Zone VI meter modifications (reprise)

Some time ago, I compared the performance of my Zone VI modified Pentax Digital Spotmeter, my unmodified Pentax Digital Spotmeter, and my Sekonic L-508 meter. Part of the goal was to try to gather some real data on the performance of different meters when metering different color targets, through different colored filters, and to perhaps come to some conclusions about the merits of the claims that the Zone VI meter is better than the unmodified Pentax. That article can be found at zone VI worth it.htm.

Despite the results I found (which was that there was no significant different between the unmodified Pentax Digital Spotmeter and the Zone VI modifed one in terms of color response, but that the Zone VI modifications worsened the meter's response in low light and increased meter flare) as far as I know, no one has attempted to perform any similar testing. (or, if they have, I haven't seen their results, although I've been watching).

Since I wrote that article, I've seen repeated pointers to several sources that folks claim support the Zone VI claims, as well as a number of photographers contesting my results.

I figure I'll examine all of that, in one go, and be done with it.

The Zone VI catalog

Kevin Crisp generously scanned several pages from an old Zone VI catalog and forwarded the scans to me. The scans can be found here, here, and here. Rather than force readers to refer constantly to the scans, I'll instead quote extensively here, as I go through the various claims and statements.

The first scan reads

Do you need a modified meter? Here's how to find out:

Take readings with your meter of a variety of single toned subjects. Adjust your camera and make exposures as the meter directs (use zone V, the unmanipulated meter reading). Subjects might include flesh tone, green foliage, clear sky, dar wood, a black card in shade, a red door, etc.

Develop the film

Make a proof of all the negatives. Because you placed all the subjects on the same zone, all frames should show the same shade of grey. If they don't, you need a modified meter.

Fair enough. Let me just point out that, in order for the tones as rendered in the final proof to differ because of meter differences, the modified and unmodified meter must produce different recommended exposures. However, when I did my testing, I found no significant difference between the modified and unmodified meter which could not easily be ascribed to unit-to-unit variation. That is, the results of the two meters differed by about the amount I would have expected if I had gone and purchased two identical meters.

Furthermore, the meter tests I performed should be replicable - that is, if you perform a similar test, you will get the same results I did. All the information about my methodology is there. I used a standard, available test target (a MacBeth Color Checker) which is in the possession of a large number of serious photographers, is noted for its consistency, and is well known. The filters I used are standard, top of the line B+W glass filters, used worldwide by hundreds of thousands of photographers and easily purchased in any serious camera store.

So, on the face of it, it appears that I have, in fact, performed the test recommended here, and my conclusion is that no one needs an modified meter.

One more observation: quite a few people have mentioned to me this test. No one I know personally has actually performed it (except for me).

The next page starts out

Without a modified meter, you can't win.
A useful meter provides exposure information that results in a negative density corresponding to the photographer's placement. NO meter, as it arrives from the manufacturer, is able to peform this function. The reason is that all meters measure light impartially. (they respond the same to infra red or ultra violet light of the same intensity.) But film can't see infra red very well (that's why your foliage is always distressingly dark) and the film is extremely sensitive to ultra violet (that's why your skies are always surprisingly light).

Please understand - I think many of Picker's products are excellent (were excellent?). However, Fred Picker's grasp of science was either sadly lacking or else played second fiddle to his admirable marketing talents. (remember that Fred Picker is the guy who told us that fixer laden water was heavier than pure water, and that for this reason, it sank to the bottom of a print washer. This is demonstrably untrue.)

In particular, Picker's claim that "all meters measure light impartially (they respond the same to infrared or ultraviolet light of the same intensity)" is, in fact, untrue. The light sensing elements in various light meters (CdS cells, Selenium cells, Silicon photo diodes) all have different, non-linear spectral response. The fact is, there's probably no meter made which actually responds to visible, infrared, and ultraviolet light of the same intensity in the same way, and you wouldn't want one if you did.

What you want (and what Fred says elsewhere) is a meter which responds to light of different wavelengths in the same way film (or your camera's sensor, if it's digital) does. The fact that Fred goes on to discuss this very issue indicates to me that he knew this, and that the preceding paragraph is just more of the infamous Picker pseudo-scientific blather.

The catalog page continues:

The most elegant, controlled, and graphic illustration of how any meter performs utilizes the procedure invented by Alan Ross. (See his description on the meter page.) Using a modified Pentax meter and an unmodified Pentax meter, we photographed a medium gray wall in hazy sunlight through various tri-color filters. (We first read the wall reflectance through the filters).
The contact strips illustrate that, as Alan wrote, the modified meter "sees the way film does" and using it, all exposures are less than 1/3 stop from Zone V.

