pentax digital spot meters. None of them are 100% accurate when reading through filters, especially the stronger ones like the 25A. No meter really can be; there will always be some mismatch with the spectral response of the meter vs. the film. Even the Zone VI modifications didn't fix this entirely (despite Fred Picker's claims).

However, a couple of quick tests through the two or three strongest filters you have yields an E.I. adjustment for reading through the filter that's easy to apply. Some stronger filters also affect the contrast of the negative. That's not so hard to test for either for a particular meter and film combination.

Yes, that's a bit like having a filter factor, so "why not just use the filter factor?" you may ask. Well, when reading through the filter with a spot meter, I can compare values from adjacent areas and see quickly if there will be mergers in tone or just how much separation I can expect. That's the advantage.

With weaker filters like the Wratten nos. 8, 11 and 15, the discrepancies are small and you can simply meter through them and use the reading. With the 25A and my #44A and #58 filters, I find I need an E.I. adjustment and, often, changes in development times to compensate for contrast changes when exposing through the filter.

Of course, one could just forget the adjustments, err on the side of overexposure and probably be able to deal with the resulting negatives just fine with today's VC papers (or digital adjustments), but I like to try for more accuracy, at least.

Best,

Doremus