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

alentine

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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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koraks

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I may have missed it, but there are two sets of measurements for each meter. The second set is 2/3 to 1 stop lower overall across all meters. How did you arrive at these measurements?

alentine said:
the setup(photos)
Click to expand...
I see a couple of cards, but no metering setup. What light source? Distance between metering target and meter? Possible influence of flare, UV?
 
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alentine

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Thanks so much Koraks.
That should not affect the comparison itself, because any confounder variable should affect all 3 meters readings, while the standard meters agreeing with each other, for both sets of readings, the modified Pentax is out of the herd in each set of reading.
My apologies did not add measuring environment.
Constant indirect day light, measuring from 1.8meter, full battery each meter. The size of each target is almost A4 paper size except for black which in fact the manufacturer bag of L-508 sekonic.
 
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Chan Tran

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I understand that the Zone VI meter has modified spectral response so it would read differently with the standard meter if the subject or light source color are different. However, the amount of differences are too great.
 
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alentine

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Chan Tran said:
I believe the Pentax Zone VI is wrong.
Click to expand...
Thanks so much Chan for your concise conclusion.
waited so long time to find one in a good shape.
I do not know if I'm realistic if I plan to repeated the comparison under direct daylight.

But, assume that all other meters are super perfect, and the modified Pentax meter could not be calibrated by a professional for any reason, could you share how to correct or minimize that bias?
It would be appreciated.
 

Chan Tran

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I can't tell you because of 2 reasons.
1. I don't know how to make the adjustment on the Pentax. I don't find a service manual.
2. I don't know why the people at Zone VI think it's better to have a different spectral response than the one the meter manufacturers used. Is it to match the spectral response to film better? But if so which film? Besides I don't know much about B&W film I worked with color film.
 

Nicholas Lindan

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In the measurements, the Pentax meter is consistently 1 1/3 stop low. You can just set the film speed 1 1/3 stops low on the Pentax and use it as usual. Or, the right calibration pot can be twiddled - however there is a danger that things get even worse.

The experiment should be repeated in sunlight, cloudy light, bright interior, dim interior to verify the discrepancy holds across varying light levels. There is no need to bother with colored squares, an 18% grey card would be sufficient.

The ZVI modifications seem to be overblown and as a practical matter do nothing of note.
 

Nitroplait

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For the measurements show in post #1, the Zone VI is obviously the odd one out and the one I wouldn't trust.

Fred Picker's Zone VI business was a very strange mix of wise common sense and opinionated pseudo-scientific baloney.
I don't know if one or the other applies to the meter modifications, or if you just got a meter that needs adjustment.

All meters measures differently. Like thermometers, you should only own one - and adapt the processes around it accordingly.
 

Alan9940

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The spectral response of the modified Zone VI meter was, reportedly, to match Tri-X. However, I've used mine with many other films and have never been dissatisfied with the results. IIRC, Fred had the meters "locked in" to an EV level that was different than other spot meters on the market at the time. I don't remember the specifics, but I bet the details are outlined in one of his newsletters.

Regardless of how the Zone VI meter compares to others, if you test with the Zone VI it really doesn't matter if it's "off". If you feel it needs to be looked at, I'd send it to Richard Ritter (lg4mat.net).
 

Dan Daniel

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A discussion of the Zone VI modifications, etc. from 10 years ago here. It might help the OP zero in on what is going on (or not, I haven't read it) and give some idea of how convoluted metering can actually get.

Spot Meter by Zone VI

I ran across a super nice Pentax Digital Spotmeter with case and manual. What was puzzling was there was a letter shown with it from Zone VI Studios and that they had modified the meter? Apparently the original owner had purchased it from them. Any ideas if this means Zone V won't be Zone V?
www.photrio.com

I've dealt with meter variations with ISO adjustments. But I am not shooting 4x5 chromes where dead accurate control and results are needed.
 

koraks

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alentine said:
That should not affect the comparison itself, because any confounder variable should affect all 3 meters readings
Click to expand...
Assuming metering patterns, proneness to flare and UV sensitivity are the exact same for all meters. Do these conditions hold true?

Not arguing that something's up with your Zone VI modified meter, but the question is what and how much exactly.
 

gary mulder

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

Dan Daniel

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BrianShaw said:
… and their utility as the immutable standard for metering and recommended exposure is overrated as well.
Click to expand...

If you are doing fully calibrated Zone System workflow using single sheets of film, they can be very useful. But as we are seeing here and in some of the articles, 'fully calibrated' would include doing calibration runs for specific subject colors, and also for specific filters on the lens. At the end of the day, much many of us do in taking images is as much ritual as rational. Me, these days, two cups of coffee and a pocket incident meter and I'm good.
 

marhalloweenvt

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I have fixed and calibrated some original pentax spotmeters (included analog and digital), I will find some photo which I took when I calibrated this meter (for reminding myself).
In the past, I seached alot but there is no service manual or guide available, so I chew the bullet and just open them up to try my best.
 

john_s

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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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