A note about opal bulbs in general. Try, if possible, to get a real GE or Philips. Many times if you're ordering a PH-xxx bulb on a website the picture will show a GE bulb but what you'll actually get is a piece of crap "Eiko" thing from China or wheverever. These are notorious for having very non-uniform opal coatings, particularly on the top of the bulb - concentric circles, spirals, wavy patterns etc of higher/lower density. With a condenser enlarger, these irregularities WILL show up on the baseboard. I experienced lots of problems with this in my old Omega B66. I still have a pile of crap bulbs I couldn't use. Don't cheap out on the bulb.