The unmodified meter, however, delivered exposures with a four stop spread. As you can see, unmodified meters reduce the zone system to a hope-for result rather than a precise method of film exposure.

Embedded in the middle of this text are the contact printed images of two strips of 35mm film, five frames each. The first strip demonstrates enviable consistency of exposure, and the second shows considerable variation.

I have several observations. First, in order to get significant variation in exposure, the two meters used would have to recommend significantly different exposures. However, my testing reveals that the modified and unmodified DON'T suggest different exposures when metering a gray target through differently colored filters - they agree to within 1/3 stop in all cases when metering through various colored filters.

Finally, Picker claims that when he performed the test (and produced the negatives shown in the catalog page) he got a FOUR STOP spread of exposures. Look at the second strip of negatives. Do they look like a four stop spread in exposure to you? They don't to me. I think those negatives were crafted up, with the exposure varied, not as part of a meter test, but simply as a tool to sell modified meters.

Finally, the catalog page continues:

Test your meter and find out for yourself. You can either use filters or just photograph various subjects; green grass, blue sky, flesh tones, white paint, red paint, whatever. Place them all on the same zone. Proof the negs as above. If a meter does not give you the same density for each frame, it is useless.

Left unstated (and unproved, as far as I'm concerned) is the assertion that the Zone VI modified will actually pass this test.

Let me repeat: in order for an unmodified meter to fail this test and a modified meter to pass, the modified and unmodified meters must recommend different exposures when aimed at at the same target. In all my testing, I have never found this to be the case. If the unmodified meter fails this test (as Picker claims) and the modified meter responds the same as the unmodified one, the the modified meter is, in Picker's words, equally useless.

Thousands and thousands of photographers have made millions and millions of photographs using unmodified meters. My testing of my modified and unmodified meter reveals that there's no significant difference between the modified and unmodified meters color response. Picker's claim that unmodified meters are worthless is, put simply, complete bunk.

Finally, the last catalog page, which begins:

Zone VI Modified Meters

Dr. Paul Horowitz' modifications have resulted in new levels of light measuring accuracy. The modifications include:

Installation of superior photo-electric cells

installation of a series of step down baffles to eliminate flare

installation of a broad-spectrum (ultra-black) infra-red absorbent coating to eliminate reflections.

Design and installation of four corrective filters: the infrared, ultra-violet, and visual range packs are required to match the meter's spectral response to the spectral response of the film. The filter packs are not replacements; no existing meter contains any corrective filtration.

design and construction of tools and test equipment with which we can calibrate your meter to within 1/6 stop of linearity over its range.

Let's take each of these in turn.

First, "installation of superior photo-cells". Well, if the photo-cell installed when the meter is modified does not produce different results, then the claim that it's superior is bunk. When I did my testing, I found no significant difference in response between the modified and unmodified meter.

Second, "installation of a series of step down baffles to eliminate flare." Ok, fine. If the step down baffles really do eliminate flare, we should see an improvement in the flare performance of the modified meter. Yet when I tested the flare performance of the unmodified and modified meter, I found that the modification DEGRADED the flare performance of the meter.

Likewise, with claim #3 - which should reduce flare. Why, then, did my tests show the modified meter MORE flare prone?

On the fourth claim, I have no comment, for the simple reason that I've been unwilling to disassemble my modified and unmodified meters to examine the optical path.

For the fifth claim - any reputable firm which calibrates meters will have this equipment. The fact that my modified and unmodified meter read the same for both low light levels, moderate light levels, and very high light levels indicates that calibration and linearity are not a problem for the unmodified meter.

The bottom line here is that for the modifications to be improvements, they must produce a meter which produces a different response from an unmodified meter. And, in my testing, the only significant difference in the readings produce by the modified meter and the unmodified meter are that the modified meter is more flare prone. That's not an improvement.

Finally, the catalog page continues with these glowing testimonials:

"I found the selective, precise exposures determined with this meter to be among the best and most consistent I've ever processed in black and white."
Robert Mayer, Shutterbug

"Negatives exposed by this modified meter's reading were measured, and produced densitometer scans that were less that [sic] one-half stop apart in all lighting situations. ...Picker has created the 'perfect' zone light meter."

Alfred DeBat, The Professional Photographer

"The film densities that I obtained on the readings made with the modified Soligor were signficantly more consistent over the range of my test that I obtained with my own meter (Minolta Spot Meter). Fred Picker, through his modification service, has made good better."

