Alphabet Soup? Help

[dancqu]

Is it normally the natural log or the base 10 log?
I thought the latter - with one stop being 0.3, not 0.7?

It's base 10. That base to the .3 power = 2, to the .6
power = 4, to the .9 power = 8, and on, doubling the value
with each additional .3.

More often than not exposure is not in the log format. I also
see EVs, ZONEs, and STOPs. I think 1, 2, 4 , 8, 16, 32, and on
would also due.

Perhaps the log format is used because of it's mathematical
manipulativeness. Dan

[gainer]

The purpose of all this technicality is to get the scene brightness to register on the film so that proper development will produce a density range that fits the printing material. It's nice when it happens by plan instead of accident, but the possibility of accident is why we have different paper grades.

[Helen B]

"More often than not exposure is not in the log format. I also
see EVs, ZONEs, and STOPs."

If you think about it, they're logs too. Base 2.

Best,
Helen

[fhovie]

"More often than not exposure is not in the log format. I also
see EVs, ZONEs, and STOPs."

If you think about it, they're logs too. Base 2.

Best,
Helen

That would be true for exposure but isn't tranmission density in base 10?

I have received a sign from above - it appeared on my 361t - LAMP FAILURE!
I guess that means I have to go shoot real pictures again .... (the new one is on order ... $80 from XRITE -ouch-)

[Helen B]

Frank,

I thought that we'd already agreed that Log E and density were logs to base 10 - that was all sorted out on page 1. I was referring to EVs, zones and stops. They are all base 2 logs of relative exposure.

Best,
Helen

[dancqu]

EVs and ZONEs most obviously. Dan

[john_s]

How do you generate CI? if the SBR is 5 and the DR is 1.25 - what is the CI? and how do you get it - also - I know from my step wedge that my grade 2 paper can print a DR of 1.25 - What if I do a kalitype - I need a DR of 1.75? I am always reading about CI differences from AZO to Silver to Alt process. How do you calculate CI?

The CI is the fraction DR/ER where the term ER is the Exposure Range as a log(base 10).

In this example, the ER is 5 x 0.3 = 1.5. Each "stop" is an exposure difference of 0.3. Another way is to say the brightness range is 32 (2^5) and log(base 10) of 32 is 1.5 (actually 1.505 if you want to be unnecessarily fussy). DR is already in log(base 10) units.

So CI = 1.25/1.5=0.83

[gainer]

As a matter of interest, sensitivity of human vision is pretty much logarithmic. The just noticeable difference between two brightnesses is a nearly constant ratio. There's a lot more to it than that, but it's a good approximation over the usual range of adaptation.

[fhovie]

Thanks John

The CI is the fraction DR/ER where the term ER is the Exposure Range as a log(base 10).

In this example, the ER is 5 x 0.3 = 1.5. Each "stop" is an exposure difference of 0.3. Another way is to say the brightness range is 32 (2^5) and log(base 10) of 32 is 1.5 (actually 1.505 if you want to be unnecessarily fussy). DR is already in log(base 10) units.

So CI = 1.25/1.5=0.83