I picked up a K-7 a couple of weeks ago. I think it was the £100 cashback on the K-7 + 2 lenses kit that did it for me. I have been pleasantly surprised by the K-7 and these are my initial impressions of the camera.
Build and Handling
The first thing that caught me by surprise is how small the K-7 is. It's a lot smaller than the 40D/50D and if I had to guess I'd say it's also smaller than the Sony A200 I used to own. This is good because it's a lot less conspicuous in public. I've found that the K-7 + 18-55mm draws a lot less attention than the 50D + 24-70mm. This is a good thing.
Another good thing is the way the shutter is damped. On the Sony A200, the shutter sounded loud and confident. You clicked the shutter and it went "CHUCK!!" and everyone in the county would know you've taken a photograph. The 50D's shutter in contrast was slightly quieter and had a more "flimsy" sound to it, sounded like a "flip". The K-7's shutter is even quieter, a very quiet "chuck" coupled with some (very faint) electronic whizzing. I admit it took a while for me to get used to it, but now I find that the shutter of the 50D is loud in comparison.
I won't go into detail about the build quality, the weather sealing, etc as these have been covered in detail elsewhere. Suffice to say, the K-7 with the kit lens attached feels like a very solid and professional piece of kit. I'd say you could even knock someone's teeth out with the K-7 and you'd be alright - it is weather sealed.
I like the way the mode dial has a lock. I can't count the times I've had the mode dial on my other cameras change from A to M as I fumble around changing lenses. True, it could be me that's the problem but it's good to know that this is not going to be a problem with the K-7. We'll see how this works out in practice at my next shoot sometime in January.
The main annoyance I have with the K-7 is the lack of a multi-select control. This is fantastic when you want to manually select your AF points. It also surprises me that when you shoot in AV/TV mode, you have to hit the EV button before you can make exposure changes. You can configure it so that the secondary control dial automatically does this, but why wasn't this the default setting in the first place?
It comes with a green AF assist beam! Canon had this on the EOS D60 but they removed it when they introduced the 10D. It has remained removed ever since. Even entry level Nikons like the D3000 have an AF assist beam.
Other places have complained of the sluggish Pentax AF. To an extent, this is accurate. If you leave it up to the camera to select the AF point, it hesitates a bit every time you take a picture. Given that it does this with static subjects, I can see it being a bit of a problem if you've set AF to continuous and are trying to track a moving subject. Good luck with that. On the other hand, if you manually select the focus point or just use the centre one it works fine. This is a workaround, and I hope that Pentax fixes this issue in the future. It doesn't affect the work I do, but I can see why some people are truly bothered by this.
The K-7 supports AF microadjustment, so it can correct minor front focusing and back focusing. I haven't had to use this with the supplied kit lenses, but it means that I can buy Sigma/Tamron lenses with confidence.
Exposure and Image Quality
Pentax includes a setting that allows the camera to correct chromatic abberations and lens distortion. The good news is that this works! The bad news is that this adds about 3 seconds to the time it takes for the camera to display the image on the LCD after you've pressed the shutter button. If you disable this option, it takes about 1 second from the time you release the shutter to the photo appearing on the LCD. If you enable all correction options, it takes 4 seconds. This is highly annoying! Fortunately, you can still take photos while the camera is busy processing an image so this would not affect your continuous shooting speed and it has little impact on the way I work. However, this does make the camera somewhat useless at "chimping" (i.e. take a quick snap to check exposure). Realizing this, Pentax have included a "digital preview" setting that is triggered by flicking the power switch next to the shutter release. This causes the camera to take a low resolution image that appears instantaneously on the rear LCD with a histogram and the blinking clipped highlights/shadows that photographers find useful. It's a band aid, but it does solve the problem.
With that gripe out of the way, I'm very pleased with the image quality. The automatic exposure is very highlight friendly, scenes where I'd normally have to key in -0.7 EV on the 50D just work fine on the K-7. The automatic white balance under tungsten lighting and energy saving fluorescent lighting works phenomenally well. You don't get a nasty colour cast and the images are slightly warm.
The high ISO performance is decent. Where the 50D would sacrifice detail for a "smooth" image, the K-7 produces more grainy images. This is not a problem for me as they look fine in print and on the web. If you're viewing at 100%, you'll have a grainy image where as with the 50D you'd have a smooth image with very little detail. Pick your poison.
I've been very pleased with the K-7 so far. It compares very favourably to the 50D and I'm toying with moving to the K-7 as my primary camera. I'd probably have to sell my Canon gear to fund the purchases the DA* lenses I'm after. In the short term, I'm hoping to buy the 16-50mm f/2.8, 50-135mm f/2.8 and the 60-250 f/4. That's a lot of money and will only happen once the Canon gear is sold.
I'm off to Australia for two weeks so that'll give me more of an opportunity to get to grips with the camera. Then come January I'm attending a few courses and doing a few studio shoots so will definitely be able to flex this camera's muscle then.
Hope this was useful for someone