Magnesium bodies

Started Mar 26, 2012 | Discussions thread
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Re: Nice examples
In reply to Leonard Migliore, Mar 29, 2012

Leonard Migliore wrote:

I really can't figure out why they would do this; if you're going to the trouble to use a metal frame, you really should attach the important parts (lens and sensor) to that frame; everything else can flap around freely but you do want the optics to be precisely located.

Actually, it's because engineering plastic really is perfectly sufficient and quite ideal for this purpose. The advantage of engineering plastic is that it's very rigid, and extremely moldable. The moldability is really quite key because it allows the engineers to create the exact, intricate shapes, struts, and details to the subframe that puts the material exactly where the stress points are. Plus, it's lightweight, and cost-effective. Also, keep in mind, this isn't just any old toy plastic. Plastic comes in a very broad range of compositions and characteristics, and there are a lot of ill-informed people who immediately think that "plastic" must mean cheap and poor quality. The reality is that, for the cost, weight, and rigidity, high carbon engineering plastic is the optimum material. To make the same kind of structure in metal, it would be much heavier and more costly, with little or no advantage. And the fact that there have literally been millions of SLRs and DSLRs that have been made with this plastic subframe structure is a testament to the fact that it really does work! It has definitely proven itself in the real world over the span of decades of camera manufacturing and millions of cameras.

A typical mirror box subframe structure made of high strength engineering plastic, onto which the lens mount, mirror mechanism, and sensor are attached:

In the structural diagram below, from dpreview's 500D review:

"'s primarily made from three materials; a stainless steel chassis (blue in this diagram), the mirror box which is made of high-strength 'engineering plastic' (red in the diagram) and the body made of a special lightweight 'engineering plastic' which also provides some electromagnetic shielding. Construction is good (considering the budget price) with no creaks or rattles."

If you're putting the optical elements on plastic you might as well make the frame out of goat cheese.
Leonard Migliore

Believe it or not, the engineers that have designed these cameras might know a bit more about what it takes to make a structurally sound camera than you do. And clearly, after so many millions of cameras sold, it does appear that they are doing just fine without the input of armchair engineers on internet forums telling them that they are doing it all wrong. The fact that I can go out and buy an all-plastic Canon Rebel T3i, stick a heavy Canon L lens on it, and do a full shoot with it and get excellent, sharp results is a testament to the fact that today's cameras-- even the inexpensive plastic ones-- are quite well engineered.

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