In article <46l8sk$hdr@unix13.u-3mrs.fr>, ccsj says...
>I have an AHEL enlarger with and APO-rodagon and the grains are more >distinct in the middle than in the corner, there is a very small >difference, but i'm trying to have a besser result because i blew up my >photographs to 40*60cm. i guess it's not because of the lens but >because of the condenser.

Alas, the problem is almost certainly the lens. Since you are making
such large prints, I will not suggest my usual solution (using a longer
focal-length lens [being sure to adjust the condensers to fit the
longer lens]). My guess is that you are using the lens at a wide aperture to shorten exposure times. Try f8, even if that aperture requires a very long exposure time. You should see considerable
improvement in image quality compared with using f2.8 or f4.
Hope this helps.