I currently own a Pentax K-7 with a fair selection of lenses, both zooms and primes, which is a fine setup (even too much sometimes) for my needs (photography is only a hobby, nothing more).
I am even however more and more tempted by m4/3, both for its compactness and for the overall high quality of both Olympus and Panasonic lenses lineup. I am so tempted in fact that I am seriously thinking of selling all my Pentax gear and replace it with a G3 or EP3 plus a couple of lenses.
Is there any former Pentax user who made the switch and would like to share their experience passing from one system to another?
I used Pentax gear for several years, while the *ist DS and K10D bodies were current. I had opportunity to use virtually all the current lenses available at that time and also used a large number of older M, K, A, F and FA series lenses. I have had no experience with the K7 or K5 bodies.
From there I moved to using FourThirds/Micro-FourThirds with the Panasonic L1 and G1, Olympus E-1 and E-5 bodies, with Panasonic and Olympus FourThirds/Micro-FourThirds lenses as well as with a number of adapted lenses.
Of the Pentax gear, I found many of the lenses to be excellent but also many to be mediocre; the Limited series prime lenses and particularly the DA14, DA21, FA43 and FA77 were top notch, my favorite Pentax lenses. The *ist DS and K10D bodies were good, each with its own minor foibles in use. From what I've read, the same is true of the K7 and K5 bodies but per above I have no direct experience. My personal summary: good value for money, somewhat uneven in quality.
Of the FourThirds/Micro-FourThirds gear, all of the bodies I listed proved to be fine performers and very consistently produced image quality on par with or superior to the Pentax bodies I had used before them. The G1 was the smallest and lightest, produced image quality on par with the L1, E-1 and K10D modulo small differences in sensitivity and dynamic range. The E-5 is a substantively better performer than the others in all ways: responsiveness, customizability, features, dynamic range, sensitivity and acutance. Again, with no direct experience using a K-5, I can only speculate but from what I've read and seen as samples the K-5's sensitivity exceeds the E-5 by perhaps 1.5 stops.
Regards FourThirds/Micro-FourThirds lenses, all that I've used have proven to be consistently above average to excellent quality. This includes in Micro-FourThirds mount the Lumix G 14-45/3.5-5.6 standard with the G1, Lumix G 20mm, and Macro-Elmarit 45mm, and in FourThirds SLR mount the Panasonic 14-50/2.8-3.5, 25/1.4 and Olympus 11-22/2.8-3.5, 25/2.8, 35/3.5 Macro, 50/2 Macro, and 50-200/2.8-3.5 (never mind the super-high-grade 7-14/4, 14-35/2 and 150/2 that I rented).
Since I render my images from raw captures, what image qualities ("film like", etc) come out of the bodies' JPEG rendering is mostly irrelevant in all cases. Suffice it to say that with lenses that are on par in quality, I obtained image quality from all of the above equipment that is virtually indistinguishable as to which camera made the exposure.
So, my overall summary is that Pentax, FourThirds and Micro-FourThirds can all produce superb results. Differences between the systems come down to minor differences in individual body sensitivity and dynamic range, larger differences in features and feel of the bodies, and which lenses you pick to use. The FourThirds and Micro-FourThirds gear have been consistent in quality and feel, IMO, and the FourThirds SLR lenses available up to when I stopped using Micro-FourThirds were a notch higher grade in build and performance to what was then available in Micro-FourThirds mount (this has changed as both Panasonic and Olympus have released several higher-performance Micro-FourThirds lenses). There are a few Pentax lenses that I miss for their unique qualities (the 43 Limited in particular, the 77 and 21 Limiteds after that), but I wouldn't go back to Pentax just for those.
For Olympus and Panasonic, it's pretty clear now that Micro-FourThirds is their way forwards and they are advancing both their product lines in that direction (both lenses and bodies). The big questions here are when a professional grade body that compares on par with the E-5 will be released, and what will happen to the top of the line Olympus SLR lenses as a result of the move to Micro-FourThirds.
For Pentax, the future is a little less clear since Pentax Imaging was sold to Ricoh by Hoya, and Ricoh has not yet announced their future plans for the Pentax brand and camera/lens lines as yet.
