[secateurs]

You are way off the mark with these insulting comments! Trust me, I have a brain and can think things through !

You are right, Schraubstock. I don't know what got into me. I sincerely apologise. I was especially wrong about voiding your warranty. I somehow misunderstood what you were doing and thought you were somehow taking a seal off the INTERNAL mic, not the mic jack. I saw the photo, but it didn't register what I was looking at because I didn't bother getting my own k-5 out to look. I apologise. I'm sure you haven't voided your warranty by trying your patch. But if water did through the patch you still might have issues asking for warranty with a clear conscience.

I guess one of the reasons i went off with both barrels was this comment:

always good at physics (as well as blowing my own trumpet)

Which I took as being rather arrogant. And i'm sure you know the "good old" Aussie culture of chopping down the tall poppy. But I really should know by now that it's not my place. You know, the whole seeing a speck in someone else's eye when you have a whole plank sticking out of your own!

You might also be interested to know that I had the exact same question / concern as you when I was looking into getting the K-5. I posted a thread on the forums here about it, and had a few helpful replies. However, i'm looking now and can't find it. Maybe it was lost with the server crash....

Anyhow. My humble apologies.

Changes in internal pressure are not ok. A DSLR or lens can never be airtight if it changes size.

Thanks for sharing your knowledge. I spoke out of ignorance.

[Smeggypants]

Nah, don't close the thread yet; it's still in its "informative and entertaining" phase. Hasn't quite reached "tiresome and draggy".

.

I agree. it's certainly an entertaining thread. I'm currently working on a new design to protect my K-5 from Dark Matter and beligerent Higgs Bosons.

My first attempt involved isntalling a small black hole in the HDMI port.

[Digitalis]

I agree. it's certainly an entertaining thread. I'm currently working on a new design to protect my K-5 from Dark Matter and beligerent Higgs Bosons

You forgot about shielding against neutrinos and high speed bogons. I also suggest you wrap your head in aluminium foil and use straws for breathing holes to prevent any more bright cluons from getting into your head.

[Smeggypants]

hehe

[Cannikin]

Thanks for sharing your knowledge. I spoke out of ignorance.

Always glad to put my otherwise wasted years of studying physics (and various other sciences) to use.

Oh and sorry to anyone if I seem rather... "forceful" (pun maybe intended) at times. I tend to get worked up over these types of discussions for some reason.

[fs999]

I have a good dust removal tool in PSP...

[Digitalis]

I tend to get worked up over these types of discussions for some reason.

we all get worked up over one thing or another, some of these things may seem utterly trivial to others who aren't privy to the intricacies of the issues being debated.

Like me for instance: I'm a musician I hate it with a passion when I hear other musicians use incorrect baroque ornamentation,even though such musical ornamentation is subjective there are established rules that have to be observed. I also get ticked off when people make sweeping generalisations about photographic lenses, I also get irritated when I see or Hear of people using incorrect photographic technique.

[Gimbal]

The question remains, where does the camera normally breathe?

[normhead]

The question here is did Pentax anticipate the problems these air sucking zoom can cause, and is it already appropriately filtered. Anyone have their address? Maybe an email can clear this up.

[Seamripper]

This is all just an April fools joke, Right?

[secateurs]

This is all just an April fools joke, Right?

It was posted a bit early for April Fools, even for Australia.

The question remains, where does the camera normally breathe?

Well, in the other thread that was started ages ago that I can't find anymore, many people were saying it breathed around the OK button. Not sure about filtering though.

[Smeggypants]

This is all just an April fools joke, Right?

I think it must be

[Schraubstock]

You said yourself that "I also figured all this compressed rush of air can't be good for some of the more delicate parts inside the camera." Well, if you didn't introduce such a gaping hole into your camera body, there wouldn't be all that air whistling around in the camera!

Instead, (if the camera is completely airtight) the air inside the camera gets compressed and uncompressed. There will be a small amount of air circulation around the inside of the camera, but not at nearly the velocity as with your giant hole.

Your assumption is that the camera NEEDS to breathe. Maybe the camera is designed to be able to handle changes in internal pressure. I don't see why not! I can see how high velocity air movement might be a problem, but changes in internal pressure should be quite ok.

With your argument you have overlooked the fact that when I open the rubber door to attach a cable release and use a long zoom I am creating precisely the same flow of air as in my case above. No difference ! Are you saying I should not do this ?

If I can create a "more gentle" air flow through the body in my book it has to be better then the strong negative/positive hammering delicate parts receive inside, like shutter blades or aperture blades. I could be wrong but somehow I go with the gentle breeze.

