I just finished Erwin Put's Leica Lens Compendium. I found it to be a very thorough, clear, well organized treatise on optics and a review of most of tne M

I just finished reading Erwin Put's Leica Lens Compendium. What a marvellously thorough yet concise treatise on optics and all the M&R Leica lenses! Most of the points were self explanatory or came to me with a bit of thought. I was however unable to figure out how to easily detect a focus shift in the R system lenses. The example would be the 100mm APO Macro. I understand the concept of a focus shift and realize that it is inconsequential for the most part EXCEPT that is for macro. Therefore, is there a simple way to detect focus shift when you change apertures??? Thanks....

-- Albert Knapp MD (albertknappmd@mac.com), March 03, 2002

Answers

The only way I've ever done it, and only with large format, so I don't know how it'll work with 35mm, is to focus AFTER stopping the lens down. That gives you an accurate representation of how things will be when the picture is taken. I can imagine this would be much easier with a loupe on 4X5 than through an SLR viewfinder.

-- Michael Darnton (mdarnton@hotmail.com), March 03, 2002.

Why not focus on a target subject and take a series of slides at various apertures and compare them? If there is a focus shift that is significant it should show up. If not then you can probably assume that it is simply one more to the list of things that make for interesting reading in a lens compendium, but are otherwise insignificant for practical photography.

-- Jay (infinitydt@aol.com), March 03, 2002.