Determining potential ISO rating given proper exposure in lux-seconds and density

[Wolfram Malukker]

Was chatting with some folks tonight about obtaining a current-production direct-positive orthochromatic film, and looking at the datasheet the film is not rated for ISO pictoral use, it's a copy film.

That's OK, but I'm trying to get an idea of how fast this film is.

According to the data sheet, proper copy exposure is obtained by:

Exposure unit: contact frame with halogen light source.
Original : a negative with a minimum density of 0.30 and a maximum density of 1.25.
Exposure intensity: 36 lux
Exposure time: 15 seconds.

 

[koraks]

Your speed point (Zone I) will be ISO = 0.8/(LUX-SECONDS), so add 4 stops of LUX-SECONDS to that (to get to Zone V). Since the ISO is arithmetic rather than logarithmic, I believe you would multiply by 4, perhaps someone else can confirm that.

From here: https://www.photrio.com/forum/threads/determining-lux-seconds-to-exposure.49059/
It would help if the datasheet also has a HD curve included, which you can use to interpolate the speed point. However, it may be better if you made a set of curves yourself since you may want to play with development a little to get the desired contrast, to the extent that this film responds to such manipulation.
Having said that:

Exposure intensity: 36 lux
Exposure time: 15 seconds.

Sounds like a slooooooooow film. If we (haphazardly) assume that this is about 4 stops above the speed point, then that would be around 1sec. @ 36lux, so 36lux-sec., which gives an ISO speed of around 0.02. Assuming the numbers are correct.

 

[Wolfram Malukker]

I figured somewhere around 0.8 ISO.

Here's the datasheet-Looking at Agfa Avitone continuous-tone copy film.

https://www.agfa.com/specialty-products/wp-content/uploads/sites/8/2017/06/AVITONE-PD1P-OS-PD3P-OS.pdf