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  1. #1

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    Pentax Spotmeter V and luminance questions

    I just purchased a used Spotmeter V (a 1983 vintage if the JCII sticker is valid), and I have a few questions. I have searched on the APUG site and didn't find specific questions previously answered, so here goes.

    First, my version takes the 3 silver-oxide cells, so the battery combination issues should not apply in my case. The meter looks to be in very good operating condition for 30 year-old equipment, and the meter responds quickly when engaged, the internal low-level light works and it is basically in clean condition. A quick check against a high contrast subject indicates that the "spot" is accurately identified by moving from low to high brightness.

    My questions follow:

    1. The battery check range follows about 11 1/2 to about 14 1/2 on the meter internal scale, with the 11 1/2 area seeming to be on the "high" side of a battery check. When fresh batteries are installed, where does the needle fall within the "check" range? The batteries installed currently measure "14", which is within the limits but on the low end, is this still acceptable?.

    2. The zero-point for the meter is a black circle, and I would think that the needle "centered" in the circle would be zero, is that correct? I prefer the Gossen "line" for a zero point, and I would think that an accurate zero-point is critical for the Spotmeter. Any suggestions for this?

    3. This is the luminance question. The "EV" scale of the Spotmeter doesn't agree with my Gossen meter, and my belief is that a EV level is universal, not selective based on manufacturer. For example, at a EV setting of 14 on the Spotmeter, my Gossen is 2 stops lower. And I am setting the Gossen on the EV scale not the exposure measurement scale (there is a difference), and the ASA settings compare. Maybe the question is if the Pentax scale is truly a EV measurement?

    4. How frequently do you get a Spotmeter calibrated? On the Richard Ritter site he suggests every 12-24 months which seems a little high or overly cautious.

    What I plan to do this weekend is get outdoors with it and my Gossen and start measuring comparable subjects, landscapes etc. Or go crazy and run some film based on the meter output and look at the results.

    Thanks for your suggestions, the Pentax is a little different than what I am familiar with.

    Regards,

    Joe

  2. #2

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    Which Gossen do you compare it to? The reading in the viewfinder is LV or EV for ISO100 although Pentax called it EV. Luminance to LV is a little bit different on each meter depends on the K factor. Pentax manual said that at EV 1 (for ISO 100) it's 0.28 Cd/m^2 so the K factor is 14. Gossen may use a K 12.5 but it's only about 1/6 stop difference. A reading of 2 stops different then one or both meter must be wrong or the Gossen is not a spot meter (incident or wide angle reflective).

  3. #3

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    1. My Pentax V reads 12.6 with a set of batteries that have been in for a couple of years.
    2. I zero to the center of the black dot and I get realistic readings.
    3. The scale in the Pentax is truly EV when the ISO is set to 100. Then, a gray card reading in bright sun will read 15 on the scale and when the exposure dial is set to 100 you will get an exposure of f/16 @ 125. I do find, however, that the Pentax suggests about 2/3 stop more exposure than my Gossens.
    4. I doubt that my spotmeter has ever been calibrated; I am the second owner and I have owned it for 10 years and never calibrated it and it is still spot on.

    I am also interested in which Gossen you are comparing to.
    -Fred

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    Which Gossen do you compare it to?

    Hi Chan:

    Comparison to a Gossen Lunasix 3 and Luna-Pro F. They agree with each other at the EV 14 setting. This is just a "static" comparison of what exposure is displayed at a EV 14 level on either meter, if that makes sense.

    From your other comments it sounds like the Pentax output may not be a direct EV comparison, thus the difference.

    Thanks,

    J

  5. #5

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    Fred:

    1. My Pentax V reads 12.6 with a set of batteries that have been in for a couple of years.

    Should my "14" reading suggest I should replace? Since the needle "swing" is further to 12 vs. 14? The right to left needle travel is something to get used to also.

    3. The scale in the Pentax is truly EV when the ISO is set to 100.

    I just set all meters to ISO 100, and with your other suggestions everything agrees between all meters. The ISO in the other comparisons had a 400 setting, thus the Gossen Vs. Pentax 2 stop difference.

    Thanks for the response.

    J

  6. #6

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    Be sure you use silver oxide replacement batts as opposed to alkaline batts. The alkaline batts will gradually decrease over time where the silver oxides will hold a steady voltage until the very end where they go 'over a cliff!'

    Appears your batts are weak.
    -Fred

  7. #7

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    Hi Fred:

    Be sure you use silver oxide replacement batts as opposed to alkaline batts.

    I put in a new set of Silver Oxides and the meter needle still hovered around "14" in battery check mode, and the older set of batts checked out via a voltmeter, so if the range within the battery check area is indicative of battery "strength" I might need to opt-in to a new set.

    Note to all:

    I had the chance to get out into the world over the weekend to do some comparative metering with the Pentax and my Gossen Luna-Pro F ( a meter with known accuracy) with the Gossen spot attachment, in some fairly bright, big-Sun high contrast conditions. They both metered similar objects, large enough to have consistently lighted areas with both the tight Pentax spot and the wider Gossen, with equivalent results, so I feel good about the Pentax calibration. Film was also exposed to get a "real" result vs. the meters, so I will have that back very soon.

    It is amazing the sensitivity of the Pentax to slight introductions of contrast into the metering zone, the meter responds immediately to the changes.

    If other Spot meter users want to comment on the meter or general techniques, please reply!

    J

  8. #8
    Poisson Du Jour's Avatar
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    Joe, your next action should be to move away from the computer, get your hands on some transparency film, load up the camera(s) and actually put the meters, side by side, to effective testing, metering each scene identically with each meter, taking the notes (yes, write down what the meter is telling you), exposing as per one meter, then the next, and in the end, scrutinising the results. There must be many thousands of Spotmeter Vs still in use; I have never heard of a spot meter requiring calibration unless it has been exposed to conditions which would give rise to obviously anomalous results (based on experience, not casual theory).

    I don't view the battery issue as of much relevance in the absence of testing each meter (and you!) for accuracy. There may be things you need to learn about the use of a spot meter, and these will become evident, especially with slide film (e.g. meter high values (highlights), mid-tones and low values (shadows), averaging then moving up or down based on experience. It's not all that critical or helpful in B&W because of latitude: slide film will brutally convey to you any errors in your metering; it is rarely the meter at fault, but quite often the photographer! Come back and post your observations for the world to see.
    .::Gary Rowan Higgins

    A comfort zone is a wonderful place. But nothing ever grows there.
    —Anon.






  9. #9

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    Guy,
    There is an adjustment potentiometer inside that sets the mid range position for battery indication. When a pot sits in the same position for a long time (years) some oxidation will build up on the wiper and change the resistance value thus changing the indicated value. Depends on climate/humidity how much oxidation occurs. So 14 happens to be your 'standard' value for a fresh set of batts and it will drift higher from there as the batts decline. I wouldn't worry so much about the absolute value as it can be changed by a simple adjustment during calibration. Batts last a very long time in the Pentax V. unless you are using it heavily. From what you say it sounds like the unit is still in calibration. A standard gray card on a bright sunny day will confirm the 'Sunny 16' rule and assure accurate readings.
    -Fred

  10. #10
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    Agree with what Fred said. Also, EV philosophy from various manufacturers is not consistent. I don't bother to remember the details. I've done my tests with my meter, shutter, developing scheme, and me as variables. It sounds like your meter is working - now it's up to you to work it into your system.
    juan

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