Newly purchased Pentax Digital Spotmeter not accurate?

I just purchased a used Pentax Digital Spot meter and it doesn’t match my Canon R5 or Sekonic l478dr with spot meter attachment. It came with a 6.2v silver oxide battery but the manual says 6v so I wonder if this is why it’s not accurate. If not can these be serviced or should I try and return it?

Check with Richard Ritter:

www.lg4mat.net

I think he charged me around $80-$100 for calibration, but that was a few years ago.

I’ve had no issue using the silver batteries in my meter. I’d also recommend sending it off to Richard Ritter for a calibration, but if it’s linear you could live with it by adjusting the film speed.

One important note to keep in mind... If this is a Zone VI modified meter--just having the zone sticker across it doesn't mean anything--Fred installed baffles, filters, and re-painted with flat, flat black paint internally before the meter was calibrated to his standards. I've have two Zone VI modified meters--a Pentax Digital Spot and a Soligor Spot Sensor II. Neither meter matches any other meter I own, but I don't care. I've done all my film testing with the Pentax Digital Spot and it remains my primary light meter after 40+ years.

If you really think it needs a good going over and calibration, then I highly recommend Richard Ritter, as mentioned above. But, as L Gebhardt already said if it appears linear, then you could easily compensate.

Alan9940 said:

One important note to keep in mind... If this is a Zone VI modified meter--just having the zone sticker across it doesn't mean anything--Fred installed baffles, filters, and re-painted with flat, flat black paint internally before the meter was calibrated to his standards. I've have two Zone VI modified meters--a Pentax Digital Spot and a Soligor Spot Sensor II. Neither meter matches any other meter I own, but I don't care. I've done all my film testing with the Pentax Digital Spot and it remains my primary light meter after 40+ years.

If you really think it needs a good going over and calibration, then I highly recommend Richard Ritter, as mentioned above. But, as L Gebhardt already said if it appears linear, then you could easily compensate.

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Yup, me too. I will never calibrate my Z VI meter because it is the standard I have use to calibrate/adjust/compensate ALL my meters including Sekonic, Luna Pro, and Revini labs. I do some level of equipment maintenance myself and - where I have the ability - I tweak the meter for best match with the Z VI.

I say "best match" because some meters are very nonlinear. For example, the top of the low light range of a Luna Pro very rarely agrees with the bottom of the high light range. Similarly, the Yarshica MAT 124G meter is ok in outdoor light, but it lies significantly in low light. You have to learn these quirks and adjust your technique accordingly.

What's important in analog photography isn't absolutely accuracy but repeatability. Find the meter that reads most "correctly" to your eye. Take note of how different the Zone VI is (or vice versa). Figure out a compensation factor. Say the Z VI always reads 1/2 stop higher than the meter you think is "right". When using the Zone VI thereafter, dial in an ASA that 1/2 greater that normal and the two meters will "agree".

How much off is it?

I have Minolta. Can calibrate it myself.

Alan9940 said:

One important note to keep in mind... If this is a Zone VI modified meter--just having the zone sticker across it doesn't mean anything--Fred installed baffles, filters, and re-painted with flat, flat black paint internally before the meter was calibrated to his standards. I've have two Zone VI modified meters--a Pentax Digital Spot and a Soligor Spot Sensor II. Neither meter matches any other meter I own, but I don't care. I've done all my film testing with the Pentax Digital Spot and it remains my primary light meter after 40+ years.

If you really think it needs a good going over and calibration, then I highly recommend Richard Ritter, as mentioned above. But, as L Gebhardt already said if it appears linear, then you could easily compensate.

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How do I test it for linearity?

sruddy said:

How do I test it for linearity?

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Does the Z VI meter disagree with a known good meter by the same amount across a wide range of lighting conditions?

The realistic odds are that the Pentax is correct, and the others aren't! I've got five different Pentax spot meters at the moment. The oldest is 45 years old and so heavily used that it is held together with electrical tape; but it still reads accurately. I have an otherwise unused one to periodically check the performance of the others, and have never had any of them vary more than a third stop in linearity from the others; and if one did, I sent it to Quality Light Metric in Hollywood (now out of business) for recalibration (only about once a decade). All these also perfectly matched the readings on my Minolta Spotmeter F too.

