transposing camera f/stops on the Log E axis

[John Pytlak RIP]

it's for something very important. ; )

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If "it's for something very important", all the more reason to shoot a test.

[Giles Rais]

If "it's for something very important", all the more reason to shoot a test.

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No, it isn't, because the information I'm looking for is not going to be used on a particular film, but a paper that requires a generalization on the concept and not the specific response a batch may give the filmmaker. Besides, I thought it was a simple matter, but given the fact that the more experienced members of this forum could not confirm or deny the exact points of my question, now I just "gots to know"!! Thanks anyway!

[Dominic Case]

OK, thanks to everyone who tried answering my question. I'll keep looking until I find the answer and post my findings back here. Thanks again!

I think you will be looking for a long time to find more of an answer than you have been given here. Perhaps you need to realise that the reason you didn't get a simple answer to your question is that it is unanswerable: because the original premise is flawed.

 

A sensitometric curve is designed to show you the curve shape for a typical emulsion and process.

 

As John has said, the exposure in a sensitometer for a particular emulsion is designed so that the 21 steps of the strip show the entire range of response, rather than with any precise mathematical relationship to the exposure of any other emulsion.

 

As I said, the recommended speed rating of a stock is based more on "what exposure gives a good-looking result" than the original scientific graph-plotting method that placed a certain exposure a certain density above d-min at a certain gamma. I'm not sure if the 0 point on the published curves has a precise relationship to the published EI rating - but John's post leads me to suppose not.

 

Your question - after discovering that there is no absolute significance of the 0 point on the exposure scale - is "well how do I know where to place my exposures?

 

As David said, shoot a test.

 

But if you want a little more . . . the graph that John attached to his post shows a logE scale as well as the camera stops scale. That tells you the actual exposure in log(lux-seconds). -1.0 is log (0.1). So that point on the scale is 1/10th lux second. At an exposure of 1/50th sec, that's an illumination of 5 lux falling on the emulsion. There IS science involved in the data they publish. But that's not enough to get a good-looking image on the screen.

[Giles Rais]

Dear Mr. Case:

 

"I think you will be looking for a long time to find more of an answer than you have been given here. Perhaps you need to realise that the reason you didn't get a simple answer to your question is that it is unanswerable: because the original premise is flawed."

 

The premise of my question is simply to find out the premise used by Kodak to place the 0.0 camera stop along the Log E axis. If there is no quantifiable relationship between these three scales (Density, Log E and camera stops), the flaw would be Kodak's by including them in the same graph.

 

"A sensitometric curve is designed to show you the curve shape for a typical emulsion and process.

 

As John has said, the exposure in a sensitometer for a particular emulsion is designed so that the 21 steps of the strip show the entire range of response, rather than with any precise mathematical relationship to the exposure of any other emulsion.

 

As I said, the recommended speed rating of a stock is based more on "what exposure gives a good-looking result" than the original scientific graph-plotting method that placed a certain exposure a certain density above d-min at a certain gamma. I'm not sure if the 0 point on the published curves has a precise relationship to the published EI rating - but John's post leads me to suppose not."

 

It sure wouldn't hurt to find out IF there is a precise relationship, wouldn't it?

If I didn't know better, I would think that people somehow are trying to discourage me from digging deeper...is this a world wide cinematographic conspiracy?? : )

Maybe I can force Kodak to remove their camera stops scale from appearing integrated with their characteristic curves if they are not correlated at all (as well as asking them nicely to please make sure their curves match [nobody said anything about the discrepancies I found and posted here]). Again, thanks for the time and effort of putting up with me. See you soon!

[John Pytlak RIP]

As noted, the "Log Exposure" scale (lux-seconds) along the bottom is calibrated and traceable to NIST standards. However, the "Camera Stops" scale along the top was added as a guide for those who may have difficulty understanding the normal D-LogE type notations or what a "Lux-Second" is. But the "Normal" ("0" Point) is somewhat arbitrary, and is not a "standard".

[Luke Prendergast]

I can't add anything of scientific value to this discussion but I am very amused at at the ads at the top of the page that the clever advert-omatic is trying to match to this topic.