I have a problem that I hope somebody understands as I certainly don't. I have used an Omega D2V enlarger for more than 30 years with no problems. Last week I had to replace the bulb. To do that, I removed the large condenser in the aluminum enclosure and the condenser behind the opening door above that and then reached into the enclosure at the top and changed the bulb. I then replaced everything as I have done before but since then, I have been completely unable to focus the 50 mm enlarging lens that I have used for years. No matter what position on the column the negative carrier and the the condenser is, I can get only an unfocused blob on the paper. With a 75 mm lens, I can focus. With the 50 mm lens as the bellows is closed, the image appears as if it is coming into focus but never does. I have replaced everything several times and have done this many times in the past. This is a very simple machine and the answer must be very simple (and obvious) but I can't see it. Does anybody else?