The question is, does this particular meter you got ahold of happen to be a Zone VI modified one? If so, it was meant to read differently than a standard meter. But that also means that the supplemental filters inside, to balance its spectral sensitivity to that of Tri-X sheet film, might have faded over time. Richard Ritter can handle that kind of maintenance issue too. The mere presence of that silly redundant gray zone sticker from Zone VI doesn't necessarily mean it is a modified meter. They stuck those onto unmodified meters too, and even sold the labels by themselves.

Pentax spotmeters are famous for their consistent linearity and reliability, and have long been a standard in the movie industry. They have a silicon receptor with peak sensitivity at green just like the human eye, which makes them ideal for color photography. But good ole Fred Picker seemed to think the only film in the world was Triassic-X, so there you go. You can still use it for color photography, but just need to know the offset - and then just set the ASA dial to the corrected amount.

You also need to become accustomed to metering with a one-degree spot meter versus a wider angle one, or TTL metering, which forces the light to jump through hoops first.

I don't know what you paid for it; but if it's in clean condition it's definitely a keeper. The battery is not an issue unless it's been left inside the meter long enough to decompose and cause corrosion. Either silver oxide or alkaline batteries are fine.

DREW WILEY said:

The realistic odds are that the Pentax is correct, and the others aren't! I've got five different Pentax spot meters at the moment. The oldest is 45 years old and so heavily used that it is held together with electrical tape; but it still reads accurately. I have an otherwise unused one to periodically check the performance of the others, and have never had any of them vary more than a third stop in linearity from the others; and if one did, I sent it to Quality Light Metric in Hollywood (now out of business) for recalibration (only about once a decade). All these also perfectly matched the readings on my Minolta Spotmeter F too.

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Apparently you can never have too many spot meters.

Thread title typo corrected.

faberryman said:

Apparently you can never have too many spot meters.

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That, sir, is spot on ...

Chan Tran said:

How much off is it?

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Wow it’s only off by 1/3rd of a stop now. When I first checked It was 2/3 to 1 stop off. I wonder if using it got the conatcts or whatever working better. I set up a gray screen with constant light in my studio and the R5, sekonik and Pentax all agree. Outside at balck top and gray house in shade all give the 1/3 stop under. I’m attempting to use this for black and white film in a 4x5 and maybe even with my 6x6 Rolleiflex occasionally. I will be trying the various developing types like n1 -n1 so I think it needs to be reliable for me to learn anything from it. Here are the photos of all meters agreeing in the studio.

DREW WILEY said:

The realistic odds are that the Pentax is correct, and the others aren't! I've got five different Pentax spot meters at the moment. The oldest is 45 years old and so heavily used that it is held together with electrical tape; but it still reads accurately. I have an otherwise unused one to periodically check the performance of the others, and have never had any of them vary more than a third stop in linearity from the others; and if one did, I sent it to Quality Light Metric in Hollywood (now out of business) for recalibration (only about once a decade). All these also perfectly matched the readings on my Minolta Spotmeter F too.

The question is, does this particular meter you got ahold of happen to be a Zone VI modified one? If so, it was meant to read differently than a standard meter. But that also means that the supplemental filters inside, to balance its spectral sensitivity to that of Tri-X sheet film, might have faded over time. Richard Ritter can handle that kind of maintenance issue too. The mere presence of that silly redundant gray zone sticker from Zone VI doesn't necessarily mean it is a modified meter. They stuck those onto unmodified meters too, and even sold the labels by themselves.

Pentax spotmeters are famous for their consistent linearity and reliability, and have long been a standard in the movie industry. They have a silicon receptor with peak sensitivity at green just like the human eye, which makes them ideal for color photography. But good ole Fred Picker seemed to think the only film in the world was Triassic-X, so there you go. You can still use it for color photography, but just need to know the offset - and then just set the ASA dial to the corrected amount.

You also need to become accustomed to metering with a one-degree spot meter versus a wider angle one, or TTL metering, which forces the light to jump through hoops first.

I don't know what you paid for it; but if it's in clean condition it's definitely a keeper. The battery is not an issue unless it's been left inside the meter long enough to decompose and cause corrosion. Either silver oxide or alkaline batteries are fine.

