I actually shoot 3 systems. Pentax K1/K5, Nikon D800E, and Canon 5DMark3. My K1 is currently my main camera.
I have the DA16-50 and 50-135 for Pentax.
70-200 and 24-70 for Nikon
and 35mm and 85mm for Canon.
I am not a hardware expert, so you can take my opinion on these systems to be as accurate as someone who walks around, picks 3 brand, and had to decide which one is better. That is to say, my opinion is extremely accurate
Autofocus.
Lets get this out of the way : Pentax AF is not as accurate, or as fast as the other two systems. No, I didn't measure it by micro seconds. I measured it by how many times I get extremely frustrated after I get home and look at the images and they are off. In fact, I am now shooting K1 with manual lenses only. Live view with manual lenses and focus peaking results in a lot more keepers.
Ergonomics.
If i have to rate ergonomics, Pentax would be first, canon would be second, nikon would be third. It just works for my hand. And I carry these for a whole wedding, so....12 hours sometimes. I can tell you if i have to shoot fuji or sony for weddings i will probably cry because of the lack of grip.
Button placement.
Pentax would be first, nikon and canon second.
I am not an expert on these machines, as I have pointed out before. I use them to take pictures, so I am not aware of a gazillion things that these things come included with. So how do i rate this? I rate it in the way that I can pick a camera, and figure out how to use it without a manual. immediately. And in this case, pentax comes first. The buttons make sense. I don't know how many times I've had to look up the Nikon manual because i accidentally switched a setting that i did not know existed and it was doing things that i did not want it to do.
Flash system.
Canon first, Nikon, then pentax. I love the ease of use of Canon's system. The menu make sense. I never had to open the manual for it. Nikon is the worst. Even though I love the commander function of nikon, but the flash is unnecessarily complicated. Pentax? Well...the exposure is always off. So i hate pentax's flash system.
Images.
Pentax first, canon then Nikon. I love pentax and canon's images. Straight out of the camera, they look like they have character. The colours just works for me. Pentax is typically more yellow/red, canon more red, and nikon more green. The nikon images are the ones most.....neutral. Boring. When i have a high fashion editorial shoot, i grab the nikon. For everything else, i put the nikon aside.
Also, in regards to dynamic range, I have a lot more confidence in recovering highlights from Canon than from nikon, which I rather recover shadows from. Pentax K1 is an allstar, and I can recover both highlights and shadows, and noise really nicely. I guess its the age of the technology.
Thats basically how i view these systems. Again, i am not an expert...but i think thats why I am accurate
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Feel free to view my work to see the images i have taken with these cameras :
Bottling and Capturing Images – Just For You!