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01-23-2018, 10:17 AM   #1
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Camera adapter for a Pentax bellows

I obtained a Pentax Auto Bellows K (single rail) through ebay but it came without the rear camera adapter ring. I'm wondering if those are available anywhere?

My alternate thought is to have a T-mount compatible adapter machined to fit the bellows and use a T-mount adapter for the camera (a K-1). Automatic functioning isn't required as I will mainly be using this with manually set lenses.

Appreciate any input.

01-23-2018, 11:14 AM   #2
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If the bellows was sold as complete and operational, I would send it back.

Based on past inquiries on this site, my impression has been that the mounts are hard to come by. Having a T-mount machined to fit is an option. As for "Automatic functioning", the "Auto" part of the name means support on the lens end of the bellows for the double cable release that would have come with the unit. One end would have screwed into the shutter release on the body and the other into the fitting on the front standard of the bellows. Pressing the button on the cable release would stop the lens down just prior to shutter release on the camera, thus allowing for open-aperture focus without fiddling with manual stop-down prior to exposure. The "auto" feature will not work with cameras that don't support mechanical cable release.

The manual for the essentially similar Auto Bellows A is available at the Butkus site (donations accepted) if you need a full description...

Pentax auto slide bellows A, Pentax Slide copier A instruction manual, user manual


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01-23-2018, 11:41 AM   #3
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Yes, near impossible to find on its own. I've never seen one for sale on eBay. Probably got tossed out because nobody knew what it was for.

You might be able to make a substitute using a reverse k-mount adapter and some de-glassed filters and/or step up rings or if you know someone with a lathe that could cut you the appropriately shaped tube to fit on a reverse adapter.
01-23-2018, 12:41 PM - 1 Like   #4
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Thanks Folks. I kind of figured that was the case. I obtained it used with no promises, and it's in great shape other than the missing adapter. I measured the fitting and if I have a 48.4mm tube grooved on one end (to go in the bellows fitting) and a T-thread cut on the opposite end, it should work with a T to K adapter which I have plenty of. I know some good machine shops so that shouldn't be a problem. Hoping someone would say "go here", but the alternative isn't too bad.
Thanks again.

01-23-2018, 04:26 PM   #5
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QuoteOriginally posted by Bob 256 Quote
Thanks Folks. I kind of figured that was the case. I obtained it used with no promises, and it's in great shape other than the missing adapter. I measured the fitting and if I have a 48.4mm tube grooved on one end (to go in the bellows fitting) and a T-thread cut on the opposite end, it should work with a T to K adapter which I have plenty of. I know some good machine shops so that shouldn't be a problem. Hoping someone would say "go here", but the alternative isn't too bad.
Thanks again.
Also consider that it is easier (well, for me anyway) to use an extension tube between the bellows and the camera. I use an old de-glassed teleconverter for my extension tube. Maybe you can just machine one end of an extension.
01-23-2018, 06:16 PM   #6
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I do not know if I understood correctly, but a broken Pentax lens should be easy to find on Ebay. A Phillips 01 screwdriver is likely to fit if it is the mount that is missing?
01-23-2018, 09:48 PM   #7
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QuoteOriginally posted by Bophoto Quote
I do not know if I understood correctly, but a broken Pentax lens should be easy to find on Ebay. A Phillips 01 screwdriver is likely to fit if it is the mount that is missing?
I considered that and have a couple of adapter plates which would do the job, but I have an issues with the need to drill into my bellows to attach the plate and the inability to rotate the plate (and the camera) after it's attached to the bellows.

With a 48.4mm tube, it slides into a recess and is held with a bellows setscrew, allowing quick attachment/removal and rotation.

Another problem is there's a small knob at the rear of the bellows which requires the camera to be spaced a short distance from the bellow's rear aperture, and an adapter plate wouldn't allow that. A short (1 inch) section of tube would facilitate access to the knob and prevent it from hitting the camera face. All in all, I think making a tube which fits the bellows and, at its opposite end, the camera, will work and allow for adjustments better. Appreciate the feedback though.
01-24-2018, 01:21 AM   #8
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It's best that the adapter can be rotated otherwise if you want to change from landscape to portrait orientation you have to rotate the entire bellows, camera and lens 90.

There are other issues due to the design of the rear standard of the bellows namely that the viewfinder/flash overhang and the lens mount base can prevent you from rotating the camera body. This makes it difficult or impossible to mount or dismount the body from the bellows. The solution is to add an extension tube between the bellows and camera or remove the adapter from the bellows which the design allows. All though the page from the manual below is for screwmount auto bellows the design of the k-mount auto bellows is similar and presents the same problems. As you can see in photo 1 the foot of the rear bellows standard will get in the way of the lens mount base on the camera. On the DSLR bodies this base is squared off and larger then on film bodies which are smaller and rounder as can be seen in photo 2.



01-26-2018, 05:42 PM   #9
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I think I can get around these problems with the adapter I designed and will have machined. It has about an inch and a half tube extending from the bellows socket to a male T2 thread which then allows me to use T adapters to place the bellows on K mounts or others (I still have a couple of screw mount cameras). The tube places the camera far enough back that it should allow for camera clearances needed. The only foreseeable problem might be some vignetting due to the adapter when used with the bellows extended but I think using crop mode with my K-1 will address that issue (at the cost of some pixels).

