Exposure Meter testing…any affordable devices available,or any shops still doing this

I hadn't thought of different photocells, and that certainly could account for some difference. But I just went outside and checked both meters and 2 1/2 stops difference would seem to me more than would be accounted for by different photocells. And anyway, my old, tired Weston IV is much closer.

Captil spot

RJS said:

Capital spot meter is new to me. I have Pentax, I know of Minolta and Soligor and SEI and attachments to make the Luna Pro a spot meter. What is 'Capital?'

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Well its about 20yr old ,an after market cheap imitation Pentex, don't know who makes it but it was inexpensive and works ok.It has dig. read out inside and a manual circular calculater out on its side.I think they still make them under another name, they might be east European

mike c.

mike c said:

Yes ,I have two meters all so luna pro and a capital spot meter, all though the lunna has the last say when I 'am uncertain.

mike c.

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Hi Mike,
Which model Luna Pro? It is my understanding the old Luna Pro (aka Luna-Six in Europe) is calibrated to a different standard than 18%. Have you found this to be true?

Fred Aspen said:

RJS, remember, when comparing the two meters mentioned, one is a CdS and one is a silicon photocell.

They have very different color responses. Both meters can be in calibration and give very different readings.

Somewhere on the net is the chart Pentax publishes for adjusting the exposure depending on the predominant color of the subject, up to a stop and half, IIRC.

-F.

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"They" say the old selenium cell has the most accurate response vis a vis different color temperature.

All it says John is Luna Pro,and of coarse Gossen, I use its readings for a 18%.

mike c.

Well, as I said, I think 2 1/2 stops is a bigger difference than the photocells would account for. I have a brown wall I use; in places it can be in full sun and in other places shade, so the color factor would, I would think, be a factor.

RJS said:

Capital spot meter is new to me. I have Pentax, I know of Minolta and Soligor and SEI and attachments to make the Luna Pro a spot meter. What is 'Capital?'

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The Capital looks like the Soligor, to me. I googled it.

Thank you John. Perhaps one of you would be kind enough to instruct me how to include a quote in my posting> I am very old, never have learned much about computers, and just checking the little box at the bottom doesn't seem to do it. What's the trick?

How much are they asking for them now ?if there is no price don't bother, I think mine was'nt over 100.00 20 yrs ago.

mike c.

I think Soligor was never thought to be as good as Pentax. A while back a "Pocket Spot" meter was advetrised and a couple of reviews said it was terrific. But it disappeared; apparently the people making couldn't make a go of it.

I'm sure there were many a good meter out there that droped by the wast side ,bad promotin,advertising.Adams I think had a lot to due with Pentax's success.or popularity they are a good meter.

mike c.

Well, it may be that AA did tout the Pentax, but the digital model does seem to be generally a good, sturdy tool. Earlier on he wrote about he SEI but there were few people I ever saw using one; I felt lonely and with a bunch of mis-exposed film on occasion. I just don't know of others than those I mentioned.

The SEI, is that the one with the probe that moves around in front of the ground glass in LF cameras.

mike c.

Mike: The SEI (there is a link to a description unbelievably painstaking by someone who resurrected one a bit earlier in this thread) was called a "photometer". It had a 1/2 degree spot which the user varied in brightness to match whatever spot was desired. When that was done you could, using the dial on the meter, place that spot wherever you wanted on the exposure scale. I think that is not a very good description, but if you read the above link it is much better. Anyway, many years ago I had two of them, and used them with rather 'spotty' success. I wasn't able to match the brightness of the spot to the target with any consistency.

This is becoming the adventures of an old person with weird photographic stuff. Oh well.

That is a very interesting link,the idea of matching brightnesses reminds me in high school using a Kodak step wedge densetometer aligning the Known density to the sample unknown.Interesting principled for a lit meter now.

mike c.

RJS said:

Thank you John. Perhaps one of you would be kind enough to instruct me how to include a quote in my posting> I am very old, never have learned much about computers, and just checking the little box at the bottom doesn't seem to do it. What's the trick?

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I just click on "reply with quote" at the bottom left of the box. At least that's the way it works for me. I use America On Line, maybe that makes a difference. I don't know how this stuff works. Ask the kids. They know this stuff.

"They" say the old selenium cell has the most accurate response vis a vis different color temperature.

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That's about true. The CdS cell has a peaked spectral sensitivity right in the green range, whereas silicon photodetectors have a peak in the infrared. The tail goes down through the visible range, but it's far from flat. This can be compensated for in software or with (light-absorbing) color filters, but I would doubt that older cameras or simple exposure meters go to the trouble. There's nothing really wrong with Si, they are much much faster, have no memory, and are very linear with intensity. You make your choices and you take your chances. Or at least the people that design your exposure meters do.

