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07-18-2014, 12:59 PM   #1
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M42 Auto Bellows adapter...

I have in my possession a rather nice Pentax Auto Bellows that I purchased on eBay but alas, it did not come with the M42 threaded adapter to mount a body onto the bellows (it does however have the M42 threads out front to receive an M42 threaded lens). I've read elsewhere that many others are in the same predicament -- i.e. access to a bellows but no way to mount a body onto it. As Pentax no longer makes this part, it seems to me that if I could get together an order from a machine shop of ten such adapters, then the cost could be amortized and might actually be reasonable.

So this is a kind of poll: are there ten people out there that would commit to purchase said adapter? If so, what would the max price be: $20, $25, $30 ? (I don't think I personally would be willing to spend much more than $30)

Feedback encouraged.

Cheers
Michael

07-18-2014, 01:19 PM   #2
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There are quite a few K-pM42 3rd party adapters about. The main point of concern regularly mentioned here is that some protrude beyond the proper registration plane. This is not a problem for using bellows.


Look at the geometry of the front of the camera. If you mount the adapter to the bellows and then to the camera when it comes time to take it off you could have a problem. Will you get clearance between the bellows and the flash housing?


If not you will need to consider either:
1. Buying a cheap 3rd party adapter and fixing it firmly to the bellows (glue etc) so the bellows mounts like a K bellows and presents an M42 front mount for the lenses.
2. Using a tube long enough to enable the clearance (could be either K or M42 tube, with the adapter put in the appropriate place.) This would give a minimum contraction of the bellows longer than standard design.


I have a few adapters (came with lenses I bought). One is labelled Pentax but does not have a spring and does not seem to be machined to fit a K mount properly.


I like the spring clip in because it prevents:
1. The adapter coming off when I take the lens off - real effort to get it off and put it back in for my next lens - makes for a very long lens change.
2. The possibility it could come out with a lens attached - not a nice prospect - because there is nothing to stop it rotating and coming out of the K mount.
07-18-2014, 01:30 PM   #3
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QuoteOriginally posted by MJSfoto1956 Quote
I've read elsewhere that many others are in the same predicament -- i.e. access to a bellows but no way to mount a body onto it.
I take it that you are wanting to make an item with a bellows-side flange designed to engage and rotate within the existing fitting on the bellows rear standard. I ask, because that is what it would take to work properly. This is not a situation where gluing a hacked-up M42 adapter would do any good and perhaps by inserting that information into this thread, the inevitable* rat hole can be averted

As you said, there seems to be a recurring request for information regarding these rear mounts. Have you considered simply having a small batch made and attempting to sell on eBay?


Steve

* Happens every time due to the well-intention suggestions of people not familiar with how the unit is put together.

---------- Post added 07-18-14 at 01:39 PM ----------

...One more thing...If you do have one made, remember to add a bit of a spacer to allow for clearance of the flash overhang found on modern dSLRs.


Steve
07-18-2014, 02:06 PM   #4
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QuoteOriginally posted by stevebrot Quote
I take it that you are wanting to make an item with a bellows-side flange designed to engage and rotate within the existing fitting on the bellows rear standard. I ask, because that is what it would take to work properly. This is not a situation where gluing a hacked-up M42 adapter would do any good and perhaps by inserting that information into this thread, the inevitable* rat hole can be averted As you said, there seems to be a recurring request for information regarding these rear mounts. Have you considered simply having a small batch made and attempting to sell on eBay?
Yes, Steve has understood correctly -- it is the missing (i.e. rotating) flange that needs to be fabricated.

Trying to gauge how many people would be interested if such a custom-fabricated replacement part became available and at what price point they would be willing to spend.

Thanks
Michael

07-18-2014, 03:18 PM   #5
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Is this the part you want?

It is to mount on the K_mount camera, and it fits into the bore of the Pentax Bellows-M
The diameter of this adaptor (the black ring that fits in the bore) is 48.25 mm (1.900 inch)
The black ring has a groove that the grubscrew on the bellows locks into, allowing rotation if loosened
I am not sure if the bore of earlier Asahi Pentax ( M42 style) bellows is the same, I expect so.

