I can buy Durst Laborator 900 + colour head from someone who is selling his dead father equipment. He can't operate the enlarger at all and has no manual. I checked the enlarger, it is mechanically OK, but I can't focus the image... I have tried all the knobs and lens plate, but image is still out of focus. I can set focus in the half way from the head to the board. As far as I know, L900 had dedicated lenses Schneider or Redenstock, but the set I could buy do not contain them (I used my el-nikkor 50mm). Does L900 work only with original lenses?
Thanks in advance for help.
kris

I don't know that enlarger but if it is 4x5 enlarger which the other laborator enlargers are, then it may be won't focus a lens with that short a focal length. On my L1200 I need to use a recessed lens holder for a 50mm lens to allow it to focus. The holder is called a siriotub. If you were using a flat lens holder that could be the problem.

I have found some pictures of L900 here: http://www.irgendeine.de/durst/. You can see original lens plates called BIMAPLA 5039 (50mm lens and 39mm mount) and BIMAPLA 8038. Unfortunately, in the set I can buy there is no BIMAPLA 5039 there is only SIRIOPLA 39 (it's plastic but looks like BINAPLA 5039). Do SIRIOPLA and BIMAPLA differ from each other so much to get such hirrible out of focus image?
Thanks for response, anyway

well the siriotub on my L1200 is only approx 3cm deep but without it won't focus a 50mm lens. It doesn't take much as the bellows is at full compression without it.

You should not have much problems obtaining a Bimapla 5039 (here for example - http://cgi.ebay.de/OBJEKTIVPLATINE-BIMAPLA-5039-DURST-VERGROSSERER_W0QQitemZ200185419138QQihZ010QQcatego ryZ15424QQcmdZViewItem)

It is common for enlargers that can handle larger negatives to require a recessed lens holder when using a 50mmm lens for 35mm film.

Good luck, Bob.