Alphabet Soup? Help

[fhovie]

Could someone please explain the meaning of all those abreviations used in sensitometry ... CI etc. How are these generated? I can guess Dmax, Dmin B+F etc but many terms are used that still confuse me. Gamma?? etc

[Jeremy]

CI = contrast index

That is what I have always thought it meant, but I'm not sure so this is a good question!

[Jorge]

SBR = Subject Brightness Range.
DR = Density Range
ES = Exposure scale of the paper.
Gamma = Method used by Ilford to define the two necessary points to claculate the slope of the straigh part of a H&D curve. Similar to CI which is what Kodak uses.
Log E = Natural logarithm of the exposure. If we expose in units of light which double then the progression is 1, 2 , 4 , 8, 16, 32, 64, 128, 256. It is simpler to write the log than the numbers.
Lux= Unit of light measurement, I leave it up to you to see your physics book..

These are all I can recall off the top of my head, let me know if you need more definitions and which are they.

[Helen B]

"Log E = Natural logarithm of the exposure."

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

Thanks,
Helen

[Jorge]

"Log E = Natural logarithm of the exposure."

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

Thanks,
Helen

You know Helen I dont recall exactly, I remember many years ago sitting with a calculator and workig out the numbers, so it might be base 10. In any case it is simple to figure it out...no?

[Claire Senft]

dmin least density
dmax maximum density
bf base density + fog for a particularl amount of development
fb+f as above
SP speed point, the amount of exposure to xreate minimum density

[gainer]

It is the common log, base 10, that is used. Gamma was not first used by Ilford. It was employed many years ago by Hurter and Driffield and other research scientists to represent the slope of the straight line portion of the characteristic curve. If you only used that portion, gamma and CI would be the same value. Some films have practically no straight line. In any case, we use more of the curve than was thought proper in H&D days.

[Helen B]

The base 10 log is used for both the density and the exposure, with 0.3 being one stop. I wrote my previous post as a question because that seemed more conversational than a blunt contradiction. To be honest I find these internet discussions very difficult style-wise - I feel that I write in an overly harsh manner.

Best,
Helen

[fhovie]

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?

[Jorge]

The base 10 log is used for both the density and the exposure, with 0.3 being one stop. I wrote my previous post as a question because that seemed more conversational than a blunt contradiction. To be honest I find these internet discussions very difficult style-wise - I feel that I write in an overly harsh manner.

Best,
Helen

No need to do so, anybody can make a mistake and it is no sin to correct it.