[Laci.4400]

Hi everyone!

I’ve two Pentax 67 lenses and I didn’t want to sell them as somehow I just felt later on I might use them.
An idea is orbiting in me for a while that I’d like to build a camera. Previously I shot on obscuras as well and kinda like them. As they were all large format the double exposure wasn’t an issue as I could freely choose when I wanted to take another exposure and on which sheet.
I’d like to do this on medium format as well. I can but I don’t want to scan two frames on the top of each other as I like to play and compose in the camera.
I decided to make a camera body with the possibility to wind the film in both directions.
I checked on the flange focal distance and one source mentions 84.95mm and 85mm also. Another source says it’s definitely 85mm.
Can you help me which one is correct?
Can it happen that 85.00mm to the film pressure plate and 84.95 to the front edge of the film (.05mm film thickness)?

[photoptimist]

Cool project!

I'm not sure which one is "correct" but would probably pick the shorter distance because picking too long a distance might mean one or both of your lenses can't achieve focus at infinity. Note: if your lenses (assuming they are primes) are designed to a different flange focal distance than the one you build into the camera, you'll find that the distance markings on the lens barrel will be slight off by a some rotation distance of the barrel.

The other key issue is to ensure that the plane of the film emulsion and the plane of your focusing system are the same.

If you plan to have no focusing aids at all (e.g., relying instead on separate rangefinder distance measurements, setting the lens to that estimated/measured distance, and using DoF to hide minor focusing errors), then you might do a lens calibration with a sheet of ground glass against the film rails and a careful comparison of the barrel position when set to the estimated distance versus adjusted to a distance with sharpest focus. That will tell you that you might need to twist the lens barrel a millimeter or two to the right or left to get focus relative to the measurement. (Or you could shim the mount flange to get the right distance.)

Good luck! (We look forward to seeing pictures of your camera and of what comes out of your camera!)

[swanlefitte]

Sounds cool. Do the lenses have a hard stop at infinity? I would think you could the use a makeshift obscura to find best focus distance and measure.

[Laci.4400]

Thanks guys for your input and sorry for my late response!
I feel it’ll be a tricky one as the flange focal distance has to be accurate and I also need to make a mount which can hold the lenses in place and be able to release them in case I want to change the two lenses.
I was thinking about a Mamiya rb67 back to help this project a bit but then I won't be able to wind the film in both directions which I want it to have as great feature.
So I'm about to get in contact with a handmade camera/camera build site/forum to gather information about how to start and accomplish this project.

[tuco]

My Pentax 67 measures 85.5mm from the flange to the pressure plate.

[Ken50]

Cool project!

I'm not sure which one is "correct" but would probably pick the shorter distance because picking too long a distance might mean one or both of your lenses can't achieve focus at infinity. Note: if your lenses (assuming they are primes) are designed to a different flange focal distance than the one you build into the camera, you'll find that the distance markings on the lens barrel will be slight off by a some rotation distance of the barrel.

The other key issue is to ensure that the plane of the film emulsion and the plane of your focusing system are the same.

If you plan to have no focusing aids at all (e.g., relying instead on separate rangefinder distance measurements, setting the lens to that estimated/measured distance, and using DoF to hide minor focusing errors), then you might do a lens calibration with a sheet of ground glass against the film rails and a careful comparison of the barrel position when set to the estimated distance versus adjusted to a distance with sharpest focus. That will tell you that you might need to twist the lens barrel a millimeter or two to the right or left to get focus relative to the measurement. (Or you could shim the mount flange to get the right distance.)

Good luck! (We look forward to seeing pictures of your camera and of what comes out of your camera!)

I'm not sure which one is "correct" but would probably pick the shorter distance because picking too long a distance might mean one or both of your lenses can't achieve focus at infinity.

Is this correct ? If you take the flange too short, you could, so to say, focus after infinity. The shortest setting distance on the lens barrel therefore increases, for example, from 3 meters to 5 meters.
I am asking this because I am facing the following problem.
I had an adapter made for a Pentax 67 lens to be used on my Canon Eos. (Flange = 44.00 mm).
Normally 84.95mm (fllange Pentax 67) -44.00 mm (Canon Eos) = 40.95mm.
My adapter is 41.85 mm long and I cannot focus on infinity (astrophotography / moonphotography ).
Would my solution be to shorten the adapter by 1 mm, or better 1.5 mm so that I can still focus after infinity?
Is 1 mm so critical?

[photoptimist]

Is this correct ? If you take the flange too short, you could, so to say, focus after infinity. The shortest setting distance on the lens barrel therefore increases, for example, from 3 meters to 5 meters.
I am asking this because I am facing the following problem.
I had an adapter made for a Pentax 67 lens to be used on my Canon Eos. (Flange = 44.00 mm).
Normally 84.95mm (fllange Pentax 67) -44.00 mm (Canon Eos) = 40.95mm.
My adapter is 41.85 mm long and I cannot focus on infinity (astrophotography / moonphotography ).
Would my solution be to shorten the adapter by 1 mm, or better 1.5 mm so that I can still focus after infinity?

Yes, that would fix it.

Is 1 mm so critical?

Yes, lenses, especially shorter focal length (wide angle) lens are extremely sensitive to added distance in the mount-to-sensor distance.

A 1mm excess flange distance with 28 mm lens moves focus from infinity to about 0.84 meters (about 3 feet). Even a 50 micron excess in the flange distance is enough to move the focus of a 28mm lens from infinity to about 16 meters.

Telephoto lenses are less susceptible. A 1mm error with 300 mm lens moves focus from infinity to about 90 meters.

