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05-31-2012, 05:15 PM   #1
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Magnesium chassis vs. polycarb/stainless steel body?

I was looking at the difference between the K5 and the K30 and one of the differences was the magnesium chassis of the K5 versus the polycarbonate/stainless steel chassisof the K30.

What practical difference does that make? You can't feel the magnesium alloy, since it's coated with plastic anyways so they should feel the same. Both cameras are of approximate weight. Does it make it more resistant to being dropped? I would imagine that anything strong enough to damage the chassis would irreparably damage the outer body of the camera anyways. So aside from sounding cool, what difference does it realistically make?

05-31-2012, 05:27 PM   #2
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AFAIK stainless steel is heavier than titanium. I'll hazard a guess that a titanium chassis weighs a few dozen grams less than its kevlar+stainless counterpart. That might not much matter for casual usage; for someone grasping the camera+lens for many hours during serious shooting, it could make a considerable difference in comfort.

This is only a guess. I haven't looked at any Official Pentax Pronouncements to see if they're expressed a rationale. Maybe someone here with more intimate knowledge can correct me.
05-31-2012, 05:56 PM   #3
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EMI is the only thing i can really think of.

with a drop the magnesium might dent and as such disperse the energy of the fall with the hopes the inner workings will stay intact, polycorbonate will crack.
05-31-2012, 06:10 PM   #4
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Basic difference is the weight, compare the K-5 against the K-20D, the last flagship camera with the stainless steel chassis.

05-31-2012, 06:11 PM   #5
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Polycarbonate is pretty tough, must get hit really hard for it to crack!.
05-31-2012, 06:56 PM   #6
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QuoteOriginally posted by Ex Finn. Quote
Polycarbonate is pretty tough, must get hit really hard for it to crack!.
Indeed. It's the same stuff they use for bullet-proof glass. The K-30 knocks 90 grams off the K-5's weight, that's a significant difference when the weight of the K-5 is 740 grams. Realistically, I wouldn't expect it to affect the durability much at all.
05-31-2012, 07:11 PM   #7
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When you make something out of a specialized metal, as in Magnesium, you are looking for strength/wear or thermal characteristics. By having a magnesium body, you can make it much thinner and maintain the same strength. When you have many openings/buttons on a camera, like the K5 has, it becomes difficult to make a chassis that is strong and make it out of plastic. Fine edges for buttons and such can be made thinner with a metal vs. a plastic. The K5 has an LCD top and more openings on the camera and accepts a battery grip. The K5 has to withstand use with a grip or without and the different loads that entails. To make the K5 out of plastic would be very difficult to do. The K30 allows for a "simpler" chassis and Polycarb is a good/easy choice.
05-31-2012, 09:33 PM   #8
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QuoteOriginally posted by Ex Finn. Quote
Polycarbonate is pretty tough, must get hit really hard for it to crack!.
The insides are probably broken before that, so if the magnesium shell gives in then it would be beneficial.
Replacing the shell is cheaper then replacing the motherboard for example.

05-31-2012, 10:20 PM   #9
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Thermal stability is quite OK with magnesium alloys, better than plastic anyway for the same strength. Therefore better precision can be achieved in a magnesium body.
06-01-2012, 12:12 AM   #10
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The difference is that if you use two divert materials body you have more mounting elements to deal with; rivets, screws and etc., they will probably brake first.
06-01-2012, 12:31 AM   #11
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Hmm, nice question by the OP, and explanations from the replies. I was wondering about that too, stainless steel + polycarb and their differences

so is the magnesium alloy not really that far up the toughness scale vs. pc+s.s?
06-01-2012, 12:39 AM   #12
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I forgot mention that composite materials have thermal expansion problem that can brake them.
06-01-2012, 01:31 AM   #13
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So it looks like we have several reasons for premium titanium vs plebian kevlar+steel: weight, structural integrity, thermal expansion, trauma reactions -- all for a cost, of course. The TANSTAAFL rule. I suspect either package is more rugged than similarly-priced competitors.
06-01-2012, 02:23 AM   #14
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QuoteOriginally posted by i83N Quote
I forgot mention that composite materials have thermal expansion problem that can brake them.
Sounds like you're saying that all composite materials have thermal expansion problems, thank god they don't make aircrafts out of them... oh wait...
06-01-2012, 02:25 AM   #15
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QuoteOriginally posted by RioRico Quote
So it looks like we have several reasons for premium titanium vs plebian kevlar+steel: weight, structural integrity, thermal expansion, trauma reactions -- all for a cost, of course. The TANSTAAFL rule. I suspect either package is more rugged than similarly-priced competitors.
Pentax always use a steel frame, something you don't find with other entry level cameras at least, but hey who gives that a second notice?
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