The easiest way to make this would be to use the shiny K-mount off a dead lens, and machine the ring, then attach the two together using the existing K-mount screws.

I can do such machining here on my hobby lathe. I would need a donor lens ( having used all mine up !) . Send me a pm if you want.
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07-18-2014, 03:56 PM   #6
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I wasn't thinking to make a bayonet mount version, but rather the M42 (universal) mount version which would allow people to extend the system anyway they wanted. But yes, this is basically the core of the idea.

Michael

---------- Post added 07-18-14 at 07:08 PM ----------

do you have a close up of this adapter?
(trying to gauge the depth of the groove around the inside of the adapter)

Michael
07-18-2014, 04:17 PM   #7
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QuoteOriginally posted by MJSfoto1956 Quote
but rather the M42 (universal) mount version
I made an M42 threaded adaptor recently. But I think for this application, the direct K-mount would save all the hassles i read about of the M42 threaded adaptor inside the K-mount.

Edit: I see used M42 complete bellows are available for between ~ $30 to $60. They should come with the adaptor you prefer.
I have a simple one here with M42 male on one end and female on the other


Last edited by wombat2go; 07-18-2014 at 04:32 PM.
07-18-2014, 04:50 PM   #8
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QuoteOriginally posted by wombat2go Quote
I am not sure if the bore of earlier Asahi Pentax ( M42 style) bellows is the same, I expect so.
IIRC, this is not the case. There was an inquiry some time back where a person was hoping to scavenge the adapter from a K-mount bellows to use on a M42 bellows. I believe that the M42 adapter has a smaller diameter.


Steve
07-18-2014, 05:57 PM   #9
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I've been tracking the eBay auctions recently, they seem to go for $60-85 (or more) these days. Perhaps people are overpaying, but that is what I have observed as of late. Notwithstanding, there are a lot of people out there who have obtained Pentax Auto Bellows bellows without the flange and I was still trying to gauge how many would be willing to purchase the item should one become available. Agreed that there is an upper limit as to what it is worth given that there are plenty of available bellows for auction. But that is not the point of the thread -- is there any interest or not?

Michael
07-18-2014, 08:48 PM   #10
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I measured the adapter ring on my screwmount Auto Bellows as 41.5 - 42mm. I don't have a set of calipers so I cannot give you a more accurate measurement but the threaded side of the adapter fits into the opening on the bellows like a glove.

Here's a fast picture of the adapter from the side.
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07-19-2014, 06:44 AM   #11
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Thanks for the photo -- I was thinking that since this would require mostly just a lathe operation, the cost to reproduce it might be reasonable.

Michael
07-19-2014, 07:57 AM   #12
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If I had a set of calipers I could get accurate dimensions so someone could fabricate one of these. You could always make the knurled part with a smaller diameter so less material would have to be removed. You can always grab the tube that goes into the bellows to unscrew it. I would add some extension between the body and bellows so you can rotate the body into portrait mode without having to detach the adapter from the bellows. It's a very tight fit with the stock adapter.
07-19-2014, 08:25 AM   #13
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I just measured my (empty) opening and it measures precisely 42mm diameter -- actually not surprisingly since the thread is M42. That's engineering for you!

Michael
07-19-2014, 08:44 AM   #14
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It would be easy enough to make this in two parts. Turn the first part on a lathe, out of plastic, wood (maple or birth) or aluminum and then glue a flanged m42 adaptor to it. As others have noted registration distance is NOT an issue with a bellows.


I did a similar thing to adapt a Miranda bellows to a k mount. I took the Miranda 4 leg bayonet to Miranda screw mount (44mm I think it was) and cut the threads off and glued a flanged adaptor to it.
07-19-2014, 09:02 AM   #15
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You can make the first part similar to the stock adapter minus the flange. Then thread it into a flanged m42 adapter. You can always glue a washer/flange or just 3 or 4 stops on the tube to take place of the stock flange - so it won't fall into the bellows. That way you can still use the adapter on a screw mount body.
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