It seems Canon's new super-duper macro lens is made from "engineering plastic".
[Chuck Westfal said: "The focus ring, lens mount and name plate are made from aluminum, and other parts are basically made with engineering plastic."]
Does anybody know how common this is? Is normal plastic-bodied lenses made of this, or from cheaper plastic? How about camera bodies? The shell of high-end camera, for instance.
I'm all for plastic, despite loving a good metal object. A metal object is beautiful on the shelf, but when you carry it around all day, a pound less weight is a blessing.
And they can make plastic look good if they want. I suspect they could make it look pretty much like anything instead of the horrible "silver" plastic they use for cheap phones (shudder). Just for one thing I found out that the early Canon AE-1 had a top plate of chromed plastic, and I had never suspected it! It totally looks like metal.
To my knowledge, the most common of engineering plastics is Polyoxymethylene, or Acetal, better known by its DuPont trade name Delrin.
I use this material routinely to fabricate all kinds of small parts, and it truly is a wonderful invention. With properties rivaling those of soft metals (think aluminum, for instance), it offers unmatched ease of machining, self-lubrication, outstanding dimensional stability and excellent overall resistance (it's main weakness is poor performance with acids and chlorinated compounds). Many more-or-less specialized variants of Acetal are also available for mass production of different product types.
It is however not the easiest plastic to mould by injection, as it exhibits a high thermal expansion coefficient. It is therefore necessary to oversize mould cavities to compensate for heavy shrinkage upon part cooling. This can lead to expensive tuning of the mould geometry if precise dimensions are sought for the finished part. Mind you, modern design software makes this a much lesser concern, so Acetal is being used in more and more applications every day (popular in automobiles), which in turn drives the cost down to a level similar to other high-end commodity resins (still a tad on the expensive side, though).
And that's just one engineering plastic, there are many more available, each with a unique set of properties. The thing is, some of those resins are incredibly expensive, at several thousand dollars per kilogram, so their use is pretty much limited to applications where absolutely nothing else will meet the requirements!
Of course, I cannot tell exactly what resin(s?) Canon are using in the fabrication of their lens and camera housings, but I really wouldn't be surprised to learn that it actually is some variant of Acetal, modified to increase impact resistance (the "standard" formulation is somewhat easy to nick).
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12 comments:
To my knowledge, the most common of engineering plastics is Polyoxymethylene, or Acetal, better known by its DuPont trade name Delrin.
I use this material routinely to fabricate all kinds of small parts, and it truly is a wonderful invention. With properties rivaling those of soft metals (think aluminum, for instance), it offers unmatched ease of machining, self-lubrication, outstanding dimensional stability and excellent overall resistance (it's main weakness is poor performance with acids and chlorinated compounds). Many more-or-less specialized variants of Acetal are also available for mass production of different product types.
It is however not the easiest plastic to mould by injection, as it exhibits a high thermal expansion coefficient. It is therefore necessary to oversize mould cavities to compensate for heavy shrinkage upon part cooling. This can lead to expensive tuning of the mould geometry if precise dimensions are sought for the finished part. Mind you, modern design software makes this a much lesser concern, so Acetal is being used in more and more applications every day (popular in automobiles), which in turn drives the cost down to a level similar to other high-end commodity resins (still a tad on the expensive side, though).
And that's just one engineering plastic, there are many more available, each with a unique set of properties. The thing is, some of those resins are incredibly expensive, at several thousand dollars per kilogram, so their use is pretty much limited to applications where absolutely nothing else will meet the requirements!
Of course, I cannot tell exactly what resin(s?) Canon are using in the fabrication of their lens and camera housings, but I really wouldn't be surprised to learn that it actually is some variant of Acetal, modified to increase impact resistance (the "standard" formulation is somewhat easy to nick).
the horrible "silver" plastic they use for cheap phones
Actually, making decent-looking silver plastic is quite difficult, so cheap silver plastic parts are usually painted (that's why the finish wears off easily). I, for one, cannot wait for this fad of all things silver to pass!! 'nuff said.
the early Canon AE-1 had a top plate of chromed plastic
It is indeed possible to electro-plate suitably prepared plastic parts, thus depositing real metal coatings onto the parts. This was quite popular during the sixties, especially for automobile trimmings. That's probably what you are referring to here.
I can see the shell of the lens being made out of engineering plastic, like the camera bodies. But I suspect the internal parts are probably magnesium like the camera bodies or some other alloy.