David Brooks, Petersen's PhotoGraphic

Let's take these one at a time.

First, Mr. Mayer's comments don't really bear on the question of whether the modifications produce an improvement. In fact, they're couched in the usual sort of wary ad-speak. If the Zone VI modifications produce a meter which produces the same readings as the unmodfied meter, it would, in fact, be 'among the best and most consistent' wouldn't it?

Same issue with the second recommendation - it does not actually comment on a comparison of the modified meter to an unmodified one. If the modifications have no effect, and the Pentax meter we started with is a good meter, then we may well have started with a 'perfect zone light meter'.

Finally, in the third claim, we get someone who says that his modified Soligor meter was significantly more consistent than his Minolta spot meter. Ok, does this mean that the modifications were good, or does it mean that the Minolta spot meter is bad? We can't tell.

Alan Ross's various comments

Calumet have an article written by Alan Ross discussing the modifications on their web site here. If that link doesn't work, and instead lands you on the what looks like the Calumet front page, click on one of the flags to choose a country, and then try the link again.

In the article Alan discussing metering through filters, and describes a test where film is exposed according the meter readings (with the meter readings made through filters, or metering color patches) and then developed to demonstrate any differences between meter sensitivity and film sensitivity.

In the first part, he writes:

One of my most important tasks as a teacher is to impress upon my students that most meters, and metering systems DO NOT see colors the same way typical panchromatic film does, and that this can lead to significant exposure errors when measuring strongly colored objects or when metering through their filter of choice. Some meters see the red end of the spectrum much the way film does, but not the blue-violet end. Some other meters are exactly the opposite! The exceptions to this admonition are the Zone VI "Modified" meters, which seem to see the world pretty much the same way black-and-white film does. My Zone VI-Modified digital Pentax meter's color accuracy is so good in fact that I use a set of small filters for my meter which match the ones I put on my camera. I make readings directly through the filter on my meter and expose accordingly - no more filter factors to calculate. This also allows me to tell exactly how any given filter will affect various tones in the scene, meaning I can actually read how much more a red filter will darken a sky compared to a yellow! The modified meters are good for color film too!

Now, I'd observe that nowhere in this entire thing does Mr. Ross actually claim anything other than:

Some meters are bad

The Zone VI modified meter is good

In particular, he does not claim that the modifications make any difference at all. Given my testing, which showed no significant difference in color response between the modified and unmodified meters, I am not suprised that he does not make this claim.

Mr. Ross then goes on to describe, in more detail, the test described on the Zone VI catalog page - photographing a neutral target through various filters, developing the film, and then measuring the negatives:

Set up a large gray card outdoors in the sun on a clear enough day so that the sun won't be dipping in and out of the clouds every three minutes. A full 32x40 sheet of some kind of medium gray mat board is perfect. Focus on infinity and set your camera up on a tripod so that the card fills the frame. Gather the most extremely different color filters you have from opposite and in-between ends of the spectrum. Maybe include one or two particular filters you like to use a lot. These don't even have to be actual photo filters, they could be theatrical-lighting gels or other strongly colored transparent material. In my own test I used a #47B (tricolor blue), #58 (tricolor green), #25 (strong red), #15 (orange), and #12 (strong yellow).
Using the meter you want to test, take a reading of the gray card and expose exactly as the meter indicates. Take another reading through one of your filters. Place that same filter over the lens (if you were using a hand-held meter) and expose exactly as the meter indicates and note the exposure and which color it was in a notebook. Do the same for all the other colors you have handy. If you don't have a wide range of filters, you could exchange the gray card for strongly colored ones, or photograph a range of strongly colored objects, filling the frame with each object. Develop the film. Ideally, every exposure should have the same density. If any exposures, such as red for example, are significantly underexposed compared to your "no filter" exposure, then you know that your meter "sees" red as being a lot brighter than your film actually does, and you will have to compensate for this if you are forced to base your exposures on something red. If any color, blue for example, is denser (on the negative) than your "no filter" standard then you know that the meter "sees" that color as being darker than the film does and will over-expose it.

Again, let me underscore one simple point: if I perform this test with an unmodified meter and it fails, and the modified meter produces the same readings (as it did in my testing) then the modified meter will fail as well. We are confronted with two possibilities: the unmodified meter passes this test, as does the modified meter, or else they both fail.

Furthermore, I'd note that nowhere in this text does Ross advance the claim that the modified meter will outperform the unmodified meter in this test.

Introduction

The Zone VI catalog

Alan Ross's various comments

Kirk Gittings' claims

My (no longer tentative) conclusions