Greetings

[Schraubstock]

Sorry, but this is still not valid. You're talking about hydraulics, which is a completely different principle to atmospheric (static) pressure.

A hose or water cannon is powered by a pump. A pump is designed to move a certain volume of water in a given amount of time (e.g. liters per minute) by applying a constant total force. Because the nature of the pump means that you must move a given volume of water in a given amount of time, the pressure increases when the area (and thus volume of water that can pass through at a given time) decreases.

This is not a valid extension to atmospheric pressure. The atmosphere is not powered by a pump. The atmosphere does not have to move a certain amount of air in a certain amount of time. Atmospheric pressure (not atmospheric "force") is the result of the static weight of a column of air of any given cross-sectional area. Decrease the size of the area and you decrease the size of the column of air, thus the force decreases and the pressure remains the same. You cannot "channel" atmospheric pressure. Atmospheric pressure at sea level is defined as 101,325 pascals. This is constant at any point on Earth at sea level, no matter if you are looking at a 1mm^2 or a 1km^2 area. Pressure differential is the net result of atmospheric pressure outside (constant) pushing against the pressure inside. Any hole is completely irrelevant (heck, there doesn't even have to be a hole at all). This is basic physics and fluid mechanics.

Try this. Take a bottle of water and poke a tiny hole in the bottom. Take another bottle and punch a huge hole in it. Which produces a bigger flow? Obviously the big hole. The tiny hole produces a very tiny trickle. The static pressure exerted by the water is exactly the same in both circumstances. The bigger the hole, the more water molecules get moved at a time, but for any given molecule of water (analogous to a dust particle), the force exerted on it is exactly the same. The end result is the same (empty bottle), just that the smaller hole takes a much longer time to do it.

This is the principle behind static pressure, and completely different from a pump/hose which moves a constant amount of water in a constant amount of time.

Precisely, the long Zoom is a pump. The only difference in this analogy: Air is compressible water isn't. Principle is the same. I just keep things simple and express elementary physics.

Greetings

[Cannikin]

Precisely, the long Zoom is a pump. The only difference in this analogy: Air is compressible water isn't. Principle is the same. I just keep things simple and express elementary physics.

No, the principle is not the same. With water, the volume of a given mass cannot change, and therefore attempting to change the volume means that the water must be forced out at a given rate of flow, driven directly by the total force of the pump. The pump itself is directly pushing the water out. Flow (volume of water per unit time) is invariable (the size of the hole makes no difference in amount of water that is pumped through in a given amount of time). This is the principle behind hydraulics. The principles of pneumatics are quite different. A compressible gas can easily change its volume with compression, and flow is not directly dictated by the external force of a pump pushing it out, but by differential pressure (in essence, the air is pushing itself out). Unlike with liquids, flow is variable.

Anyway, the lens exerts no force in the zooming out (expansion) stage, which is when dust gets pushed inside. Zooming in ("pumping" stage) is irrelevant, because that forces air/dust out (and as I'll explain below, that makes no difference either). When expanding, all it is doing is allowing the air molecules inside to spread out more, lowering the pressure. Internal pressure is dictated solely by the volume of the internal cavity, and the quantity of air inside (and temperature, but that's not a concern here). Pressure differential is dictated solely by the difference between internal pressure (given) and external pressure (constant). No holes or whatever. Pressure is exactly the same on all internal surfaces (the same for all external surfaces).

There is no such thing as "suction" in physics. The only force, and the only thing that pushes anything here is atmospheric pressure, which is a constant 101,325 pascals (that's constant pressure, not constant force); this is not arguable. This is driven by the principles of static pressure, and zooming does nothing to change this. If you zoom at the same rate for both a small and big hole, the pressure differential change is exactly the same (both zooming in and out), and thus the net pressure at the interface (hole) is exactly the same. The size of the hole dictates flow rate (volume per unit time) by allowing more/less air to pass through in a given amount of time (opposite of a pumped liquid, where the size of the hole changes nothing about the flow rate), but the pressure and thus force exerted on an object of given surface area (dust) is constant.

Your idea of making a larger hole is indeed valid in terms of controlling where air flows, as the larger area means a greater proportion of the total air moves through that hole (compared to smaller holes that are simultaneously present), but the force experienced by any given particle of dust is constant.

Seriously, your theory and analogy are simply not correct. Any reference on fluid mechanics will tell you this. There are many examples I can give you (a balloon, a compressed gas cylinder, pneumatic machinery, etc.), but the end result is the same: the idea that a smaller hole creates more "suction force" given constant atmospheric pressure and a given internal pressure is nonsense, in more ways than one (pressure remains constant, total force decreases).