Quote Originally Posted by Kevin Kehler View Post
I have found on my colour head that moving the knobs, it is possible to move the alignment of the head slightly so that the second blast of light makes my pictures ever so slightly unsoft. Or, the head is still vibrating when I start the exposure and it is completely out of alignment. Under the lens filters was my solution. So, if you are going to use the filters in the enlargers head, do so slowly/carefully and give it 5-10 seconds to make sure it is not moving when you start the exposure.
I also use under the lens filters rather than the colour head settings. I posted in a similar thread recently about my experience with establishing reliable highlight times when changing colour head settings which can lead to frustration, more test strips and wasted paper. Some people enjoy struggling with complexity but I find using Ilford papers with Ilford multigrade filter gels simplifies the path to a good print.

As a generalisation, diffuser heads mean longer exposure times and what I would call more "smoothness" in rendering of grain rather then less contrast. This is usually most evident in expanses of clear sky. It is worth experimenting with the same negative at the same enlargement in both. I prefer condenser for some images and diffuser for others but it's not about contrast, which can be managed, more about the content of the negative and subject matter.