Thanks for the warm welcome. This site seems like a great resource.
Before I get to the reason I moved from EOS to Pentax, I need to explain a little about me and how I use my cameras.
I'm a biologist. For dissertation work I studied bats in Central American rain forests. At the same time, my wife studied frogs in the rain forests of Madagascar, and I was lucky enough to tag along with her. So for a number of years I got to spend some nice long periods in some pretty interesting places. That was back in the AF / Film era, and I had an EOS 100mm 2.8 macro, TTL flashgun and a couple L series lenses that together took me from (35mm) 28-200 at f2.8. At that time Canon was alone in providing rapid/silent focusing and good image stabilization (if I'm remembering right) both of which were essential for shooting skittish creatures in low light (the macro auto-focussed noisily, but one tends to focus that one manually anyway). I had an EOS 1N body, and a lesser EOS body so I could have two ISO/lens combinations in ready-to-go-mode. In any case, It was a system I could carry into the field. I kept it all in drybags in my backpack. The system was both durable and versatile.
But it had a built in problem. The raininess (and sweatiness) of the environment meant either 1) risking the equipment by keeping it out and accessible, or 2) missing shots by protecting it. That choice is a no-brainer if you are a sponsored pro. It's tougher if you are a freelancer, but still pretty clear I would think. But I was neither. I was a guy who understood the technical aspects of photography well (I learned on fully the manual Canon F1) and had a reasonable eye, but what I had that was most photographically special was a relationship with the forest (and other researchers who knew the forest) and that put me face to face with extraordinary creatures on a regular basis. I wasn't making money from photography, so I protected my equipment out of necessity, since I had no money to replace it. I got a lot of shots, but missed a large number as well, sometimes because there was no time to un-bag my gear, and sometimes because it was too wet to shoot at all.
In the end, I was able to keep my equipment alive well in central america, where I was able to get my gear into a dry environment on a regular basis. But my wife's remote site in Madagascar was just too damp--several months without a dry room and all my lovely lenses were crippled by fungus. Painful to even think about it.
Since grad school, I have not spent much time working in the field. I've been teaching and raising kids instead, so my wife and I bought an EOS 20D and a nice-ish 17-85 lens, but have not otherwise invested in camera gear. This past summer, however, my family went on a trip to Ecuador in preparation for my wife and I to take students there in future classes. We borrowed my father in-law's new EOS Rebel (since it had video capacity and took SD cards), and shooting with it I began to see just how digital photography has changed over the last decade. It became instantly obvious, for example, that ISO is now on a par with shutter speed and aperture as a setting since 1) it can be reset for every shot, and 2) sensors are now fine-grained enough that higher ISO shots can look pretty good.
At the point we got home I knew that my wife and I wanted a new body (to replace that very dated 20D) and some good lenses. And after adapting to high ISO shooting in rain forest this summer, it became clear that we probably wanted a full frame body--a bigger sensor is like a bigger lens, right? It collects more photons over a bigger area, allowing faster shutter speeds in conditions where that counts a lot (moving animals, in low light). And so I was looking at the Canon EOS 5D Mark III. I was pretty well settled on it, in fact. Then my wife asked if there wasn't a credible waterproof option. 'No' I thought. But it was certainly worth a quick look. That brought the Pentax K5 II/IIs to my attention. I wouldn't have thought to look at Pentax absent that feature, but it forced a complete rethink. I liked the camera, but I was sure I wanted a full frame sensor...
So there I was, on the fence. No simple choice. The Canon has full frame sensor, and tons of options for lenses. But frankly, the murmuring around Canon (and also Nikon) is that the build quality isn't what it once was. And the L level glass is so expensive that I wasn't likely to be getting Canon's best build quality except in the body. At the same time, the word on the current top-end Pentax stuff is that it is absolutely solid, and well thought out, with only a few flaws. Pentax certainly has cheaper high end glass. And by far, the most important argument in favor of Pentax for me was true downpour tolerance. That feature can reduce the number of missed shots dramatically-- If I stick to certain lenses and flashes, I can keep it out in the rain and not worry. How many great shots would I have caught before if I could have kept my camera out in all weather conditions?
That put me in two binds.
1) Rain forests are incredibly dark, so I would love (and would pay for) a bigger sensor, which Pentax doesn't offer, and wouldn't work with many Pentax lenses. But rain forests are also very wet, and so waterproofing is a huge plus.
2) Pentax is already a bit sparse on the variety of good glass, and that problem gets even worse when one is limited to WR lenses.
I was debating this conundrum when the K3 came out with its AA simulator. I was really impressed with the idea. Every review I saw of the K3 was strongly favorable. Pentax looks committed to WR, and though my choices are more limited, I can build up a complete system faster than I could with high end EOS gear. And the fact that there is a lot of legacy glass that I can buy cheaply (for use in dry conditions) appeals to my tinkering side... Optics are fun, and the fact that Pentax is committed to backwards compatibility makes them my kind of underdog.
With the camera in hand, I do already feel some twinge of regret over the small sensor (using the 18-135 kit lens, which is all I have so far). Actually, I was really impressed with the solid feel of the kit lens. It is so much more sturdy than my Canon kit / walk-around lens I can hardly believe it. But I do want more light sensitivity!
The bottom line is this, though: I shot in the rain the other day and felt so liberated to have my camera out, without worry. I smiled the whole time. It's a huge deal and though full frame vs. rain-proofness is a real trade-off, I made the right choice. The K3 is a great camera, and I'm looking forward to some very sharp glass to go with it, as our budget allows.
My hope is that sensor sensitivity continues to improve, and that investing in good Pentax WR glass now pays off with future bodies that are better in low light. But even at the K3 level, I have a lot of the functionality that I wanted, cheaper than I expected. And I have one major thing I didn't think to want--I can shoot in the rain forest on the forest's own terms.
Two final thoughts:
1) I miss the big dial on the back of EOS pro bodies. My thumb hunts for it...
2) I have always wanted lenses with fully uncoated glass for tropical forest work, so that fungus would be a non-issue. Just as a thought experiment, how would uncoated versions of high end lenses perform? How much benefit is really in those organic coatings?
