Spot meter

[Ricardo Maydana]

Hi, guys.
This issue of isolation. Leads me to the next question
Measuring candlelight with the photometer. It has a certain EV value. I have two photometers and they both read differently. How do I know which one is more accurate?
Greetings


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[Luis-F-S]

Are they both reproducible? Give the same reading of the same light source?

The man who owns one watch will always know the time. The man who owns two watches will never know the time.............

[C. D. Keth]

How much do the meters disagree?


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[Ricardo Maydana]

2/3 respondí rápido y luego lo paso en inglés. La diferencia de lectura entre ambos es de 2/3.


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[Dan Fromm]

Cual fotometros tiene?

[Ricardo Maydana]

Pentax ambos uno el digital y el otro V


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[Vaughn]

Use the one that will give you the most exposure -- better to have shadow detail than not. If your negatives are denser than they need to be, then use the other.

PS...make sure the glass is clean on the meters.

Use el que le brindará la mayor exposición, mejor tener detalles de sombra que no. Si sus negativos son más densos de lo necesario, entonces use el otro.

PD ... asegúrese de que el vidrio esté limpio en los medidores.

[Ricardo Maydana]

Buen punto de vista. Gracias


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[DHodson]

Which batteries are you using for your V Ricardo?

[Ricardo Maydana]

Tres 3 - R44


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[Leszek Vogt]

I'd probably add to the variable by using digital (gowd forbid camera :>) to make the visual determination.....adjusting exposure on both sides of the spectrum. Shooting a candle is one thing, but having it reflect on someone's face or adding additional light (matching K degrees) to do so....just gets more convoluted. Some of us had this assignment from Vilmos Zsigmond, during one of his workshops....so this has some echo.

Les

[Luis-F-S]

Use el Digital! L

[Ricardo Maydana]

If there's any consistency to it, the point is to get a digital camera. Thank you for participating.

[Ricardo Maydana]

gracias, es un buen punto usar el que da mejor detalle en las sombras.. la diferencia entre ambas es de 2/3, como ultimo recurso solo ajusto 1/3,
solo la prueba y error me dará algo de seguridad.

[Ricardo Maydana]

Use el Digital! L

Which of the digitals do you recommend?

[Jeff Conrad]

Ricardo,

Is there a camera-repair place that can check the calibration of your meters? It’s a pretty simple procedure with a proper calibration light source.

One thing to bear in mind when asking “which one is more accurate”: spectral responses of meters vary considerably. Pentax meters are quite broad, with response extending into the near infrared; others such as Minolta (now Kenko) were much narrower, corresponding (sorta kinda) to the 1931 CIE observer. Neither, of course, may correspond to the spectral response of film or an electronic sensor. Under ordinary conditions, depending on the color of the metered subject, I’ve seen 2–3 step differences between my Pentax meters (the digital is a Zone VI) and my Minolta Autometer IV. In an extreme case (a semiconductor photolithography room under yellow light), I once saw a five-step difference between my Pentax V and my Minolta Flashmeter III. I don’t know what the spectral response is for Sekonic meters.

Bottom line: “accuracy” is loosely defined at best. But for starters, try to get a proper calibration check. It may not be perfect, but it’s more reliable than most home-brew solutions.

[Ricardo Maydana]

jeff,
i totally agree, a camera repair shop is the right thing, the point is that where i live there are no analog camera repair shops, there is very little material for photometers. so i am looking for a home made solution that will give me an idea of which one is better calibrated. i have to do tomorrow with the lus of day, checks and see if the 2/3, are maintained in all values. i am looking for low and high areas. All agree that not all respond to the same illuminated subject with the same value. and that some photometers are calibrated for zones V or IV, and another subject as much as both are Pentax, both are different...
Calibara is a better choice than any homemade attempt.

[Jeff Conrad]

Ricardo,

It’s been a while since I’ve been to a repair shop, so I’m not sure where I’d go for a meter calibration (San Francisco Bay Area) these days. The best I can suggest is to call a few places and ask (and ask what type of calibrator they have and see if they understand the calibration factor K). Meters aren’t really calibrated to “zones” (the calibration standards were aimed at everyman rather than Ansel). Pentax meters (analog and digital) used a K of 14 (1.3 if you work in cd/ft2); Minolta did the same. Sekonic use 12.5, which is closer to the most recent standard (ISO 2720:1974; yep, that old). Canon and Nikon did the same the last time I checked, though few people at either company even knew what I was talking about. Any of these is somewhat artificial, and most calibrators don’t exactly follow the standard, which calls for a filter to create a 4700 K light source; the calibrators I’ve seen use an unmodified CIE A illuminant (2856 K). But at least it was standard. You get your calibration from the instruments you have; they’re not the instruments you want or might wish to have at a later time.