[Ken50]

Yes, that would fix it.

Yes, lenses, especially shorter focal length (wide angle) lens are extremely sensitive to added distance in the mount-to-sensor distance.

A 1mm excess flange distance with 28 mm lens moves focus from infinity to about 0.84 meters (about 3 feet). Even a 50 micron excess in the flange distance is enough to move the focus of a 28mm lens from infinity to about 16 meters.

Telephoto lenses are less susceptible. A 1mm error with 300 mm lens moves focus from infinity to about 90 meters.

Thank you for your quick reply.
I will start first with 1 mm and see what's happening.
I want to use both the 300 mm ED-IF and the 400 mm ED-IF Pentax67lens

[johnha]

Thanks guys for your input and sorry for my late response!
I feel it’ll be a tricky one as the flange focal distance has to be accurate and I also need to make a mount which can hold the lenses in place and be able to release them in case I want to change the two lenses.

The easiest way to create a mount would be to build the short extension tube (about 12mm long?) into the face of the camera. I've been toying with the idea of doing this for my 4x5 camera for my 90mm L/S 6x7 lens (in this case bellows focussing sorts the flange distance problem).

[3dreal]

it seems i have a similar problem. here is my setup.
1. Special Bessa I with bellows/lens removed. P67-mount. done by unknown person for Pinhole-use. i calculated 85-38mm register. maybe i must add 0.5, as described in this discussion. will measure with film mounted. i know register must be very precise. had a big fight with doragoodman zone Z1-crap cam system. precision not that important. register off by 0.85mm and i measured precisely and tested on MUP-cams. dont wanny discuss it further: only dont buy its wrong design. both mounts crap and non-universal.^
Have no P67 cam also not in near future so i must check my new 200/4 67(used but newest version) on other cams with and without adapters.
yes this bessa has no GG or darkslide i must add GG. no easy shooting with lenses. have other short register cam which has built in frame of RB67/70 mag. special version for 61.5mm too. no plans for it now. need cam with removable mags. graflok 23 -mount
also have Nikon-copal 1-HBV-cam where i checked p67 lens. also tested on eos 60D. must repeat the testings. first to check if scale is correct. infinity reached.
my setup is precise withing 1mm on 2m.

[titrisol]

According to Lens mounts - Camera-wiki.org - The free camera encyclopedia
P645 70.87mm
P67 84.95mm

[3dreal]

47mm i measured for short register cam bessa I special. NB: cheap Laser wasnt able to measure at that short range. caliper did it.
84.95-47=37.95mm shorter register.i added a piece of 0.15mm film. but it doesnt matter pressure plate and film are always at right 84.95mm.
on EOS 60D with two adapter i can focus to 103m only. counterchecked with bessa I Special. but i have nothing else in sight farther away. i only see very sharp subject at 103m. fully extended(accidentally its 38mm(or 37.95 when measured precisely)-i also cannot focus beyong these 103m. means 200/4 lens doesnt reach infinity. of course i will test three 200mm lens for infinity here 4.6km skyscraper. will now check on other cam what scale is showing. forgot it... if true what i found out at 2m scale must be below.
Nikon-copal 1-HBV with matte screen.
chipped adapter only has MF cannot do focus-trapping. aka no AF.
wiil try to get new chipped adapter. maybe will get P67-eos-adapter. already have P67-P45. maybe P45-eos then

---------- Post added 07-27-22 at 05:32 AM ----------

Very insteresting but expensive Universal P67-adapter
Adapter combination Pentax 67-lenses to Canon EOS cameras

[3dreal]

Is this correct ? If you take the flange too short, you could, so to say, focus after infinity. The shortest setting distance on the lens barrel therefore increases, for example, from 3 meters to 5 meters.
I am asking this because I am facing the following problem.
I had an adapter made for a Pentax 67 lens to be used on my Canon Eos. (Flange = 44.00 mm).
Normally 84.95mm (fllange Pentax 67) -44.00 mm (Canon Eos) = 40.95mm.
My adapter is 41.85 mm long and I cannot focus on infinity (astrophotography / moonphotography ).
Would my solution be to shorten the adapter by 1 mm, or better 1.5 mm so that I can still focus after infinity?
Is 1 mm so critical?

Non reaching infinity when using old analogue lenses on digital cameras
THE EXPLENATION
Just got an astonishing answer by a german expert after i recognized weird unsharpness not only with new P67 200/4 on K+F comfort EOS-adapter(also have Nikon-version but not yet Dsrl) but also with Zeiss C/Y 200/3.5 with different but also K+F comfort-adapter. measurements are telling adapter is ok. but i must make shooting-tests. Distance real terrestrial infinity. 7.7km. on scale when shooting 2.7km marker was inbetween lying 8. at stop subject TV tower and church were equally unsharp with both lenses. then i checked it with Novoflex Noflexar 200/3.8 followfocus which is going beyond infinity which i didnt know. can now get perfectly sharp images. f8 and f11 are best eos 60D 18MP APS-c-
Explenation why unsharp: analog lenses are corrected for IR-sensitibe film whereas digital sensor are not senstitive to IR.
Interestingly Novoflex has now also a new P67-adapter system for FF etc. not MF. adapter goes slightly beyond infinity i was told. 300 euro compl- one additional mount: 70euro
see also my thread about Rafcamera-adapter for P6 and K60. have now the latter but its nailed for infinity. ok when lens is perfect. thats why he must make a special one going beyond infinity for lenses slightly deadjusted. NB: dont trust split-images.