G-Bar/CI/Density Clarification

[Arvee]

I'm finding conflicting information on this subject and hope someone can supply confirmed numbers:

Kodak says something like a CI of .58 for diffusion and .43 for condenser, a recommendation of 30% less development for a condenser enlarger (point source?),

Roger Hicks says something like a G-Bar of .62 for diffusion and .57 for condenser/diffusion, about a 10% reduction in development,
and there are other numbers in between floating around out there. I realize that G-Bar and CI are virtually identical but derived slightly differently.

I also realize these are starting points and I can find a workable number empirically but I would like to know if there is a reference(s) one can hang his hat on?

What are the recommended G-Bar/CI (or density) numbers for the following:

Diffusion/Cold light enlarger,

Condenser/diffusion (condensers with opal glass, which most condenser enlargers are),

True condenser (point source)?

And what is the reference/source of your information?

And, how valid is the old practice of reading a neg when placed on a printed page and observing a negative density of .8 when one can barely read the print through the densest part of the neg, which would be suitable for condenser enlarging?

And it also states a density of 1.1-1.2 (print just barely visible but not legible through the neg) are the target numbers for diffusion enlarging.

This practice is referenced by Phil Davis in BTZS, I have forgotten which edition.

I don't have a densitometer. I print with both diffusion and condenser/diffusion enlargers.

In college, we used the old Kodak 1A and went for a max density of 1.05 for Omega D2 enlargers, but I seem to recall that prints were typically 'hot'.

I need some idea of what the present day standards/recommendations are for each enlarger type.

Help, someone, please!

Thanks!

 

[jeroldharter]

I'm just asking: if you don't have a densitometer, how can these numbers be meaningful?

The general idea is that point light and condenser light sources are more contrasty than diffusion light sources so the negative can have a lower CI for prints on a point/diffusion light source.

You don't mention what format of film you print. What is the purpose of using two different light sources? Different formats? Obviously you will have to do your own testing which will be somewhat empirical without a densitometer.

 

[ic-racer]

We actually need a new word. Everyone is familiar with Exposure Index and understands how it is unique to your equipment.

Likewise, the contrast to which you develop your negatives to is personalized (ie your development time). Too bad the word "Contrast Index" is already taken (it is a specific way to measure negative contrast using a lucite "Contrast Index Gauge.)

I have been using the term "Personal Contrast" (which for me is slope of the linear regression of the first 11 datapoints above 0.1 on the HD curve) to be the analogy to "Exposure Index." Your "Personal Contrast" will, of course, vary depending on a myriad of circumstances (including the way you define it). You can use some of the published values as a starting point.

If you don't have a densitometer and sensitometer you can use trial-and-error. Simply increase you development time if you are always printing in the grade 4 to 5 range, or decrease you development time if you are always in the 00 to 0 range. If you can't make a good print on any grade of paper, you are probably underexposing your negatives.

 

[Arvee]

I was baffled by the variation in the numbers: Kokak says there are big differences in enlarger light sources, Ctein says there is very little difference and host of others in between.

I have arrived empirically at my development times for my different light sources and I don't see much difference.

My question goes to the conflicting information floating around out there. I am wondering if this is another myth or possibly carryover from the 'olden' days when enlarger light sources were somewhat different?

Surprising how some of these 'wives tales' persist for decades and there is no substance/underlying data to support the arguments.

Does everybody make allowances for the different light sources or not? If so, how much difference? Or do most folks print with diffusion/cold light sources and very few use condensers and therefore are not aware?

Still baffled!

-Fred

 

[ic-racer]

I have arrived empirically at my development times for my different light sources and I don't see much difference.

May have to do with how well your condenser lamphouse collimates the light. May be a few diffuse rays bouncing around in there

 

[Arvee]

Could very well be! I use a teeny-weeny M300 with a clear bulb/opal filter and an Omega B-22, which has the opal bulb. I think the Durst is closest to the diffusion head.

That M300 is almost like a toy but it is my fav for 35mm for either 5x7 or 8x10.

-Fred

 

[ic-racer]

! I use a teeny-weeny M300

Thats a neat little enlarger!