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03-18-2010, 08:07 AM   #91
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I have some questions for the expert tinkerers. What I have in mind is adapting a Mamiya 645 lens to Pentax K mount. There should be plenty of flange distance to play with (63.3mm to 45.46mm), and I even found an adapter on the auction site. The pre-fab adapter is really pricey at $100 + shipping. What I want to do is try to hack my own adapter with a Mamiya extension tube (so I don't have to mess up the lens mount) and some old garbage K-mount lens lying around. What I am not too sure at this point is the difficulty in joining the metal barrels together. Without access to a metal workshop do you think it's feasible to construct a sturdy adapter from the components mentioned? Would epoxy such as "JB weld" be strong enough for the job?

Your inputs/suggestions are much appreciated.

03-18-2010, 09:20 AM   #92
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mamiya to pk

Hi Squinty,

I had the same idea and there is the shortest 645 extension tube still in the tinkerer queue.

You see my considerations are as theoretical as yours at the moment .-)

Nevertheless I would think the easiest would be to take that short extension ring, unscrew the camera part, build a spacer ring to sit between the extension ring and a PK-mount backside of any given lens with a flat rear surface and screw it all together .-)

So, basically one more part is needed (apart from that PK-back).

This spacer ring would probably be staggered and have two sets of holes, one in the outer ring to fit to the extension ring and one set of holes in the step leading to the Pentax camera.
Probably not feasible without a lathe, a drill stand and thread cutting devices (please update me on the correct terminology). I am adventurous with conversions but I could not use epoxy to put this together.

The more you get into these things the cheaper those adapters appear .-)

Best, Georg
PS: I like your Cerro Torre pic
PPS: I guess if you would have exacting measurements on a drawing somebody here or there could do such ring for you and send it (2x4 long screws needed as well)

Last edited by georgweb; 03-18-2010 at 09:25 AM.
03-18-2010, 11:01 AM   #93
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Thanks Georg. I think you're right, there's definitely one more part that's required for bridging the flange distance and for providing the mechanical support. The lens I'm interested in will be used for portraits, so I wasn't too concerned about getting the flange distance exactly right (losing infinity focus is not such a big deal).

I guess for now I can gather the material and do the said measurements. Maybe sketch up the part drawing and see if I can find someone to make it for me.

Thanks!
04-04-2010, 11:49 PM   #94
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My 2.8/300mm L is ready!


I managed to turn it into a crippled K-mount, so now I can focus wide open and meter with the green button. Or I can just shoot wide open in AV.

The hardest part of the conversion was getting the aperture ring to work. I ended up using the existing parts of the FD-mount. I just bypassed the original (complex) mechanism and attached the arm that closes the aperture inside the lens straight to the aperture ring with a couple of small screws. I had to file some parts of the aperture mechanism down a bit to get them to move without binding and this resulted in wrong aperture ring index markings in the wide end. F2.8 is correct but the actual F4 can be found from the aperture ring position F5.6

There was an aperture lever very much like the one in K-mount lenses already present. I had to remove one spring and shorten and bend it a bit it to get it to work like in the K-mount. And then I had to attach the chinese M42-PK adapter to the lens in such a position that the lever would be in the right spot when mounted on the camera. I used the existing holes in the lens and attached the K-mount with three screws. This resulted in the aperture ring index (and the drop-in filter slot) to be at 9 o'clock position (viewed from behind the camera) which IMO is actually better than under the flash housing.

Infinity focus was easy to achieve after removing the breech-lock parts. There is a focus limiter with a hand screw so I could (and can) adjust the infinity point without shims etc.

After some test shots I can say that sharpness even wide open is very good there is no CA and contrast is OK (not great, but easy to correct). And what surprised me the most was that I could hand-hold and track and get even a few sharp shots of flying birds. Even though the lens together with my K200D weighs approx 3.5kgs.

Here's a few 100% crops:





Will post more shots (hopefully) soon.

04-05-2010, 01:39 AM   #95
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Interesting conversion, I'm happy to see that the 300mm worked out for you. After you repositioned it the aperture lever moved in the correct direction and had a range of motion that was compatible with the aperture actuator on the camera body?
04-05-2010, 02:02 AM   #96
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QuoteOriginally posted by Steinback Quote
After you repositioned it the aperture lever moved in the correct direction and had a range of motion that was compatible with the aperture actuator on the camera body?
Pretty much. There was a small difference in the levers travel but it seems to work. With non K-A mount the lever is just on/off type thing. It holds the lens wide open while focusing and releases it fully to stop down the lens to the desired aperture when taking a shot.
04-08-2010, 12:59 PM   #97
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The 300mm f/2.8 looks like it will be a lot of fun to use, good to see that you got it all working properly. I have deliberately left a few of my conversions with the aperture marks etc not at the 12 o clock position also, it makes it a whole lot easyer to see what your doing. I look forward to seeing more shots from it. What is it like with a teleconverter?

