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film speed for old films



 
 
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  #1  
Old March 5th 10, 12:24 AM posted to rec.photo.equipment.medium-format
Geoffrey S. Mendelson[_2_]
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Posts: 26
Default film speed for old films

Sorry, but I have lost the original thread. I was posting about film speed
of pre-WWII films to compare with modern film in a Kodak Brownie camera.

It just so happens that Popular Science has made their archives publicly
availaible and I looked up the December 1941 isssue as that was the last
one before the US entered the war.

The Kodak ad in there was for Verichrome (not Verichrome Pan, which came in
the 1950's) which was ASA 50. It also mentions Super XX (100 daylight, 80
tungsten) for night shots.

In comparison, Kodacolor was ASA 20.

I'm not sure about Kodachrome it was either ASA 8 or 10.

Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.
  #2  
Old March 5th 10, 04:26 AM posted to rec.photo.equipment.medium-format
Alan Browne
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Posts: 12,640
Default film speed for old films

On 10-03-04 18:24 , Geoffrey S. Mendelson wrote:
Sorry, but I have lost the original thread. I was posting about film speed
of pre-WWII films to compare with modern film in a Kodak Brownie camera.

It just so happens that Popular Science has made their archives publicly
availaible and I looked up the December 1941 isssue as that was the last
one before the US entered the war.

The Kodak ad in there was for Verichrome (not Verichrome Pan, which came in
the 1950's) which was ASA 50. It also mentions Super XX (100 daylight, 80
tungsten) for night shots.

In comparison, Kodacolor was ASA 20.

I'm not sure about Kodachrome it was either ASA 8 or 10.


We've come a long way. I remember shooting a lot of Kodachrome in the
early 80's and thinking 25 was a fine speed of film... Since I shoot a
lot from a tripod, it still is, I suppose.


--
gmail originated posts are filtered due to spam.
  #3  
Old March 5th 10, 06:03 AM posted to rec.photo.equipment.medium-format
[email protected]
external usenet poster
 
Posts: 428
Default film speed for old films

Geoffrey S. Mendelson wrote:
Sorry, but I have lost the original thread. I was posting about film speed
of pre-WWII films to compare with modern film in a Kodak Brownie camera.

It just so happens that Popular Science has made their archives publicly
availaible and I looked up the December 1941 isssue as that was the last
one before the US entered the war.

The Kodak ad in there was for Verichrome (not Verichrome Pan, which came in
the 1950's) which was ASA 50. It also mentions Super XX (100 daylight, 80
tungsten) for night shots.

In comparison, Kodacolor was ASA 20.

I'm not sure about Kodachrome it was either ASA 8 or 10.



I have some old tower catalogs and they pretty must say to only use
print film in the box cameras due to their limited control. From my
experience with the simple Tower and Ikon ones I have shot with, 50 ASA
print film in daylight works pretty well (Ilford pan F) or I have put a
deep yellow gel inside and shot with 100 speed B&W. The yellow filter
helps the image quality quite a bit!

I would guess if you wanted to "dial in" one of these for modern film in
daylight you could play with ND filters till you got the exposure right?
My old Ikon has 3 waterhouse stops which helps. You might be able to add
one to a brownie, which would probably help image quality too.

Stephanie
  #4  
Old March 5th 10, 07:43 PM posted to rec.photo.equipment.medium-format
Richard Knoppow
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Posts: 751
Default film speed for old films


"Geoffrey S. Mendelson" wrote in
message ...
Sorry, but I have lost the original thread. I was posting
about film speed
of pre-WWII films to compare with modern film in a Kodak
Brownie camera.

It just so happens that Popular Science has made their
archives publicly
availaible and I looked up the December 1941 isssue as
that was the last
one before the US entered the war.

The Kodak ad in there was for Verichrome (not Verichrome
Pan, which came in
the 1950's) which was ASA 50. It also mentions Super XX
(100 daylight, 80
tungsten) for night shots.

In comparison, Kodacolor was ASA 20.

I'm not sure about Kodachrome it was either ASA 8 or 10.

Geoff.


Beware that the original ASA sytem had a one stop
safety factor. All those speeds doubled when the ASA dropped
the original method and adopted a modification of the DIN
method about 1958. The original ASA method was based on
extensive research done at Kodak Research Labs by Loyd A.
Jones and his associates. There intension was to find the
_minimum_ exposure which would result in good tone
rendition. The problem came when the ASA adopted this system
as a standard. For some reason they decided to halve the
speed determined by the test.
Up to the adoption of the ASA system about 1943 Kodak
published "Kodak Speeds" which were determined directly by
the Jones method. These were four times the ASA speeds and
exactly double current ISO speeds. The two to one change was
made to adopt the speeds resulting from the test to existing
meters which used mostly either the Weston or General
Electric scales. The ASA speeds fell exactly in between
these two so could be used on either kind of meter with
minimal error.
The main reason for changing the standard speed method
from Jones' minimum usable gradient method to the DIN
minimum density above fog and support density was the
difficulty of making the Jones type measurement which
requires finding the point on the toe where the gradient
(contrast) is exactly one-third the gradient of the
straight-line portion of the curve. The ASA found that the
DIN method would result in just about the same speed point
if a fixed factor of 1.25 was applied to the indicated speed
point. The DIN method and the current ISO method is to
expose and develop the film in a controlled way that results
in a specified density range corresponding to a specified
exposure range, i.e. essentially a fixed contrast index. The
speed point is then the point is then where the density is
log 0.1 above the gross fog and base density. A multiplier
of 1.25 is applied to this to get the speed.
This method applies _only_ to black and white
silver-halide negative film intended for use in still
cameras. A different standard exists for motion picture
negative film and other standars for color films and for
reversal films.
The reason Jones wanted to find the minimum exposure
was that, in general, film yields the finest grain and
sharpest image for minimal densities. This is, of course,
mainly a concern for small negatives. Jones found that he
could get "excellent prints" when the minimum shadow
exposure was on the toe where its gamma or gradient was
one-third the overall contrast. Decreasing exposure rapidly
degraded the image quality but increased exposure had little
effect up to many stops over-exposure. Probably the ASA
wanted to adopt a speed standard which would be reliable in
terms of producing a usable image so took advantage of the
overexposure capabilities of film. Of course, they lost the
original intent of producing the finest grain and sharpest
images.
Color films were always measured by a different system.
Reversal films especially must be accurately exposed because
they use virtually the full range of densities possible and
have very little latitude. I am of course writing about
reversal for direct viewing. There are low contrast reversal
films for duplicating purposes.
The original Kodachrome had a speed of about ISO 8 to
12 depending on whether it was daylight or tungsten
balanced. However films like Plus-X and Super-XX had speeds
much like today, i.e., around EI 125 for Plus-X and 200 for
Super-XX, exactly double what the published speeds of the
time were. The biggest difference in these emulsions for the
later ones was grain. Current Plus-X is substantially finer
grain than the original version and is sharper. All of these
old films used multi-coated, thick emulsions which had
considerable light scattering (irradiance) which caused a
loss of resoution and sharpness. In fact, the use of
ultra-violet light was adopted for making motion picture
sound negatives in the 1940s in order to confine the
exposure to the surface of the emulsion and so increase
resolution and reduce distortion.

--
Richard Knoppow
Los Angeles, CA, USA



 




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