[rollei_list] Re: TMax 100 Development
----- Original Message ----- From: "Jan Decher" <Jan.Decher@xxxxxxx> 
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, October 20, 2008 8:50 AM
Subject: [rollei_list] TMax 100 Development
Thanks for the expert answers on my TMax 100 question. Looks like there are some real photochmical experts on this list. I will try the D76 1:1 approach. If I like the TMax characteristics I might also try the TMax developer, but some chemicals hard to get here and 
developer shipping is restricted.
Riachrd, is a "diffusion enlarger" the same thing as a "cold light enlarger" ? I have an Aristo cold light head for my Omega B22XL but never actually tried it. I certainly have lots of B&W negs that 
appear to have too much contrast for the condenser head.

Jan
Cold light enlargers and most color head enlargers are diffusion types but there are plenty of older enlargers using incandescent lamps and a diffuser like ground glass which are also diffusion types. Most condenser enlargers are partially diffusing, they typically have a large lamp with a highly diffusing surface (so called opal lamps). This diffuse light is imaged on to the enlarging lens by the condensers. These produce perpaps one paper grade greater contrast from negatives with silver images than diffusion sources. The reason has to do with the scattering of light from the relatively large silver grains of the negative. In a condenser system most of the light striking the negative comes from one direction and some of the transmitted light is scattered away from the direction of the lens while in a diffusion system the light comes from a hemisphere (assuming a perfect Lambertian diffuser) so some light is scattered away as in the condenser system but much is scattered _toward_ the lens. The ratio between the density as measured with collimated light (condenser approximates this) and a diffuse source is called the Callier number and the effect is known as the Callier effect. The smaller the particals and the thiner the emulsion layer the lower the Callier number will be. So that the dye particals in color film have virtually the same contrast regardless of the quality of the illuminant. While fine grain film should have somewhat less Callier effect than coarse grain film, in practice there is not enough difference in practical pictorial films to be significant and the one paper grade factor seems to be close enough. Note that the _shape_ of the tone rendition curve is _not_ affected so that exactly identical prints can be gotten from either type of enlarger or from either type of negative by adjusting the contrast of either the negative (by varying the development and adjusting the exposure accordingly) or by adjusting the paper grade. While a diffusion head may make your high contrast negatives easier to print I would resort to one only if you can not get acceptable prints by simply adjusting the paper contrast. If your negatives are consistently too contrasty reduced the amount of development. Try about 15% for tabular grain films (Kodak T-Max, Ilford Delta, Fuji Acros) or about 20% for conventional films. If that is not enough go up to about 25% for t-gran and about 33% for conventional films. That may be too much but will allow you to find the approprate value. Also, while B&W is not as critical of temperature as color film it is still sensitive so make sure your thermometer is reasonably accurate. If you have the ajustable dial type its probably out of adjustment. There are very accurate electronic thermometers availabe for reasonable prices (much less than for a calibrated mercury thermometer) and should be used as a secondary standard for adjustment or calibration of your working thermometer. Most of the electronic types will not take immersion so I recommend not using it directly. Agitation is another often overlooked factor. Agitation makes a lot of difference in development results. The method is not as important as being consistent but I generally follow the method suggested by the development charts where one is specified. Kodak and Ilford recommendations vary a bit. Also, remember that the effective speed of the film will vary with the development so, if you want to keep the maximum density about the same you must adjust exposure. For a one paper grade contrast difference (either increase or decrease) the speed change will be about 3/4 stop for both tabular grain and conventional films. The ISO standard is written around a contrast index about right for diffusion printing while Ilford uses a non-standard variation that is about half way between the two contrast values and rates the film speed accordingly. 

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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