Sony A58 "plastic lens mount"

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Greg Beetham
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Re: Sony A58 "plastic lens mount"

Unread post by Greg Beetham »

I would doubt it would be any cheaper, those kinds of ‘plastics’ are probably closer to two or three part specialized/modified epoxies than regular plastics, and that last one for example is either machined (which means just as labour intensive as a machined metal mounting) or compression molded which means you have to machine or cast a tool and dye mold for mounting and aligning with precision in a press to make the thing you want (while the stuff is still viscous).
But that one I referred to does have at least one drawback, it absorbs moisture.
It would be interesting to know what ‘plastic’ Sony is using, I have doubts it would be a really expensive one or it would defeat the purpose one would think.
Greg
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bfitzgerald
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Re: Sony A58 "plastic lens mount"

Unread post by bfitzgerald »

Actually there is one detail that has not been noticed (if it matters or not who knows). If you look at the A58 mount pictures the inner part of the plastic is "at an angle" bevelled for want of a better word. This was not the case on previous Minolta film bodies where the all plastic mount was flat ie the same look as the metal mount.

This "engineering plastic" stuff whilst mildly interesting is what is clearly is, marketing speak and likely of no significance. I'm sure it's fine for kit lens or plastic lens users, personally I'd run a mile with metal mount lenses

There is some more interesting info here:
http://www.imaging-resource.com/PRODS/s ... y-a58A.HTM
Whilst he's made the mistake of calling the aperture ring control a load bearing surface (sigh)

I was surprised to read this:
That the Sony A58 is based around a less powerful image processor seems fairly clear from its burst-shooting performance, which not only trails the A57 by some distance, but also doesn't quite manage to match the capabilities of the previous entry-level model, the A37. Of course, that will in part be due to the higher-resolution image sensor, and all those extra pixels that must be handled in capturing, processing and writing each image. Still, the five frames-per-second burst rate is just a little less than the 5.5 fps reported by Sony for the A37, and well behind the eight fps of the A57. Buffer depth for the Sony A58 is said to be just seven fine JPEG, six raw, or five raw+JPEG frames. The A37, by contrast, managed 17 JPEG fine, seven raw, or six raw+JPEG frames, and the A57 allowed up to 25 fine JPEG, 21 raw, or 19 raw+JPEG frames.


Buffer depth is way down v the A57 (which is actually surprisingly big for that class of camera) if that info is right that's another deal breaker for some folks.
Oh and he's calling the "Sony's proprietary Multi-Interface hot shoe" ;-)
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Greg Beetham
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Re: Sony A58 "plastic lens mount"

Unread post by Greg Beetham »

Yes that is some blooper from a review site, calling the aperture control ring part of the lens mounting itself when it is obviously isn’t.
As I mentioned previously there is the circular leaf spring that is most likely still there (although I don’t have an exploded view of the A58 mounting to confirm), that spring is what takes most of the punishment when mounting and demounting a lens so the inside face of the mount doesn’t actually wear much, if at all, maybe the leading edge ramps of the bayonet flanges do get some abrasion but it’s the spring that has to cope with the majority of the sliding motion wear.
Of course the inside edge of the bayonet flanges on the lens itself have no protection from wear so I would think the ones with plastic flanges might wear more than the ones with metal but I have no idea how much difference that would be in practice, the plastic ones might even be more slippery and resist galling more than the metal ones perhaps but it’s not a high speed or high load (generating heat) type of interface so there might not be much wear even with those.
What I think can happen with plastic mounts on the camera is the danger of the gradual spread of the plastic under screw head tension and may be more pronounced without any load spreading metal overlay, (apparently there are different versions of those with some not as good as others in stiffness).
Overall stiffness in the metal overlay means the difference between a clamping effect that does not transfer the screw head tension in a localized manner and one that isn’t as stiff and does.
If compression spread does occur then the mounting can be deformed slightly over time, mostly between the screws, buckling up slightly there, which could perhaps affect the electrical contacts and the correct register distance.
Of course Sony might be using some super dooper kind of plastic that will not compress under local screw head tension (ever) so the above conjecture might not come into play, we’ll see eventually I guess.
Greg
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