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Archive 2009 · Conversion process of a Konica Hexanon 57mm AR 1:1.2 lens to Canon EOS

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p.1 #1 · p.1 #1 · Conversion process of a Konica Hexanon 57mm AR 1:1.2 lens to Canon EOS

Upon request here is a writeup on most steps of the conversion of a Konica Hexanon 57mm lens to Canon EOS mount.

The register distance of this lens is much shorter than that of a Canon EOS. There will be a collision with the mirror of a not modified full frame camera like an EOS 5D.
On Canon EOS cameras with an APS-size sensor (crop factor 1.6) are no problems whatsoever, at least on my EOS 300D.

This lens is rare and can be found rather seldomly, at attractive prices.
There are not many photographers using it on an EOS camera.

I made no pictures from the beginning of the conversion and the major modifications have been done already when all photos have been made, so I hope it is possible to follow.
Please excuse the poor picture quality.

I can not be held responsible for any consequences as a result of my desrcription, be it wrong or right. Please use this guidance at your own risk.

- M42 EOS adapter
- Dremel tool and some drills (1mm and 2mm) and milling / grinding bits
- a belt sanding tool, or a lathe
- strong gloves with rubber coating
- some small precision screwdrivers
- a small spring
- grease (e.g. molybdenum grease)
- 2-component epoxy glue
- some thin piece of sheet metal, e.g. from the lid of a can

A) Remove the mount, keep the rear screws.

B) Remove all rings and stuff inside, but leave the little lever (a knob of 1mm) in place, and the ring at the rear of the "inner lens body" where the lever is solidly fixed to.
This unit directly controls the aperture.
I don't know any more whether opening of the outer lens body at this point is required to remove all unnecessary rings, but it does not really matter since you need to open it for the next steps, anyway.

C) In order to disassemble the outer lens body, first take a marker, set the lens to full infinity and make a clear mark over all outer body parts (namley the front element, the middle element and the rear element). This is done in order to find the correct position when you later re-assemble it. Just make a line from the front to the end, over all elements. Otherwise it can be very frustrating later on.


D) Remove the two pairs of screws from the rear and take the two little brass "splints" out. Store the splints and screws safely away, you'll need them again.


E) Take the gloves and, with the help of the friction they provide, unscrew the "front ring" (where the lens name is engraved).


F) Look inside the gap which became visible right now. It's between the front glass and the "front element". There are three screws which must be unscrewed in order to remove the "front element". You need a very thin screwdriver.


G) Everything is loose now, and it is possible to dismantle the entire lens (unscrew the helix).


H) Now take the "rear element". Obviously it does not yet look like the one on the picture.
Here, the real conversion starts.
The "rear element" needs to be sanded down. Take care to turn it continuously in order to maintain parallel planes! It will take endlessly and you better have a belt grinder or something similar, or you will become frustrated. If you have a lathe, you may use that.
From time to time, check to make sure that the aperture ring is always narrower than the part of the "rear element" which sits within the aperture ring. In other words, the upper surface of the aperture ring must sit slightly below the upper surface of the "rear element" (silver). Thus, it is ensured that you later have approximately the correct registration distance and that you will be able to turn the aperture ring.
Please note that grinding of the rear of the aperture ring is NOT required to such extent! (Don't grind it so much like I did, just leave it black in the outer parts and remove only the narrower part!)



I) There is a gap on one side where the aperture coupling will enter. Open this gap, i.e. remove the thin rim which will stay after grinding of the "rear element" (pictures above, on the right).

J) Now you can use the opportunity to clean the two helix threads properly, and then re-assemble the largest part of the lens. The three screws from step "F" are a pain in the a** but it is possible to put everything back together. Be prepared to repeat all of that a couple of times, if necessary. You need to do it at least one more time.

K) Take the aperture ring and form a small shape out of a metal tin in order to operate the little aperture lever.
You can see it two pictures above. Make sure it is long enough to reach the little aperture knob when the lens is fully expanded (close focus) and not so long that it collides with the "inner lens body" in infinity position. It must be straight so that there is no aperture shift when focus is changed. It took me two prototypes until I got it right. Be careful when you screw it onto the aperture ring; the two screw threads in the aperture ring are very fragile. Test the whole function while the mount is not attached - you can check the aperture opening through the front glass.

