Convertable Question

I have a Symmar 135/5.6 that if you use the rear element only gives 235/12. So far so good. Then I notice that both elements have the same thread. So what happens if I take the front element and screw it into the rear of the shutter? :confused:

My guess is a focal length & f-stop range between the other two, but I don't have enough of the theory to know if that's correct or not. I really need a copy of Kingslake I fear... ;)

I'll probably try it anyway just to see. Still, any ideas?

Thanks!

William

Most true convertable lenses have equal abilities with either front or back elements, which is to say, not quite as good as the whole lens. By all means try the front element alone and see what you get. It will probably be very close to using the rear element alone. Another sub-class of convertable lenses are called triple-convertable, and these have distinctly different focal lengths with the front or back elements used alone and of course, a third focal length with both elements used together as the whole lens.

Look forward to hearing your results. Experimenting is great fun, after all by using the front element, you can't break anything.

You get a rather poor 260mm f:14.

Try using the front element alone instead of the rear element alone, and leave it on the front. It is a somewhat different focal length. If you stop down to f:22/32 or lower (use the existing aperture scale for the longer option, it is close enough) I think you will be surprised at how well it does work. Double check the focus with a loupe after you stop down and before you take the picture. The conventional wisdom is that using half a convertible Symmar gives you a fuzzy picture. Sometimes it is best not to accept the conventional wisdom as wisdom and try these things for yourself.

It would be a not very good triple convertible, emphases on not very good.