I just purchased a De vere 504 with an Ilford 500H head. The enlarger is fitted with Nikon 50mm f2.8 lens.

The problem i have is that I can only get a sharp image when set the enlarger for a very small print. For a 35mm negative the image is only a few inches long side. Even then the bellows have to be closed tight. If I try for a bigger enlargement it is impossible to focus. I have tried a 6x7 negative and get the same problem but I can print a little larger - around 6inches on the long side.

I am using the correct light mixing box's and negative holders- changing them appropriately.

I took off the lens and checked to ensure make sure it was seated correctly and screwed into place properly. I noticed the back element was loose. I tightened by hand and replaced. I still have the same issue of not being able to get a proper enlargement.
Have I missed something basic in the setup of the enlarger ?