Aperture setting when using reversed lens ?

[AndrewC]

When using a reversed lens (say an El-Nikkor 50mm f2.8 ) reversed on a bellows, what aperture setting do you use ? I know that most lens when used conventionally have a sweet spot at about f8 to f11 but I'm not quite so sure when reversing them.

[rjlittlefield]

The sweet spot depends on magnification, and it's generally at a wider aperture when the lens is reversed than when it's used normally.

I haven't tested that exact lens, but other people have reported a sweet spot around f/5.6.

See http://www.photomacrography.net/forum/viewtopic.php?t=424 and http://www.photomacrography.net/forum/viewtopic.php?t=676 for some discussion of things to think about.

--Rik

[AndrewC]

Thanks for the answer Rik, it seems like most of the lenses work best one or two stops down from wide open. I'll run my own series of tests once my current eBay shopping spree bears fruit but it is always nice to benchmark against others.

Andrew

[Cyclops]

The problem with reversing a modern fast lens is that one end is bigger than t'other. The lens is asymmetrical so that when reversed you end up with a smaller aperture(the rear of the lens is now the front element and its 2 lot smaller than the true front element) This isn't too bad if you have good TTL flash and its digital but on older systems it can be a nightmare,especially with wide angles,which give the highest mag. I remember doing this with a 24mm on a film camera and having to factor in the pupillary magnification factor then work out the new subject to flash distance by hand!
_________________
Canon 30D | EOS Rebel 2000-film(aka EOS 300) | Panasonic FZ-7 EB | Vivitar/Cosina 100mm f3.5 macro lens | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Vivitar Series 1 19-35 f3.5-4.5 | Slik 88 Tripod. | My new blog:
http://mybackyardsafari.blogspot.com/

[rjlittlefield]

Ah yes, the "good old days" of film, when one did elaborate calculations to figure out what should work best, bracket around that to cover the likelihood that the calculation was not correct or not appropriate, and wait from hours to days to discover which setting in the bracket really did work best.

Somehow I don't miss those days at all.

These days, I find that theory is still critical to understanding what varies with what and where the fundamental limitations lie, but experiments are so quick and easy that most questions like "what's the optimum aperture" are best answered by just trying them.

In the specific case of the EL Nikkor 50 mm f/2.8, the lens is definitely asymmetric (the rear element is very strongly curved), but the pupillary magnification factor is so close to 1 that it's not an issue.

--Rik

[Cyclops]

Thing is if i want to do true macro I have to use the Canon which is a film camera,i so wish i could afford to upgrade to a DSLR!
_________________
Canon 30D | EOS Rebel 2000-film(aka EOS 300) | Panasonic FZ-7 EB | Vivitar/Cosina 100mm f3.5 macro lens | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Vivitar Series 1 19-35 f3.5-4.5 | Slik 88 Tripod. | My new blog:
http://mybackyardsafari.blogspot.com/