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Old February 16th, 2006, 02:09 PM   #1
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screw mount lenses

Hey there all,

I've recently aquired Mr W. Kinneys very beautifully formed SG35. I'll post a proper write up (or add to the others) once its up and running properly, but for now I have a lens question on just that subject - getting started.

I haven't saved enough to buy a selection of Nikon lenses yet, but a friend has offered an alternative to tide me over until then.

He says he has a huge range of old screw-in lenses that fit his practica bayonet-mount camera body with a simple $2 adapter. I've had a look on ebay, and there are indeed adapters available that will allow a 42mm screw mount lens to attach to most all Nikon mounts. The only problem is that you won't find infinity focus with them - you will, however, find everything up to infinity.

So he suggests i buy a screw to bayonet adaptor, take his screw lenses, and use them on SG35 until i can save for Nikon or Nikkor primes - all I'll sacrifice for now is infinity.

Has anybody on here ever used such a setup with a 35mm adaptor? Has anybody even considered it or heard of it???

Any advice much appreciated - i'm a big time newbie in many respects and i've got a sneaky feeling that this all sounds too good to be true. In fact, i think i can almost predict your responses ;-)
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Old February 16th, 2006, 03:58 PM   #2
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I use my M42 screw-mount lenses with a Canon FD to 42mm screw mount adapter all the time. Steev Dinkins uses/used them also with his homemade adapter, I believe. They're nothing new.

Good try though :)
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Old February 17th, 2006, 02:10 AM   #3
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Damn...

...I am so weak. I'll come up with something more impressive next time...
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Old February 17th, 2006, 05:18 AM   #4
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The reason you can use screw-mount/M42 lenses on an FD mount successfully is that the FD mount is built around a 42.00mm lens registration distance, whereas the M42 lens registration is longer at 45.46mm.

If, however, you attempt to use a lens mount that has a LONGER registration depth than that of the lens you are going to adapt onto it (for example, FD lens at 42.00mm, onto an EF ("EOS") mount at 44.00 mm), you will have to either sacrifice infinity focus (you'll have built your own macro spacer with your adapter, basically), or have an optical element in the lens adapter, to compensate for this. Here is a picture of an adapter that lets you use the lenses and mount in the above example (FD lenses on EF mount):

http://static.zoovy.com/img/goshotca...covers_gsc.jpg

As you can see, there is an optical element in the center.
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Old February 17th, 2006, 07:37 AM   #5
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Thanks Bill...

...that adds a lot of clarity to what i'm learning about this.

You've mentioned FD's. In my quest to see if M42's will work on my Nikon mount SG35 I've just been down to my local camera shop where they found a boxed, unused 'Sunagor' Body mount for M42 to Nikon with a removable 'specially designed concave optic' built in. Do you think this optic is what you talk about compensation for longer registration depths?

Any advice much appreciated.
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Old February 17th, 2006, 09:28 AM   #6
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That will compensate for the back focus difference. But be careful. If this optic is not of very high quality the image quality will suffer. I have used a PENTAX Takumar 135/3.5 lens (M42) with an adapter from ADORAMA (for NIKON mount) on the LETUS 35 and obtained very good results..
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Old February 17th, 2006, 09:39 AM   #7
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Remember, with an additional lens in between the Nikon and the ground glass, this will change the properties of that lens, and likely widen its DOF as compared to without. It may only be subtle but i have seen this happen when i was experiementing with condenser lenses between SLR and GG. Just something to look out for.
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Old February 17th, 2006, 05:55 PM   #8
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I've already got a 55mm screwmount lens from Ebay on the way, and I'll probably be ordering more in the future. Right now I'm going to use an adapter between the Nikon mount on my 35mm adapter (also currently in progress) and the lens, but eventually I'm going to add the Thorlabs coupler to my adapter, at which point I'll be able to step from the M42 thread directly to the coupling tube, and just adjust the length of the tube depending on whether I'm using the Nikon mount or the M42 lenses. So I get infinity either way. :D
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Old February 17th, 2006, 07:54 PM   #9
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Wayne / Quyen,

If you can offer a PENTAX K mount version, then the screw mount lenses can be used with out any optical element, because they are equal in the back focus. Only a mount converter is required.

A K mount will allow the use of many K mount lenses and Screw mount lenses with the SG35 and the LETUS 35.
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