How to calculate Tetenal's Beta

Kodak has CI, Ilford has G, And Tetenal has Beta. I know roughly how to calculate the Kodak and Ilford, but what is the formula for Tetenal's Beta? And before somebody tells me to look and Tetenal's web site for it I already have and cannot find it...

Greetings,

 

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The Gamma, or Contrast Index, should be the ratio of exposure to

density, per given film development. I'm not familiar with Tetnal's

Beta, but assume it's the same thing. If it is, then you would graph

the density vs exposure (using Log units) and find the slope; the

slope is the contrast index or gamma.

 

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While Tetnal's WEB site may not be of help, JOBO-USA is the US

destributor and they have very good technical support. If I remember

correctly their WEB site is JOBO-USA.COM and you can find an e-mail

address for their technical support (I think it's tech@jobo-usa.com,

or something like that.)

 

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Regards,

Beta has nothing to do with Tetenal, but is a standardized expression

of the the relation of the amount of light and the "blackening" of the

emulsion. The term has been used in sensitometry for a long time.

That's how you find it:

On a standard graph of the film you determine "point A", 0.1 log.

densities above base fog. This determines -- as everyone knows -- the

filmspeed. Then you determine "point B" on the graph, which received

30 times the exposure of "point A". You now can draw a triangle and

the tanges of angle alpha is refered to as "beta". It tells you how

steep the Line AB runs. Most film manufacturers used to state

developing times for beta 0.7 and beta 0.55. The first was considered

the optimum for diffusor type enlargers, the second the optimum for

condensor type enlargers. With a contrast ratio of 1:30 you would get

a negative that would print on a "normal" paper grade. 1:30

typically would be a landscape scene without direct sunlight. This was

a far superior system then to state a gamma of around 0.6-0.65 which

is most commonly done today, which will not give an adequate contrast

negative for optimum quality. This all may sound a bit complicated in

the description, on the standard graph it will become evident. Tetenal

has excellent literature which explains sensitometry.

Ok, that sounds like an explaination. So, if .1 density is zone I

then 30 times more exposure is roughly zone VI, right? So the formula

would be (zone VI density - 0.1) / 1.5 ? Or am I doing something

wrong with the math? Thanks again...

Someone came back to me in email and confirmed the formula.<br>

beta = (zone VI density - 0.1) / 1.5<br><br>I guess I have been

underdeveloping my negatives a bit. Now I have to go back and test...