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05-15-2018, 02:50 PM   #16
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Thanks for responses. Interestingly, my suspicions seem to be confirmed – the problem seems to be not so much the material as our perception or preconceived notions. a.t. seemed to be close to the mark with "We humans are subjective, idiosyncratic beasts." Consequently, at this point in the discussion, I don't think I have read anything that would prevent me from buying a plastic lens. But I am open to more thoughts.

QuoteOriginally posted by .a.t. Quote
We humans are subjective, idiosyncratic beasts. I get a lot of tactile enjoyment from simply picking up and holding a substantial, metal lens.
I understand. On the other hand, I have some old lenses I can take off the shelf if I get the urge to fondle metal.

QuoteOriginally posted by DeadJohn Quote
I am fine with plastic lenses. Plastic has lower thermal conductivity so my hands don't get as cold supporting a telephoto lens. Plastic expands and contracts less than metal, so has less focus drift as the temperature cools down during a photo sequence of the night sky.
These are interesting points and are never addressed when reading about lenses. Why is that?

QuoteOriginally posted by 6BQ5 Quote
I think the plastic vs metal stigma may be a left over from the past when plastic was not so easily engineered and designed as today. Today's plastic can be tough, slippery, compliant, and stable all at the same time if done right. I'm all for plastic where it makes sense.
Valid point, and one I suspect hits the nail on the head. Consider all the plastic in today's automobiles, or for that matter, everywhere. Even contractor-grade tools are made with plastics.

QuoteOriginally posted by 6BQ5 Quote
My dream is to see plastic lens elements that match the performance of glass. Then lenses will be super, super light!
Like the plastic in my trifocal "glasses?"

QuoteOriginally posted by jatrax Quote
And to be fair 80's plastic lenses have not held up nearly as well as metal takumars.
Are you really buying a lens for it to last 30 years? Most people don't expect to live in the same house 30 years. As for an old guy like me, 5 years is probably a lifetime guarantee. To be serious, I don't think it is fair to compare the plastics technology of the 80's to today.

QuoteOriginally posted by stevebrot Quote
Filter threads
Filter threads (yes, twice). A bent metal thread is usually repairable. A split plastic part may compromise the lens fatally. Threading onto plastic generally feels like...(description edited due to graphic nature of language).
Yes, and yes. A very valid point.

QuoteOriginally posted by stevebrot Quote
Dubious durability of plastic mounts. I would qualify this as pertaining mostly to challenging (gritty) environments and heavy use. Ditto for plastic mounts on cameras.
Have you ever had problem with plastic mounts? I did a quick search of the forum and found only two mentions – in one the guy dropped his lens 5 feet to a linoleum covered concrete floor and in the other there was a problem with some mounting screws for some reason I couldn't determine.

QuoteOriginally posted by stevebrot Quote
Brittleness of plastic chassis over time
Is this from experience with a lens or just plastic in general?

05-15-2018, 03:05 PM   #17
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It's not about the material, it's about build quality.
The Angenieux zooms with policarbonate barrels were very well built, and have proven durable, but at the time they didn't enjoy the commercial success they deserved because photographers expected high quality lenses to be all-metal.
I'm testing turn of the century "silver" FA zooms. The construction is awful, but the average optical quality is superior to better built early FA and F counterparts.
The problem lies in durability and easy/possible repair procedures.
If a lens group is glued or set in a plastic casing, the only option is to find a spare.
BTW, I never found a metal zoom out of whack, but with no signs of damage. TWO expensive f/2.8 zooms looking absolutely pristine had bent focusing/zooming "tubes", causing vignetting and other problems.
The day the spares will be unavailable those very good and highly valuable lenses will be usable only as doorstops
Sigma still has spares for film era objectives. If I'm not mistaken some Pentax spares for slightly newer lenses are nowhere to be found.
If a partly plastic lens has brass-on-aluminium retaining rings, and cams/tubes/helicoids made of durable materials, that would be a high-quality objective that would last forever.
Plastic is not the devil.
Unfortunately a wobbly, plasticky barrel is often the sign of a very poor construction. A few of my wobbly zooms are surprisingly good... but I made sure to buy like new examples.
Some of my vintage lenses with great all-metal build are very worn and have horribly bent filter threads, but the optical performance is so good to make me think they perform as when they were new. A plastic lens would never survive a crash that causes that kind of damage.
When I mention durability I'm also referring to electro-mechanical problems. Some FA lenses are failing. My FA Macro 100mm, that is NOT cheaply built, had a problem with the limiter switch (AF problems). It has gone under surgery to repair the switch. I don't believe a cheap poorly made zoom would be as easy to repair, because containing costs has a price, if something fails.
Most of my favourite Pentax were purchased second-hand in the late seventies or early eighties. All of them work as the first day. Three of my very expensive zooms had to be repaired (one of them because it became a fungus nest while the other metal lenses stored in the same place where unaffected). Yes, plastic welcomes fungi more than metal. Personal experience.

