I am planning on using it on an APS-C XSi. I would need a helicoid if I don't use the original backplate (which I do have but contains small welded on parts which may get in the way of a simple filter. The T43 came off of a Smena Symbol with the shutter button behind the lens itself.) Wouldn't a helicoid increase the distance of the lens from the sensor too far away for it to function - not even considering focusing to infinity..
Even if you use the thinnest helicoid, you may only be able to focus very close to the subject. Thus, limit the use of the modified lens in macro photography.
