Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-08-2010, 04:56 PM   #1
Loyal Site Supporter
pacerr's Avatar

Join Date: Jan 2008
Location: Henry, TN
Photos: Gallery | Albums
Posts: 2,909
DIY Mamiya-Sekor M645-to-PK lens adapter

With half a dozen Mamiya M645 lenses staring at me it was only a matter of time before I devised a way to use 'em on the Pentax bodies. (45, 55, 80, 150mm + 2X TC, etc)

Materials = salvaged PK or PK/A mount + Mamiya rear lens cap + 2 3/8" OD PVC pipe + epoxy glue and about 1 1/2 hours of head scratchin'. You could also use a bayonet-type Pentax body cap. And I assume you could match a PK/A mount to the equivalent aperture Mamiya lens if you cared to, but...

This could have been done with hand tools/Dremel tools but I was lazy and used a lathe and drill press. Its hardly worth the time to explain the steps as they should be pretty obvious from the pictures. The PVC ring hasn't been completely fitted and glued to the Mamiya Lens cap in these pictures. Flat black paint for the inside yet to go.

Coring out the lens cap to fit the PVC ring is the only fiddly step. I started by using a 2 1/4" hole saw and finished with a Dremel sanding drum chucked in the drill press.

The adapter simply has to make up the difference between the Pentax and Mamiya lens registry distances from flange to flange to attain infinity focus. There's no reason why this can't be adapted to other lenses with long registry distance such as the Pentax 645's, etc.

Mamiya 645...bayonet .....63.30 mm
Pentax.......... M42 & K.... 45.46 mm
....................................-17.84 mm

Call it 18 mm and slip-fit it in the lens cap as necessary. Intentionally adding greater distance will act as an extension tube.

Now I'm working on a two-piece center section that will allow a vertical shift and another that will incorporate threaded center rings from an extension tube set to accommodate that function.







H2

I can assure you there will be NO SDM motor or AF failures with this set-up!

--------------

Edit: First optical test results -- although the mechanics work fine, I'm unimpressed and disappointed with the IQ of all of the Mamiya MF lens combinations I've tried so far -- 45, 55, 80 & 150mm -- mediocre to say the least. Slightly soft and the appearance of grain on the order of over-pushed Tri-X film.


Last edited by pacerr; 04-09-2010 at 10:02 AM. Reason: Add optical results
04-08-2010, 08:54 PM   #2
Veteran Member
Jewelltrail's Avatar

Join Date: May 2008
Location: Rhode Island
Photos: Albums
Posts: 4,180
Wow--very impressive, proving once again necessity generates inventions! Kudos to you. Now you can shoot like crazy with all that great glass. I hope you share the results with us here @ the forum too.
04-08-2010, 09:47 PM   #3
Loyal Site Supporter
pacerr's Avatar

Join Date: Jan 2008
Location: Henry, TN
Photos: Gallery | Albums
Posts: 2,909
Original Poster
Mmmm

QuoteOriginally posted by Jewelltrail Quote
...again necessity generates inventions!
More like boredom creates busy work for idle hands 'n minds. H2
04-08-2010, 09:49 PM   #4
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
Sweet, great way to use those lenses!

04-08-2010, 11:14 PM   #5
Veteran Member
Pentaxor's Avatar

Join Date: May 2009
Location: Vancouver, B.C.
Photos: Gallery
Posts: 6,513
when are you going to start production and sell them?
04-09-2010, 01:38 PM   #6
Loyal Site Supporter
pacerr's Avatar

Join Date: Jan 2008
Location: Henry, TN
Photos: Gallery | Albums
Posts: 2,909
Original Poster
Some results

After further mechanical tweaking and comparison with other digital lenses I'm pleased with the potential of the Mamiya 645 lenses.

The worst results I've had with these Mamiya lenses were generally comparable to the average DA 18-55. The best results are comparable to my Tamron 28-75 and DA 16-45. It seems worth continuing to develop a more sophisticated adapter capable of lens-shift using their wide image circle anyway.

The common, manual focus Mamiya-Sekor C M645 lenses between 45 - 210mm are relatively inexpensive today, costing $70-170 used in good condition. Of course these will operate as Pentax M-mount lenses with the known issues of exposure compensation to contend with. Split image focusing was possible all the way to F22 with care.

I don't believe I'd go out of my way to acquire these Mamiya lenses but since they were on hand it seemed reasonable to develop an adapter. Besides it's an excuse for LBA in the under $200 arena.

The attached image gives an overall idea of the potential compared to the Tamron 28-75/2.8. Lens identification is in the file names but the the layout is the Tammy at 50mm and 75mm on top and the Mamiya 55mm/2.8 and 80mm/2.8 below. All at F8 with only resizing and a very small, equal sharpness tweak applied in Faststone Image Viewer. Body was a K200D @ ISO 200 using Natural-mode, best JPG processing. Target at 76 feet.

More experience with the exposure adjustments will undoubtedly improve the images but color was generally pleasing. Additional comparisons with the Mamiya 45mm/2.8, 150mm/3.5 and 2X TC will follow later.

H2

http://www.pbase.com/image/123455997.jpg



H2
04-09-2010, 02:06 PM   #7
Senior Member
SquintyEyes's Avatar

Join Date: Aug 2008
Location: Toronto, Canada
Photos: Gallery
Posts: 100
I've been thinking of a M645-PK adaptor for some time. And your solution seems pretty practical. Any concern with using so many plastic parts to hold these rather hefty lenses? I don't think the back-cap of the M645 holds it very tightly. Is the epoxy glue strong enough to hold the PK mount to the PVC tube? I'm sure you've tested it, but these are some of the concern in my mind when I look at your setup.

