How do you calibrate a light meter?

[Grandpa Ron]

I have been working with an old 4x5 cut film view camera and I have an old selenium light meter. (no battery needed.)

My question is, how do I check to see if the light meter reading is correct?

I have tried comparing it to the values show on my digital camera set to the same ISO. Also checking it against the exposure settings of my old 35 mm SLR and another non-battery meter on my old twin lens camera. Sometimes the readings agree and some times they do not. After a lot of tail chasing, I decided that each of these cameras probably had a different field of view, hence the inconstant agreements.

I do not want to blame development issues, if it is an exposure problems.

 

[ac12]

The "old" way was f/16 at shutter speed 1/ASA, when pointing at a "18% scene." Sunny 16.
The problem was, back then, I really did not know what an 18% scene was. We "thought" we were smarter than we actually were. The ignorance of youth.
Today I would use a grey card instead. Although learning HOW to use grey card is an issue.

As for matching to another meter.
Unless you KNOW that reference meter is accurate, you could be matching to an inaccurate source.
I would not rely on digital camera meters. I've found that the SAME scene metered and shot with different cameras, resulted in different exposures.

Probably the best way, requires film use.
Before testing, I would exercise the shutter at each position, several times, to try to get the lubricants moving again.
Get a grey card and a grey scale.
Expose for the grey card, then bracket in a half or a full stop steps.
Then after you develop, see how much of grey scale you can see, and where in the scale it is (low, centered, high). The one with the centered grey scale would be your correct exposure.
To save film $$, I would do the test with a 35mm camera (35mm film being cheaper than 4x5 sheet film). Then verify the result with one frame on the 4x5.
The problem here (there is always a problem) is that with old gear, the shutter speeds may not be accurate. When lubricants dry out, they can get sticky/stiff. And sometimes the shutter speeds can be off, WAY off. And the deviation from labeled, can be inconsistent.

 

[dxqcanada]

Field of view would affect the reading, and also many modern cameras do not give you a "general" reading ... your old SLR is probably closer.
The selenium cell does not age well, so it may read differently throughout the light range ... so I am not surpised you get different readings of things in comparison.
Many of the old meters did not have a user method of calibration/adjustment ... most you have to open up.

 

[ac12]

Oh, do NOT use your digital camera meter in "matrix" or other similar metering method.
In matrix metering, the camera is metering various parts of the scene, then evaluating them to come up with the exposure.
The problems is, we have no idea, how the camera is determining the exposure setting (and likely never will).

 

[ac12]

Field of view would affect the reading, and also many modern cameras do not give you a "general" reading ... your old SLR is probably closer.
The selenium cell does not age well, so it may read differently throughout the light range ... so I am not surpised you get different readings of things in comparison.
Many of the old meters did not have a user method of calibration/adjustment ... most you have to open up.

I used the simple method.
Once I determined the "correct" meter exposure, I determined it's offset from the rated ASA.
I taped the ASA offset onto the meter/camera.
Example, - 2/3 stop.
Then I would set the meter ASA (ISO to you youngsters), to 2/3 stop lower than the film's rated ASA.
Example, for 200 ASA film, at -2/3 stop, I would set the meter to 125.
The "-" referring to the off-set from the rated ASA number. Remember, it had to be simple. No wondering if "-" means a lower or higher number. "-" is a lower number and "+" is a higher number.

 

[mrca]

And for the younger, the folks at ISO intend for it to be pronounced as a word, not spelled. That's from the people that created the term.

 

[dxqcanada]

eye-so ?

 

[mrca]

eye-so ?

Yes, not spelling I-S-O. They wanted it to be universal in all languages. If you used the first letters, in some languages it would be different.

 

[NS: Nikon Shooter]

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Calibration is not relevant in this but proper referencing is.
As mentioned, that is done using an 18% grey card.

 

[mrca]

When I bought an 18% gray card at Kodak in Rochester in 1969 it came with instructions to adjust camera off the reading from the card. There is a variance on what digital cameras from different manufacturers use as their "middle gray " and I calibrated my meter using color checker passport and the meter software to my specific sensor, plotting exact highlight and shadow clipping. For an older meter, I would find someone with a meter and compare. Keep in mind, meters vary as well.

 

[Grandpa Ron]

I wish to thank everyone for the advise, and a reminder to use the gray card. I had to dig out the film photography books for that.
While I have done some experimenting with the view camera, it was mostly to learn all the steps necessary to capture the picture I wanted.

It seems the easiest approach, is to choose a sunny day and shoot the swing set in the back yard. I will attach a gray card to the swing and expose per the gray card's light meter reading, then bracket two stops.

This leads to another question; can I judge the middle gray tone by comparing the gray card to the gray card images on the on the negatives?

With a two stop bracket, I would expect one gray card shot to be very dark and one to be very light and hopefully one light meter shot to be fairly close.