04-08-2010, 01:15 PM   #98
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I've only done a little testing with my Kiron 7-element X2 TC but it actually looks very good.

Here's a few test shots (of a very intersting subject) taken handheld @ISO400 on a very grey day. Converted from RAW with Ligthroom defaults.

wide open 300mm:


100% crop of the above:


wide open 600mm with the Kiron 2X TC (f5.6):


100% crop of the above:


On this last crop there's some purple fringing visible if you look close enough but not too bad IMO.
04-08-2010, 03:09 PM   #99
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The IQ looks pretty good there. I would not be put off by the purple.

And actually, I like the subject, though it might not be the most creative shot of it. ;-)
04-08-2010, 09:15 PM   #100
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That 300/2.8 looks like a lot of fun. Not that bad image results either. It may be worth testing with different converters. Some certain combinations may be better than others. Usually the MC7's are good, but the best I've ever tried is the SMC Pentax-A 2x-S. That one is of course not cheap.
04-08-2010, 11:15 PM   #101
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I'm waiting for some decently bright weather to test the TC again, but so far I like what I see.

Here's another shot without TC from this morning wide open handheld through the kitchen window. @ISO400 cropped to about 1/4 of the original shot from my K200D.
Lightroom default conversion with curves adjust, crop and resize for web.
04-09-2010, 07:33 AM   #102
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That looks nice, especially for hand-held, and a I am sure would be even better with further PP (contrast etc). Well done on this one!
12-19-2010, 10:08 PM   #103
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Large format Kodak lens, with 3 full sets of M42 extension tubes (about as long as a 135mm Takumar w/hood). I think this was wide open at f/4. It doesn't have any markings beyond aperture values anywhere on it, but I'm making an educated guess that it is around 250mm.

12-20-2010, 05:03 PM   #104
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QuoteOriginally posted by SquintyEyes Quote
I have some questions for the expert tinkerers. What I have in mind is adapting a Mamiya 645 lens to Pentax K mount. There should be plenty of flange distance to play with (63.3mm to 45.46mm), and I even found an adapter on the auction site. The pre-fab adapter is really pricey at $100 + shipping. What I want to do is try to hack my own adapter with a Mamiya extension tube (so I don't have to mess up the lens mount) and some old garbage K-mount lens lying around. What I am not too sure at this point is the difficulty in joining the metal barrels together. Without access to a metal workshop do you think it's feasible to construct a sturdy adapter from the components mentioned? Would epoxy such as "JB weld" be strong enough for the job?

Your inputs/suggestions are much appreciated.
Duct Tape. Just watch any episode of the Red Green show and you will get the idea.

Eric
12-20-2010, 06:11 PM   #105
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QuoteOriginally posted by SquintyEyes Quote
Thanks Georg. I think you're right, there's definitely one more part that's required for bridging the flange distance and for providing the mechanical support. The lens I'm interested in will be used for portraits, so I wasn't too concerned about getting the flange distance exactly right (losing infinity focus is not such a big deal).

I guess for now I can gather the material and do the said measurements. Maybe sketch up the part drawing and see if I can find someone to make it for me.

Thanks!
Remember that most all the parts for lenses are made with aluminum or brass so grinding, drilling, thread cutting and polishing are all very possible using Dremel tools and standard cordless drills. The distance you need to make up to get your flange distance close can be done with aluminum plate. If you have any metals supply places close to you it is possible to get the pieces you need from their scrap bin. Much less expensive and the next 'however' is that you can't generally use the screws from old mounts or lenses due to there being odd sized with odd thread pitches which require the purchase of incredibly expensive thread taps. What I have done is find the size of screw and pitch that I can buy a common thread tap for that is close or equal to one of the larger screws in a lens and then use that throughout the modification or repair. Common thread taps are able to cut thread in mild steel a few times and aluminum many times if you do not try to do it fast. Bronze or brass are even softer metal so one does have to go slower so that you do not build up little bits of melted metal in the thread cutting tap which would make your threads all wrong and force you to buy another thread tap. Do Not consider using stainless for the thread taps for that are very expensive. I build parts for my sailboats all the time and have repaired several lenses and am almost through rebuilding a lens into a K mount with manual aperture. It had a 5.6 mm flange distance, shorter, to start with. Good Luck,
Alan.

Last edited by kacansas03; 12-20-2010 at 06:15 PM. Reason: spelling
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