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10-10-2010, 11:32 AM   #1
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A question on body materials (magnesium alloy, polycarbonate, etc)

In these forums and those of Canon/Nikon users, we often praise the cams using magnesium alloy and criticize those cams that use polycarbonate.

I really don't have any clue, but is this criticism really warranted? I ask this because I am not a materials engineer, and for all I know, perhaps polycarbonate offers the same (or better) qualities of magnesium alloy at a lower cost. The downside being that we are all accustomed to thinking that plastic is inferior/worse than metal or alloys, so cam manufacturers need to play to this thought in their camera segmentation.

So I wonder whenever people criticize those plastic bodies, is it just a "feel" thing or are they actually aware of factual material engineering qualities that make polycarbonate worse than magnesium alloy for cameras?


Last edited by uchinakuri; 10-10-2010 at 05:01 PM.
10-10-2010, 03:44 PM   #2
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QuoteOriginally posted by uchinakuri Quote
In these forums and those of Canon/Nikon users, we often praise the cams using magnesium alloy and criticize those cams that use polycarbonate.

I really don't have any clue, but is this really true?
Yes, its true that we often criticize the plastic bodies and praise the mag alloy ones.
10-10-2010, 03:57 PM   #3
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QuoteOriginally posted by uchinakuri Quote
So I wonder whenever people criticize those plastic bodies, is it just a "feel" thing or are they actually aware of factual material engineering qualities that make polycarbonate worse than magnesium alloy for cameras?
Depends on the quality of the plastic. One thing's for sure, a metal exterior is *thinner* per volume of stuff you can pack in there.
10-10-2010, 04:22 PM   #4
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My friend dropped his K-7 on the pavement and there was only a small dent on the edge of the bottom plate. I held the damaged magnesium plate when it was removed from the camera and it weighed next to nothing. Now if it was a polycarbonate body, it would have been a nasty crack for sure. With magnesium, expect some paint wear at the edges over time. Give me magnesium over polycarbonate any time.

10-10-2010, 04:42 PM   #5
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QuoteOriginally posted by creampuff Quote
My friend dropped his K-7 on the pavement and there was only a small dent on the edge of the bottom plate. I held the damaged magnesium plate when it was removed from the camera and it weighed next to nothing. Now if it was a polycarbonate body, it would have been a nasty crack for sure. With magnesium, expect some paint wear at the edges over time. Give me magnesium over polycarbonate any time.
I am in the business of plastic. I sold Polycarbonate for 20 years. Magnesium is lighter because they can put thinner wallbut polycarbonate will absorb shock better. No polycarbonate would have no crack .
PLastic is more versatile as you can put more function in the molding than magnesium .One of the best advantage of magnesium is an electronic shielding.

Volume is also an important criteria. Polycarbonate molding , when part come out of the mold , they are ready for use, not the case with magnesium, deburring is often needed.
This is why you see magnesium in higher end model and plastic in lower end because of cost more than anything else.

But also most of the exterior part avec PC
10-10-2010, 05:01 PM   #6
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QuoteOriginally posted by enoeske Quote
Yes, its true that we often criticize the plastic bodies and praise the mag alloy ones.
Thanks for that. I fixed the question
10-10-2010, 05:05 PM   #7
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QuoteOriginally posted by bobmaxja Quote
I am in the business of plastic. I sold Polycarbonate for 20 years. Magnesium is lighter because they can put thinner wallbut polycarbonate will absorb shock better. No polycarbonate would have no crack .
PLastic is more versatile as you can put more function in the molding than magnesium .One of the best advantage of magnesium is an electronic shielding.

Volume is also an important criteria. Polycarbonate molding , when part come out of the mold , they are ready for use, not the case with magnesium, deburring is often needed.
This is why you see magnesium in higher end model and plastic in lower end because of cost more than anything else.

But also most of the exterior part avec PC
Very interesting! So from your response, I gather that the advantage of magnesium is that it can allow for thinner cam bodies and less EMI? At the same time, the advantage of polycarbonate is that it offers more durability and a lower cost?

In that sense, it seems that our perceptions are actually wrong when we criticize the polycarbonate bodies as being less durable than those that use magnesium alloy, right?
10-10-2010, 05:24 PM   #8
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QuoteOriginally posted by bobmaxja Quote
I am in the business of plastic. I sold Polycarbonate for 20 years. Magnesium is lighter because they can put thinner wallbut polycarbonate will absorb shock better. No polycarbonate would have no crack .
PLastic is more versatile as you can put more function in the molding than magnesium .One of the best advantage of magnesium is an electronic shielding.

Volume is also an important criteria. Polycarbonate molding , when part come out of the mold , they are ready for use, not the case with magnesium, deburring is often needed.
This is why you see magnesium in higher end model and plastic in lower end because of cost more than anything else.

But also most of the exterior part avec PC
My son-in-law dropped his D90 from a low level in his camera bag to the floor. It broke the lens mount and required a trip to Nikon for repair. I'm guessing that Polycarbonate isn't too strong.

10-10-2010, 05:40 PM   #9
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QuoteOriginally posted by jimH Quote
My son-in-law dropped his D90 from a low level in his camera bag to the floor. It broke the lens mount and required a trip to Nikon for repair. I'm guessing that Polycarbonate isn't too strong.
I just at my DAL and this look different. The product is probably a polycarbonate glass filed or phenolic. When you add Glass , you loose flexibility but gain stiffness.

