Way Beyond Monochrome 2nd ed. - some clarification needed please

[swmcl]

Just trying to get my head around things ...

I refer you to Figure 7 of the chapter titled, 'Customising Film Speed and Development' (pp.221 in my book)

My query relates to the feature which is noted 'exposure = 0.80'.

This is the amount of exposure that was required to produce 0.17 density above f+b I believe.

0.80 is 2.666 (2 2/3) times 0.3 which means 2 and 2/3rds stops does it not ? So it would mean the film was rated at say box speed of say 250 for the test and the test reveals a truer speed in the region of 40 or so ?

Am I correct ?

This would mean the reference of 0 on the graph correlates to a point 4 stops lower than 'Zone 5' ... correct ?

Two separate questions from the same graph.

Cheers in advance.

Steve

 

[Alan9940]

Hi Steve,

I don't have or have ever seen the book you reference, but...

0.17 above f+b is defining the exposure threshold of the film tested. That is, the minimum amount of exposure required to have any measurable density on the film. IMO it's a little high; I usually shoot for about 0.10 above f+b.

No clue what the 0.80 number means. Without the "exposure =" part of it I'd look at that number and think CI (contrast index) which is a parameter of development. Again, a little high if you're printing on graded silver gelatin papers; maybe close for variable contrast silver gelatin papers; and a little low for alternate processes such as platinum/palladium, gum, etc. Many folks develop their film to a certain CI, but I have always developed for a printable Zone VIII density. Btw, I'm talking about B&W film here.

I hope something I've said helps.

Best regards,
AlanH

 

[Nathan King]

I'll take a look at my book when I get home, if the co-author of the book doesn't respond first, which he probably will.

 

[Stephen Benskin]

0.80 is relative log exposure. In this type of example it relates to the differences in the step tablet densities. Let's say the step tablet is in 1/2 stop intervals (0.15), 0.80 is 5 1/3 steps from the densest step. Most step tablets have a 10 stop (3.0 log) range. Notice the last density point for the "Normal" curve has a relative log exposure of 3.0.

 

[swmcl]

Thanks all for your replies.

I'm not sure things are that much clearer for me. (It's me not you I'm sure ...!)

Silveror0 I am trying to relate it to the AA book too. It sure can be a head-spin !

 

[swmcl]

I've got an understanding that Mr Lambrecht is measuring the speed point at Zone 1.5. I believe Mr Lambrecht is also saying the correct speed for the film has been chosen when the density at Zone 1.5 is 0.17 above f+b. As I understand it, the Ansel Adams way is to measure the speed at Zone 1 and with a density of 0.1 above f+b.

Effectively, Mr Lambrecht is measuring the speed point a little higher on the curve.

For what its worth I think Mr Lambrecht is probably on the money with his methods for practical people.

I'm still no clearer on the 0.80 thing though ...

 

[RalphLambrecht]

Steve,I caught this on my laptop;later todayI'll get to my desktop ,can look at the book at the same time and will answer again

 

[RalphLambrecht]

Hi Steve,

I don't have or have ever seen the book you reference, but...

0.17 above f+b is defining the exposure threshold of the film tested. That is, the minimum amount of exposure required to have any measurable density on the film. IMO it's a little high; I usually shoot for about 0.10 above f+b.

No clue what the 0.80 number means. Without the "exposure =" part of it I'd look at that number and think CI (contrast index) which is a parameter of development. Again, a little high if you're printing on graded silver gelatin papers; maybe close for variable contrast silver gelatin papers; and a little low for alternate processes such as platinum/palladium, gum, etc. Many folks develop their film to a certain CI, but I have always developed for a printable Zone VIII density. Btw, I'm talking about B&W film here.

I hope something I've said helps.

Best regards,
AlanH

Alan is close,I try to make negatives with a tonal range from ZoneI.5 to Zone VII.5 and my target densities for those are 0.17and 1,37, respectively for atotal density range of1.2,which is roughly a grade 2 paper.I think the 0.8 value refers to negative contrast but again ,I'll check later to be sure

 

[swmcl]

Thanks Ralph. Looking forward to further discussions.

 

[Stephen Benskin]

The 0.80 relative exposure is part of how to determine the film's EI. The relative exposures at the 0.17 speed point from the different development times are plotted on a gradient/relative exposure graph (figures 12a - 12c). EIs for different gradients can then be calculated from the graph.