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07-25-2013, 07:04 AM   #1
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Strength of K-mount

Hello all,

I have recently acquired some large heavy lenses, ie Tair 3 PhS and Jupiter 6. Very cool to impress those canon tourists with their white lenses with. The Tair comes with a gun-stock to properly support everything, but the Jupiter is just mounted on the camera (or better, the camera is mounted on the lens). Both lenses are M42, which I use with an original M42-K adapter. The M42 can be screwed on pretty tight. Too tight?

Has there ever been occasions where the K-mount has broken due to heavy lenses or too tightly screwed on M42 lenses?

Thanks,

07-25-2013, 08:04 AM   #2
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I broke the mount off of my K10d a few years back. It took some doing, but it's possible.

What basically happened is that a non-genuine M42 adapter got stuck and I had to unscrew the mount. That seemed to work, until suddenly the KA-related functions stopped working. Thinking something was amiss, I disassembled it again. The problem seemed to be a black cord that should connect to the mount plate, supposedly grounding it. I managed to solder it back and attach the mount ring, but to no avail. The KA functions didn't come back. I went on like that for a while, considering an upgrade to K20d, and keeping my K10d for M42 and pre-da-lenses in manual mode.

One day, however, the mount physically broke. I was holding the camera by the lens and the body (minus the mount ring) just fell off, bounced against something sharp (breaking the LCD glass). I got a K20d and moved on.

Part of the problem is that the part of the body to where the mount ring is screwed in isn't metal, but plastic. That has apparently been true on all pentax DSLRs. I'm guessing I re-assembled it wrong and somehow induced pressures into the assembly, evenually cracking it. I don't believe I'll be taking a screwdriver to my main camera again anytime soon.

As for normal usage, I wouldn't worry too much. I've used pentacon 6 gear with my pentax cameras (CSJ 300/4 adapted to P645 adapted to K) and walked around hand-holding it, no problem. I've used several heavy M42 lenses as well, though not the ones you mention. If used right, the adapter shouldn't be a problem.
07-25-2013, 08:12 AM   #3
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With a few, rare, exceptions I've not heard any stories of camera mounts breaking due to the weight of the lens. Turn around too quickly and smack the lens into a wall while just holding the camera, or drop the camera so it hits wrong, yes that will break the mount.

I do firmly believe that if the lens is heavier than the camera you should be treating it as a lens with a camera attached not a camera with a lens attached. Tripod mount on the lens instead of camera for example. In most cases it is just easier to handle that way any how and I assume is part of the reason we don't see more mounts break.

My heaviest lens is a Sigma 50-500 and I always handle it as a lens, not a camera. The big tripod foot makes that easy.
07-25-2013, 08:32 AM - 1 Like   #4
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There are 5 tiny screws that hold a Pentax lens mount to the body/mirror box.
The mount itself is metal, but what those screws, screw into, varies.

The more torque you put on the mount, the more risk you take.

My "Rule of Thumb" is, if I can't hold the camera and lens steady with my thumb and three other fingers, the weight is too much. Which is coincidently, what your hand's work is when you take pictures - your index finger is used to press the shutter.



07-25-2013, 09:03 AM   #5
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If the lens is too heavy to take a photo holding the camera in only my right hand (yes, I understand that's not proper technique), then I always support the lens rather than the camera. The only lenses I have that need this extra care are a Sigma 50-500 and telescopes. An M42 adapter adds an extra point of weakness and probably needs more caution than k-mount lenses.

P.S. Never walk around with the camera hanging from your neck and a very heavy lens mounted. The bounce from every step will stress the mount. Put a strap on the lens foot to carry the weight.
07-25-2013, 09:07 AM   #6
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We had a Nikon mount blow off a Phantom camera once. All it took was having the camera too close to the explosion. Guess there are always some situation where something will break or fail given enough pressure/force etc. Pentax sold some pretty big lenses themselves plus the adapters for 645 or 67 lenses and doubt they would have done that if there were chances of the mount failing
07-25-2013, 09:17 AM   #7
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QuoteOriginally posted by DeadJohn Quote
P.S. Never walk around with the camera hanging from your neck and a very heavy lens mounted. The bounce from every step will stress the mount. Put a strap on the lens foot to carry the weight.
There is the other worry - I have one of those straps that fit into the tripod mount screw (carryspeed in my case) and carry it over my shoulder. When the lens is pointing down the force on the lens should be a little less. There is no safe provision for a strap around my lens. The lens itself has an attachement point for a tripod, but unfortunately it is 3/8th instead of 1/4th for normal tripod screw. I yet have to find an adapter to attach 1/4th to 3/8th.
07-25-2013, 09:20 AM   #8
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QuoteOriginally posted by JohntheThird Quote
There is the other worry - I have one of those straps that fit into the tripod mount screw (carryspeed in my case) and carry it over my shoulder. When the lens is pointing down the force on the lens should be a little less. There is no safe provision for a strap around my lens. The lens itself has an attachement point for a tripod, but unfortunately it is 3/8th instead of 1/4th for normal tripod screw. I yet have to find an adapter to attach 1/4th to 3/8th.
I believe Manfrotto makes an adapter and think I have seen ones listed in B&H as well as on eBay. The adapters are not that uncommon, I have several as well as some quick releases in 3/8 inch thread size.

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