That much of discrepancy? Standard spot meters Vs the modified Pentax!

john_s said:

In the early 1980s (I think) I bought two Pentax Digital "modified" meters directly from Zone VI. A spare, just in case. They have had a very easy life. Now they differ from each other by more than 1 stop, and both of them are not useful: even if I adjust the film speed to other meters* they are not linear, so each can be made accurate at one light level but both will be inaccurate at other light levels, and different to each other. I had a go at opening one in the hope that there were a couple of potentiometers that could correct them but I couldn't get it open. I didn't try very hard.

* by other meters I include several very good cameras and two Minolta spot meters and two Sekonic middle of the range meters paying particular regard to the various angles of sensitivity and they all agree with each other very closely. Even if they are not quite right, the lack of linearity of the Pentax meters makes them unacceptable.

Maybe someone knows how to calibrate them and They can have them for a very reasonable price.

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There is 1 screw below pentax label (near the bottom of handle, right above battery chamber) and 1 screw ring in eyecup (the trick for this ring is unscrew eyepiece as much as possible, then you will see at bottom of eyes piece, there is a ring with 2 small hole, try your best to unscrew this ring until eyes piece come out. After that, you can easily seperate both plastic shells of meter)
When open it up, you will encouter 3 potentiometer which is: 1 for dark point, 1 for high point and 1 for slope (those are mine personal definitions due to no service manual available)

alentine said:

That much of discrepancy?
Standard spot meters Vs the Zone VI modified digital Pentax spot!
Photos attached for EV comparison.
Could the modified Pentax spot meter, correctly be in average 1.5 EV or more( range: 1 ~ 1.8 EV ), lower than standard meters, and still considered accurate?
Borrowed other meters, the gap could not be better.
AFAIK, the setup(photos) is ideal for a correct methodology & measurement from each meter and for the conclusion later.
I may add more readings later for comparison.
Please let me know?
I think the Zone VI modified digital Pentax spot, is not working properly!
Thanks indeed for any input.

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Twebty years ago ,I had the exact same thing happening to me after buying a brand new Zone VI. After nothing but frustration, I sent it back and got a regular Pentax Spotmeter and a Gossen. The modified Zone VI is nothing but hype, just like many of Fred Picker products.

marhalloweenvt said:

There is 1 screw below pentax label (near the bottom of handle, right above battery chamber) and 1 screw ring in eyecup (the trick for this ring is unscrew eyepiece as much as possible, then you will see at bottom of eyes piece, there is a ring with 2 small hole, try your best to unscrew this ring until eyes piece come out. After that, you can easily seperate both plastic shells of meter)
When open it up, you will encouter 3 potentiometer which is: 1 for dark point, 1 for high point and 1 for slope (those are mine personal definitions due to no service manual available)

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Thank you. I will try it and let you know.

RalphLambrecht said:

....... The modified Zone VI is nothing but hype, just like many of Fred Picker products.

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I'd have to agree with you. But in the days before the internet I did learn from his newsletters and the cold light head in the days of graded papers was great.

john_s said:

I'd have to agree with you. But in the days before the internet I did learn from his newsletters and the cold light head in the days of graded papers was great.

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he must have been a very good printer but I felt mislead numerous times by his advice and couldn't help feeling that his info was mainly aimed at supporting his business interests.

Not very scientific but I bought a used Zone VI meter from KEH some 15 years ago and compared it to my stock Pentax. There were differences in reading but so negligible I thought shutter error, various processing errors like temperature, dilution and agitation inconsistencies would probably play a larger impact. I suppose perfectionists would appreciate it.

I currently have four unmodified Pentax digital meters. The oldest one has gone through hell and is held together with electrical tape. The latest one is like new and kept in a drawer as a reference to the other ones, with its battery temporarily installed only for such occasions. All of them read identically over their full range. I also once had a Minolta spotmeter which itself read identically to the Pentax meters. A few times, when a deviance was detected, or I outright dropped a meter in a stream, it was sent in to Quality Light Metric for recalibration. That was an average of one meter per ten years! - and even then the odd duck was only slightly off from the others.

One of the problems with the Z VI modified meters is that their supplemental internal filters can fade; and the added flare reducing internal paint can flake off. You can still send them to Richard Ritter for a tuneup. I myself have taken the alleged benefits of that meter conversion with a grain of salt; but there are even Hollywood cinematographers who swear by them, while others in the same trade stick with the unmodified ones.

Fred Picker was an interesting salesman, patent medicine wagon n' all. He did have some really good products, but also some questionable ones. Technique-wise, I'm quite skeptical of his advice to taking meter readings through b&w contrast filters, versus applying proven filter factors after a straight reading. He alleged his super-duper improved meter solved that dilemma. But how can that be, since it was optimized for one specific film, namely Tri-X 320? - and even pan films differ from one another in specific spectral sensitivity. For example, TMax 100 and Delta 100 are alleged to be comparable films; but I know from careful testing that their filter factors differ - half a stop in the case of a medium green filter. Then you've got orthopan films like Acros, which differ even more. And heaven help you with true ortho film.

@Dan Daniel for me it’s a Nissan Thermos of Port Townsend Pantomime coffee and five SEI photometers against a couple ( 9 and 100 foot lambert ) reference light sources.

