I'm assuming you're talking about the distance between the lens and the paper when enlarging an image. The higher the enlarger head is, the softer the image gets. You need to adjust the contrast and add more time.
Originally Posted by Quinten
But the "less sharp" doesn't mean blurry just to be sure.
If you're using 35mm negative, 50mm is the normal setting and give you the closest range. If you go up the number, you simply have to raise the enlarger head higher, and that makes everything less stable.
And as you said if you're trying to make real large prints, the 50mm is the best way. You could use 63mm or 75mm for compensation, but you have to watch out the height for the head to go up.
I use 63mm lens, and that's flexible for all the sizes of the images I normally make (on 8x10, 10x12, 11x14, and 16x20" sized paper). But when I go for real large prints (16x20" and up), I will have a 50mm lens as an option, and when I go as small as 5x7" or so, I will switch to a 90mm lens, so I don't have to lower the enlarger head so much.
If you can't see your grain sharp enough, that probably has to do with either the focusing system on on your enlarger or the grain focuser itself. Also, if you're using the Omega D2 or LPL 7700 types of condenser heads, you have to set the condenser lens according to each specific lens type, otherwise you will have trouble focusing the image.
And if you're getting the edges of the image blurry, you have to close down the apature on your lens. Stay with F8 or higher numbers, though it depends on how the image appears. But anyway a 50mm lens is what you need.