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04-26-2007, 09:11 AM   #1
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Composite vs metal construction

First of all, I prefer metal lenses with the "solid feel".

STILL, I am somewhat confused about the terms we all use when talking about lenses: Plasticky, light, heavy, solid. We praise lightness when we focus on carrying the lens along us, we praise another one for feeling solid and all glass! A zoom lens can be said to be poor because it is very plasticky and light unlike the the good old ones with the "proper feel".
When we drop a metal-body lens, the body survives and the glass breaks; the lens becomes useless. When we drop a plastic (!) lens, the body breaks and the lens becomes useless. Am I exaggerating?
First of all, what we call plastic is probably called "composite material" technically. (Please correct me, if I am wrong). Similar materials are also used in dentistry, I believe.

There is also the rather unoptical question of lens sounds! When I shake a plasticky lens (I know, you don't!) I hear clicks and sounds of some moving parts as if something is going to stop working properly. When I shake (OK, you would not) an old lens, it remains gracefully silent.

My questions are:
- How strong are the newish "light" body materials?
- Is it fair to equalize lightness with lack of durability?
- What materials/metals were used in general in the lens bodies we collectively refer to as "metal"?
- Do the "sounds" matter?

Why do I ask?
Because I do not how can I evaluate the words about a lens properly. Optical performance only? "Feel"? Weight? Which should come first? (I mean, the relative value of each property; surely optical quality must be the first).

Also, I wonder how different are the current lenses (by Pentax or others) with regard to their "bodies"?

Engineers or like-minded friends, could you help illuminate this confused guy?

04-26-2007, 09:35 AM   #2
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I thought this essay had a good take on plastic vs. metal in lens design:

sm-02-05-02
04-26-2007, 06:19 PM   #3
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In industries where passion plays small issues can become false major issues. Plastics issues in cameras and lenses is copied by battery issues in portable electronics, gear sets in bicycling, etc. Amplifying the small issue is leftover mania caused by improper use of plastics when they were first adopted for new applications.

A lot of polymers are more expensive than metals, yet plastics' parts cost less than metal parts due to ease of net shape manufacturing. Plastics generally don't perform well when exposed to wear and shear (gears, threads, bayonets), especially if their use and egagement is occasional and uncontrolled. There are lots of plastic gears and linear motion components specifically engineered for their applications, but these type of polymer's are not conducive to quality optical assemblies.

How strong are the newish "light" body materials?Exceedingly strong. Polymers excel at elastic deformation: give and return to position. Metals' plastic deformation result in gouges or cracks.

- Is it fair to equalize lightness with lack of durability?Yes and no, depends on the application. Aluminum tripods, bike frames and wheels can continue performing with slight scuffs, gouges or cracks; in carbon fiber these components are garbage immediately upon such minor damage.

- What materials/metals were used in general in the lens bodies we collectively refer to as "metal"? Aluminum, brass, bronze, steel.

- Do the "sounds" matter?Yes. Some companies in certain industries pay great attention to the sound of mechanisms, static (in your hand, tap it, knock on table top) and dynamic (gears, motors, mechanisms).
04-26-2007, 07:04 PM   #4
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QuoteOriginally posted by bc_the_path Quote
Why do I ask?
Because I do not how can I evaluate the words about a lens properly. Optical performance only? "Feel"? Weight? Which should come first? (I mean, the relative value of each property; surely optical quality must be the first).
Well, not always. I would say that the FA50/1.4 has a slight edge on my Super-Multi-Coated Takumar 50/1.4 optically but I don't like using the plastic-wrapped lens nearly as much. There is another guy who is even crazy enough to sell an FA 31/1.8 Limited - twice! - for (mostly) other-than-optical complaints.

They're as valid as any other complaint - if you hate using a lens, it doesn't matter how good it is optically because you'll never use it!