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When Alan Ross recommended that I buy a Pentax Digital Spot Meter at his Yosemite week long class and get it and all my cameras calibrated at the same place, if possible, and the same time, I took it to Quality Light Metric in Hollywood (now out of business retired). Since then all my camera meters and hand held meters agree. If one wants to adjust one of two meters, how does one know which one is correct.

Exactly. The people you want to calibrate meters do so relative to hard industrial standards, and have the requisite equipment. You'll notice that these Pentax meters have an IRE scale relative to standardized conditions applicable worldwide, making them useful to TV crews, film crews, and obviously accurate still photographic applications. But just digging up another old meter of your own and chanting over it, hoping for the best, doesn't quite cut it. As you can see, a number of us sought out the same professional meter service as the Hollywood pros relied on. And that's the only thing George did - light meter calibration and repair. Too bad he's retired; but he earned it.

But you'll iron it all out soon enough, Sruddy, and in the long run might even agree with me that the Pentax is most likely the one that's right on. But there's no way to prove that in any specific case unless you send it to a service with the requisite diagnostic equipment - typically around $100 out of your pocket.

sruddy said:

I just purchased a used Pentax Digital Spot meter and it doesn’t match my Canon R5 or Sekonic l478dr with spot meter attachment. It came with a 6.2v silver oxide battery but the manual says 6v so I wonder if this is why it’s not accurate...

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L Gebhardt said:

I’ve had no issue using the silver batteries in my meter...

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The meter has no electronic voltage regulation and relies on the flat discharge curve of a silver battery for consistent operation. See this decades-old thread for details, ignoring the naysayers:


PX28 silver batteries typically exhibit around 6.35V open circuit when brand new, but decline to 6.2V after a few readings in this meter, then stay there for the rest of their service life.

sruddy said:

Wow it’s only off by 1/3rd of a stop now. When I first checked It was 2/3 to 1 stop off. I wonder if using it got the conatcts or whatever working better...

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The spot meter in my Nikon F6 reads around 2/3 stop different than my Zone VI-modified Pentax digital spotmeter. Since I never use the Pentax for 35mm, relying on Nikon's Matrix mode, and perfectly exposed negatives result from that approach as well as large format film exposed according to the Pentax / Zone System, I don't care about the difference.

sruddy said:

Wow it’s only off by 1/3rd of a stop now. When I first checked It was 2/3 to 1 stop off. I wonder if using it got the conatcts or whatever working better. I set up a gray screen with constant light in my studio and the R5, sekonik and Pentax all agree. Outside at balck top and gray house in shade all give the 1/3 stop under. I’m attempting to use this for black and white film in a 4x5 and maybe even with my 6x6 Rolleiflex occasionally. I will be trying the various developing types like n1 -n1 so I think it needs to be reliable for me to learn anything from it. Here are the photos of all meters agreeing in the studio.View attachment 342627

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I think the Zone VI meter has a modified spectral response so it would response differently with different color temp .

Chan Tran said:

I think the Zone VI meter has a modified spectral response so it would response differently with different color temp .

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Just because the meter has a Zone sticker doesn't mean it was one of the modified ones. The stickers were for sale to use on any meter. .....
Either way they are an fine light meter. I've used my non-modified version for years.

Chan Tran said:

I think the Zone VI meter has a modified spectral response so it would response differently with different color temp .

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The zone VI has filters to block infrared and to adjust the color sensitivity of the meter to be closer to film. I tested a Zone VI Pentax Digital against a non-Zone VI Pentax Digital, a Gossen Ultra Spot 2, and a Sekonic L-758DR.

The Zone VI is the only one that had no sensitivity to IR light. A B+W 486 filter could be added to the other meters to eliminate their IR sensitivity. Regarding color sensitivity, the Sekonic L-758DR and the regular Pentax Digital Spotmeter had about the same color sensitivity. The Zone VI modified meter was slightly less sensitive to red and slightly more sensitive to blue, which would make it a little more accurate for most B&W films. The Sekonic and normal Pentax I think are more accurate for color film, digital work, and Kodak Tmax films. The Gossen was way too red sensitive.

