I recently picked up a De Vere 54 enlarger for a bargain price. It’s a 1950s machine, designed to take 5×4″ negatives. In order to use the light most efficiently when making large prints, the enlarger is fitted with a condenser to give parallel illumination to the negative. However, the flip side of a condenser enlarger is that you have to match the condenser to the lens you are using and you have to match the lens to the size of negative you are using. It is usual to use a normal lens for enlarging your chosen negative format, so that’s (approximately) 50mm for 35mm negatives, 80mm for medium format and 150mm for large format (5×4″). Every time you change negatives, you have to change lens and condenser. The condenser in my enlarger is not labelled but is probably designed to work with 150mm lenses, and also seems to work well with my 135mm lens. However, when using any other focal length, there is extremely bad light fall-off on the print.
I made a 10×8″ print from a 6×9cm negative using a 75mm lens and the print only had sufficient density in the central area of the print, tailing off almost to white in the corners. Lighter areas mean not enough exposure was given to the print. For comparison, the left hand image was scanned directly from the negative while the right hand image was scanned from the print.
Given that it is expensive and difficult to get hold of different condenser lenses for this enlarger as it went out of production in the 1950s (not to mention the size and weight of the condensers, and the pain of having to change the condenser each time you change the lens) I decided to convert this condenser enlarger to be a diffuser enlarger instead. This will basically involve:
- Removing the condenser lenses
- Inserting some kind of diffusing material to provide even illumination
- Painting the inside of the lamp house and condenser chamber white to make a mixing box
- Replacing the light bulb with a more powerful one, as diffusion enlargers are more wasteful of light
Removing the condenser is easy enough. The enlarger head comes apart into chunks and the condenser lens set simply lifts out. It’s a big ol’ chunk of glass, about 8″ across.
I decided the best places for diffusion material to go would be in the filter drawer, and in the bottom of the condensing chamber – just above the negative. This is pretty much how the mixing box in my old LPL C7700 was constructed. So I ordered two sheets of Perspex online – one translucent white and one frosted transparent. The filter drawer takes 5″ square filters so it was easy to make these.
Slightly harder to make were the filters for the condenser chamber. They need to be circular to fit in the hole and have small overhanging tabs to support them. Again, I made one white and one frosted so I can choose between them later.
Upgrading the light bulb was an easy job. The enlarger came with a 75W pearl light bulb, and I replaced it with a 75W halogen reflector. Not only does the halogen bulb give more light output, it also directs it all towards the diffusers and the 95mm reflector on my chosen halogen lamp is almost as wide as the top of the lamp house.
Finally, I came to the less-easily-reversible step: painting the inside of the enlarger. From the factory, the insides of the various components were either painted matt black, or the same hammerite teal as the outside. Interior reflection just isn’t necessary for condenser enlargers. Diffusion enlargers have a white mixing box where the light bounces around before hitting a diffuser and then illuminating the negative, so I decided to paint the interior of the lamphouse and condenser chamber in matt white to aid this.
While I was making these modifications, I made a number of test prints at different times. Here are some scans of the test prints for comparison.
The exposure of these prints is well-off; they were only made quickly for comparison. The prints are from a 5×4″ negative which uses the largest possible area (i.e. if these are fine, smaller negatives will be fine too). All were made at grade 2 with 14 seconds of exposure. I varied the aperture in whole-stop increments, just to compensate for the differing amounts of light that each method of diffusion let through.
|1||Both diffusion layers were the clear frosted type. Interior of enlarger was in original black. Halogen reflector lamp.||f/16||Fairly bad light fall-off in the corners|
|2||Both diffusion layers were the clear frosted type. Interior of enlarger was repainted white. Halogen reflector lamp.||f/16||Didn’t really have any effect. Possibly even made it worse.|
|3||Same as print 22, but I switched the halogen reflector bulb back to the tungsten pearl bulb.||f/11||The pearl bulb is over two stops slower than the halogen!|
|4||Top diffuser was clear frosted, bottom diffuser was translucent white. Interior of enlarger was repainted white. Halogen reflector lamp.||f/8||Changing the lower diffuser to the white one helped enormously, but costs about three stops of light, compared to print 2. It also has lower contrast.|
Test print 4 has a pretty even illumination. It’s not perfect, but the effect is minimal and easily cured with minor edge burning. As I mentioned, these test prints were made from a 5×4″ negative so when printing from a smaller size, the problem will be much reduced anyway.
I’m a little disappointed in the amount of light available through the translucent white diffuser. The larger the negative, the more light that is available (imagine the negative as the light source) and the smaller the print, the brighter the concentration of light upon it. In this case, with a large 5×4″ negative and a small 10×8″ print it still took 14 seconds at f/8. The enlargement time will only get longer if I want to have smaller negatives or larger prints, or if I want to stop the lens down more.
In the future I may try to find some perspex that is a little thinner than the 3mm sheets I used for this, and perhaps less optically dense than the translucent white (but more diffuse than the frosted clear). For now, this setup gives me sufficiently even light and allows me to work with all my negatives.
Another possible idea I’ve had is to put a semi-opaque dot on the front of the halogen reflector lamp, like you see on car headlights bulbs. This means that light cannot leave the bulb in a forward direction from the filament directly, which causes a brighter area in the centre.
Having the opaque cap on the front of the bulb (or in my case, painted on the front of the reflector window) means all light that leaves the lamp must have been reflected from the curved reflector, and should be more even. It shouldn’t have a central bright area. Obviously I will have to think very carefully before painting the front glass of the reflector bulb, since it becomes very hot.
If the modification works, it may mean I’m able to get away with using two of the clear frosted diffusers which let more light through. If I decide to make this modification, I will write about it here. For now, back to the darkroom!