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DIY Metal Body for P6X7 90mm LS
Posted By: wombat2go, 07-07-2013, 01:12 PM

The lens is a "Super-Multi-Coated Takumar/6X7 1:2.8/90"

The camera body is based on an Eddystone die-cast aluminum box.
These boxes are used in electronics for radio frequency shielding. They are accurately made and the walls are thick enough for machining.
The box lid has a ridge inside that forms a light tight seal.
Using the Eddystone box saved a lot of work in this project.

A square with a groove for light seals was milled in the bottom of the box to form the mount for the lens board.
The lens board of 2 laminated plates of 6031 aluminum is somewhat based on the Graflex 4x5 lens board.
A P6X7 bayonet mount was turned in the lens board using the lathe.
The back is clamped to the lid which is machined with the film gate and a light seal.
On Graflex cameras, the back is held with quick release clamp slides, but on this camera the clamps are bolted

The Graflex (Singer) RH/10 roll-film back contains a truck for 120 film giving 10 exposures of film gate size 57.4 by 67.5 mm.
Also it will take the truck for an RH/8 back, giving 8 exposures for a total of 18 shots if the spare truck is loaded and taken in the camera bag.

The published register for Pentax 6X7 is 84.95mm
The estimated register of this camera is 85.09mm at 25 C and 84.89mm at -10 Celsius
The TIR of the lens mount parallelism was measured as 0.05mm. However that does not include the Graflex back.
A 6X7 ground glass was made to fit against the film slides.
The camera was checked with a loupe at 4 metre and infinity and the lens scales were found to accurate.

The bottom of the camera contains a tripod mount machined in brass and threaded 1/4_20 into a blind hole.
The side has a stainless steel industrial handle angled for a personal grip.
Tho top has 4 bolts for optional viewfinders.

The present viewfinder is very simple, the lenses were chosen by flipping lens elements in the junk box until an arrangement of 2 meniscus lenses from the front of an old zoom were placed to give about 3+ diopter (focal length 300mm or so).
The eye cup is much larger than on a normal camera
The viewfinder has significant barrel distortion which is actually an aid in centering the image.
The spirit level is easily visible in the bottom of the vf with the help of the lenses.

The camera with film , back and lens weighs 1.96 kg (4 lb 6 oz)

There is presently no rangefinder or meter, so the Pentax MX with the SMC Pentax-M 1:2.8~4 40~80mm is taken in a compartment in the camera bag
The zoom makes a good rangefinder at 80mm and being of wider aperture than an ordinary zoom, has a bright image in the MX viewfinder.

The roll film back has a dark slide which is not really necessary as the leaf shutter is normally closed.

photos with the MX alongside

rear view
https://www.box.com/s/ayxl4s45tpq9as0xtgld
side view
https://www.box.com/s/bsf4ca4fy3v149skqxw9
with AF360 Flash
https://www.box.com/s/44lzyxxte8c3v1ipj2kj

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07-07-2013, 06:30 PM   #2
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Very cool! How's it working out so far?
07-07-2013, 07:00 PM   #3
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CS,
It is working very well thanks,

Here are some images that I already posted in other threads
https://www.box.com/s/uuoa84o1gawletwfc02g
https://www.box.com/s/pzzorays1lydomsk9rre
https://www.box.com/s/c24zem8vrsml7391kiud

These shots on Fuji 400 were focussed just by estimating distances and using the DOF scales on the lens.

Also the C41 seems to be not too critical for exposure. I just took an occasional reading on the MX through the day and slowed the shutter a bit for shady tree etc.
The next roll I have in now is Fuji 160 so I will be more careful with focus distance especially on the closer subjects.
07-07-2013, 07:22 PM   #4
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Great photos. Congrats on your build. I bet it was a fun project!

07-08-2013, 10:38 AM   #5
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Man, where were you 45 years ago when Asahi was planning the original 6x7 body? You probably could have shaved a pound off the final product with this design.
07-08-2013, 11:19 AM   #6
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Well, TL, this camera is no match for P6X7 body.
It cost less than $30 in parts
But if I added the sketching time and workshop time it would go a long way toward a Phase One 45 back!
I do have an idea for version 2 (...next winter/spring maybe...) with slr focussing that should not add much weight.
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