There are endless arguments about whether condenser printing or diffusion printing is best. Most of my experience is with diffusion printing with various color enlargers and most recently with the Ilford 500 head on an Omega D5. I tried the condenser head on the Omega, but not enough to gain an appreciation for it.

The Durst 138S has an excellent set of condensers. With the new enlarger I got a full set of the T condensers (T indicates they are coated).

Three LED Light sources for the Durst 138S.
From the left 1) Variable Contrast diffusion, 2) Variable Contrast condenser, 3) point light

When I first got the Durst I didn’t have any choice but to print my 5×7 negatives with the condensers. I was able to get good results and found that the conventional wisdom on the subject is generally true. They really do print the same negative with more contrast. Prints do seem slightly sharper. The grain is better resolved. Scratches and dust on negatives is more apparent. But the conventional wisdom is wrong that a diffusion enlarger means you don’t need to spot as much. Diffusion still shows the dust, and it must still be taken care of.

The biggest issue I had with the condenser setup is that I can’t use pencil masking techniques. This is due to the fact the condenser setup relies on focusing an image of the light bulb at the nodal point of the lens. By adding an opaque mask above the negative you get some very uneven illumination since the condensers can no longer focus on the lens. Also, I lost the ability to finely adjust the contrast grade with VC papers, due to the use of VC filters only coming in 1/2 grade increments.  This last part wasn’t much of an issue, but the loss of masking techniques was going to impact my printing.

So I built a diffusion light source for the enlarger, which is documented in a few posts. This is an LED diffusion head that has both green and blue LEDs for contrast control. This gave me the ability to print negatives with diffusion if I wanted to mask, but if I wanted the sharpness of the condensers I had to go back the old filtration control method with the hot tungsten bulb.

Another issue with the Durst 138S system is that it relies on large discontinued Opal bulbs. I have a few in various wattages now, and I found a PH/303 500watt bulb that works pretty well. The Opal bulbs are expensive and I doubt I’ll be able to find replacements as they get used up. The PH/303 runs pretty hot and requires a blower, which is a bit loud.

LED Condenser Light Source

I decided to build a head to get the advantages of the condensers along with the variable contrast control of the green and blue LEDs. I replaced the Opal bulb with a piece of milk glass that fits in the heat absorbing glass tray. Behind this I built an LED source with three green and three blue LEDs with the same specs as the ones used in the earlier head I built. I arranged these in a ring, alternating colors, on a piece of aluminum plate screwed to some aluminum angle iron. A few holes allow it to mount to the movable stage in the Durst head using the existing thumb screws. The plate also acts as heat sink. The LEDs were glued down with Arctic Alumina heat sink compound.

The Variable Contrast light source installed in the enlarger. Note the cable setup with a DIN plug mounted on the enlarger head wall and the quick connect plug on the light source.

Another view of the VC light source showing the opal glass installed in the heat absorbing glass holder. Milk plexiglass works just as well here.

I also installed a matching DIN connector in the body of the Durst light chamber so I can simply plug one of the cables used for the diffusion head into this and reuse my controller and the LED drivers.

I’ve only printed a few negatives with this system, but in testing it works very well. The light source is as even as the original bulb (corners are 1/4 of a stop dimmer than the center), and contrast control works as it should. Because of the efficiency of the condenser design it’s only a 2/3 stop slower than the diffusion head, even though it’s using 1/4 of the LEDs. I’m not sure what else I could ask for.

LED Point Light Source

The Durst has an optional point source lighting system, which I haven’t used or seen. It occurred to me that while I was messing around with LEDs that I could build one with a single LED, since they are very small (almost a perfect point) and very bright. I took a single CREE High Noon LED that I know gives a very good light for printing on VC paper with filters. I mounted this on a similar place of aluminum as I had for the other source.

This is used without the diffusion glass in the heat absorbing tray. The Durst system comes with controls to adjust the position of the bulb in three dimensions. Once I figured out how to position the LED I was able to get very even coverage over the whole frame. Every time you adjust the enlarger height you need to reposition the bulb. I now appreciate how well the Durst controls work for this.

So how does it work? Well you need to use contrast filters again since it’s a single white light. The single LED used as a point source is several stops brighter than the other light sources. It’s so bright I needed to add a neutral density filter under the lens. With a point source setup you need to use the lens wide open, so you can’t adjust the brightness using the aperture ring.

I printed the same image with grass that I used to try out the diffusion head. First print was very sharp, but odd looking. Took me a while to realize it was the pattern from the anti-newton glass in the negative holder. I removed the glass and made another print. This looked good. The point source is much sharper than the diffusion head and quite a bit more contrasty. It also shows every little flaw in the negative. There are a few odd areas that are on the negative and can be seen with a good loupe. These are barely perceptible on the diffusion print, but are almost glaring on printed with the point light source.

I don’t have enough prints made with this setup to know if I’ll keep using it. But I can see how it could be really interesting with some grainy 35mm film and large enlargements. Should be very sharp, and have clearly defined grain. I plan to experiment.

Conclusion

I now have three different options that all work well in the Durst 138S. I can use the same F/stop based controller for them all, and switching them takes only minutes. I can now choose the best lighting type for each image or printing situation.

What’s next? Well I may buy an LED star that has a green and blue LED in very close proximity. This might allow me to have a variable contrast point source. It’s possible thought that even a few mm offset would not align correctly. It will run about $20 to test that out. I also plan to spend more time making prints and less making enlarger parts.