Wrong about Zone VI Modified Pentax Meters

[Paul Butzi]

Browsing back over the threads I saw this one, and Kirk's experience doesn't match mine.

So today, I took my three meters (a Zone VI modified Pentax digital spot, an unmodified Pentax Digital Spot, and a Sekonic L-508) outside and did some head to head comparisons.

My test procedure was as follows - for each test situation, I took a reading (carefully metering from the same angle for each test patch) off of each of the 24 color patches on my MacBeth Color checker. I recorded the metered values for each meter on a worksheet.

I ran the test under 3 different lighting conditions: direct sunlight, open shade, and direct sunlight but metering through a B+W 090 (red) filter.

My goal was to see if there were significant variations in readings between meters, and especially between the modified and unmodified Pentax. By metering off the differently colored patches, I could test spectral response as well as just intensity, and by using the Macbeth color checker, other people should be able to replicate my experiment easily (I figure most folks own a Color Checker or can get one easily).

The RMS differences between the modified and unmodified meter in the different situations were: direct sun RMS= 0.16 stop, open shade RMS=0.23 stop, direct sun through 090 filter RMS= 0.20. I did not check to see if there was a systematic bias between the two meters (it's likely there is) nor if removing that bias would reduce the RMS differences between the meters.

That is, I see no statistically meaningful difference between the modified and unmodified meter, reading test patches of various colors, including reading the patches through a red filter.

Both meters seem to be of similar vintage. Interestingly, I did see some significant changes in readings between what I got with a hot meter (left out in sun for a few minutes) and a cool one (taken from cool room). I'll have to perform some more experiments to explore THAT!

Kirk, did you ever compare the modified and unmodified meter head to head?

[Kirk Gittings]

Paul,

At the time I had one of each. After my tests I sent the other in to be modified also. The modified one did have different and more accurate exposures through various filters than the unmodified one. Reading through the filters with the modified one gave me very similar exposures to the filter factors that I had worked out over the years based on Gordon Hutchins published filter/exposure tests. Not perfect but very close. Interestingly the first modified one reads 1/3 of a stop higher than the more recently modified one. I am going to have that one checked by Ritter this winter when things slow down a bit.

The best way to use one in my opinion is to read thru the filter on a Zone III shadow being very careful to avoid reflections on the back, meter side of the filter, which can skew the reading. The blue skylight in the shadow read thru various filters was where there the bad color responce of the unmodified showed up the worst. Unfortunately I have been so buried with commercial work that I have not done much b&w since then, but what I have done (maybe 50 negatives) are very consistent.

[Paul Butzi]

Kirk-

Thanks for your rapid reponse. You say that "The modified one did have different and more accurate exposures through various filters than the unmodified one."

What testing procedure did you use?

[Kirk Gittings]

My aim is to maintain consistent shadow exposure. I have accurate meter-through-filter-plus-factor exposures that I worked out using Gordon Hutchins method that I have used for years. His scheme is based on preserving shadow exposure. I compared those to unfactored readings thru the filters with the modified meter and found comparable results many filters. I then shot some film (FP4 in HC-110) with a #16 filter and 23a (my favourites) and compared the shadow exposure results using Beseler color head and Picker's minimum-exposure-necessary-to-render-film-edge-as-black contact sheets on Ilford Multigrade in Ultrablack developer. I don't use a densitometer. The results were encouraging. I love simplicity. Too many calculations and I make mistakes when I shoot in a rush. This enables me to not have to wory about filter factors.The Alan Ross article, available through Calumet's website, gives similar experience though I had previously thought it was caca-propaganda. Some pretty credible people have been saying this all along. I wish I had listened years ago.

[Paul Butzi]

Kirk, thanks for the details.

I am stumped. I spent about 45 minutes today, attempting to construct a situation where the modified and unmodified meter produced different readings. I metered the patches on my ColorChecker, I metered foliage, I metered rocks, I metered in shadows, under overcast sky, in direct sun, under tungsten light. I metered through a host of different filters.

And darn if I could come up with anything where the modified meter and unmodified one disagreed by more than 1/3 of a stop.

On the other hand, even a simple test with a white card with a hole in it, illuminated from the front, with a matte black drop behind the hole - that setup easily and definitely convinced me that the modified meter is less plagued by flare.

The next weeks schedule will prevent me from typing up my results. After that, though, I hope you might take a look at them, and perhaps point out to me what I'm missing.

[Kirk Gittings]

Paul,

Ritter has mentioned something about the color correction filters coming loose in the modified meter. I would think that this situation would also throw off the meter reading. He says:

"...the only thing I do is repair and make sure all the filters are in working order."

This would seem to indicate that they can come loose or fade or something. He also says:

"...I do know that Calumet at some point in time changed the standards the meters were set to."

This seems to indicate that there could be a difference between an "new" and an "old" conversion.

Maybe he will tap into this thread and shed some light on the issue.

[Kirk Gittings]

Paul, I emailed Ritter to take a look at this thread. Kirk

[Douglas Stewart]

Desperately seeking a source for a new ZONE VI MODIFIED PENTAX DIGITAL SPOT METER. Any help would be greatly appreciated. Thanks!

[Mark Sampson]

Douglas, they were, maybe still are, sold by Calumet Photographic, who have owned Zone VI for 10 or 12 years. They would be the only source for a new "modified" meter.

[Jeffrey Sipress]

Kirk, I was the one who asked the original question.. Thanks for the additional data. It takes a real man to admit he was wrong and then publish that fact! I found my modified meter on ebay, nearly mint, for a whole lotta money. Calumet does list them, but never has any in stock. So it's the used market for most of us.