For me, I'm using a M645 extension tube as the main part for the converter (as discussed here). I'm in the process of hunting for the metal ring with the correct size to match the PK lens mount to the M645 adapter.

I totally agree with you that there are a slew of good lenses floating in the market, waiting to be used. the image circle of M645 projected on APS-C sensor means we're getting the center/sharpest portion!
04-09-2010, 02:54 PM   #8
Loyal Site Supporter
pacerr's Avatar

Join Date: Jan 2008
Location: Henry, TN
Photos: Gallery | Albums
Posts: 2,909
Original Poster
QuoteOriginally posted by SquintyEyes Quote
Any concern with using so many plastic parts to hold these rather hefty lenses? I don't think the back-cap of the M645 holds it very tightly. Is the epoxy glue strong enough to hold the PK mount to the PVC tube?
I think in practice you'll find that the PVC, plastic and epoxy are more than adequate, rather robust in fact. As a matter of interest, I'm using J B Weld, a metal-filled epoxy. Nice, smooth fillets will make you feel more confident too.

If you have a loose fit with the lens cap, apply coats of acrylic fingernail polish to build up a comfortable friction fit in the cap.

QuoteOriginally posted by SquintyEyes Quote
...hunting for the metal ring with the correct size to match the PK lens mount to the M645 adapter.
Check the plumbing section of a hardware store for useful plastic and copper fittings. eBay has a useful, cheap ($11 US) PK extension ring set. A future mod will involve a PK-Mamiya hybrid ring set using a mating bushing. It seems the really right stuff never shows up til you've finished the first two prototypes of anything.

H2

04-09-2010, 03:11 PM   #9
Senior Member
SquintyEyes's Avatar

Join Date: Aug 2008
Location: Toronto, Canada
Photos: Gallery
Posts: 100
QuoteOriginally posted by pacerr Quote
Check the plumbing section of a hardware store for useful plastic and copper fittings. eBay has a useful, cheap ($11 US) PK extension ring set. A future mod will involve a PK-Mamiya hybrid ring set using a mating bushing. It seems the really right stuff never shows up til you've finished the first two prototypes of anything.

H2
Haha, isn't that the truth! Kudos to you for going ahead and making the first prototype. I think that's a good approach to work out some of the kinks before attempting a full-blown conversion. Thanks for the hint on where to hunt for the ring.

I'll document my attempt when I get around to doing it.
04-09-2010, 11:06 PM   #10
Site Supporter
Steve Beswick's Avatar

Join Date: Apr 2009
Location: Ontario, California
Photos: Gallery
Posts: 1,578
Your adapter is very nice, but for those of us with limited tools or a lazy demeanor, I have come up with a simpler version.

It takes two pieces:

1. A "White dot" Pentax body cap. This cap has a dot (that's white!) that points up towards the prism when it is on the camera. It is also thick on the outside and slopes in towards the center. Sorry, I wasn't smart enough to take pictures of it before I made the adapter.

2. A standard Mamiya 645 rear lens cap.

Assembly its four simple steps:
Put a 3/4 inch hole in the center of both caps.
Remove the bump where the white dot is on the Pentax cap. I used a razor blade.
Figure out the alignment.
Glue the two caps together.

Now here is the kicker - this setup is almost dead on for infinity focus. It took me staring through the lens at the split image for a couple of minutes before I even realized it is off. If I had ever so slighly sanded the ring on the Pentax cap before gluing it would have been perfect.

I also made two other unnecessary tweaks to mine. First I notched the Pentax cap so it would latch on the body like a normal lens. I also glued the whole thing to an 80mm f2.8, since it is the only lens I'm ever going to use with it, and I'm not going to use the lens anywhere else. The whole setup, including the lens and the two caps, cost $13, plus an hour or so of my time.

Pictures of the setup can be found here.
04-10-2010, 06:03 AM - 1 Like   #11
Veteran Member




Join Date: Aug 2009
Location: NY
Posts: 407
I did a conversion on a 80 mm 645. All I did was remove the Mamiya mount, grind down a small ridge so it is flat, screw on a PK mount from a dead lens, then use a PK extension set without any of the rings. That gives just over infinity focus.

The results I like.
04-10-2010, 06:28 AM   #12
Veteran Member
vizjerei's Avatar

Join Date: May 2007
Location: Toronto
Photos: Gallery
Posts: 1,418
now you can start making tilt-shift M645-to-PK adapter
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
cap, distance, flange, k-mount, lens, mamiya, mm, pentax, pentax lens, pvc, slr lens, tube
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Why no love for Mamiya Sekor? Shamwow Pentax SLR Lens Discussion 62 10-14-2016 05:26 AM
Mamiya M645 vs. Bronica ETRS questions Steve Beswick Non-Pentax Cameras: Canon, Nikon, etc. 52 07-12-2012 06:22 AM
New Arrivals: Mamiya/Sekor 55/1.8 (Third of three) stevebrot Pentax SLR Lens Discussion 2 03-01-2009 10:42 PM
Mamiya/Sekor M42 lenses frederik9111 Pentax SLR Lens Discussion 8 03-23-2008 02:42 PM



All times are GMT -7. The time now is 07:26 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top