VCCE Assistance Needed

[mtnman]

While I know the difference between condenser & diffusion enlargers, VCCE heads are confusing me. Are they condenser or diffusion or a different animal? Also, I understand variable contrast but what exactly is constant exposure? Any help will be much appreciated. Thanks.

 

[pelerin]

While I know the difference between condenser & diffusion enlargers, VCCE heads are confusing me. Are they condenser or diffusion or a different animal? Also, I understand variable contrast but what exactly is constant exposure? Any help will be much appreciated. Thanks.

Hey,
VCCE is an LPL trade term. It refers to diffusion head that uses a dichroic filters to provide the color filtration necessary to vary the contrast. (the "VC" part) In the 4x5 models the pair of dichroics is used in conjunction with an ND filter. The ND filter compensates for the fact that increasing or decreasing the color filtration not only changes the color of the light but also affects the amount of light reaching the paper. (the "CE" part) A good example of how increasing the amount of filtration affects print density can be gained from the table of filtration values Ilford provides in their literature for MGIV.
Celac.

 

[JBDeal]

I have not been at this long but I do have LPL 670 VCCE. Diffusion -B&W only. Theoretically... you find your exposure f-stop & time>Constant Exposure< and just dial-up your perferred contrast. Mine has a 2 channels - one Kodak setting the other Ilford settings. Very simple & easy to use. Contarst is different than a condensor. I find that "normal" contast with VC paper is 3.5 and above on the contrast setting. I hope this helps a little

 

[jp80874]

I think (opinion here) that “normal” may have more to do with your film exposure in the camera and lighting conditions rather than the enlarger. From me (opinion again) on my LPL 4550 XLG VCCE, normal seems to be 2.5 on good lighting days. If I’ve shot on cloudy days, which are pretty common in northern Ohio, normal creeps up to 3 and 3.5.

This is using T Max 400 film, Rollo Pyro film developer, and Kodak Polymax F paper. I use Rollo Pyro because I will be doing some platinum printing.

John Powers

 

[Donald Miller]

Normal contrast has to do with film development rather then exposure. It also has to do with the exposure scale of the paper that one is printing on. The density range of the negative must correspond to the exposure scale of the paper.

When we adjust filtration with VCCE enlargers we are adjusting the proportion of majenta (minus green) and yellow (minus blue) with which we are projecting the negative onto the paper. As we increase the contrast upward to four and beyond we have virually eliminated the exposure with yellow (minus blue) to the point that only one of the two emulsions on the multigrade material is being exposed. Hence the need for increases in time at this contrast level.

VCCE light quality is best discribed as diffusion which is the same effect as cold light heads for all pratical purposes. Diffusion light is non-collimated and this is what causes the difference in contrast to a condenser light source which is collimated light. Collimated light is generally best described as having the light rays bundled and aligned along a common axis. Diffusion light sources do not provide this collimation.