Last edited by cyberjunkie; 05-15-2018 at 03:11 PM.
05-15-2018, 03:08 PM   #18
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QuoteOriginally posted by E-man Quote
Metal = 'Tool'
Plastic = 'Toy'
The K-1 body has a metal skeleton. It's encased in plastic, though, for a whole bunch of good reasons. Does that make the K-1 a toy?

Metal and plastic each serve a purpose. In the non-camera world, screwdrivers, hammers, and many other tools often work best with a combination of materials.
05-15-2018, 03:18 PM - 1 Like   #19
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QuoteOriginally posted by AggieDad Quote
Are you really buying a lens for it to last 30 years? Most people don't expect to live in the same house 30 years. As for an old guy like me, 5 years is probably a lifetime guarantee. To be serious, I don't think it is fair to compare the plastics technology of the 80's to today.
I think you missed my point (or I stated it poorly). The 'plastic is bad' stigma is largely from the 80's lenses. Modern (DA and DFA) lenses are also almost all plastic but it is completely different. I don't expect the issues with 80's plastic to show up on modern lenses.

But yes, when I buy a new lens I am expecting it to last 30 years. And whether that is plastic or metal is, and should be, immaterial. The standard that a lens is built to is what counts. If the materials meet those standards it matters not (to me) if it is plastic or metal.

I love my metal takumars but there is no question the modern DFA lenses are built to a very high standard as well and should with care last 30 years as well.

05-15-2018, 03:21 PM - 1 Like   #20
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QuoteOriginally posted by AggieDad Quote
These are interesting points and are never addressed when reading about lenses. Why is that?
I don't think designers pay much attention to temperature because it's a small factor. Sharpness, contrast, flare resistance, distortion, etc. are all much bigger concerns for the vast majority of photographers.

Thermal conductivity: When it gets very could, most people wear gloves, at which point metal and plastic lenses don't make that much difference in comfort.

Thermal expansion: A typical use case has us refocusing before every photo so thermal expansion doesn't matter. It's only when you are taking photos for an hour at the same focus setting, such as with astrophotography stacking and time lapses, where temperature can change enough to be an issue.

Astrophotography is a niche. Long telescope tubes do consider materials. Metal tubes need more frequent refocusing than carbon fiber.
05-15-2018, 03:29 PM   #21
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QuoteOriginally posted by DeadJohn Quote
The K-1 body has a metal skeleton. It's encased in plastic, though, for a whole bunch of good reasons. Does that make the K-1 a toy?
From PENTAX K-1 | RICOH IMAGING :-

"The K-1’s exterior casing is made of highly rigid, lightweight magnesium alloy, which provides excellent shock-resistance and electromagnetic shielding performance. By coupling it with a high-rigidity metallic chassis housing the core components, the K-1 forms a compound structure to assure outstanding durability and exceptional reliability."

However, it doesn't bother me in the least that my K-70, 18-135 and 28-105 have plastic in their construction.
.
.

Last edited by MrB1; 05-15-2018 at 03:37 PM.
05-15-2018, 04:25 PM - 1 Like   #22
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I sold plastic all my life and mainly the engineering type . Most plastic use in Camera are glass fill(GF) polyester , GF polycarbonate or similar. The glass content is between 30-50% giving strenght, stability and stifness. These products cost more per lbs than metal. The major difference, you can mold different function with plastic versus you need to machine most metal parts. Their tolerance are also well understand and can be very tight. One major advantage, it's a lot harder to dent a plastic part made with these grade

Also using the term plastic dont mean anything same as metal. Their more than 10,000 different grades of plastics made with about 100 different families..
Why cheaper or low end bodies , use plastics, again mainly they use GF Polycarbonate or blend with lower GF content to keep a nice fining on the exterior, is because you can mold complex shape than make assembly of component easier. When you choose the proper grade for the application, it will last a long time.


05-15-2018, 04:34 PM   #23
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QuoteOriginally posted by reeftool Quote
I put my broken pieces in a box and sent it to Sigma and had it back 2 weeks later for under $200 including shipping. It was easily fixed.
That $200 is pretty amazing and your story indicates one of the fuzzy areas regarding plastic/composite construction. In some cases, it is better to sacrifice the outer covers in order to preserve the critical innards and it appears our 17-70c (I have one too) meets that design goal.


Steve

(...love my Sigma 17-70, though not for manual focusing...)
05-15-2018, 05:15 PM   #24
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QuoteOriginally posted by AggieDad Quote
I don't think I have read anything that would prevent me from buying a plastic lens. But I am open to more thoughts.
You may want to re-read my comments. There is little reason to draw a line of junk|gem between plastic and metal, though there is plenty of reason consider materials (build quality) when making a purchase. In many ways, my DA 50/1.8 a fine performing throw-away lens and I have foster no illusions that it will be usable forty years from now. My Pentax-M 50/1.7 was made almost 40 years ago and I am confident it will continue to perform a notch above the DA 50/1.8 for at least the rest of my life and probably longer. OTOH, the DA does have AF and is very light, hence its position on my shelf. FWIW, I also own the Pentax-A 50/1.7 and its plastic aperture ring is a wretched piece of work and although it is optically equivalent to my M 50/1.7, it will likely need a partial teardown in the near future to allow full functionality on the Super Program to which it is mated. I may yet replace it with a Pentax-A 50/1.4 or 1.2.