04-26-2007, 09:32 PM   #5
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An interesting post. It's remarkable how - even after literally billions of pounds of synthetic organic materials have been developed, manufactured and used since the '30's and '40's - people's perceptions of "plastics" differ depending upon the application. For example, those that find that a thermoplastic lens barrel feels "shoddy" will delight in the look and feel of polypropylene bumper covers on even very high-end cars.

I've been a polymer chemist for over 30 years, and I've invented and developed a number of thermoplastic and thermosetting resins, one of which is successful commercially in barrier packaging applicatons. No one understands better than I how effective polymeric materials are when applied appropriately. Yet even I find the "feel" of thermoplastic materials in lenses and camera bodies less satisfying than that of metal (although I revel in the weight savings).

The fact is synthetic materials - thermoplastics, thermosets and elastomers - are durable and effective light-weight materials when properly engineered. After all, many of us have been sailing large "plastic" boats for decades.

Jer
04-26-2007, 10:57 PM   #6
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I won't say much, except that I prefer Metal lenses unless I'm going on a long hike, or the temperature drops below freezing. That's when you'll see me reach for the plastic lenses.
04-29-2007, 06:35 AM   #7
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I prefer the feel of metal lenses. They seem to have tighter tolerances in the mechanics. Plastic may be as strong or stronger. Kind of like plastic outer camera body shells. Much nicer to hold in cold temps. The thing that worries me is the longevity of the materials. Many things made of plastic have self destructed over the years. The plastic seems to change composition and fall apart. This may take 20 years or so. Never had similar problems with metal (as long as it isn't rusting).
Would rather have my plastic bicycle helmet than metal. It has saved me a few times. Carbon fiber may have a competitor soon. Called Carron. It uses carrot fibers in place of carbon. Supposed to be more durable. Interesting times.
thanks
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04-29-2007, 07:10 AM   #8
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I can also prefer metal lens barrels. But not the aluminium ones... To get the real feeling it takes something more precious. Then the stuff has to be designed the right way as well. The focusing ring should not be narrow and it should not be close to a part of the barrel that scratches your fingers when you focus manually. There are a lot of details...

I prefer a good design making use of polycarbonate (or whatever it is) to a half sloppy metal thing.

The plastic often being superior in cold, heat and wet environments doesn't make it bad either, the light weight is also an advantage.

All in all it comes down to every single lens. Sweaping statements like "I prefer metal" is on the same level as saying "I prefer Pentax lenses over Canon lenses" not to mention "I like the color rendition from xxx".

I agree with barondla about the interesting times comment. Will we see ceramic glass used in lenses, for example?

04-29-2007, 07:12 AM   #9
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QuoteOriginally posted by carpents Quote
There is another guy who is even crazy enough to sell an FA 31/1.8 Limited - twice! - for (mostly) other-than-optical complaints.

They're as valid as any other complaint - if you hate using a lens, it doesn't matter how good it is optically because you'll never use it!
What a shilly-shally b@stard! Maybe he didn't read the LL article about the limiteds?

04-29-2007, 09:11 AM   #10
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QuoteOriginally posted by Jonas B Quote
What a shilly-shally b@stard! Maybe he didn't read the LL article about the limiteds?

Best lenses made by anyone ever!!!!!!

(LOL!)
04-30-2007, 11:07 AM   #11
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People with more experience (carpents and Jonas) and more knowledge (Sailor and Donald) have already weighed in on this issue. I have four "favorite" lenses: Zenitar 16mm f2.8 fisheye...metal; Pentax SMC 50mm F1.2...metal; Pentax FA 50mm F1.4...plastic and the Tamron 90mm F2.8 macro...plastic. Two of each. Each one has good "ergonomics" it feels good, focuses smoothly, does what it is supposed to do smoothly and effeciently. If you put a gun to my head and forced me to make a decision I'd prolly go with the metal, but I wouldn't be happy about it.
BTW the original "composite" material is....(drum roll).....wood! It is a fiber (celulose) embedded in a "plastic" matrix (lignin)

NaCl(so Sailor is even more right about boats than he knows)H2O
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