Quote Originally Posted by Mr Bill View Post
Marco, I presume you're using VC paper? If so, does a UV filter, say a 2B or stronger, improve the focus situation substantially? (If no UV filters around, perhaps adjust for the softest grade possible.)
I still have the same questions - I am heading somewhere with this. The idea is basically that your VC paper may be sensitized well into the UV range. The enlarging lens probably isn't well-corrected for UV, so the result could be a significant focus error (you can't see the UV light). Ctein explored these ideas in detail in his book.