QuoteOriginally posted by AggieDad Quote
Are you really buying a lens for it to last 30 years? Most people don't expect to live in the same house 30 years.
I have carried my cameras and lenses though moves to more that 15 different houses and have several lenses and one body that I have owned for almost forty years.

QuoteOriginally posted by AggieDad Quote
Have you ever had problem with plastic mounts?
Hand me a piece of sandpaper and a current model plastic mount lens and I will provide a short object lesson showing the abrasion resistance of those materials.


Steve

Last edited by stevebrot; 05-15-2018 at 05:22 PM.
05-15-2018, 05:16 PM - 1 Like   #25
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QuoteOriginally posted by 6BQ5 Quote
My dream is to see plastic lens elements that match the performance of glass.
For aspheric elements, that happened decades ago.


Steve
05-15-2018, 05:30 PM   #26
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QuoteOriginally posted by bobmaxja Quote
Also using the term plastic dont mean anything same as metal. Their more than 10,000 different grades of plastics made with about 100 different families..
Why cheaper or low end bodies , use plastics, again mainly they use GF Polycarbonate or blend with lower GF content to keep a nice fining on the exterior, is because you can mold complex shape than make assembly of component easier. When you choose the proper grade for the application, it will last a long time.
Good point and the point might also be made that not all metal is durable or suitable for lenses. I have several Soviet-made rangefinder lenses and on many, the bodies are made of something that is quite generously referred to as aluminum...the kind used for cheap cookware. Pot-metal might be a better description and with tear-down there is a huge risk that screw threads might not survive the service process.


Steve
05-15-2018, 05:43 PM   #27
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QuoteOriginally posted by jatrax Quote
I think you missed my point (or I stated it poorly). The 'plastic is bad' stigma is largely from the 80's lenses. Modern (DA and DFA) lenses are also almost all plastic but it is completely different. I don't expect the issues with 80's plastic to show up on modern lenses.
Thank you for clarifying. You are right, I did miss your point, and now that I get it, I do agree with you.

QuoteOriginally posted by bobmaxja Quote
I sold plastic all my life and mainly the engineering type...

... using the term plastic don't mean anything same as metal. Their more than 10,000 different grades of plastics made with about 100 different families.
Your points are well-taken – especially the one quoted above. Unfortunately, there is typically no discussion of the type of plastic used in manufacturing a lens, but only the (usually disparaging) comment that the lens is made of plastic.

QuoteOriginally posted by stevebrot Quote
Originally posted by AggieDad
Have you ever had problem with plastic mounts?
Hand me a piece of sandpaper and a current model plastic mount lens and I will provide a short object lesson showing the abrasion resistance of those materials.
Come on stevebrot. That's not having a problem under normal use, that's willful destruction. Hand me a hammer and I will provide a short object lesson showing the dent resistance of metal lenses.
05-15-2018, 06:16 PM   #28
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QuoteOriginally posted by MrB1 Quote
From PENTAX K-1 | RICOH IMAGING :-

"The K-1’s exterior casing is made of highly rigid, lightweight magnesium alloy, which provides excellent shock-resistance and electromagnetic shielding performance. By coupling it with a high-rigidity metallic chassis housing the core components, the K-1 forms a compound structure to assure outstanding durability and exceptional reliability."

However, it doesn't bother me in the least that my K-70, 18-135 and 28-105 have plastic in their construction.
.
.
Thanks. It feels like a plastic/rubber/composite skin over the metal to me, to improve grip and handling, but from that link I see I am wrong. The metallurgy team developed a fantastic alloy.
05-15-2018, 06:40 PM   #29
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A point that hasn't been made is that 'plastic' lenses came when cameras were first getting cost-cutting engineering. The same mind set that lead to failure-prone plastic mirror gears in the MZ/ZX series of film cameras.



While plastic has certainly come a long way in quality and robustness, the transition from metal to plastic lens bodies left a bad taste in the whole industry.
05-15-2018, 06:55 PM   #30
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My issue with plastics has been failures due to aging, usually because of the plastic becoming brittle. I know that plastics are constantly evolving, and I'm sure the formulations have improved since the time the things I now have falling apart on me were made 20-30 years ago, but we were told then how great plastics were, and one of their selling points was longevity - no corrosion, maintain color..... Based on all the aged plastic things that have broken on me, I've become a bit disenchanted with the stuff. That said, I've got some great modern lenses made of plastic bodies, and I've got my fingers crossed they'll never fail due to the materials. But given the choice, like if I were going to buy an Irix where you have the option, I'd spend the extra bucks to get the metal bodied version.
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