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05-15-2018, 08:33 AM   #1
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What Is The Deal With Plastic?

I've been looking through the lens reviews (more dreaming than planning) and have noticed that every time a lens is constructed of plastic that the issue is considered a negative. So I got to wondering...

Has there been a problem with plastic constructed lenses? Do they fall apart? Do they suddenly stop focusing? Why does the plastic seem to be considered is a major negative?

I have no background in chemistry or plastics (I'm a math guy, a teacher), but I do know that there are many, many things built of some pretty tough plastics. In fact in many instances, plastic construction can be an advantage I do like the weight savings with my Sigma 150-500.

Anyway, what am I missing? What I am going to lose other than some weight to carry when I buy a plastic lens?

Just wondering.

Don

05-15-2018, 08:35 AM   #2
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The biggest thing is that plastic is cheap, and doesn't feel as solid as metal.
05-15-2018, 09:15 AM - 2 Likes   #3
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Plastic lenses come in many quality levels. But the taint of the lowest cost worst built lenses (I'm looking at you Sigma UC) sticks in people's minds.
05-15-2018, 09:39 AM   #4
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QuoteOriginally posted by AggieDad Quote
. . .
Anyway, what am I missing? What I am going to lose other than some weight to carry when I buy a plastic lens?

QuoteOriginally posted by timw4mail Quote
The biggest thing is that plastic is cheap, and doesn't feel as solid as metal.


I agree with timw4mail.

We humans are subjective, idiosyncratic beasts. I get a lot of tactile enjoyment from simply picking up and holding a substantial, metal lens.
Light weight is near the bottom of my list of desirable lens criteria.

Also, being a fan of manual focuising, most plastic lenses -by design- don't give me the physical feedback I appreciate.
I delight in long focus throws and nicely damped aperture rings.

And practically speaking, plastic filter threads can be a pain. It often takes me many tries to get a metal filter threaded onto a plastic lens.

05-15-2018, 09:57 AM   #5
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Bad plastic can crack too easily. Most people don't realize that there are many types of plastic, and there is an assumption that metal is always higher quality than plastic.

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.
05-15-2018, 10:10 AM   #6
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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.

My dream is to see plastic lens elements that match the performance of glass. Then lenses will be super, super light!
05-15-2018, 10:41 AM   #7
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Plastic Lyrics
05-15-2018, 10:41 AM   #8
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I think it is a held over stigma. And just saying plastic is like saying metal. What plastic or what metal? Finely machined steel or aluminum or brass can be a pleasure to work with. But cheap 'pot' metal castings are just as 'cheap' as poor plastic.
High end plastic is not cheap in any sense of the word and can be stronger and more stable than metal. But the stigma of generic 'plastic' still sticks.

And to be fair 80's plastic lenses have not held up nearly as well as metal takumars.

05-15-2018, 10:50 AM - 3 Likes   #9
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QuoteOriginally posted by AggieDad Quote
Has there been a problem with plastic constructed lenses? Do they fall apart?
It depends on the lens. Some do and many don't. I have a handful of modern lenses featuring mostly plastic construction and have had no issues with them in terms of durability or performance thus far. Do I prefer metal lenses? Absolutely! However, here are a few talking points:
  • Notes on reviews regarding plastic build help potential buyers to temper expectations and price point
  • 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).
  • 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.
  • High quality plastics come into their own for long focal-length zooms where weight of a metal lens might be excessive
  • I don't buy consumer grade plastic-body zooms used, with heavy prejudice against 1980s vintage product. Double prejudice against store brands. These were cheaply made to start with and don't improve with age.*
  • Most metal-bodied consumer grade zooms also suck
  • I like my optics to feel and act like precision-made products, not toys. Even new, the focus and zoom mechanism of many plastic lenses feels dry and cheap.
  • Some plastic lenses are quite good and feel nice too. My DA 50/1.8 is simply fun to shoot with well worth the money in its price bracket.
  • Brittleness of plastic chassis over time
  • I have metal body lenses dating back to the mid-1950s, all of which operate with factory-fresh smoothness after application of fresh grease. I doubt that any of my plastic lenses will be serviceable at even 20 years due to brittleness of screw threads and the the use of self-tapping screws.
  • Is all Nirvana in the land of metal lenses? Nope. Fore example, I have three Carl Zeiss Jena lenses in Exakta mount that have gone crummy with age and are difficult to service with the needed new grease and cleaning of aperture mechanisms.
I hope this helps to show a few of the reasons for prejudice and also dispel notions of clear superiority of metal.


