[ovim]

Sorry about the title.

I've bought and repaired quite a few lenses recently and thought I'd give a conversion from one mount to another a try. So I was looking around for some Olympus OM lenses (register distance close to K-mount=easy conversion), but then I found a Vivitar Close Focus 2/28mm in Canon FD-mount for BIN £19.90 and without much thought I bought it. I knew there was a pretty big difference in register distances (M42/PK 45.46mm vs FD 42mm) but I thought I'd give it a go.

So after the packet from UK reached Finland I had myself a used but fully working Vivitar Close Focus 2/28mm with a filter with the sellers fingerprint on it



Then I chose an "organ donor" to get a mount from. An M42 Praktica 4.5/80-200mm Auto Zoom with hazy inner elements was my choice as it's mount part was about the same diameter as the Vivitar.


to be continued...

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Last edited by ovim; 11-24-2009 at 01:36 AM. Reason: Edited title to be more informative

Hope it goes well and I'll be watching with interest.

[ovim]

Thanks Dom, it did go well. Actually the lens is on my K200D now, focusing to infinity and all.

Next I opened the Vivitar from the mount end. The Canon FD breech-lock was quite complex but the good thing about it is that there's a lot of stuff under the aperture ring (as you can see in the side pic in my prev post) . So I was thinking maybe by removing all the breech-lock parts I could get closer to the right register distance for Pantax.

Here's the mount-end opened. I carefully removed all the parts and saved all the small screws and springs because I thought there might be use for them later.

Before removing all the parts I made notes and drawings and calculated how much I would have to shave from the end of the lens to reach the correct register distance.

Now I had taken apart everything I could from the mount end, and also increased the register distance by a little bit. But I couldn't get any further as there was no screws left to open. I also had tape over the rear element to protect it


So it was time to go in through the front. At this point I started making small markings on every part removed to help to put them back the right way.

I'll be right back.

[MattGunn]

I have sucessfully converted 3 lenses now. For one I used a mount from a donor lens which worked quite well but for the last two I have used flanged M42 mounts which are dirt cheep and are remarkably accurate.
OM lenses are quite easy as the registrstion distance is longer than pentax so you have an extra 0.5mm to play with. I posted my Zuiko OM conversion in the https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/34323-zuiko-lens-club.html

I have only attempted one conversion on a lens with a shorter registration distance than pentax. This was on a Vivitar 55mm macro in Konica AR mount which has a shorter registration distance even than Canon at 40.7mm. This lens had a lot of material to spare at the back and I managed to remove enough with my lathe to maintain infinity focus. This lens appears to have an aperture mechanism which gives linear area displacement so it may be possible to make it work as an A lens.

Good to hear Cannon conversions are possible, I have seen a few cheep Cannon lenses I wouldnt mind having a go with. I have 2 more Zuiko lenses to do first though...

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Last edited by MattGunn; 11-21-2009 at 03:29 AM. Reason: Lazy typing fingers...

[ovim]

Mattgunn: I saw your conversion on the Zuiko club and it was posts like yours that really inspired me to try this. I don't have such fancy tools but I think I did alright.

The front barrel/hood/filterthread part was screwed on so it came off with a little twist.


Next I unscrewed a silver ring holding the front group, and lifted the front group assembly.


After removing the silver ring I saw three screws and after unscrewing those I could lift avay the aperture mechanism/rear group assembly.


Next under the beveled edge of the focus barrel I found three screws. I spent a day finding a way to unscrew them. My smallest philips head screwdriver didn't fit through the angled opening between the bevel and the aluminum focusing helicoid (seen on the second pic of this post). And even if it did I'd have to turn it at an angle.

After not getting any good ideas I took a small flat screwdriver and was able to open the screws even though I had to turn them from an angle. Now I could remove the focusing barrel.


On top of the aperture ring there's another ring with the DOF scale held in place by three setscrews. On the side that faces the aperture ring theres also a hole for the spring/ball that clicks against the detents on the aperture ring. I carefully removed all these to reveal three screws on the main barrel under the DOF scale ring. Here you can see my markings (scratches on both parts) to help the re-assembly


After unscrewing these three screws I could lift the focusing helicoid assembly and was left with the rear end with some aperture related parts in it. Actually there was a thin aluminum ring that rotates with the aperture ring in there but apparently I took it out before taking this pic. I'll show it later. And that yellow oof thing in the background is my sons potty.


