Mfgr's suggested Dev times and C.I.

[BradS]

I'm reviewing the data sheet for Kodak's "new" Plus-X (125PX) and comparing the mfgr's suggested dev times with the time-contrast index curves, it seems like regardless of what developer I choose, the time recommended by E-K is for contrast index of 0.5....

Does this seem odd to anybody? I always thought dev times should be long enough to give a CI of around 0.7. Developing for CI=0.7 would require significantly different dev time in most cases. Why would they do this? Are they making some assumptions about how the negs will be printed? I am really perplexed.

 

[BradS]

If you look at the tech pubs for the various developers, like this one for Xtol:

http://www.kodak.com/global/en/prof....16.14.30.14.7.20.14&lc=en#development tables


you'll see that they give development times for a range of CIs from .52-.85, corresponding to various EIs. The lower CIs (usually around.58) that correspond to their recommended development times, are their recommendations for printing with condenser enlargers, at rated film speed. Contact printing, or printing with a diffused light source, require higher CIs, and push processing gives higher CIs. Essentially, Kodak is saying that PX125 @ EI 125, should be developed to a CI of .43 for printing with a condenser enlarger, and that a CI of .7 would correspond to an EI of around 320 in Xtol. Does that make sense?

Jay

Hmmm, yes, I see your point and it does make sense. CI==0.43 seems really thin to me...even for a condenser enlarger. Is this just another instance of E-K being really conservative?

 

[BradS]

....Maybe we've all become contrast junkies!

Jay

Contrast Junkies...I like that.
Can I use that for the name of my Band?

 

[Stephen Benskin]

The equation for determining the required CI is:

Desired DR or Paper LER / log Subject Luminance range - flare

The DR - LER is based on the printing conditions (diffusion 1.05 to 1.10) (condenser .75 to .85). For Kodak's recommended normal processing, LSLR is bases on the statistical average luminance range of 2.2 or 7 1/3 stops. Average flare was 0.34 and is now considered 0.40.

If you are thinking about 0.70, you are really thinking about Gamma and not contrast index. Average Gramma is around 0.70.

 

[BradS]

<snip>
If you are thinking about 0.70, you are really thinking about Gamma and not contrast index. Average Gramma is around 0.70.

Ah-Ha!!!

That's it!

Big light bulb going on in my little brain. Thank-you!