I discuss calibration and its effect in some detail in https://www.largeformatphotography.info/articles/conrad-meter-cal.pdf (boy, was that a long time ago ...).

[ic-racer]

Since the last time I contributed to a light meter thread like this I got a Sekonic meter that allows one to calibrate it via the menus. That is, one does not need to take it apart to find trimmer pots. I have been using a known film (using its indicated ISO) as a standard. Works better than a 'standard candle' for me.

[Robert Bowring]

My advice is to use the meter that works best for you and then put the other meter away. Trying to get 2 meters to agree all of the time is like chasing unicorns. I had one meter calibrated and then I sort of set all my cameras and meters to somewhat agree with the calibrated one and then never bothered to check them again. That was about 40 years ago and everything seems to be still working fine.

[Pere Casals]

Hi, guys.
This issue of isolation. Leads me to the next question
Measuring candlelight with the photometer. It has a certain EV value. I have two photometers and they both read differently. How do I know which one is more accurate?
Greetings


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> Use a camera with a reliable photometer (like nikon F-65) and see what photometer matches.

> Buy a $ 10 yo $20 cheap Luxmeter, search: https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=luxmeter&_sacat=0&LH_TitleDesc=0&_osacat=0&_odkw=luxmeter

[Rod Klukas]

The battery idea is a good one, but another one to look at is what kind of metering cell the meter uses. The earliest spot meters used a CDS cell(Cadmium Disulfide) which had some issues with some kinds or colors of light. It also had memory. If you pointed it at a very bright light, it was like humans and retained that for a while. Look at the sun and you see a bright ball for a while until your eyes/brain sort of let it fade.
Then came the Gaspd (Galium Arcsenide photo diode). Big improvement. This one also was blessed with a wider light spectrum. It also did not have a memory problem like the earlier spot meters. The soligors, and the Pentax Spotmeter V, were among the CDS types that were common. The Pentax Digital was of the GASPD type and also had few moving parts making it sturdier.

If both meters are the same model, they should or could be tuned to match. If not, the above info may explain.

One other point you cannot get a good meter reading through a filter with most spot meters except the Minolta M, Pentax modified by Zone VI, and the later GASPD meters like the Pentax Digital and the new Sekonics.
For Zone system the Pentax Digital with a Zone system sticker installed is by far the easiest to use.

[LabRat]

Then there is the basic test... Bring both outside on a sunny day, meter a grey card with both, one should read close to the "sunny 16" rule, which is in normal bright sunlight, at f16 set, the shutter speed will be the same as the ISO box speed rating, so one meter will be close, but the other not...

Then a film test with color chromes about right with the highlights and shadows, or with B/W, the neg should have a good balance of shadow and highlight detail... You can fine tune this in later tests...

Good luck!!!

Steve K

[Jody_S]

Bring both outside on a sunny day..

Part of the issue may be that the analog Pentax V meter reads far into the infrared range. In fact I use mine to shoot infrared, I mount my filter on the front of the meter with step-up rings, take my reading at the lowest ASA setting (I have to use the internal light to see the needle and of course I can't see what the meter is pointing at so I wave it around until I find my spot), then adjust by the number of stops necessary for the film i'm using. My exposures come out perfect every time.


If you're using a Pentax V to shoot say transparencies outdoors in strong sunlight, I would recommend using an IR blocking filter on the meter, because it has none internally.

[Jeff Conrad]

Part of the issue may be that the analog Pentax V meter reads far into the infrared range.

I think the Pentax Spotmeter V and Digital use the same silicon photodiode, and both read well into the infrared (the brochures show the response juxtaposed with that of the 1931 CIE observer); the curves appear to be the same. I had a rough spectral-response test done many years ago that pretty much confirmed the advertised curves; the result for my Minolta Flashmeter III more or less matched the curve marked “Visibility” in the Pentax brochure. Neither curve, of course, matches that of a particular film or a digital sensor. In my experience with a fair number of samples of both meters, they track very closely for normal subjects (e.g., a gray card), nearly always within ±1/3 step over the entire range.

Interestingly, the same is true for my Zone VI–modified Digital, though it diverges from my unmodified Spotmeter V when reading through a red filter.

So I think the difference Ricardo is seeing is more likely a calibration issue than a design difference.