Arista EDU Ultra 100 ISO

[rydolan]

I also had a question regarding the true ISO of the film I use, but for the sake of future searches, I thought I'd better title a new thread...

I have read many times that people who shoot with Arista EDU Ultra 100 actually rate it at about ISO 50, and sometimes ISO 32 as well.

How do I actually treat a 100 speed film as if it were ISO 50? In my mind I have thought about it in the following ways:

Do I just double my exposure times and develop normally?
Do I expose regularly and halve the developing time or the developer dilution?
Do I double the exposure AND change the development time?

I've also wondered if there are actually multiple correct approaches just like there are multiple combinations of aperture and f/stop for the same light reading...Any info would be much appreciated.

Thanks much,
Ryan

[earlj]

Ryan:

The rule of thumb is 'Expose for the shadows, develop for the highlights.' People usually rate a film below its stated ISO because they are not getting sufficient exposure to give good shadow detail. But you still want the density in the highlights that the recommended development time gives. So build an exposure chart for iso 50 or 32, but use the development time recommended for the film at iso 100 (I like the Massive Development Chart).

If you are getting good details in the shadows, then your exposure is good. If your highlights are blown, then reduce your development a little. If your highlights could use a little more density, then increase your development time a little. With pinhole pictures, reciprocity failure plays such a big role that it gets hard to know whether your exposure or your development is out of whack. I tend to stick with one development scheme for a film, and then play with the exposure if I am getting less than optimal results. With a film like Arista EDU, when in doubt, double the exposure. Or open the aperture and then go have a beer.

If you really want to calibrate exposure, development, film, and camera, then go buy a book. Phil Davis' book Beyond the Zone System is a very technical book on how to control the variables in your photography. He shows you how to measure the true iso for your film, your developer, your camera, and your darkroom conditions. There are other descriptions of how to rate your film that are not as technical in books by other authors. BTZS can be a bit daunting when you first look at it.

[rydolan]

With a film like Arista EDU, when in doubt, double the exposure. Or open the aperture and then go have a beer.

Haha! I've noticed that the reciprocity failure of Arista EDU is pretty nuts after about a second or two. Thanks for the info. I was hoping for exactly that amount of information; not technical, not vague. Thanks much!