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01-14-2013, 02:34 AM   #31
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QuoteOriginally posted by vonBaloney Quote
no such thing as a plastic optical element that isn't a toy.
you sure?

01-14-2013, 02:43 AM   #32
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The Pentax FF camera should be W&DEETR - can't do without it in Scottish summers ;-)
01-14-2013, 03:01 AM   #33
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Going back to Adam's idea about taking a lens apart, I'm happy to help out, as I am handy on the tools.
So, I need a few donor lenses to make up a decent sample size. Send me any Limited lenses not currently attached to your camera, and some A series stars as well. A 50-135 might be interesting too. I'll get back to you on what I got for them how much plastic and blah blah blah.

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01-14-2013, 03:30 AM   #34
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I recall seeing a DA21 Ltd disassembly online somewhere, and most of the internal (non-glass) components were plastic, despite the metal exterior. It doesn't seem to bother people here too much! I'm very happy with my mostly-plastic DA35/2.4, for my part.

01-14-2013, 11:06 AM   #35
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QuoteOriginally posted by vonBaloney Quote
I can assure you that all the glass parts are still glass -- no such thing as a plastic optical element that isn't a toy.
Optical grade plastic and related coatings have reached a point where in certain applications they seem to be superior optically to glass. I used to be dead set against against viewing my world through plastic lenses. Today, I can't imagine going back to glass. It is probably mostly the flare control, but my plastic glasses have better resolution. Personally, I wouldn't be afraid of an all plastic optical system for my camera, but naturally I would expect the same review process as with glass lenses.
01-14-2013, 03:27 PM   #36
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QuoteOriginally posted by sam-joseph Quote
A 50-135 might be interesting too.
Have seen one open, (opened it myself), disappointing amount of plastic, the bayonet is metal, but behind that, is a plastic part connected to the rest of the lens with only four tiny screws in another plastic part.

All K-mount pentax lenses after the M series have plastic in them, the newer, the more.plastic.
Some more expensive A lenses have very little plastic in them.
The FA series power zooms, have metal gears for the parts which move the focus and zoom mechanisms, and plastic gears for the encoder wheel that signals the motor movement to the system (new in the FA, not present in the F series).

The lenses are of glass, but again the FA series introduced the aspheric molded plastic on those lenses.
I have seen a FA * 1:2.828-70, with a strange artifact, which was probably caused by a faulty fabricated aspheric molded layer.

If you want solid durable K-mount or screw mount lenses, stay with the M or older series.
01-15-2013, 02:28 PM   #37
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QuoteOriginally posted by glasbak Quote
Have seen one open, (opened it myself), disappointing amount of plastic, the bayonet is metal, but behind that, is a plastic part connected to the rest of the lens with only four tiny screws in another plastic part.
This feature came up in a thread here a couple of months ago.
The consensus seemed to be that it is a deliberately weak point,
designed to shear under impact to protect the rest of the lens.
01-15-2013, 02:41 PM   #38
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QuoteOriginally posted by lytrytyr Quote
This feature came up in a thread here a couple of months ago.
The consensus seemed to be that it is a deliberately weak point,
designed to shear under impact to protect the rest of the lens.
Find that unlikely, if you want a deliberate weak spot, take the bayonet instead, by making it from plastic..

01-15-2013, 03:19 PM   #39
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QuoteOriginally posted by glasbak Quote
Find that unlikely, if you want a deliberate weak spot, take the bayonet instead, by making it from plastic..
No, that would then have to be weak for normal circumstances as well.
Shearing fasteners is pretty standard technology, like in the bases of street lights.
01-15-2013, 04:48 PM - 1 Like   #40
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It seems we'd be well served on this forum if someone with respected credentials were to to author an article on modern industrial plastics and polymers, their definition, the pros and cons and their relative economy in terms of manufacturing cost.

One doesn't hear the same biased discussions of the value of modern materials in sports accessories such as tennis, golf, fishing, and yes, firearms, aircraft, or medical prosthesis for examples. Esthetics shouldn't be confused with durability and strength.

While the dents and dings that accumulated on my brass and aluminum SLR bodies may appeal to some as signs of honest wear, I'm quite pleased with the durability of the present "plastic" camera bodies and lenses; not to mention the weight savings. There were "cheap" metal components in the past too.

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01-15-2013, 05:43 PM   #41
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QuoteOriginally posted by pacerr Quote
Esthetics shouldn't be confused with durability and strength.
True, they are not the same. They are however, both considerations in the product. For example, Plastic cups can be unbreakable and far more durable than bone china. Which do you prefer to drink from; which is more sensible on a picnic? One sees the blending of aesthetics and practicality in modern station wagons. The practical and sensible Volvo wagon of old has traded in some of it's practicality for looks in modern designs. The balance between aesthetics and practical function is set by personal preference.
01-16-2013, 12:12 AM   #42
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QuoteOriginally posted by lytrytyr Quote
This feature came up in a thread here a couple of months ago.
The consensus seemed to be that it is a deliberately weak point,
designed to shear under impact to protect the rest of the lens.
Could be, BUT people are complaining, who use some brands, that these plastic parts are not replaceable. So what is being protected when they make an supposedly designed-in weak point, but the part that's designed to fail to protect what it's attached to is not replaceable?
01-16-2013, 01:47 AM   #43
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QuoteOriginally posted by snake Quote
Could be, BUT people are complaining, who use some brands, that these plastic parts are not replaceable. So what is being protected when they make an supposedly designed-in weak point, but the part that's designed to fail to protect what it's attached to is not replaceable?
The discussion concerned a specific Pentax lens (the DA* 50-135),
not hypothetical questions about "some" (unspecified) "brands."
01-16-2013, 01:53 AM   #44
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QuoteOriginally posted by lytrytyr Quote
The discussion concerned a specific Pentax lens (the DA* 50-135),
not hypothetical questions about "some" (unspecified) "brands."
Specified: Olympus 4/3 lenses, including SHG.
01-16-2013, 02:12 AM   #45
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QuoteOriginally posted by snake Quote
Specified: Olympus 4/3 lenses, including SHG.
What was the designed failure mode in those lenses?
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