Somewhere back in the dim distance of photography there was the extinction meter. A little (not much) before my time. The idea, if I remember correctly, was that you looked through ahole which somehow (I would have to look this up) you slowly occluded the hole until the brightness of what you saw through it matched a reference. I really will have to look this up as I'm sure I've muddled it badly. I do remember that old Kodak densitometer and I think it worked fairly well I have an old Weston desitometer so if you are familiar with the old Weston meters with a selenium cell, you can imagine how it works. There is a light bulb run by a rheostat, and you vary the brighness of the bulb to where the meter reads zero, which becomes your starting point. Muddled.

Thanks John, but I've tried that and it doesn't seem to happen. I have a Cox high speed line, but I don't think that has anything to do with it.

The densitometer that I used had a lit source that lit the neg and the step wedge form underneath while you would look down to them true a lens arrangement and compare visually the match and write down the the wedge density that was inscribed along the side of the tablet . No meters just a visual comparison.

mike c.

RJS said:

Somewhere back in the dim distance of photography there was the extinction meter. A little (not much) before my time. The idea, if I remember correctly, was that you looked through ahole which somehow (I would have to look this up) you slowly occluded the hole until the brightness of what you saw through it matched a reference. I really will have to look this up as I'm sure I've muddled it badly. I do remember that old Kodak densitometer and I think it worked fairly well I have an old Weston desitometer so if you are familiar with the old Weston meters with a selenium cell, you can imagine how it works. There is a light bulb run by a rheostat, and you vary the brighness of the bulb to where the meter reads zero, which becomes your starting point. Muddled.

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Don't forget the Leudi!

RJS said:

Thanks John, but I've tried that and it doesn't seem to happen. I have a Cox high speed line, but I don't think that has anything to do with it.

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I use Cox Cable, but, although it requires works through Internet Explorer, I have it segue to AOL because I am familiar with AOL. Dinosaur, that is I.

Getting back to the original thread, I guess the answer to the original question is, no, there is no inexpensive way to test an exposure meter against a known light source. BetterSense can buy us one for 20K USD, but I'm a little cash-strapped this week, so that one is out.

One idea came as a result of the instructions someone linked to the Lumi-disk. Such a procedure would remove the caveats raised by others about pollution, time of year, etc. etc. And incident light meter pointed directly at the noonday sun should, I would think, produce sunny 16. I read, years ago, about making an incident cone for a camera using the translucent hemisphere from a L'eggs panty hose package glued to a lenshood.

I bet BetterSense could tell us whether something like that would work.

I believe when two light meters disagree it's most likely one of a few factors. Analog light meters can easily get out of calibration because of the delicate needle balance. The motion picture Spectra meter was the standard, but if you look at it wrong, it would need recalibrating. Older meters have older photo cells and older technology. But mostly, I believe it's do to the spectral sensitivity of the photo cell.

The basic values in the exposure equation haven't changed since they were established in the early forties and except for a small change as the result of better measuring devices, is the same from the point of the first ASA standard for exposure meters sometime around 1948. The changes in the standards over the years seem to be mostly attributed to the changes in the materials that make up the photo cells.

I remember reading something from the late 50s or early 60s about a change in the kevin value used to calibrate the meter. It was to change from something around 2700K to the cooler 4700K used today. At that time, films tended to have a different EI for daylight and incandescent light. I believe it wasn't because of the emulsion, but because of the spectral sensitivity of the light meter and the color temperature of the calibrating light source. If I remember correctly, the paper said that after the adoption of the proposed change to a cooler calibration light source, there would be no further need for two film speed ratings for each film. According to the paper the goal was to "make more accurate in daylight and eliminate the need of different tungsten speeds for most panchromatic materials." And by the mid or late 60s, I believe this was the case.

So when comparing an older light meter with a newer one, even discounting the affects of age, the older meter might have a different photo cell that responds differently to the same color temperature in addition to being calibrated to a different light source which under under certain circumstances could combine to make quite a difference.

If anyone wonders if the sensitivity of the photo cell makes much of a difference, there's the infrared test. A quick test to see if your meter is sensitive to infrared is to point it at a remote. Meter the remote, then push a button on the remote and see if the meter reacts. If it does, then it's sensitive to infrared. Many people tend to use foliage like grass to key off of. As anyone who has shot infrared knows, chlorophyll reflects tons of infrared. A meter sensitive to infrared will see the grass as brighter than it really is which may cause underexposure.

Stephen,are you useing a tv remote control?

mike c.

I haven't noticed anyone mention the ANSI tolerances which are on the order of +/- 25%.
When I was doing repairs we used a standard light source built into a Kyoritsu tester.
It used transmitted light not reflected and in addition to the brightness being variable there was a "K" factor that would also change the value perhaps by slightly changing the spectrum?
Anyway if you have two meters differing by 1/2 stop, each of them could be within tolerance but at different ends of the scale. If you want them to agree you would need to send them in at the same time & have them calibrated to each other.