Why are different lensboards needed for different lenses?

[geyes30]

Hi,

I am completely new to printing (have been doing the Develop-Scan-Inkjet Print routine) and I just got my hands on a Beseler 23CII XL. Was expecting something much smaller but for 40 bucks local pickup I am not complaining.

Anyway, I read in the Beseler manual that if I want to make prints of 6x6 negatives I need at least a 75mm lens. Why is that?

Secondly, the lenses also require different lensboards. What are the differences between the lensboards? They seem to have the same mount so my guess is that it has something to do with the distance behind the rear lens element. How hard is it to make my own lensboard? I have some spare extender tubes lying around so I figure I might be able to rivet them onto some plastic/aluminum plates.

Finally, is it at all possible to use M42 (or other mounts) lenses for enlarging? In particular, if my M42 lens is for a 35mm camera, will it work at all as an enlarging lens for medium format film?

Many thanks!!

Regards.

 

[MattKing]

Lots of good questions here. Some of these answers will simplify things somewhat.

The focal length of the lens will determine what sort of magnification you can do with it. With enlargers (and projectors) the shorter the focal length, the greater the magnification. A 6x6 negative is larger than a 135 negative, so it needs less magnification.

In addition, with the exception of certain special purpose lenses, the coverage of lenses increases with focal length. By that I mean that the longer lenses can be used to magnify from a larger original (negative) without the corners being blurred or vignetted.

The standard lens for 135 is about 50mm - both for cameras and enlargers. The standard lens for 6x6 is about 75 or 80mm - again both for cameras and enlargers.

As for lensboards, they tend to have the same exterior dimensions, in order to fit the enlarger. They vary, however in certain ways:

1) For some focal lengths they incorporate cones, in order to either move the lens closer, or farther away from the negative, in order to permit convenient focussing;
2) Some boards have built in threads, which the lenses screw directly into, while other have just a hole. For those, the threads at the back of the lens go through the hole, and a threaded retainer ring or jam nut is screwed on the back, to hold the lens on the board; and
3) different lenses have different threads at the back - some require a bigger hole on the board than others do.

A 39mm thread is probably the most common current size.

Enlarging lenses are designed to project short distances. Camera lenses are generally designed to work at much greater distances, up to infinity. A camera lens will usually be a poor enlarging lens.

Hope this helps.