L) Since the lens is substantially shorter now, I could not make the original aperture click mechanism to work properly.
At least I was not happy with it after several different attempts to make it click nicely.
I went through a complete new assembly of my own click-stop mechanism. You'll need the clicks to hold the aperture ring against the spring of the aperture, which will otherwise always pull and close it.
To make such an own mechanism, first find a position in the aperture ring which is thick enough for a hole of 2mm (perpediccular to the lens axis!). There, make one mark on the aperture ring. Then, make corresponding marks on the rear body element, while you turn the aperture ring: one mark for every aperture where you want it to "click".
There, you must drill holes later on. You can see what I mean if you look closely at the next picture, where the holes are visible on the rear ring of the rear element. I made one mark for every full aperture plus one extra mark at approximately f/1.4.


M) Now take everything apart a second time. It is not nice - you know by now that it is a bit fiddly... Nevertheless I would rather do it, since drilling the holes while the lens is fully assembled may likely introduce dirt into the "inner lens body", which would be a pity.

N) Take the aperture ring and drill the hole through it. On the picture above you can see the hole - I put the long spring inside it.
Here it is 2 mm thick but until step "P" you better use a 1mm drill.
Be very careful during this step.

O) Take the rear part of the housing and slide the aperture ring over. Now turn the ring over each position from step "L" and drill with the 1mm drill through the hole which you made in step "N", straight into the "rear element".
Be very careful during this step.
If you make a mistake, you could try to fix things with some epoxy glue.

P) Take a 2mm drill and make the hole in the aperture ring wider.
Be very careful during this step.
If you make a mistake, you could try to fix things with some epoxy glue and re-model some material.

Q) Take a spring (I had it left in my box, from another lens). Clip it to the correct length (depending on the modulus of elasticity, it may be exactly the width of the aperture ring, or if it is softer perhaps 1 mm more). Glue it into the hole, but be careful to glue only the rear end, from the outer side of the aperture ring. From the inside, it must later press the small metal ball inwards, towards the "rear element".
Let it dry 24 hrs - it will not hold if you "load" the spring too early.

R) Clean and re-asseble all parts a second time. You may want to apply grease to the helix. Consider that there are types of grease which might not be suitable for a lens at all!

S) Take the M42 adapter and mount it on your EOS camera. Make a 12 o'clock mark (next picture).
You don't need to modify the M42 thread like in the picture.


T) Take it off and use the old Hexanon mount as a matrix to drill the holes. Make sure the aperture indicator is on top (align with the 12 o'clock position on the mount).

U) Use the Dremel milling bit and then grinding bits to work on the adapter so that the screws will not interfere with your camera mount, and that they can sink properly and will be flush with the surface.


V) Put everything together. Don't forget the aperture ring and the metal ball.
Be careful when you screw the EOS mount onto the lens, since the metal of the "rear element" became quite thin!
Now you can check for infinity focus. Make a few pictures and check on your computer.
If infinity is not reached, you must sand the lens body or the adapter (the flange from the lens side).
If you are at over-inf, you may fabricate a small shim and place it between the adapter and the lens.
However, if you followed step "H" it should be perfect or close to perfect.

A sample at f/1.4.
I am really happy with this lens and sort of proud that the aperture clicks are so nice ;-)
Have fun!


Jul 20, 2009 at 12:33 PM
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p.1 #2 · p.1 #2 · Conversion process of a Konica Hexanon 57mm AR 1:1.2 lens to Canon EOS

Thank you for the guide, Max. This lens has been on my "to-get" list for a while...

Jul 20, 2009 at 08:23 PM
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p.1 #3 · p.1 #3 · Conversion process of a Konica Hexanon 57mm AR 1:1.2 lens to Canon EOS

I just picked up a copy of this lens. My favorite thing is that it has half stop clicks, which is very rare for an SLR lens. I have an Autoreflex T3 coming to shoot it on. Thanks for posting the conversion process. I may end up coveting mine.

Jul 20, 2009 at 08:34 PM
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p.1 #4 · p.1 #4 · Conversion process of a Konica Hexanon 57mm AR 1:1.2 lens to Canon EOS

debuggerus: get it!

I love my Rokkor on a 5D, or my Zeiss 85/1.4 but I am not sure if I love the Hex on a 300D even more... perhaps because we went through a lot of trouble together (described above)

TWoK: Yes, but the half-stop-clicks are gone in my case, apart from an extra f/1.4. With some more effort it should be possible to restore them as well.

Some more samples:



And here's the combo:

Jul 21, 2009 at 02:12 AM

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