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Have to admit I am doing what Art recommended with Olympus E300/330 and older OM lenses. Not by choice since Oly changed the OM system to 4/3. Was stuck with expensive lenses like OM 180 f2, 350 2.8, etc.
There are some disadvantages.
1. Just because the lenses have the same fov doesn't make them look the same in other ways. The dof field is different between a 600 on the pentax and a 450 on 4/3. The backgrounds don't look the same. You don't get the same perspective either. Oly won't have as much of the depth compression.
2. The 4/3 has a different aspect ratio vs. 3:2. For most things I like 3:2 better.
3. Using the older OM lenses requires an adapter. This is constantly being moved from lens to teleconverter and back when on digital bodies. Newer E lenses would get rid of this but mean no using the beautiful OM 4Ti film bodies. With Pentax they all work seamlessly. Film or digital.
4. There is no Olympus with enough Megapixels to match K20D. Find cropping is often as good or better quality than using a 1.5 teleconverter. Do that on K20D and pixel resolution would about match E3.
5. Untill recently, Oly never made a good teleconverter over 1.5X for their large "pro" lenses. The 2x OM was a "consumer quality" unit. This may have changed with the new E 2x.
6. Olympus does not allow you to use two lens accessories at the same time!
No 1.5X converter and extension tube to get a foot or two closer to a birds nest. Stupid, stupid, stupid Olympus. You call that professional? Can't use two teleconverters together at the same time nor more than 1 extension tube for macro. Used both 1.4 matched and Vivitar 2x on 350. Won't happen on E series digitals. Have bitched to them so much it might happen some day.
7. A bigma is not even in the same league as a high quality 30 2.8/600 4 lens. As much difference as comparing a 18-55 kit lens to a Limited.
8. If we save that much by going to 4:3 why not just buy Oly's prosumer bridge camera with 18X lens? Same size as K200D (approx) with 18-55. Quality suffers. Dynamic range, noise etc. Oly dslr may be even in noise vs K20D (haven't shot one) but they don't likely match it in dynamic range.
thanks
barondla (still wanting big Pentax lens)
Check out POINT & SHOOT CONTEST #9 in P&S forum. Enter #10. Any type camera except slr. Any brand. Any subject. Enter now.