I know I could probably look this up somewhere, but where, I don't know?
I'm looking for ASA/ISO speed equivalents to H&D Plate speeds. The H&D speeds are 150, 225-250 and 400.
The reason if anyone is interested... I just got a Zeis/ICA Diaphot extinction meter and thought it would be interesting to see how it works. Well, it works on the H&D plate speeds... Roughly. Any of them. Take your pick. But make sure to double it under 9 yards... Interesting instructions
Thanks to anyone who knows...

Rich...

Well I've got lots of data, but very little information.

I don't have any books correlating H&D to ASA. The best i"ve got is H&D to Weston & DIN but the numbers are far off from yours. this is from Photo lab index 1946. The columns with the * is from Handbook of Photography, 1939. You'll notice the only thing consistant was the DIN although they marked it as 18/10 instead of 18°

Weston Weston* DIN H&D H&D* H&D**
40 69 18° 1000 1740 8300
50 93 19 1250 2320 11200
64 116 20 1600 2900 14000
80 148 21 2000 3710 18000
100 186 22 2500 4640 22500
125 232 23 3120 5800 28500
160 24 4000
200 25 5000
250 26 6250
320 27 8000


Wetson* Apparently between '39 and '44 Weston moved their scales about

H&D vs H&D* These should have been the same and are noted as "American & British H&D"

H&D** This was noted as "continental H&D" which I would have suspected as being the right scale for your meter, But unless there's a little "X100" on it, Obviously I'm wrong.

ISO 400 and DN of 27 is the same, according to my Tmax box of film. That suggests our benchmark of 100 is a DIN of 25. However that may be in error because old Panatomic was ASA 25-32 or a DIN of 23 but is listed as Weston 40 or a DIN of 18. Some of this variation may be explained below.

Although I think I've kept this out of the table above, there was a 'transistion' during the 40s. Early tests done on 'minimum gradient density' while accurate were often divided by a factor of 2 stops to come up with the speed of the film for pictorial use. Thus TriX was in the 80-160 range instead of 320-400. by the 40s they were abandoning the 'safety factor'

BTW for those interested in the insanely trivial, H&D stand for Hurter and Driffield, two Rochestarians who came up with the concept that 18% grey was the average for all objects. The real story was they based all of their experiments on the cloudy Rochester sky, so they divised the grey card to make the Rochester sky portable.

Wow, thanks Les. I did search the internet and only came up with a side mentioning of H&D 2500 being equal to ASA 200. Off from your list I think. They didn't mention which H&D or anything else though. But it's only one stop and how accurate could this type of meter be in the first place. Their description of adjusting it to look like a "moonlit night" is a bit arbitrary at best... I doubt I'll ever use it for real, but it would be an interesting thing to play with and see how it was done, or attempted, back then. I'll print this out and do some experimenting...

I remembered that I had the big instruction sheet for this meter stashed away. It gives a bit more detail. One interesting this is the plate speeds. It lists for "Normal plates about 225-250 H&D" as:
Inperial Special Rapid
Ilford Special Rapid
Gem Meteor
Wellington ExtraSpeedy
Wellington Anti Screen
Marion Brilliant
Barnet Special Rapid
Barnet Self Screen
Kodak film

The last one seems a bit odd

I've heard that story about the Rochester sky and I see that 18% sky half the year here. Thank goodness Spring is on it's way!

Thanks again...


<font size=-1>[ This Message was edited by: RichS on 2003-03-19 12:24 ]</font>