Quote Originally Posted by Mainecoonmaniac View Post
So all good lenses will hold the same focus throughout different magnifications?
I can't speak for too many enlarger lenses, but the ones I use hold their focus as you stop down, that is, they seem to show no focus shift: El-Nikkor 150 (both the old, knurled one, and the superior new one), Rodagon 150, Rodagon 135, and Apo-Rodagon 80. Like others here, I find it easier to focus wide open, in my case with a Peak magnifier, then to stop down. This way I can see if anything is not parallel, for example, focus at one edge might be off while the other is fine if I titled the lens stage without returning it properly to zero, or if there's an issue with the way I inserted the carrier. I also re-check focus after stopping down and before making exposures, in case anything has shifted etc.