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Making a Topcor UV to Nex mount adapter

This post covers how I constructed a Topcor UV to Nex lens mount adaptor so that I could use my vintage Topcor UV lenses on my Sony Nex 6 mirrorless camera.

A couple of years ago I purchased a Hanimex Topcon RE Auto camera and a couple of lenses from eBay UK. The camera was sold as ‘For Repair’ and at the time I purchased it I could see by the pictures that it was going to take some work to get it back to working order.

Topcor UV to Nex adapter images

Well, after I took delivery I found that it was in an even worse state than I thought. The Mirror had become separated from the plate which flipped it up during exposure and the plate itself was bent and had been pulled off the rod it was supposed to pivot on. It was also partially dismantled, with the lens mount in pieces, and not all the bits were still there as far as I could see. I decided the best thing to do with it was to make it a donor camera to fix another RE Auto, or possibly another Topcon camera and had a look at the lenses instead.

There was a Topcor 53mm f/2.0 and a Topcor 135mm F/4.0 as well as a UV mount 2x convertor. I thought at the time these would all be useful additions to my growing Topcon collection, joining my Topcon Unirex and Topcon IC-1 along with the 28mm f/4.0 topcor and 50mm standard lenses I already have.

Recently, I began thinking about these lenses and looked on-line to see if I could find an adapter to use them on my digital cameras, but unfortunately adapters are not made for these lenses. I suspect this is  because of the design of the lens, the aperture adjustment being a part of the camera lens mount rather than fitted to the lens itself. This makes any adapter more tricky to make and since the lenses are not that popular, I guess no commercial company has bothered making one.

And then I thought, ‘Since I have some Topcon parts laying about, what’s to stop me making one?’

And of course the answer is, ‘Nothing’!

So I found the actual lens mount part of the old RE Auto which has the aperture adjustment on and sure enough it will attach to the bayonet mount of the lens, click into place and adjust the aperture. The bayonet release on the lens will allow it to be removed so all I needed to do was find a way of attaching this lens mount on to an existing camera adapter at the correct distance and it should be ok.

Ideally I would like to make an adapter to fit on my Fuji X-T1, but since this process would probably ruin an existing adapter I decided to try to make one for my Nex 6 instead because I’m less likely to need those adapters again.

First I looked up the registration distance of various cameras to find which adapter I had which would work.

  • Pentax K-Mount = 45.46mm
  • Pentax M42 = 45.46mm
  • Exakta = 44.7mm
  • Canon EF = 44.0mm
  • Minolta MD = 43.72mm
  • Topcor UV = 54mm

Of all the adapters I have the Exakta is the only one I don’t actually use (I bought it because I bought an Exakta camera and then the guy I bought it from just didn’t send it) and also gives me a bit of room to work with when making the Topcon mount fit.

To see if it looked likely that I could make this work I took the Exakta adapter and the UV mount and tried holding them together with the Topcor 135mm set to f/4 (its widest aperture) fitted to the mount. This showed me that the combination would work, but the lens focused well beyond infinity so I needed to add a bit of distance if I could. I found the part of the camera that the lens mount would fit on and tried adding that into the trial. With these three pieces in place the trial was better and although the lens still focused slightly past infinity it seems good enough for what I needed.

The lens mount and the piece it would normally have fitted on were simple to fit together because they already had threaded holes which aligned, so the only problem was how to fit the lens mount plate to the Exakta mount. I did that by simply drilling holes in the top plate of the exacta mount adapter in the same places as the mounting holes in the lens mount plate and used tiny bolts and nuts to joint them together. To allow room behind the Exakta top plate for the bolt heads, I drilled bigger holes in the body of the mount to give clearance.

When I bolted the lens mount plate to the Exakta top plate I sealed the nuts onto the bolts with some superglue so that they wouldn’t come free easily and then screwed the UV mount onto it’s mount plate with the three screws originally used for the job in the camera.

With the pieces all bolted together I’m pleased to say the lens fits nicely on to the mount adapter and both the aperture and the focus can be easily adjusted. The focus is still a little bit beyond infinity at the furthest, but it’s better to be that way than can’t reach infinity.

Since I can remove the original Exakta top plate and attach it to another Exakta mount adapter, I could also buy one for my fuji x-t1 and try the Topcor lenses on that camera as well!

I’ll probably post a few example pictures which I’ve taken using this combination in a future post.


I’m a software developer by profession but I’ve been taking pictures since I was about 8 years old. In that time I’ve owned cameras of all types and sizes from 120 roll film thro’ 35mm to my current Pentax K-5, Ricoh GXR + P10/S10/A12 28mm/A12 50mm, Canon S95 and recently acquired Sony NEX 6.


  1. BL says:

    I have an old Topcon Uni that is not running, and I recently purchased a Sony Alpha a6000. I have two UV Topcor lenses I would like to try on it, UV Topcor 1 : 2 f=53mm (5473080)
    UV Topcor 1 : 4 f=100mm (9712353). Any idea which adapter I would need to try this with the Uni

    1. Hi BL – which ever adapter you use as the basis for the conversion you are going to have to do some work to get the registration distance right or you will have problems focusing. On my adapter I got the distance a bit short, but that meant I couldn’t focus as close as the lens was designed for – that’s better than being the other way unless you only want to use the lens for macro. I made mine by removing the lens mount from the topcon first and seeing what size it was and then padding my exakta mount to get the distance about right – I guess you need to first remove the mount from your uni and do the same.

  2. TF says:

    Hello! I have 3 Topcor UV lenses (35 f/3.5, 52 f/2, and 135 f/4) and I was wondering if it is possible to get them to mount to a Nikon f mount. I’m pretty new to all of this, but these were my grandpa’s old lenses and they are in great condition still. I was hoping to get some use out of them both on his Topcon Auto-100 (which works great still!) and on my Nikon d3400. Would I need to salvage parts from another auto-100/Uni?

    1. Hi

      It’s unlikely that you would be able to get them to work on your d3400. The Topcor UV lenses have no aperture control because that is fitted to the camera, so in order to get the lenses to fit you need to remove that part of an old scrap Topcon camera and fit it to an adapter which fits your camera. Although that is do-able, the lens would sit too far away from the camera to focus at infinity, so the lenses would only work as macro focusing lenses. The reason I could get it to work on my Nex 6 is because it is a mirrorless camera.

  3. Orlando ANGEL says:

    Hi. Great post.
    Which camera did you take the aperture control from?

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