Enlarger condensers - negative size or focal length?

[xtolsniffer]

I'm curious. I have an old Gnome Beta II enlarger that I use only for the 6x9 negatives I get from old folders (My LPL 6700 diffusion will only go up to 6x7, plus it seems appropriate to use an old enlarger for an old camera). Anyway, the enlarger has two plano-convex 4 1/2" condensers which I use with a Ross Resolux 11cm enlarging lens. From the admittedly rather vague instruction manual, it's also suggested that 2 1/4" and 3 3/4" condensers are available, presumably for different formats (though I've never seen them for sale, nor the elusive Beta II filter unit). This got me wondering. If the role of the condensers is to collimate the light, why would different condensers be needed for different formats? Or is it the fact that different formats need different focal length enlarging lenses? If the light rays are parallel going though the negative, why would you need a different condenser?

 

[photog_ed]

My Omega D2-V has a variable-focal-length condenser setup, with two fixed condensers and one that can be repositioned or removed to change the focal length. The instructions inside the lamphouse door tell where to position the movable condenser depending on the focal length of the enlarging lens being used. This indicates that the purpose of the condensers is to focus the light source on the enlarging lens, to maximize the brightness of the projected image and reduce stray light. This is more important for smaller formats. I have not tested this, but I suspect the condenser position for shorter focal length enlarging lenses will also provide illumination over a smaller negative area.

Ed

 

[wiltw]

The purpose of the different condensors is simply to focus all of the light on as large/small an area of the negative being enlarged. The relationship may be stated in terms of focal length of lens, but the coverage of the lens is selected based upon the size of the negative as well! By focusing light into a smaller area, it is made brighter thru the lens (whichever lens happens to be in position). My own 45V-XL specifies the source in terms of max film size which is illuminated, not in terms of lens FL.

 

[xtolsniffer]

I suppose if it's negative-size related, then if you were to use say a 110 mm enlarger lens with condensers for 6x9 negatives then there would be no reason why you couldn't just slip a 35mm neg in there instead. You'd get a pretty small enlargement but I guess in principle it would work?

 

[MattKing]

I suppose if it's negative-size related, then if you were to use say a 110 mm enlarger lens with condensers for 6x9 negatives then there would be no reason why you couldn't just slip a 35mm neg in there instead. You'd get a pretty small enlargement but I guess in principle it would work?

It will certainly work.
There are actually two different factors at work.
The first, and by far the most important, is that the condensers are chosen or adjusted to ensure even and complete illumination of the negatives. In addition, the choice tends to maximize the efficiency of the enlarger, by focusing the light nearly exactly to the negative area, and not larger. That efficiency may also limit flare.
The second, and normally of little or no importance, is that with some light sources - point sources in particular - the entire optical system is carefully calibrated to maximize contrast and acutance. Position and nature of the condensers is critical to that calibration. Point source enlargers have their role, but they also create their own challenges, and are not necessarily easy to use. They are relatively rare - I don't know that any of the several darkrooms I've ever worked in have ever had one.