70D and 7Dmk2 is coming what to expect?

Started Feb 28, 2013 | Discussions thread
Dale Buhanan
Veteran MemberPosts: 3,788Gear list
Re: May I?
In reply to bobn2, Mar 5, 2013

bobn2 wrote:.

I don't believe there are significant downsides to a plastic chassis, but if someone for whatever reason decides the must have a metal chassis in their camera, the 7D is not the one for them, and it is right that they be properly informed. End of story.

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Hi Bob,

I looked at the pictures you posted of the 7D DSLR cutaway with interest.  It looks obvious that from the lens mount through the mirror box and to the sensor mount and pentaprism housing that there is some sort of plastic material as the main construction material alright  I have been thinking through the ramifications for Canon doing that.

Pros:  It is weighs less and is very likely less expensive to manufacture, easy to cast and form and would be very repeatable.  Net result... camera is less heavy and less expensive.

Cons:  It would likely not have the same strength for lens mount screw threads, and the fiber filled Polycarbonate plastics have very nearly double the thermal expansion coefficient of stainless steel.  This would make lens to sensor spacing more susceptible to change with ambient temperature.  I don't know if this is sufficient to cause a problem or not, but they use metal on the 1-series... so Canon did that for a reason.

Whatever the reason, it seems to work adequately well for the XXD series and 7D.  But it may not be as strong with a long heavy lens as the 1 series cameras I would think.  I have never removed the lens mount screws, so I don't know how long they are for thread bite, or if they go all the way through and have a nut on the back... Which would of course make the lens mount considerably stronger.

Do you have a feeling for the lens mount screws?

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kind regards

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