# A7RII - Design Flaw?



## meywd (Aug 30, 2016)

Found this today while browsing on flickr, not sure its true, but she seems angry, if you follow the photo to flickr, you will find two comments with videos about the issue, didn't watch them yet.




DON’T BUY SONY MIRRORLESS SYSTEM - MY HUMBLE REQUEST by Viki Velcheva, on Flickr


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## Maximilian (Aug 30, 2016)

meywd said:


> Found this today while browsing on flickr, not sure its true, but she seems angry, if you follow the photo to flickr, you will find two comments with videos about the issue, didn't watch them yet.
> ...


I have some doubt to believe that.

Having some basic knowledge in materials science I know that the body is made out of magnesium *alloy*. I know that there is no "*RAW*" magnesium and that alloy normally does not need any kind of painting to get protection from corrosion or humidity.
Only really extreme conditions (temperature close to the melting point) and agressive chemicals could cause problems with magnesium alloy. 

And magnesium oxide is non conducting and insoluble in water. So what problem could it cause on electronic circuits?

_Edit:
But if Sony has some sealing leakage here other parts inside the body could react with humidity or sweat or else._


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## Mikehit (Aug 30, 2016)

I have to say I was a bit sceptical as well. 
She goes into a lot of detail about Boyle's law and all that which is largely unnecessary - IME this is often the sign of someone with a little knowledge desperately trying to apply it to think of a reason.


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## IglooEater (Aug 30, 2016)

Maximilian said:


> _Edit:
> But if Sony has some sealing leakage here other parts inside the body could react with humidity or sweat or else._



Well now, that would apply even if there were no magnesium heat sink exposed, now wouldn't it? Sobasicly the end of the analysis is that, if the Sony has a sealing problem, then the Sony has a sealing problem.. :?


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## Dylan777 (Aug 30, 2016)

I saw this on SR site. I didn't finish watching the clip. Couldn't stand the guy for 1min. Sounds Bsss

https://www.youtube.com/watch?v=dQbN9Ymm1Wk


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## meywd (Aug 30, 2016)

Maximilian said:


> meywd said:
> 
> 
> > Found this today while browsing on flickr, not sure its true, but she seems angry, if you follow the photo to flickr, you will find two comments with videos about the issue, didn't watch them yet.
> ...



Don't know much about it myself, however here is a quote from Wikipedia - Magnesium alloy



> Corrosion troubles may be expected even with protective treatment in poorly designed assemblies where moist air is trapped or where rain is allowed to collect. Where such designs are avoided, unpainted magnesium alloy parts that are oily or greasy operate indefinitely with no sign of corrosion. Magnesium alloy parts are usually painted, however, except where the conditions of exposure are mild. To assure proper adherence of the paint, the part is cleaned by grinding, buffing, or blasting, then given an acid dichromate dip.



I guess that means, if there is really a design flaw, and humid air is stuck around the heat sink, it will cause corrosion.


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## Tugela (Aug 30, 2016)

meywd said:


> Maximilian said:
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Humid air will not stick around a heat sink. Because it is hotter, that area will actually be drier.


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## IglooEater (Aug 30, 2016)

Tugela said:


> Humid air will not stick around a heat sink. Because it is hotter, that area will actually be drier.



So is that why exhaust lines never rust? :


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## Tugela (Aug 30, 2016)

IglooEater said:


> Tugela said:
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> > Humid air will not stick around a heat sink. Because it is hotter, that area will actually be drier.
> ...



Corrosion through oxidation are electrochemical reactions. They don't require exposure to water, they require exposure to air. Heat will accelerate those processes.


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## Ozarker (Aug 30, 2016)

IglooEater said:


> Tugela said:
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> > Humid air will not stick around a heat sink. Because it is hotter, that area will actually be drier.
> ...



Driest place on earth? Antarctica.

Warm air is generally wetter than cold air.

Heat sinks don't get rid of moisture. They just take heat away from specific parts. If there is moisture in the camera the heat sink will turn it into vapor if it gets hot enough. There is no chimney stack taking the heat out of the camera... especially one that is weather sealed.

Good observation IglooEater   

I actually wish bodies were made from Titanium. Never rusts, very low conductivity (lower than magnesium which happens to be similar to aluminum). Titanium can be cast just like magnesium can.


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## Tugela (Aug 31, 2016)

CanonFanBoy said:


> IglooEater said:
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The only way warm air could have more moisture is if you physically have water in the camera, in which case you have bigger problems than humidity.


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## Tugela (Aug 31, 2016)

CanonFanBoy said:


> IglooEater said:
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Magnesium alloys are pretty tough and don't corrode under normal circumstances. This is due to the almost instant formation of a magnesium oxide coating on the surface which then stops most other reactions. I am a chemist and we have a lot of magnesium alloy fittings in the lab. We also commonly use magnesium turnings to generate organometallic reagents, so I am very familiar with how stable the stuff is. Generally you only see noticeable corrosion on fittings if something is sitting in a water bath for a long time, or if it is exposed to things like hydrochloric acid fumes.

The corrosion seen in those cameras in the video is more likely due to current leakage, and that is starting electrochemical oxidation reactions with air in the cameras. And most likely the same current leakage is what is causing the camera failures. All that "humidity" and "slicking" nonsense has nothing to do with it.


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## Ozarker (Aug 31, 2016)

Tugela said:


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Sorry, not true.


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## bwud (Aug 31, 2016)

I've designed a lot of titanium parts (usually 6Al4V). It's not something I'd use without a compelling reason. Compared to magnesium, both the raw material and the machining costs are substantial. Additive manufacturing may mitigate the latter (as would casting, although you have to cast in a vacuum or inert gas environment), but either way making the body from titanium would increase the cost and thus sales price of a camera with arguably little benefit (and in fact perhaps with detrimental effects, such as being a far less effective heat sink).


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## IglooEater (Aug 31, 2016)

Tugela said:


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Agreed. The illustration is somewhat flawed, but it's point still holds. Just because something is hotter doesn't lower it's propensity to oxidation necessarily. In general, oxidation is accelerated as temperature increases.


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