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09-28-2010, 07:21 AM   #1
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k5/kr lens mount - metal frame?

in the k5/kr (and all other pentax DSLR's for that matter), is the lens mount bolted on a plastic or metal frame?

i know all pentax dslrs have a stainless-steel sub-frame. is that where the lens mount is bolted on to?

hmmm.... looking at the D7000 image, it seems like their lens mount is bolted on to a plastic frame? i could be wrong.

09-28-2010, 09:44 AM   #2
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QuoteOriginally posted by opiedog Quote
in the k5/kr (and all other pentax DSLR's for that matter), is the lens mount bolted on a plastic or metal frame?

i know all pentax dslrs have a stainless-steel sub-frame. is that where the lens mount is bolted on to?

hmmm.... looking at the D7000 image, it seems like their lens mount is bolted on to a plastic frame? i could be wrong.
In falconeye pictures of dissected K-5 it is clearly seen that lens mount is also bolted on to plastic part. I doubt that K-r is different in this regard.
09-28-2010, 12:30 PM   #3
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interesting. i thought the lens mount would be bolted more securely to the stainless steel chassis.

so in this regard, it seems the lens mount is bolted on the same way for both k5 and d7k
tnx
09-28-2010, 12:34 PM   #4
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Here it is clearly seen that lens mount is screwed into plastic mirror box:
Falk Lumo -- Pentax K-5 hands-on preview

09-28-2010, 12:48 PM   #5
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QuoteOriginally posted by Edvinas Quote
Here it is clearly seen that lens mount is screwed into plastic mirror box:
Falk Lumo -- Pentax K-5 hands-on preview
Correct me if I am wrong, from the profile cut photo, it looks to me the k-5 lens mount is bolted on the steel chassis, not plastic.
09-28-2010, 12:58 PM   #6
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QuoteOriginally posted by aleonx3 Quote
Correct me if I am wrong, from the profile cut photo, it looks to me the k-5 lens mount is bolted on the steel chassis, not plastic.
That would be good news, since it is one of the places where falling camera can get expensive damage.
On the other hand, if it doesn't detach after such shock, what damage the frame might get (e.g. misaligned sensors etc).
09-28-2010, 01:59 PM   #7
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The bottom screw in the image is screwed to plastic.
09-28-2010, 02:54 PM   #8
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This is common for all DSLR designs. The mounts are never screwed onto the magnesium front panels. I wouldn't worry about it since the engineers who design these obviously have far more knowledge of it than me or you so there has to be a reason.

09-28-2010, 03:56 PM   #9
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I don't know what kind of magnesium alloy is used in the body, but generally magnesium is pretty soft. It's entirely possible that the plastic is actually stronger.

Also, I'm not sure I'd like to have two dissimilar metals touching. Not only could it create stray currents, but it would corrode like crazy.
09-28-2010, 04:38 PM   #10
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QuoteOriginally posted by noser Quote
Also, I'm not sure I'd like to have two dissimilar metals touching. Not only could it create stray currents, but it would corrode like crazy.
Good point.!

Surely someone will now start a thread about galvanic corrosion..
09-28-2010, 06:26 PM   #11
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QuoteOriginally posted by Ex Finn. Quote
Good point.!
Surely someone will now start a thread about galvanic corrosion..
It's true, the screws on my K-7 show signs of it. The few that get wet and salty from my hands turn white and the corrosion has to be removed periodically.

--The lens mount on the body is designed to separate from it if the stress is too high, to preserve the integrity of the body and avoid bending it out of shape, which would mean the complete loss of the camera. i think the screws that hold the mount on are designed to fail and break before too much stress is transferred into the body.

That's what i read abt it anyway. Some of the folks here will know a lot more abt it than me.
09-28-2010, 06:35 PM   #12
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QuoteOriginally posted by opiedog Quote
in the k5/kr (and all other pentax DSLR's for that matter), is the lens mount bolted on a plastic or metal frame?

i know all pentax dslrs have a stainless-steel sub-frame. is that where the lens mount is bolted on to?

hmmm.... looking at the D7000 image, it seems like their lens mount is bolted on to a plastic frame? i could be wrong.
From chatting with a Pentax techie quite a while ago, while he checked my K100D...The Pentax lens mount is deliberately built with a weak point (the mounting screws), but strong enough for any normal usage with even the heaviest lenses.
That way if the lens hits the pavement (it happens...) the lens mount will come off and may need to be replaced, but you have a better chance to avoid permanent damage to the camera chassis..
09-28-2010, 06:58 PM   #13
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QuoteOriginally posted by conradj Quote
It's true, the screws on my K-7 show signs of it. The few that get wet and salty from my hands turn white and the corrosion has to be removed periodically.

--The lens mount on the body is designed to separate from it if the stress is too high, to preserve the integrity of the body and avoid bending it out of shape, which would mean the complete loss of the camera. i think the screws that hold the mount on are designed to fail and break before too much stress is transferred into the body.
Good point, and good to know if it is indeed the case by design.
09-28-2010, 08:08 PM   #14
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I've rarely had less than 2-7 lbs of lens and TC hanging off any of my Pentaxes for the last four years, and I'm not concerned with the strength of the mounts at all. If they're screwed into plastic, then it's obviously good enough to support this kind of weight on a daily basis.

I'm retired, so up to this year, my habit had been to shoot almost every day for a couple of hours from March to October. The main lenses I use have been an FA* 300/4.5 ED (IF), FA* 300/2.8 ED(IF), Tamron SP 300/2.8 LD, Sigma EX 300/2.8 APO, and Sigma EX 180 APO DG Macro, all with at least one TC more often than not. I carry my cameras with the lenses attached to be able to take advantage of any photo ops that might offer themselves on the way to and from any of my normal shooting locations, so one of these lenses is almost always mounted on one or more of the bodies.

If there had been any weaknesses in the design and execution of the lens mount attachments on the DS, K100DS, K10, K20, or K-7, I think the weight of these lenses, and the frequency that they're mounted and carried on my cameras would have exposed them.

I used to worry about this, I got over that a long time ago. . .

Scott
11-08-2010, 05:56 PM   #15
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User bobmaxja thinks the plastic is "a Glass filled composite part who is more stable than metal".
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