Rotelar 400mm f:6

<p>I have had this lens for years. It is in a barrel about 5 and 3/4 inches long. Since it is a telephoto design, how should I determine the optical center so that I can cut it in two for mounting in a shutter such a universal synchro #5. I know I will have to cut both halves down to accommodate the shutter thickness. The lens will cover 4x5. In the past I have had Rotelars for MF in 180 and 270 focal lengths and they performed quite well.</p>

<p>If it is a telephoto, the optical center is in front of the front element. Pretty much the definition of a telephoto lens.<br>

On the other hand, it if is a long focus lens, then the focal point is inside it. In which case, the optical center would be about 400mm from the film plane when the lens is focused at infinity. (Exactly if the lens is symmetric, not quite if it isn't symmetric.)<br>

You would want to put the shutter and iris where the image is smallest in the lens. That would require some rough ray tracing. Perhaps a laser pointer would help at that.</p>

 

<p>John, are you sure that the lens' elements aren't mounted in cells that can be unscrewed from the barrel?</p>

<p>FWIW, a couple of years ago I got a 270 Rotelar in Copal 1 as part of a bundle. Lip of front cell to cell's flange, ~ 66 mm. Lip of rear cell to cell's flange, ~ 55 mm.</p>

<p>I fear y'r project is an example of the corrupting power of found money, sorry, lenses.</p>