Light meter help

MCB18

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Hi, I have a question for you guys, I just today got a PD prism for the RB67, and I was comparing it to my Luna Pro F to make sure it works. Unfortunately, it’s reading 1 stop dimmer than my Pro F, although it seems to be consistent. Testing with some other cameras, some agree with the prism, and some agree with the meter! So, my question is, what do I do? Do I just expose at whatever sent meter tells me to? Do I compensate for an error? But which meter do I use to compare if I don’t know which one is right?

Thanks.
 

BrianShaw

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Different light meter readings can result from different light meter designs, such as acceptance angles and weighting and metering cell differences. Best thing you can do is shoot a test roll and keep very accurate notes. Use a “normal “ scene and meter each way. Then you can look at the negatives and determine which meter gives the best results.

But first… double-check that each of the meters you are using are configured the same.
 

xkaes

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Brian's right on. There usually are a lot of variables between meters. Think about incident vs reflective!!!

You need to standardize on one, and adjust for the others. None of them are right or wrong (unless defective -- but that is easy to figure out).
 

Chan Tran

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The PD prism has Average and Spot mode. Also crosshair type D focusing screen can not be used. I don't know what kind of angle the spot meter cover.
 

Sirius Glass

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Send both of them to a light meter calibration at the same lab and the differences will disappear.
 

RalphLambrecht

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If I were you, I would check which is closer to sunny 16 and go by that
 

Dan Daniel

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MCB18 said:
But which meter do I use to compare if I don’t know which one is right?
Click to expand...
What counts is the negatives. If the shadow density is what you want, the meter is guiding you correctly. If it isn't you need to adjust. Usually I will nudge ISO around to make up for variances in meters. This will be on a case by case basis. I had two same model Pentax SLRs overhauled by the same tech, Eric Hendrickson. They were different by over half a stop. If I nudged one by 1/3 stop lower ISO and the other to 1/3 higher ISO, negatives both matched and gave me the shadow density I want.

And as has been mentioned, lots of variables go into metering. Both of yours could be 'right' for how they were meant to work.

Go ahead and play meter off of meter all you want. Castles in the air. The meter is a tool to help you get the negatives you want.
 

JPD

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I have a Gossen Sixtomat Digital and it's exactly one stop more "optimistic" than my Capital/Soligor light meters, and the meter on my Rolleiflex 3,5F (that works and was adjusted by Rolleiservice). I agree with Brian and Dan, that it's best to go with what gives you the best results. It's easier with black and white and negative colour films, but you could try a less tolerant transparency film (E6) and see which metering gives you properly exposed results.
 

Philippe-Georges

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I think that one should set with one type of light meter(-s) and the test thoroughly and adopt a way of working: metering, interpreting, exposing and developing, accordingly.

When I (had to) change from Gossen Variosix's to Gossen Digipro's, I measured a difference of nearly one stop. I tested with the emulsions and cameras I mainly use, and adopted my way of working.
I have no TTL meters.

BTW, I always keep a set of two of exactly the same light meters (one in each camera case as I forget...), same manufacturer, —type, —generation, just to simplify things and get some ease of mind...

I use a Pentax Dial Spot meter just to check the subject's contrast when I have doubts.
And I still keep my old Spectra Combi-500 as a souvenir, but I saw that it deviates with only les than 1/3 of a stop with the Gossens...
 

ic-racer

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You have determined you equipment is faulty. Next step is to repair it. Any competent repair shop should be able to calibrate a meter.
 

Ian C

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Regarding Post #1

That’s not an unusual situation. I have several cameras with modern built-in meters, including a Mamiya RZ67 AE prism finder. I also use a Minolta Flash Meter IV and a Sekonic L-508. All were bought new and seem to work properly.

In some situations, they are in close agreement. In other situations, the readings differ. Some are more of an average reading. Others “see” more limited parts of the scene. My Sekonic L-508 has a zoom lens spot meter. The spot meter almost never gives the same readings as the averaged readings received through the diffuser in incident light mode.

If the readings are consistently too low relative to the actual negatives you get (resulting in overexposure), you can simply set the film speed 1-stop higher to compensate. Most likely, there’s nothing wrong with the PD finder’s meter, just the way it “sees” based on its design (the way it meters).

One practical way to figure this out is to shoot and process narrow-latitude transparency film. Chose a scene, meter with a trusted incident meter and shoot. But also shoot a second frame using the PD meter’s recommendation. Keep careful notes so that you know which is which. Use the transparencies to judge which meter recommends the best exposure.
 
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Sirius Glass

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Alan Edward Klein

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Chan Tran said:
Anything has tolerance. You should know your measurement within the tolerance. Your meters, clock, rulers none is absolutely accurate but you know they are accurate to within a tolerance.
Click to expand...

But which is right when you look at two?
 

MattKing

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Eff64

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Best is to compare to another meter, both aimed at the same material. If you have a grey card, that is ideal, but if not just use the same field for any/all readings.

If you have other hand held meters, great, if not you could use another camera or two. In a perfect world, you have 3 different readings-with three separate meters-and two will mostly agree. If you have to adjust your prism, do it with the ISO setting.
 
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Marco Gilardetti

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Sirius Glass said:
Send both of them to a light meter calibration at the same lab and the differences will disappear.
Click to expand...
It's not necessarily so. Light meters, especially "vintage" or "simple" ones, are not really linear. They once used to have a pair of calibrating points in order to fit their response curve curve to a line as best as possible, but as far as I know in all cases there are ranges in which they are quite precise and other ranges in which they are less precise. Even by sending both to calibration, perhaps they will end up marking the same light value in some ranges, but would mark disagreeing values in another range.

RalphLambrecht said:
If I were you, I would check which is closer to sunny 16 and go by that
Click to expand...

Again, not necessarily. Personally, I would rather pick up the one which behaves better under difficult light conditions (cloudy / night). When it's sunny, a light meter is not even really needed.
 

beemermark

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My standard reply - shoot some film. Do it at the recommended exposure. Is you film properly exposed? If not apply an exposure compensation to the meter. I have numerous cameras and also a lot of meters. They never agree with each other.
 

btaylor

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RalphLambrecht said:
If I were you, I would check which is closer to sunny 16 and go by that
Click to expand...

This has gotten me out of trouble with defective or out of adjustment meters. Yea, it won’t parse low light or linearity questions but at least you’ve got a starting point- all you need is a sunny day.
 
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RalphLambrecht

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if you only have one light meter, you know exactly how to expose the film. If you have two, you can never be sure.
 
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