If only I could get a Corning 5900 filter

I think @dcy has the best meter though. He picked up a Gossen Luna-Pro F

As usual in this wonderful place,
the magnitude of participations and the exchange of experiences is unparalleled.
l could not thank you enough.

The concern now is,
in the context of the 4 spot meters, and
of course assuming the modified Pentax has linear response, no light spectral variations!

How much of EV correction should be adopted to bring the modified Pentax meter in the area of being acceptably precise tool to go alone for zone system approach photography?

The added series of reading(hand written, attached photo) is taken in a constant indirect daylight(same setup as in post 1).
Most of the meters belongs to photographers from different cities.


Tried multiple time to bring another set of readings in direct constant sun light, but failed due to clouds every day.

BTW, the post-test incident light metering at the site of setup, was within 0.2 EV from the incident metering of the pre-test.

gary mulder said:

The usefulness of spot meters is highly overrated. Thats way I have accumulated three.

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alentine said:

How much of EV correction should be adopted to bring the modified Pentax meter in the area of being acceptably precise tool to go alone for zone system approach photography?

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You don't really need to do any modification, the Zone system is about standardisation where you make your own accuracy, and if you do your initial exposure tests with the Pentax meter, to establish zone V etc., your workflow will be accurate. So the precision you look for is repeatability. Admittedly using another meter won't work but given every meter has it's own quirks (response, metering angle, etc.) you shouldn't be swapping meters anyway unless you do the tests all over again.

alentine - the as-is Pentax meters are tightly calibrated to specific industry standards. They have been widely used in the Hollywood film industry, in TV studios, in professional photographic studios, and of course, by many of us in the field.

They don't need to be "corrected" for the Zone System. They already read more precisely than mere Zone segments.
By comparison the Zone System is like a rubber band that can be stretched all kinds of ways, and these spot meters are more than adequate for that kind of application. Zone V is simply the central triangle reading on the meter, based on comparison readings of your shadows and highlights to determine their placement, higher and lower, on the dial scale. The basic rule for the Zone System is, "Expose for the shadows, develop for the highlights".

I really wouldn't get hung about about the alleged need for a modified meter for specifically ZS work. That's snake oil mythology. If someone gives you a modified meter, or you find an extremely good deal on one, fine, go ahead and use it.
I'd personally rather have unmodified Pentax meters which all match one another right out of the box from the factory,
all calibrated to a very specific industry standard for sake of ongoing consistency.

alentine said:

That much of discrepancy?
Standard spot meters Vs the Zone VI modified digital Pentax spot!
Photos attached for EV comparison.
Could the modified Pentax spot meter, correctly be in average 1.5 EV or more( range: 1 ~ 1.8 EV ), lower than standard meters, and still considered accurate?
Borrowed other meters, the gap could not be better.
AFAIK, the setup(photos) is ideal for a correct methodology & measurement from each meter and for the conclusion later.
I may add more readings later for comparison.
Please let me know?
I think the Zone VI modified digital Pentax spot, is not working properly!
Thanks indeed for any input.

Click to expand...

If you would sent all your light meters to be calibrated by a standard source, the light reading would be the same.

It would be impossible to calibrate the modified versus unmodified Pentax meters exactly the same, because they read light differently. Full calibration has to take into account the full range of meter sensitivity, not just the centerpoint. The Zone VI modified ones contained supplemental filters which altered their spectral sensitivity distribution somewhat.

From talking to Hollywood cinematographers who owned both kinds, and had both serviced at the same place (Quality Light Metric nearby, where I sent my own meters for recalibration, but no longer in business) - I know they juggled the two versions somehow. More often, one cinematographer preferred one version, a different cinematographer the other version. But the unmodified ones were inevitably far more dominant, because they came straight from the factory properly and identically calibrated, and remained available new long after Z VI folded. Barely used ones still sometimes turn up for sale. But anything modified is going to be pretty old by now, and potentially in need of service.

Sirius Glass said:

If you would sent all your light meters to be calibrated by a standard source, the light reading would be the same.

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DREW WILEY said:

It would be impossible to calibrate the modified versus unmodified Pentax meters exactly the same, because they read light differently. Full calibration has to take into account the full range of meter sensitivity, not just the centerpoint. The Zone VI modified ones contained supplemental filters which altered their spectral sensitivity distribution somewhat.

From talking to Hollywood cinematographers who owned both kinds, and had both serviced at the same place (Quality Light Metric nearby, where I sent my own meters for recalibration, but no longer in business) - I know they juggled the two versions somehow. More often, one cinematographer preferred one version, a different cinematographer the other version. But the unmodified ones were inevitably far more dominant, because they came straight from the factory properly and identically calibrated, and remained available new long after Z VI folded. Barely used ones still sometimes turn up for sale. But anything modified is going to be pretty old by now, and potentially in need of service.

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I too used Quality Light Metric right up to the end. Samy's Camera on Fairfax has another calibration lab that they use, but I do not have the contact information. Call Samy's and ask them.

Oh, I doubt I'll ever need another meter tuneup. Among the four matched meters I have, only one out of four needed recalibration per ten year period, and it was relatively minor. Dunking a meter in a mountain stream was a different story, because it had to be taken apart and cleaned first. I keep one of them entirely unused as a reference, and only insert the battery when making comparisons.