Building an Imagon
I've seen a few adaptions of the Rodenstock Imagon lens to various medium format cameras. I've never been able to afford one for my rb67, unfortunately, so i think I should just make one. The lens itself is nothing more than a achromatic doublet, from what I've read. If that's the case, all I really need is a shutter/lens mount that will fit on an rb67 and a screw on diopter (and a tube to connect the two, of course), correct? As for the diffusion disks that come with the imagon, I could replace those with a set from mamiya's soft focus lens.
The problem is, I've no idea what I'm doing...
I assume that screw on diopters magnification is related to the focal length, so how does +1.0 or +2.0 translate into focal length? Will I have problems with the image circle being big enough? How do I figure out where infinity focus would be? Most importantly, where can I get a high quality, 2 element diopter?
Why don't you have a look at ebay and look for the 150SF ?
I got mine cheap.....
The 150SF and the Imagon are related, I will test both early september in Holland: I have the 150SF and got a 200mm for my Rollei SL66.
(and a 250mm for 4x5")
Basicly the Imagon is a kitted anachromat, a + lens kitted to a - lens, and both lenses are of diferent types of glas.
Well of course I could just buy the soft focus lens for the RB, but what fun would that be? :P the point of this project is to learn something, rather than to just get the final product instantly.
Agree, and after you made succesfully the learning curve how to use this lens starts..............
I have my 250mm since 1980.....
Just one thing: the Imagon has a flat focus field, not a curved one like the Lensbaby.
I will be doing some experimenting when I am back in Europe again: I want a Baby-Imagon for my 35mm.
several years ago a photographer named john siskin
wrote an article for view camera about building lenses and using them.
he was doing something very similar to what you are trying to do ...
you might find the view camera article helpful
don't forget the drain-strainer-fstop-thing instead of
the traditional iris with a single hole.
instead of diopters
you could remove lens cells from different lenses and use them.
i do that from time to time :)
Dioptre is a measurement of inverse focal length, so +1 is 1m, +2 is 500mm, +3 is 333mm, etc. Therefore a dioptre used for close-focus work would want to be a very strong one (at least +5) for it to have a focal length short enough to be used as a lens in its own right. You can stack them though, with a +2 and a +3 being very nearly the same as a +5. I don't know enough optics to say how well that will work but my suspicion is that stacking them like that will lose any a(po)chromatic properties.
As for aperture and bokeh control, you can buy a set of cheap holepunches from the hardware store and stamp your own arbitrary patterns out of thin brass sheet. If you wanted to be ultra tricky, try to get a bit of glass that is clear in the centre and darker towards the edges to use as an apodisation filter and you could build your own STF clone of the Minolta classic. There is nothing with better bokeh.
Thanks for the replies, everyone. Keep them coming. :P
Right now, for lenses I'm looking at a Nikon 5T/6T or a Canon 250d/500d. Both are two element achromatic close up lenses. I believe Schneider also makes lenses of the same design but they're even more expensive than the Canon or Nikon.
If I actually get this idea to materialize I'll try to keep this thread updated.
If you want an achromatic doublet how about an objective lens from an optic other than a camera?
I don't know what focal length you are after, but thinking telescope / binocular / microscope - something must be in the right area.
New objectives would obviously be very expensive but for this application I would have thought a discarded objective from a repairman would probably do the trick. I have a couple of old 50 mm dia. binocular objectives that I was given by a repairman to use a close up lenses for intricate work. I suppose they could be around about 5 dioptres, since they work as magnifying glasses, so maybe f=200mm? (I'm guessing, I haven't got one here with me) Is that of any use?
Something like that would be very useful. After some searching i've somewhat realized the impossibility of using screw on achromatic diopters, due to my budget. I'd have to figure out how to mount a bare lens. Though that's probably an easier problem to fix than my money situation. Worst comes to worst, I'll just use single element lenses and upgrade later when I have the money.
On that note, I think i've found my lens. I've got an old pair of binoculars that never get used laying around, so I unscrewed one of the front lenses, went outside in the dark, and I was able to get an in-focus image of the moon on the focusing screen of my rb67 just by holding the lens in front of the camera body. Its pretty small, looks like 35-45mm in diameter, but there's no noticeable vignetting on the focusing screen even at infinity, so the size of the image circle seems not to be a problem. All I need at this point is a crappy rb67 lens. Lets hope KEH has some nice ugly lenses.