Old Exposure Meter and New(er) Film Speeds

[John FB]

Folks,

I have a question regarding the ASA (ISO) ratings of today's B&W negative films when used in conjunction with old exposure meters. I have a GE DW-68 serial No. R02119 which I've been using for a while now with decent results, I believe it's giving fairly accurate readings.

A couple of days ago I read that back when my meter was built there was a safety factor of one stop built into the film ratings. (I probably read that years ago and completely forgot about it.)

What I'm wondering is: Will I improve my results if I exposed ASA 100 film using an ASA 50 setting on my (older) meter?

When film manufacturers dropped the safety factor in their film rating did meter manufacturers alter the numbers on the meter dials?

Also, the dial on my meter reads"EXPOS INDEX" on the outer ring, so those should be ASA numbers, not the older GE film numbers, correct?

Pax,
John

P.S. I've asked this question on a couple of other forums-sorry for the redundancy-if you've come across it elsewhere.

 

[cmc850]

The use "American Standard Exposure Index" which is ASA and ISO equivalent. Not sure what the reference to safety factor is - negative films can certainly tolerate a stop over, even under exposure, but reversal films don't tolerate that as well. If you are getting good results - all is well?

There may have been a time when manufacturers recommended setting a lower ASA for negative films when there might be large errors in measurement - but film, then and now, tends to have an optimum speed rating where the best contrast and tonal range are achieved.

Back in the day, we would often rate reversal films like Kodachrome, a critical film, a bit "faster"....like 64 rated at 80 etc to make the colors a bit richer in well-lit situations...but never under-rated, as once you blow out the highlights, they are gone.

 

[John FB]

cmc850,

Thanks for responding.

Back some time in the 1950s film manufacturers removed a safety factor that had been built into film ratings-suddenly a film rated ASA 50 was ASA 100 without any actual change in the film. (I hope I'm explaining it correctly.) [see: http://www.photomemorabilia.co.uk/Ilford/Film_Speeds_1960.html]

Since I'm using a meter made back before the change, I'm wondering if I could improve my shots by setting the meter dial to 25 when shooting a roll of ASA (ISO) 50?

Pax,
John

 

[cmc850]

I see - after reading this it does suggest films were under-rated specifically to guard against under-exposure - and that it applied to bw negative films only. Color was and is rated differently, and should be shot as rated.

Hard to say if the meters of the day "accounted" for the ASA variance for bw film, but what I might do is compare readings taken with your old meter to those taken with a modern meter or camera from the same scene to see what setting makes sense.

BW ASA ratings are always a starting point, as actual film "speed" is dependent heavily on processing and printing variables.

 

[charjohncarter]

Too confusing for me, I usually do one stop over and then develop to that speed. I use mid-tones as the development guide and and exposure as the shadow guide (and agitate to highlights as a guide). If you just use a few films, it is easy. The only problem is film companies are either changing there films with the same name or discontinuing films. So, you have to keep checking things.

Many really good B&W photographers say to expose for the shadows and develop for the highlights. Some others, although a few say; expose for the shadows, develop for the mid-tones and agitate for the highlights. I believe in this second method. If things go wrong; I just post process digitally for the mid-tones. Therefore, I've broken my rule of too confusing.

 

[Ranchu]

Test your meter against another modern meter in a camera or whatever on closed sunlit blinds. If in general your pictures are underexposed, lower the asa on the meter. Shoot some shots at both to see what you like.

 

[Luddite Frank]

Going from memory here ( which is probably going to bite me in the hind-quarters...)

For a while, I was on a kick collecting old light-meters, working where possible, all the way back to Weston's "Bakelite bricks" of the 1930's.

I am not sure which book or booklet I read it in, but it explained / compared all the various film speed ratings in use, circa 1950:

Weston
G.E.
A.S.A
D.I.N.
British Scheiner
etc.

I will look for that "Rosetta Stone"...

In the meantime, I think I remember Weston 100 being equivalent to ASA 80 ?

Ranchu's suggestion is probably a really good idea, if you want to shoot with your meter.

The metal G.E. DW / DY meters are reliable ( if heavy )...

Good luck !

Luddite Frank

 

[Mr_Flibble]

When film manufacturers dropped the safety factor in their film rating did meter manufacturers alter the numbers on the meter dials?

Short answer: no.

They didn't need to.

 

[Luddite Frank]

Some success !

I pulled a couple of plastic "shoe-boxes" of light-meters and booklets out of my camera closet today, and found some information.

The best of all is a little 2" x 3" booklet:

"Film Values" ( American Standard exposure-index numbers )

For use with the General Electric Exposure Meter ( All models )

Publication # GED - 744M (published 12-49, according to date on back cover, lower-left corner).

The back cover has advertising for two meters: the "new" PR-1 Deluxe model, and the DW-68 (Regular model) - " It's 3 meters in one "

Okay, on to the good stuff:

On Page 3, there is a Comparison Table, translating "ASA Exposure Index to Former G.E. Film Values".

It begins with ASA 0.6 and runs up through ASA 1000.

More importantly, there is an informational paragraph above:

"All G-E meters manufactured after January, 1946, utliize the American Standard exposure indexes. Although the new ASA values can be used with the previous model G-E meters, interchangeable calculator-hoods with American Standard exposure indexes are available for Types DW-48, DS-49, and DW-58 meters. They may be procured from your photographic dealer."

Which is to say, your DW-68 is ready-to-use, as-is with the "new" Post-WW II ASA film ratings - no conversion necessary. 🙂

That said, however, this assumes your meter is still in optimum operating condition / calibration. 😉

Comparison with another meter ( such as a modern CdS ) of good quality and perhaps some actual test shots will confirm your meter's accuracy.


For academic information, the other conversion table I found is in the instruction manual for my Leica III-f, printed in Sept. 1955 (?), which compares/translates:

DIN, British Standard and ASA ( in both Arithmetic and Logarithmic expression), General Electric [pre-1946], Weston, American Scheiner, and European Scheiner .

Generally speaking, for a given ASA rating, old GE speed rating runs about one value higher ( ASA 100 = old GE 125), and Weston runs about one value lower ( ASA 100 = Weston 80 ).

I will try to scan an post these two tables, as soon as I can get my newer computer to talk to my almost new printer. (Thank you, Windows 8 ! :bang: :bang: :bang: )

 

[charjohncarter]

Frank, thanks for that explanation. I grew up with DIN and ASA, so the pre-war information is very interesting.

 

[John FB]

Thanks everyone for the insight and info, thank you Frank for digging out all that info as well. At the moment I have three meters none of which match up. A beautiful Weston that's near dead and a little GE Mascot which is a couple of stops off from the DW68. I'm getting a new type meter soon thanks to a heads-up from another forum and I'm going to see what the photo lab I use says. Blush-I've been taking photos since 1973 and I've yet to learn how to develop my own stuff.

Thanks again everyone,
John B.

 

[David Hughes]

Hi,

About the old Westons, I had a model II (1940's) and wondered about it. I got it sorted out easily and talking to them was told that they very seldom failed but often needed rebalancing to adjust for age.

As for very elderly meters, no two people or speed rating ever agreed, most of the meter makers tested films and told you what their meters would make of them.

Before meters the film was insensitive to red light (unless you were rich enough to afford Panchromatic film) and so they developed them in dishes and stopped when the negative looked OK. It worked best with cut film and glass plates.

As for 30's film, I've books showing how to get a print from negatives with a tenth to 300 times the correct exposure. That's a lot more latitude than we'd expect. One negative was so thin the image could barely be seen but it was printed reasonably well. (That was in "The Selo Text Book of Amateur Photography".)

Regards, David