Extending magnification range of PN105?

[Lou Jost]

Hmmm, where exactly did you put the extender on the PN the first time? The right place is between a properly-mounted lens and the camera; for the PN, that would mean having the PN on the proper extension to get 1x, and then adding the TC between that extension and the camera. I imagine that's what you did, but can you confirm?

[ChrisR]

A thought:
I've been surprised how well putting a teleconverter reversed on the FRONT of an MP-E65, works.
I haven't tried it with the PN. But who knows!? At one time we'd have been though silly to to suggest using a $50 Raynox with a $3000 objective.

[austrokiwi1]

Hmmm, where exactly did you put the extender on the PN the first time? The right place is between a properly-mounted lens and the camera; for the PN, that would mean having the PN on the proper extension to get 1x, and then adding the TC between that extension and the camera. I imagine that's what you did, but can you confirm?

As you said it was placed at the camera end of the bellows

[Lou Jost]

Austrokiwi, thanks for confirming that.

Chris, can you tell us more about that experiment?

[rjlittlefield]

The vignetting is due to exit pupil location. austrokiwi's TC must be designed for use with lenses whose entrance pupil is pretty far back, typical of telephotos. But with the PN on bellows, the exit pupil is so far forward that rays angled so as to hit the corners of the sensor, after being bent by the TC optics, in fact never get through the TC optics because they strike the TC too far off-center.

This effect is not limited to TC's. Any full-frame camera with an M42 screw thread mount will vignette if you mount a sufficiently long lens on bellows, because the hole at the mount will be about 39 mm while the diagonal of the frame is over 43 mm. The Nikon bayonet mount has a similar issue; even my thinnest wall extension tubes have a clear hole only about 41 mm. Using a thick wall auto tube in combination with bellows, on full-frame, almost guarantees vignetting with Nikon mount.

Of course in most practice this is no problem at all because it takes a lot of extension to make the rays angled so as to be blocked. That said, I have a collection of 35mm film left over from the late 1960's in which there is consistently a shadow of the mirror support on the edge of film, due to shooting with long bellows extension.

As for placement of the TC, well, a TC is just a strong negative lens, computed so that when mounted on the camera it serves as a Barlow lens that magnifies the projected image by the rated value. If placed in other positions, it has other effects.

Through sheer good luck, it turns out that sticking some TCs in front of an MP-E 65 produce a combo that has lower magnification with pretty good image quality.

I have also seen a TC used, by accident, in such a way that in combination with other optics it ended up constructing a Galilean telescope positioned in front of a camera's already long lens, resulting in a 3-piece combo that had ridiculously high magnification albeit only modest image quality. It was described in a forum post as "a macro of a flies head from over 5 feet away". Checking my emails from 2006, I find the combo described as Nikkor 70-210 + 1.4 tc, mounted in front of a CD1000 camera.

Fun with refraction...

--Rik

[nathanm]

Rik, your depth of knowledge is an incredible resource to the forum....

and on top of that, Zerene does a great job!

[austrokiwi1]

austrokiwi's TC must be designed for use with lenses whose entrance pupil is pretty far back, typical of telephotos

Its a Minolta MD 300 S. Although it will work with short focal length lenses( I have used it with a 7.5mm) it seems to work best with 85 mm through to 300mm lenses. So that is a confirmation of Riks point.

[rjlittlefield]

Rik, your depth of knowledge is an incredible resource to the forum....

A lifetime of confusion, with scattered moments of clarity. I try to share the latter.

Thank you for the kind words.

--Rik

[Lou Jost]

Great to have this explanation Rik, thanks. That's what makes this forum different from almost all other photography forums.