You can read the whole test and methodology here:

chris - "filters ... to adjust the color sensitivity of the meter to be closer to film"... First of all, WHICH film? Yeah, Fred Picker pickerfied Tri-X 320, that much we already know. But even panchromatic films differ in specific spectral sensitivity. Even TMax itself differs somewhat in red sensitivity between its first and second generations. Current ACROS ii differs in blue sensitivity from the prior version; and both of them are Orthopan (diminished red sensitivity, and not true panchromatic at all). So you've got that kind of issue. And am I really supposed to believe that an ole medicine wagon snake oil salesman knew better than the Pentax engineers? Well, I'll let Richard Ritter decide that one. But I've encountered both opinions among Hollywood cinematographers, at least in a random sense. I doubt anyone has ever done a survey. One just gets accustomed to the idiosyncrasies of their own meter over time. But the modified version does have a potential strike against it in the sense the supplemental filters fade over time; and that can't be corrected with a simple recalibration procedure.

Ad far as flare goes, I just attach a collapsible rubber lens hood to the meter just like with a small camera lens, and avoid aiming at either directly at the sun, or a specular reflection of the sun. And it might be interesting to compare the Soligor spot meter, which is not multicoated like the Pentax.

Thanks for providing your results. That should be a help to those trying to understand the basics. And Pentax published its own spectrogram of the sensitivity of their meter, which is relatively symmetrical on either side of the green peak.
I also do tests using the same MacBeth Color Checker chart, but with respect to photographic mean daylight (coior temp meter accommodated). I don't trust LED lighting, though I did buy a relatively expensive set for sake of my copy stand. Then I make specific sheet film exposures of the chart, develop those, and take densitometer readings of each patch. Or I did. Got all that filed away in binders. Now everything is largely intuitive anyway. Spd meters are now pretty much standard. Old Cds ones aren't in much use anymore.

Something else that hasn't been mentioned yet is that Fred Picker had the habit, and taught, metering through colored black and white contrast filter, which, as far as I'm concerned, can be a minefield, especially if different films are used. It's a topic no doubt with its own past threads; but it's a darn poor and potentially leading substitute for intelligent use of tested filter factors per se.
But it colored his notion of how a meter should be "improved" - again, improved with respect to which film, and "unimproved" with respect to which? But the patent medicine man said, "Just drink it; it's the elixir to cure all your ailments". Yeah, I spent a fair amount of money with Zone VI myself, and some of Fred's products were great; others, well ... not so great.

You don’t have to do all the industry standardized calibration if it’s not important to you. You can just test it against the actual exposures you make on the film you’re going to be using. It’s close enough. If the pictures look good then why bother taking it any further? It’s not like you’re going to be making meaningful adjustments of less than half a stop anyway.

Depends on the film. Going with chrome film or a higher contrast color neg film like Ektar, or even with some black and white films tempting their contrast limits, half a stop of error can ruin a shot. And color films should mostly be reckoned with according actual rated box speed. Hence the midpoint setting of the meter itself should equate to what the film manufacturer had in mind too. Of course, if one recognizes how much a particular meter might be off in that respect, they can simply tweak the ASA setting on it or whatever to achieve the same thing. But it helps to know.

_T_ said:

You don’t have to do all the industry standardized calibration if it’s not important to you. You can just test it against the actual exposures you make on the film you’re going to be using. It’s close enough. If the pictures look good then why bother taking it any further? It’s not like you’re going to be making meaningful adjustments of less than half a stop anyway.

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DREW WILEY said:

Depends on the film. Going with chrome film or a higher contrast color neg film like Ektar, or even with some black and white films tempting their contrast limits, half a stop of error can ruin a shot. And color films should mostly be reckoned with according actual rated box speed. Hence the midpoint setting of the meter itself should equate to what the film manufacturer had in mind too. Of course, if one recognizes how much a particular meter might be off in that respect, they can simply tweak the ASA setting on it or whatever to achieve the same thing. But it helps to know.

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I agree with @DREW WILEY especially if one is using slide film. It will make a difference if one is using the Zone System or the Zone System with darker filters.

I'm just saying I would try that first. Since you're going to be shooting and developing the film anyway it's almost free. And if that ends up being good enough for whatever you want to do with the meter then it's good enough and you can stop there. If it's not good enough then you can take further steps.

I mean obviously if I just bought a meter, before I did anything else like try to repair a suspected problem I would shoot some film with the meter and see if there is actually a problem. The first step in checking the meter should very definitely be to try it out.