When removing these small screws and such I usually wrap things that go together inside a piece of clear tape. I store these small "packages" in a small jar/box. This way they stay together and organized and I might even write something on the tape like "set screws from under the dof scale ring" (in finnish of course ) to help when trying to remember which three screws were which.

btw one should actually use JIS -japanese industrial standard screwdrivers with these lenses as the head is a bit different from philips but I don't have 'em and I haven't stripped a screw yet.

[pacerr]

btw one should actually use JIS -japanese industrial standard screwdrivers with these lenses as the head is a bit different from philips but I don't have 'em and I haven't stripped a screw yet.

Ahh, you're not tryin' hard enough!

H2

[jadedrakerider]

Wow, Ovim! What a great way to put a dead systems glass to work!

I recently found a K/AR (Konica, I think) Vivitar 135mm f/2.8 (Komine made) at a Goodwill, and thought what a pity that all the great glass from these other systems won't be able to see the light of day. The optics were pristine, too!

If you were to put a price tag on the conversion, would you do it and how much would it be? It would make scoping out eBay a bit more exciting.

[MattGunn]

The vivitar K/AR lens I converted to K mount last weekend took about 5 hours work with the right tools and equipment including a small lathe. If I were to charge a remotely sensible rate for my time and facilities (£10 per hour would be pretty cheep, you would expect to pay upwards of £30 per hour for a professional) then the conversion would probably cost at least £50 plus parts. It is therefore probably not worth paying to have anything but the most specialist lenses converted. For something like the Zuiko shift lens it might be worth having a conversion done as there are few equivelents in pentax compatible mount.
However if you have the skills, equipment and time then it can be worth doing just for the satisfaction.

[ovim]

If you were to put a price tag on the conversion, would you do it and how much would it be? It would make scoping out eBay a bit more exciting.

Although I really like tinkering with lenses, I couldn't start doing this for money for a number of reasons:

I can't really put a price on this kind of work. This conversion took about three weeks (I worked mainly at night after kids had gone to sleep and I didn't count the hours). Most of that time I spent just thinking as I had some problems with the aperture which I'll explain in my next post hopefully later tonight. If I started counting the hours and wanted to get proper compensation for the time spent the price might get on the high side.

As all lenses are different I could not guarantee the results.

Also as I basically work on my kitchen table with pretty basic tools/materials I can't quarantee how long these hacks will last in real use.

And the biggest reasons are aged 2 and 5. As I already have a fulltime job and two small kids I really don't have much spare time (I'm also renovating part of our house which is supposed to be done in time for christmas)

So for now I'll do this just for myself.

[ovim]

MattGunn: I was just about to pm you about jadedrakeriders question but I see you beat me to it

...it can be worth doing just for the satisfaction.

This is exactly the reason why I do these things. You can't beat the feeling you get when you've repaired/built something with your own hands. Especially if you beforehand were unsure if you could do it or not

[MattGunn]

And the biggest reasons are aged 2 and 5. As I already have a fulltime job and two small kids I really don't have much spare time (I'm also renovating part of our house which is supposed to be done in time for christmas)

I have very similar time contraints to you except that mine are 2 and 8. I am in the process of buying a house so the forseable future will be spent renovating, I'll have to get all my conversions done before I move

[jadedrakerider]

The vivitar K/AR lens I converted to K mount last weekend took about 5 hours work with the right tools and equipment including a small lathe. If I were to charge a remotely sensible rate for my time and facilities (£10 per hour would be pretty cheep, you would expect to pay upwards of £30 per hour for a professional) then the conversion would probably cost at least £50 plus parts. It is therefore probably not worth paying to have anything but the most specialist lenses converted. For something like the Zuiko shift lens it might be worth having a conversion done as there are few equivelents in pentax compatible mount.
However if you have the skills, equipment and time then it can be worth doing just for the satisfaction.

Wowzer. I didn't realize how much money that would be. Still, might be quite a good hobby!

[ovim]

Next I started the actual modification. After removing the breech-lock mechanism I still had to get rid of about 2.5mm (don't remember the actual amount but it's not far off) of the rear of the lens to meet the right register distance.

I started with the M42 mount from the Praktica zoom. The mount was easily removed from the lens by unscrewing four screws.


I removed all the parts from the inside of the mount and once again saved all small screws. I didn't have access to a lathe so I carefully Dremel:ed, filed and finally sanded (sandpaper on a piece of glass) the underside of the mount flat. I measured the thickness of the flange left around the screwmount with a caliper and filed/sanded until the differences were <0.1mm.


