Originally posted by mutley The 4:3 system? What does that mean? Just because of the sensor size it doesn't get CA? Do you mean that if you stick Oly's 70-300mm lens on a Pentax body, it will have PF & CA all over the place?
That Oly lens has 3 full ED elements in it for $349. Does the Pentax 55-300? I mean Hoya owns them! It should have 4 ED elements!
If the 4:3 system has been designed to eliminate bad lens IQ, then Pentax should figure out a way to design APS-C system to do that.
I mean you tossed away a Tamron 70-300mm like it was a piece of disgusting junk because you got a bad sample with excess PF, and I love mine. The bit of PF I get can be processed out like you say, but for the $200 extra price of a camera brand lens, Pentax should design lenses that work with APS-C eliminating CA & PF.
The four thirds system was designed specifically for digital sensors. It's optical design allows the light to reach the sensor more evenly, at more straight angles. That eliminates all PF and lessens CAs, ghosting and flare, and also improves sharpness.
You can learn all about it here:
Four Thirds
You can't "design APS-C system to do that". It's a completely different animal. It might only be doable if you don't mind having lenses that weigh 2kg each (you probably get a little bit of these benefits using 645 lenses on an APS-C body).
An Oly 70-300 won't cover half the frame of the pentax sensor.... but the exposed part will probably have NO fringing. The lenses are part of the equation too, it's all in the proportions.
I'm very confident that the 55-300mm will exhibit insignificant PF and CA compared to the Tamron. Yes, it was disgusting. I took a picture of a receipt over the counter to test the macro ability, and it had PF all around the blue lines on paper. It was even visible in the LCD at full size (not zoomed in). Small apertures didn't fix it. Bad copy or not, if a lens like that is allowed to be sold, I don't want any of them. I'm sure you can take wonderful pictures with it, as can be done with many other not-so-great lenses, and it's well worth the price. I just thought I could invest my money in something better, what I did later on with the Sigma 17-70 and 10-20.
The ED elements count is not criteria for image quality. It doesn't mean anything without knowing the design of the lens. They might be needed to compensate for light loss at another element :]