I will agree that for lens mount , alumiunium is better
10-10-2010, 05:47 PM   #10
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QuoteOriginally posted by jimH Quote
My son-in-law dropped his D90 from a low level in his camera bag to the floor. It broke the lens mount and required a trip to Nikon for repair. I'm guessing that Polycarbonate isn't too strong.

That'll be about the chassis, really. Both materials will have advantages for say, a skin, in different conditions and all, but you do want a nicely-solid chassis, however it's made. (ie, metal less likely to get brittle in cold: ) but a light plastic camera might *bounce* where a heavy plastic one would crack or shatter, etc etc.

You basically don't want to drop any of these highly-electronic cameras, whatever they're made of, though: it's not good for any optical instrument, but there's no real getting around how much there is in there to break, no matter how tough the body may be. Not that you need any extra troubles.

My things mostly just need to wear well: I don't jump out of airplanes with em, or anything. You don't want to have to baby things overly, or have a little mishap put you out of action, though.

Last edited by Ratmagiclady; 10-10-2010 at 05:57 PM.
10-10-2010, 09:29 PM   #11
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QuoteOriginally posted by bobmaxja Quote
I just at my DAL and this look different. The product is probably a polycarbonate glass filed or phenolic. When you add Glass , you loose flexibility but gain stiffness.

I will agree that for lens mount , alumiunium is better
Stainless is better for the mounts than aluminum.
10-10-2010, 09:33 PM   #12
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Polycarbonate bodies aren't all created equal either. It also depends on what the chassis is made of. A metal chassis offers rigidity to keep things from flexing and stretching too much during use. However, with magnesium alloy, that problem is solved, but some of those are better than others, i.e. the K-5/K-7 is better than the D7000. The D7000 leaves the front as polycarbonate which defeats part of the purpose of having the alloy in the first place.


sarcasm
10-11-2010, 06:02 AM   #13
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Broken D90 Lens mount

QuoteOriginally posted by Ratmagiclady Quote
That'll be about the chassis, really. Both materials will have advantages for say, a skin, in different conditions and all, but you do want a nicely-solid chassis, however it's made. (ie, metal less likely to get brittle in cold: ) but a light plastic camera might *bounce* where a heavy plastic one would crack or shatter, etc etc.

You basically don't want to drop any of these highly-electronic cameras, whatever they're made of, though: it's not good for any optical instrument, but there's no real getting around how much there is in there to break, no matter how tough the body may be. Not that you need any extra troubles.

My things mostly just need to wear well: I don't jump out of airplanes with em, or anything. You don't want to have to baby things overly, or have a little mishap put you out of action, though.
Yes, but his D90 was in a fitted Nikon sling bag, and the whole works fell about 2 feet. It should have been well cushioned in that bag, but it still broke.
10-11-2010, 10:54 AM   #14
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QuoteOriginally posted by jimH Quote
Yes, but his D90 was in a fitted Nikon sling bag, and the whole works fell about 2 feet. It should have been well cushioned in that bag, but it still broke.
*wince* Well, that's no good, is it? Are you saying the chassis in there was polycarbonate? I'd probably be leery of things being *that* breakable. Sounds like that camera just wasn't made with much of a heavy lens in mind, if that could happen.

I do carry just about everywhere, and even if I'm pretty easy on my gear, considering, it's hard to avoid that kind of knock forever. I'm pretty confident of my K20d, (The chassis looks kind of like an Erector set in there, but it's strong pieces where they need to be, nothing's become mushy or loose in there, and the outer case inspires enough confidence for what that does, but I admit it wasn't a selling point from Internet distance. Once this fellow arrived, the feel was 'OK, this is good.'

I'd buy another body like this, ...though of course with the K-7 they seem to have gone one better. I wonder if those plates would get a little brassy after a while. (I kind of have a thing about good old tools. Signs of use show a bit of soul and all. )

Light things can be resilient, too: I have a little Lumix bridge camera that probably had the worst spill of any camera around me lately: I'd thoughtlessly slung the camera on the factory strap and a few minutes later, thanks to a kind of slick-surfaced jacket I was wearing, plunk. (This camera shortly thereafter got a Lowepro Speedster strap, which is much much grippier) Bounced right off the lens hood, which protected the works of the lens and all. Not having much mass and being all plastic, though, the little feller survived a spill that'd make me worry about something made of the old brass and glass. The old F=ma equation.

So, plastics can be good for some things, it's a question of what's the right material for the right application.
10-11-2010, 03:38 PM   #15
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QuoteOriginally posted by Ratmagiclady Quote
*wince* Well, that's no good, is it? Are you saying the chassis in there was polycarbonate? I'd probably be leery of things being *that* breakable. Sounds like that camera just wasn't made with much of a heavy lens in mind, if that could happen.
You know RML I'm not sure that the body on that camera is Polycarbonate, but whatever it is, it's not very strong. It does have a metal lens mount, however, the reviews that I've read don't mention anything about chassis construction, must not be something they want to talk about. I'm guessing that if they were proud of the chassis design and construction, it would have been mentioned in one of the reviews.

I understand what you mean about the build of the K20, I've got a K10 which shares the same chassis with the K20, and Just the other day as I picked up my sling bag, I had neglected to zip the camera section of the bag shut, and out tumbled the K10 from about a foot off the floor onto my carpeted floor and it just nicely bounce once with my Tamron 17-50 f2.8 on it, which is a heavy lens, with no ill affects. I breathed a sigh of relief, picked up the camera, tried it and everything was normal. I don't doubt the strength of the build of our Pentax DSLRs and as you say the K7 and now the K5 have gone one step further in build quality.
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