Thanks for the illustration, by the way, Not a Number. It makes the original design clearer and I got a better idea for the adapter from it (relative to the grove that secures the tube in the bellows).
01-27-2018, 09:47 AM   #10
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Here's the corresponding page from the Auto Bellows-A. The adapter for the A is actually two pieces. The bayonet could actually be a series K or M bayonet. The part that goes into the bellows has a textured (anti-reflection) that extends into the bayonet. The two parts are held together with screws. The black part is textured for finger grip just before the groove for the set screw.
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01-27-2018, 10:10 PM   #11
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QuoteOriginally posted by Bob 256 Quote
I think I can get around these problems with the adapter I designed and will have machined.
I think you can too, especially now that you see what the original adapter looks like and understand the body clearance issue.


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01-28-2018, 12:19 PM   #12
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QuoteOriginally posted by stevebrot Quote
I think you can too, especially now that you see what the original adapter looks like and understand the body clearance issue.


Steve
Yes, the cast gearbox for the bellows stick out about 1/2 inch from the face of the rear end of the bellows and makes it impossible to rotate the camera (and probably even mount some cameras) using the OEM flange. In my design, I allowed a little over an inch of projection beyond the rear flange which should work nicely for rotating the camera as long as the rail isn't extended too much beyond the gear box. If, for some reason, the rail is extended, almost the same limitation applies. I can understand why they went with the shallow rear mounting flange to get the camera close to the rear opening, but some newer cameras don't handle that design well (including the K-1).
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01-28-2018, 01:40 PM   #13
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QuoteOriginally posted by Bob 256 Quote
Yes, the cast gearbox for the bellows stick out about 1/2 inch from the face of the rear end of the bellows and makes it impossible to rotate the camera (and probably even mount some cameras) using the OEM flange.
Yes, rear standard clearance is an issue with some versions of Pentax bellows with some bodies. There may also be interference with the rail itself with some bodies. I have the Bellows Unit K which was the slimmed-down version of the auto bellows. It has a slender rear standard foot that provides full clearance down to the rail top. FWIW, rare is the body that can manage the rotation to portrait orientation and still allow full use of both front and rear standards.

You may want to consider having a shallow adapter machined as well. A 30mm extension is pretty significant considering the full depth of the bellows "stack". 1:1 reproduction comes up very fast even with the original adapter. My bellows has minimum 1:1.7 (0.6x) with a 50mm mounted.


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01-28-2018, 06:18 PM   #14
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QuoteOriginally posted by Bob 256 Quote
Yes, the cast gearbox for the bellows stick out about 1/2 inch from the face of the rear end of the bellows and makes it impossible to rotate the camera (and probably even mount some cameras) using the OEM flange. In my design, I allowed a little over an inch of projection beyond the rear flange which should work nicely for rotating the camera as long as the rail isn't extended too much beyond the gear box. If, for some reason, the rail is extended, almost the same limitation applies. I can understand why they went with the shallow rear mounting flange to get the camera close to the rear opening, but some newer cameras don't handle that design well (including the K-1).
You should have a flange on the bellows side ( 58.2mm), which secures a correct fit against the face of the bellows standard. Check the bellows unit out, you'll find the smooth ring that it fits flush to. The grove is just there to secure the mount, not for a precise fit. The groove extends to about 3.2mm from the flange, measured at the top. It is angled, maybe to 60 degrees (instead of 90 degrees). Check your locking crew, best to ask the shop to fit its angle. This way, the pressure to the flange is progressive as you tighten the locking screw. The outer diameter of the tube would be 48.5mm, the inner 43.8mm - with groves (ripples) some tenth of a millimeter deep to diffuse residual reflections in addition to the blackening. You may however just line it with some astro anti-reflection material. The groove bottom diameter is 46.4mm, it starts about 1.0mm from the flange - not overly critical but that 1mm should aid positioning.

Hope this helps to get a correct fit.

I'd strongly advise to make the adapter no longer than necessary to avoid extra strain on the rail/prism - a K-1 is very rear-heavy compared to most mechanical cameras already. My 11mm extension is plenty for the K-1 to mount cleanly. Best take your cameras and give it a try. Remember to share a picture of the result!
01-28-2018, 07:03 PM   #15
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QuoteOriginally posted by JensE Quote
You should have a flange on the bellows side ( 58.2mm), which secures a correct fit against the face of the bellows standard. Check the bellows unit out, you'll find the smooth ring that it fits flush to. The grove is just there to secure the mount, not for a precise fit. The groove extends to about 3.2mm from the flange, measured at the top. It is angled, maybe to 60 degrees (instead of 90 degrees). Check your locking crew, best to ask the shop to fit its angle. This way, the pressure to the flange is progressive as you tighten the locking screw. The outer diameter of the tube would be 48.5mm, the inner 43.8mm - with groves (ripples) some tenth of a millimeter deep to diffuse residual reflections in addition to the blackening. You may however just line it with some astro anti-reflection material. The groove bottom diameter is 46.4mm, it starts about 1.0mm from the flange - not overly critical but that 1mm should aid positioning.

Hope this helps to get a correct fit.

I'd strongly advise to make the adapter no longer than necessary to avoid extra strain on the rail/prism - a K-1 is very rear-heavy compared to most mechanical cameras already. My 11mm extension is plenty for the K-1 to mount cleanly. Best take your cameras and give it a try. Remember to share a picture of the result!
Many thanks JensE. Great recommendations. In looking for brass tubing, I came across a 2 inch (lens holder) to T mount astro-adapter that I think can be used if cut a bit and machined down slightly to fit the socket on the bellows. It already has a nice black interior. I checked the locking screw and its angle is 90 degrees so will adjust the groove to fit that. Appreciate your input.
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