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10-28-2011, 03:01 PM   #1
Paul Friday
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Projection method for linking two lenses

I'm after the name of a method I've seen for using extreme wide angle lenses, so that I can find out more about it. I found it a couple of years ago and then promptly forgot.
It uses a normal lens mounted in reverse on the camera body, with the wide angle mounted normally in front. The two lenses are therefore base-to-base in relation to each other. This is not the usual macro method of mounting a single lens in reverse on the camera.
The outermost lens projects its image onto where the film plane should be, which (with care) coincides with the film plane of the lens mounted in reverse ont he camera body. This lens then projects the virtual image onto the film or sensor.
It's a method for using extreme wide angle lenses - like 3-6mm - without needing a clever design with a large back focus to clear the mirror in the camera body. The other advantage is that it places the wide angle lens well out from the camera, giving you space to get in close without your shadow falling in shot.

My memory says I saw it being used on video or film motion-camera bodies and it had a special name, like the 'xxxx' method or technique.

Any ideas?

(and by the way, I've tried it and it works)

Ta.

10-28-2011, 04:32 PM   #2
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What you are describing is called lens stacking. One lens is stacked on to the end of another using their filter threads and a double male adapter.

Its a method used by macro photographers to achieve higher than 1:1 magnification.

Typically, a 50mm lens reversed onto a 200mm lens mounted to the camera will produce a magnification of approx. 4:1

EDIT: RioRico is correct (read following post), I had read through the OP quickly, and it was late. I missed the 'base to base' reference.

I've never heard of this base to base coupling of lenses. The body to lens #1 adapter is freely available, it''s a reversing adapter. The female to female K mount bayonet adapter might be more difficult to source, but a cheap set of extension tubes could provide the components to make such an adapter.

Last edited by mannesty; 10-29-2011 at 12:01 AM.
10-28-2011, 04:59 PM   #3
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I'm sorry, mannesty, but as far as I know, lens-stacking is when the lenses are front-to-front, not base-to-base as Paul Friday asked. I have never heard of the base-to-base method. That sounds very interesting!! It's time for some research. Or maybe a videographer knows the term.

Last edited by RioRico; 10-28-2011 at 05:28 PM.
10-28-2011, 05:02 PM   #4
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I hope each of you will update this thread with what you find as I like Paul am interested.


Last edited by Colbyt; 10-28-2011 at 05:03 PM. Reason: grammer
10-28-2011, 06:09 PM   #5
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Some quick googling returned nothing useful, and I don't recall seeing this method in my macro bible, FIELD PHOTOGRAPHY by Alfred Blaker. So I'll keep my eyes open.
10-29-2011, 03:22 PM   #6
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Watching this thread with interest. It'd be a crazy looking adapter to pull something like this off. I've never heard of it being done either.
10-29-2011, 04:05 PM   #7
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In a typical projection setup the front (subject side) lens casts a real image that the camera lens looks at; this can provide very large magnifications with reasonable working distances. In practice back-to-back arrangement of the lenses helps set up because you know where the lens' focal points are in space.

If the distance between the lenses is less than the sum of the focal lengths a new lens is formed.

An easy way to explore this is with two bellows and two relatively short lenses - the shortest on the subject side.
10-29-2011, 06:41 PM   #8
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I would guess that with back-to-back (or base-to-base) stacking, whatever the method's name, proper distance between lenses is critical. Let's say I use two M42 lenses of 45.46mm register. I would guess that I would want their rear elements to be separated by 45.46mm spacing. The simplest way I can think of to achieve this would be 1) a 42-42mm m2m thread-reversal ring, 2) cheap M42 macro tubes, and 3) a 16-32mm focusing helicoid. The right mixture of tube sections, reversal ring, and helicoid, would allow adjusting to the right distance. But I haven't tried it, so I don't know for sure. I guess a 42-42mm ring is on my next shopping list.

10-31-2011, 10:11 AM   #9
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QuoteOriginally posted by RioRico Quote
I would guess that with back-to-back (or base-to-base) stacking, whatever the method's name, proper distance between lenses is critical. Let's say I use two M42 lenses of 45.46mm register. I would guess that I would want their rear elements to be separated by 45.46mm spacing. The simplest way I can think of to achieve this would be 1) a 42-42mm m2m thread-reversal ring, 2) cheap M42 macro tubes, and 3) a 16-32mm focusing helicoid. The right mixture of tube sections, reversal ring, and helicoid, would allow adjusting to the right distance. But I haven't tried it, so I don't know for sure. I guess a 42-42mm ring is on my next shopping list.
I think that you would need to have the front lens set so that the 45.46mm is the distance to the node of the reverse mounted lens, rather than the rear lens element, but I'm talking through my hat, so disregard.
10-31-2011, 04:27 PM   #10
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QuoteOriginally posted by Canada_Rockies Quote
I think that you would need to have the front lens set so that the 45.46mm is the distance to the node of the reverse mounted lens, rather than the rear lens element, but I'm talking through my hat, so disregard.
You're probably close. Some lenses have fixed rear elements -- those with a retrofocus group, likely -- and some float with the focus. Finding what actually works would be a nice project with different lenses.
11-01-2011, 09:01 AM   #11
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QuoteOriginally posted by RioRico Quote
You're probably close. Some lenses have fixed rear elements -- those with a retrofocus group, likely -- and some float with the focus. Finding what actually works would be a nice project with different lenses.
I would rather just learn to use what I have better than I do.
11-04-2011, 06:44 PM   #12
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In therory, if you are always using the same kind of lens the registration distance would always be the same and you would not need a helix in the middle. While I can see the advantages of having a helix in the middle (changing the effect, fine tuning etc), if you were lucky you might be able to build a simple one (if you were able to cleate one close enough to the proper length), just by combining the lens mount size of 2 diffrent macro tubes. Some cheap ebay macro tubes have male to female threads between the sections, while some have female to male. Of course there is no telling if two diffrent brands are going to have compatible thread sizes. I guess you could message the seller. I would message them anyway and ask if it is as pictured as last time I got a set, it was not and they said it was an old photo. It might take some searching and messging, but if you could find a male to female threaded set, and a female to male threaded set, you could have a changable (depending on which tube sections you use) pk-pk tube. It would also double as macro tubes too.

Here are examples of diffrent threaded ones (not sure if they both use the same thread size though).
Macro Extension Tube For Pentax PK K20D K10D KM K200D | eBay
Macro Extension Tube Ring f. Pentax PK K Mount Series | eBay
12-03-2011, 01:41 PM   #13
paul friday
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Thanks

Thanks for the replies.
I still don't know the name of the technique, which I would want if I hope to find out more about it. The original reference I saw was in using it on a cine camera. With a mixture of extension tubes, araldite and luck I can build a coupling that has a body mount at each end and is twice the normal flange to film distance. The plan then is to try some weird wide angles - like a C mount 6mm lens - and see what happens.
Have a go yourself - mount a lens 'face in' to the camera using a lens thread to K mount adaptor, then hold another lens the right way round in front of the set and move it around until you get an image. I will be inverted, but it does work.
It's similar to the way a submarine periscope works, relaying a projected image down a long tube.
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