Then I started working on the rear end of the lens itself. There was a ~3.7mm "step" at the rear end (seen on the 5th pic of my last post with pics) which I decided to shave off. My mount part was now 1.3mm thick so if I got rid off the 3.7mm I'd have sand the mount part down to 1.2mm to reduce the total lenght by 2.5mm (to reach the correct register distance). So I sanded /measured and sanded some more off the mount. The rear part of the lens was easy because I just removed the "step" and the mount part would rest against the flat part which I knew to be straight as it had not been touched by me

Removing the "step" started with a Dremel. Here you can also see my exact technical plans

And after everything was filed down it looked like this. The mount part is also on the left. The paper under the parts has an exact lifesize print of the original rearend, I used it as a reference to attach the aperture linkage parts to the underside of the mount once I had attached it to the rearend


Next I drilled three holes on the mount part and on the rear end. I tapped the holes on the rear end to accept 1.6mm screws. At this point I had also made sure that once my threadmount was mounted to a camera the aperture ring (and focus) index would point up. Then I attahed the mount to the rear end with three 1.6mm screws.

Edit: Here's a picture of the mount after I had attached it to the rear end of the lens. The screwheads were countersunk so that they'd be on the same level with the flange. I couldn't use the original screwholes on the mount as they had gotten too big during the thinning of the mount flange. Here I was testing how the rear elememt would fit the new mount. As you can see the opening in the mount was just about the right size. The black round thing is a collar that goes around the rear element. It was a perfect fit.

[ovim]

Now that I had the screwmount attached I assembled the focusing helicoid and the aperture/elements assembly to test infinity focus. To my surpise my calculations had been correct and the focus confirmation lighted up when focusing to infinity.

I was thrilled but then I looked at the aperture mechanism and noticed that I had the aperture ring which revolved an aluminum ring inside the rear end of the lens and then nothing happened. The aluminum ring rotated but it didn't touch anything.

I concluded that originally the mechanism was something like this:

When aperture ring was turned the aluminum ring moved something inside the breech-lock mount which moved the u-shaped aperture linkage on the underside of the mount-end which moved the the small aperture pin on the lens/aperture assembly.

And all these breech-lock parts were on their way to the trashcan:

[ovim]

I edited one more pic and some text to the end of the post #13.

So I had a problem. I had an aperture ring which moved ~12mm from one end to the other. Then I had the aperture pin on the lens assembly which moved only 4mm from one end to the other. I needed to come up with a way to connect these two and transform the 12mm movement on the aperture ring to 4mm movement on the actual pin closing the iris.

Here's the complete lens assembly and the aperture pin and it's spring. (Seen from the rear)


On the original mechanism there was a u-shaped part which moved the aperture pin. The part with two screws is meant to stop the linkage from moving too much.


Here's the rear end of the lens complete with the aluminum ring which rotates when the aperture ring is turned. The fork at 6 o'clock is at the end of the u-link and is meant for moving the aperture pin. (this pic has been photoshopped from a pic which had already some conversion done)


Although I didn't have a clue how to make the aperture work I had decided to put the u-link and it's stop back in. So I drilled and tapped the holes needed to screw the parts to the inside of the mount.

Next few days I spent thinking. In the evening I watched TV with the mount in my hand and I was just turning the aperture ring back and forth. Finally I thought of a simple solution with which I would not have device complex linkages or try to calculate anything.

It's pretty hard to describe this but here goes:

First (the green arrow)
I added a spring (held in place with two screws) which pulls the u-link against it's stop.

Then I attached a piece of (red) plastic with a screw and a roller on it to the far end of the u-link (attached with two screws from the underside of the u-link).

Then I carefully filed from the inner circumference of the aluminum ring so that as the aperture ring was turned the roller would roll against it and move inward/outward. And this inward/outward movement at the other end of the u-link would cause the fork at the other end to move the aperture pin.

This is an early version, I ended up lenghtening the piece of plastic with the roller on it to get more leverage.


In order to make the iris work I had to reverse the aperture pin spring (1st pic of this post). Originally the normal position for the iris was to be open. I changed the spring from one side of the pin to the other. It was easy as there already was a hole for the screw that holds the spring also on the other side. Now the iris was normally closed.

Here's the final version of the modified aperture mechanism.