Really cheap lenses like the nifty 50--50mm f/1.8 might be mostly plastic. But I doubt a $1000 lens is.
JB, it seems that this is not your father's plastic. From the linked article:
[Chuck Westfal said: "The focus ring, lens mount and name plate are made from aluminum, and other parts are basically made with engineering plastic."]
"Actually, making decent-looking silver plastic is quite difficult, so cheap silver plastic parts are usually painted (that's why the finish wears off easily). I, for one, cannot wait for this fad of all things silver to pass!! 'nuff said."
You said it. And yes, I did think of silver-painted plastic. Awful. Worse than a bad boob-job. Almost.
"It is indeed possible to electro-plate suitably prepared plastic parts, thus depositing real metal coatings onto the parts... That's probably what you are referring to here."
Yep.
... So something like Acetal would probably *not* actually be cheaper to use in a lens? It would be used for some engineering advantage? (And weight loss perhaps.)
So something like Acetal would probably *not* actually be cheaper to use in a lens? It would be used for some engineering advantage?
Don't kid yourself, it's the £$¥ that rules the world. Choices are seldom made taking only your best interest into account, things must go in the "right" direction money-wise too.
To answer your question, Acetal is certainly cheaper than many fancy aluminum alloys if you take surface finishing into account, since aluminum parts must be anodized or otherwise coated before use. But, the high cost of production tooling makes injection moulding an expensive proposition up-front; only relatively large production volumes warrant it.
Note that Acetal can be readily machined (1), thus it sometimes makes sense to use it instead of aluminum while still avoiding high tooling costs. It can be machined using the same equipment used to make metal parts and requires no post-machining surface finishing (except for cosmetics surfaces, see comments below).
As a general rule, what governs the choice between machining or moulding engineering plastics is the anticipated production volume. Moulding is almost always much cheaper, but you must absorb the high tooling costs.
Machining might be viable for some lens parts, but it's really hard to say without having a long, hard look at each specific case. In such a context, engineering plastics are simply new contenders for the jobs traditionally held by the softer metals.
In the end, the range of manufacturing processes usable with any given material is just as important in the selection process as are the material's physical properties, its cost, the cost of the required tooling or even the available supply sources.
Bottom line, and I've said it before and I'll say it again: engineering is an exercise in compromise (actually a quote from Sir Rutherford ;). Everything is negotiable (and thus constantly negotiated) during a design exercise, provided that the end result meets the specifications and cost objectives.
There are also other, more subtle and oft overlooked forces at work, like the battle between conservatism and the need to innovate, to distance yourself from the competition. Such influences are often the real evolutionary motors in well established industries, because production people are most reluctant to change proven, well-worked materials and processes.
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(1) Machining, in this context, refers to manufacturing of parts by subtractive operations. In other words, you take a solid plate, bar or tube and cut away enough material to make the desired part.
This is somewhat wasteful in terms of material when compared to injection moulding, where molten plastic in injected into a cavity, resulting in a completely formed part in a single operation. But injection moulding also produces a fair amount of waste (sprues, etc.), and since the waste is recyclable, the added material expense introduced by machining is not that great.
On the other hand, and save the very simple cases, parts generally take more time to machine than it takes to make them by injection moulding. You therefore end up trading capital expenditure for a higher per-part cost.
Perhaps the greatest advantage of modern computer-assisted machining is that the design of a part can be very easily and rapidly altered at virtually no extra cost, while modifying an existing injection mould is always a challenge, when even possible.
Finally, it must also be noted that cosmetic finishes are very difficult or even impossible to achieve by most machining operations. Therefore the outer shell components of a product are not likely to be machinable without some sort of ulterior surface finishing... such parts are probably almost always a clear win for moulding.
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Not exactly simple, is it? ;-)
No kidding!
So we can learn that even if Canon cared to give a reason why they selected a material, and if we assume it would be an honest answer, it would still be over-simplified by necessity.
And the truth probably is that there's no absolute, definitive answer to such a question.
Change in the context of an established industry is the result of a slow, painful, yet necessary evolution process. Careers really are made or ruined on the outcome of the associated turmoil, so it's very hard to get unbiased information.
But in the end, change usually occurs when it's due, more or less... ;-)
I've had an AE-1 apart, and the top plate was anodized Al - not plastic.
That machine was made in Japan.
Possible that yours was a knock-off from Korea or China. (yes, the Asians did try to cut each other's throats)
No, I didn't observe it myself, I read on The Online Photographer that one of the ways that AE-1 was trail-blazing was the plastic top plate.
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