The filters that came with my enlarger are mounted in glass (acetate filter enclosed with two panes of glass that are taped on the edges). I mount my filters behind the heat absorbing glass. The heat absorbing glass in this configuration amounts to more "mass" to absorb heat. In your case if you are using filters that are conventional and not mounted in glass then I would mount heat absorbing glass directly in front of the lamp and then mount the filters in front of the glass. In order to keep costs down, I would probably use 1/4 in plate glass as heat absorbing glass. The light at this point is still "mixed" in orientation. It is only after it passes through the condensors that it becomes collimated.
Originally Posted by leeturner
Regarding the 138S, I would want to have all condensors. That would be two each 240s, one 200, one 160, and one 85 (depending on the lens(s) that you are wanting to use. If it comes with lenses so much the better. I would want the lens panels to mount into the turret. I would check to see that the table moves freely (up and down). That it moves freely when tilting. I would check that the head moves up and down freely and the same for the head focusing adjustment as well as the head tilt. I would check to see that the column isn't scarred from some previous owner attempting to adjust the head height with the locking screws screwed down. Check the head and table mount for "play" in the bearings. If it were me I would want the variable contrast filters. However these can be fashioned if not available. By way of price comparison, a 138S was bid to $560 US this week and did not sell because of reserve. That enlarger had only two condensors. I bought a 240 condensor this week on Ebay. Cost was $92.00. Cost of a remanufactured Durst 138 S from Jensen Optical (US distributor) is $5,300.00
The costly things about the 138S are condensors. And lamp conversion. The opal lamps are no longer available. Durst Pro USA has come up with a 1200 watt halogen conversion...cost is about $900.
This is, in my opinion, the premiere 5X7 enlarger today. My condensor enlarged prints have more sharpness, more local contrast, and better tonal representation then my diffusion enlarged prints.