I've been struggling for a couple of days now with a particularly dense negative which needs a little burning too. But since my base exposure was almost three minutes, I tend to get bored when it comes to burning in two more stops on the bright bit at the bottom and so on - and that is with the aperture wide open! I'm beginning to think that my lightbulb is about at the end of its life - but finding a replacement 240V 300W bulb for a Durst L138S is not easy.
So in a flash of inspiration I decided to try something really different: I bought a 15W low-energy bulb! Screwed it in the socket, turned it on, adjusted the placement a bit, and suddenly I had a full stop more light. Then I realised that this is essentially "cold light", and removed the heat filter: Another stop!
And then I messed around with lenses a little, and ended up swapping the 150mm with a 180mm, and the 200 condenser with a 240. The result was surprising, to say the least: More even illumination, and yet another stop more light. I would have thought the illumination would decrease, since the condensors illuminate the whole 5x7" and not just the 4x5" I was printing, but there's no arguing with the EM-10?
The drawback is the long warm-up time of the low-energy lamp, but since I had exposure times in the minutes anyway I can use a lens cap to start and stop exposure. After all, the 15W "bulb" isn't going to heat the negative much in 10 minutes, compared to what the old 300W bulb did...