[RioRico]

While sifting through the lenses I can't use, I came across a Petri C.C.Auto 55/1.8, the kit lens for some Petri SLR's. The aperture is stuck wide open. Except for that, this solid lens appears to be in great shape. It was free, and it is worthless, and I might as well try to convert it to a Pentax K-mount. That should be easy: remove the bayonet, cut away the protruding rim, and screw-down a flanged M42-PK adapter.

BUT... the bayonet is curious. Three lugs, with a screw hole in the middle of each. Flathead screws in two of those; removal is easy. But from the third hole, next to a red-marked index notch, a pin emerges, and that section of the bayonet shows no signs of coming loose. Only two other flathead screws are visible, one on the aperture ring, and one next to the A-M switch, and I am reluctant to remove those now.

Has anyone here disassembled this or any other Petri lens? I have searched for information but can find none. At worst, I could use a Dremel to cut off the bayonet, but I would rather try less drastic measures first. I am open to suggestions.

[RioRico]

'Tis now about 3.3 days later, 190 views of my post, and no responses. I guess nobody here is a Petri-head, nor raised in a Petri dish, nor caught in a Petri net. Whatever. Anyway, today I pulled out the old dremel (the lens surgeon's answer to chainsaws) and started HACKING AND SLASHING AND CUTTING! Oooh, such fun! And it turns out that the third lug, without a screw, was attached with... glue.

The remains of the lugged bayonet ring, and the collared base behind it, are easily removed. So now the base is all naked and everything, and I'm ready to attach a PK mount. My choice is between two M42-PK adapters: Bower-type infinity-focus, or flanged non-infinity. Registry comparison: Pentax is 45.46mm, Petri is 45.5mm. I dry-tested by putting the mounts in my ZX-M and holding the lens in place while peering through the VF, and the flanged adapter seems to not reach infinity focus, even with the Petri's basal hardware gone. A Bower adapter will have to do. Alas, it's too narrow to drill holes, so I'll have to secure it with... glue.

And I'm all out of superglue. So tomorrow I'll make a glue run. Stay tuned for further revolting developments.

[RioRico]

Next step: I looked closely at the hardware and noted that, with either M42-PK adapter glued to the baseless Petri lens body, lots of lens guts would still be visible. So I whipped out the Dremel and cut off the collar from the lens base. I didn't run for superglue, but used some Gorilla Glue to attach the flangeless Bower-type adapter. Clamp and wait a couple hours, then put the modded base back on the lens, then mount it on the K20D... and no infinity focus. Oy.

So I have a nice clean 55mm lens that's stuck wide open at f/1.8, good for closeups only. A couple test shots look like it's pretty sharp throughout the frame, with nice clean edges and good rendering. What do I have invested in this? The lens was free; the adapter cost about US$5; I used half of a US$2 cutting blade; and I've spent more time planning than doing.

And what are my options now?

* Live with it as-is. Sure, I can always use a(nother) dedicated portrait lens...
* Pull the base, remove the adapter, and glue the adapter to the naked lens body.
* Pull the base, remove the adapter, then throw the lens back in the junk box.

I'll worry about that tomorrow. I'm not going to the dentist. Life will be good.

[RioRico]

Time to wander back to this project. (I'm in no hurry.) As mentioned, a flangeless M42-PK adapter ring glued to the altered base piece pushes the glass out just a bit too far, so no infinity focus. I decided to try it WITHOUT that base piece. Luckily this Gorilla Glue is strong but not *too* strong, so separating the metal bit wasn't hard.

With all the glue cleaned off, I glued the adapter directly to the body base. Put a weight on the assembly in lieu of a clamp. Waited 4 hours. Tried to mount the lens. Hmmm, it won't go. Re-read the Gorilla Glue label -- ah, it EXPANDS as it dries! Scraped away some glue peeking over the adapter's edge. Tried a test shot, and it *almost* reaches infinity focus. I tightened it a bit for a better grip -- and the glue bond gave way.

But I'm on the right track, I think. Tomorrow I really *WILL* go on a SuperGlue run. And I'll apply an emory board to the surfaces, make sure they're really smooth. If this works, y'all can send me you excess Petri glass and unwanted Bower adapters. I'll put them to good use, I promise. Nothing too weird. Really.

[nlilith]

Thanks for posting this RioRico, at the very least it's an interesting read, and it may actually help someone in a similar position.

(I'm assuming pics aren't a possibility...)

[RioRico]

(I'm assuming pics aren't a possibility...)

Aye, so it'll be *pictures* you'll be wanting now, is it? Begorrah... Well, this started as a cry for help, not as a tutorial, and it's become more of a (lack of) progress report. But sure, I can provide some pictures, although I shot all these just now, not as the work progressed. So some are re-creations, especially those of the Petri mount before being totally dismembered.

First, the lens topside. Then, a recreation of the original mount. (That goo inside is the Gorilla Glue I didn't scrape off, inked to hide the mess.) Then, a comparison of Petri mount (base cap with lip, and bayonet ring) and the M42-PK adaptor. Then, the adapter sitting on the chopped base cap, which was all too thick. Last, the adapter sitting on the body base, where I'll superglue it tomorrow.

What I've learned from this exercise is that a Petri lens can be converted to PK rather simply. A small Phillips screwdriver to remove two screws, and a Dremel blade to cut away the third bayonet retaining pin. A cheap M42-PK adapter, and SuperGlue to attach it. At least, I *hope* the SuperGlue will work. That's all.

.

[albertoellobo]

I've one unit of this lens. My impressions was write in this article:

I up other picture made with her

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Last edited by Tom S.; 03-06-2015 at 06:57 AM. Reason: Link removed.

[udobam]

Aye, so it'll be *pictures* you'll be wanting now, is it? Begorrah... Well, this started as a cry for help, not as a tutorial, and it's become more of a (lack of) progress report. But sure, I can provide some pictures, although I shot all these just now, not as the work progressed. So some are re-creations, especially those of the Petri mount before being totally dismembered.

First, the lens topside. Then, a recreation of the original mount. (That goo inside is the Gorilla Glue I didn't scrape off, inked to hide the mess.) Then, a comparison of Petri mount (base cap with lip, and bayonet ring) and the M42-PK adaptor. Then, the adapter sitting on the chopped base cap, which was all too thick. Last, the adapter sitting on the body base, where I'll superglue it tomorrow.

What I've learned from this exercise is that a Petri lens can be converted to PK rather simply. A small Phillips screwdriver to remove two screws, and a Dremel blade to cut away the third bayonet retaining pin. A cheap M42-PK adapter, and SuperGlue to attach it. At least, I *hope* the SuperGlue will work. That's all.

.

I found your thread recently. I have the same petri 55mm f1.8 and already cut the bayonett part of it. I also want to attache there somehow the pk-m42 adapter. Did the superglue work for you finally? Or should it be somehow screwed there?
Can you focus to infinity with this solution?

[boriscleto]

I found your thread recently. I have the same petri 55mm f1.8 and already cut the bayonett part of it. I also want to attache there somehow the pk-m42 adapter. Did the superglue work for you finally? Or should it be somehow screwed there?
Can you focus to infinity with this solution?

RioRico is unfortunately no longer an active user.