View Full Version : changing the focus of a lens by removing the back element

13-Dec-2001, 20:09
I have heared and read about lenses that they can be diverted to a other angle b y taking of the back part of the lens.

is this right? I played around with a 270mm lens and I got only 1 plane that was sharp, and thi s was about 500mm from the lens, (1:2 ratio) how is the quality of chuch a set up?

thanks for your input

Neal Shields
13-Dec-2001, 21:22
Some of the old Protar lenses were designed to be used that way. They are symmetrical designs and you can use either element or both. It is suggested that you always put the element that you are using behind the diaphragm. Also you lose some of the ability of the lens to correct for things like chromatic aberration. Therefore it is suggested that you use a yellow filter or a ?zero corrector? when using a single element.

The only one that I am aware of that is still selling these types of lenses new is Ron Wisner. However, I don?t think he recommends using elements signally. I have an older Schneider ?convertible? which is either 150 or 270mm but most of what I hear is that it is an excellent lens at 150 but a compromise at 270. As I also have a 270 I have never used it in the 270 mode.

I suggest you check out Wisner?s web page he talks quite abit about this: Wisner.com

Ken Woodard
19-Dec-2001, 23:18
If you can find a fit a yellow filter behind the diaphram will help also. I have no idea why! Perhaps it helps with the blue spectrum.