Steve

* To be fair, I have a Tamron 70-210/4-5.6 (58A) that has the most wretched scratchy plastic construction imaginable and which rightly enjoys a 7.5 rating in reviews on this site. That aside, it is light and very compact and performs quite adequately at f/8 and shorter than 200mm. I paid $20 for it to get the PKA adapter. One of these days, I should do a comparison thread between it and the highly-regarded Tamron SP 70-210/3.5 (19AH).
05-15-2018, 11:28 AM   #10
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QuoteOriginally posted by stevebrot Quote
It depends on the lens. Some do and many don't. I have a handful of modern lenses featuring mostly plastic construction and have had no issues with them in terms of durability or performance thus far. Do I prefer metal lenses? Absolutely! However, here are a few talking points:
Great post, Steve

I prefer metal lenses too, but I also have a number of partially or completely synthetic lenses that have always worked, and continue to work, just fine. It's fair to say that not all synthetic materials are made equal, and some are incredibly durable.

That said...

QuoteOriginally posted by stevebrot Quote
Brittleness of plastic chassis over time
This is the one thing that bothers me...

I haven't had any problems with my plastic lenses, but a few weeks ago my HP ENVY 17 laptop was out of action for a couple of days. Despite being a high specification and quite expensive model when I bought it five or six years ago, the chassis is plastic. Over time, the area to which one of the screen hinges was attached had crumbled away. Clearly it was badly designed for the stresses involved (the 17" screen is heavy, and the hinges are rather heavy-duty accordingly), but the material also appears to be quite brittle and unsuited to the job. So, I had to partially dismantle the machine, clean out all the bits of crumbled plastic, then re-build that area using epoxy resin glue.

I can see that there must be some plastic components in lenses that are similarly prone to wear and, if the materials aren't up to the job (which may not be known until the item has been used for some time), breakages may occur.

Still, I've been fortunate so far... even with rather lightly-built plastic lenses such as the DA35 f/2.4 and DA50 f/1.8
05-15-2018, 11:31 AM - 2 Likes   #11
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Maybe I've been lucky but, so far, no problems with lenses with plastic mounts and/or plastic bodies.

If screwing filters into plastic threads is a problem, then perhaps give the lens a ring with metal threads:-
Get any cheap metal filter and remove the glass (or get a suitable metal step-up ring if the lens might vignette). Screw that carefully but firmly into the plastic threads of the lens, to give the lens almost 'permanent' metal threads. Screw any filter etc. gently into that, so it can easily be unscrewed after use, leaving the metal ring still attached to the plastic lens.
05-15-2018, 12:01 PM - 1 Like   #12
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I know this article has been linked to before but whenever the plastic vs metal discussion comes up, it's worth looking at. Lens Rentals | Blog
Roger Cicala has tons of experience and is familiar with lots of lenses from many brands.

I shot a wedding this past weekend and both lenses I used were plastic. Most of my shots were with a Sigma 17-70c and a few with the DA 50/1.8. I rely on both these lenses quite a bit. I get great results every time and I never think twice about using them for anything. The DA 50/1.8 is dirt cheap and I think it the best $100 camera gear investment I ever made. I think it was even cheaper, Black Friday about 4 years ago.

I dropped the Sigma last summer (and my K5). Yes, it hit the concrete and was in 2 pieces. Would one of my all metal lenses survived? Maybe, but more likely something would have been dented or bent, making it just as broken. 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.
05-15-2018, 12:56 PM   #13
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Metal = 'Tool'
Plastic = 'Toy'
05-15-2018, 01:01 PM   #14
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QuoteOriginally posted by E-man Quote
Metal = 'Tool'
Plastic = 'Toy'
With respect, I couldn't disagree more. There are some fantastic lenses with synthetic bodies. To dismiss those as toys is to utterly fail in recognising how capable and durable they are, and miss out on some wonderful optical instruments... But that is, of course, a personal choice

EDIT: ... and let's not forget that, over the years, there have been plenty of quite poor lenses with metal bodies.

Good lens (metal or plastic) = 'good lens'
Bad lens (metal or plastic) = 'bad lens'

Last edited by BigMackCam; 05-15-2018 at 01:11 PM.
05-15-2018, 02:15 PM - 3 Likes   #15
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I like things that shoot: cameras and guns. I don't buy plastic guns and I don't buy plastic lenses. Are there advantages of plastic? Yes, some. But for me personally, there are many more advantages of metal. I have steel bumpers on my truck and I don't want plastic. I have a cracked, plastic gear in my MZ-3 and I want a metal replacement. I have a 1960 camper built from wood and metal and I don't want plastic in my camper. I have a 2006 camper with lots of plastic in it and I wish it had more metal and wooden surfaces. My metal-frame guns have much less recoil and handle better. My brother loves his plastic guns, but he is starting to sell some of the popular plastic-framed guns and replacing them with metal due to the advantages and comfort.
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