100-300 lens choice: Pana or Oly?

texinwien wrote:

Other than the obvious things, I'll tell you what I know from owning the Panasonic 100-300 (purchased new about a month ago) and using it with my E-M5.

First, I purchased the Panasonic primarily due to the price difference with the Oly Mk I. I think IBIS is the way to go, for the future, so I'm less worried about purchasing lenses with stabilization.

Now, one thing I've found is that I need to stop this lens down to get sharp results. My understanding is that the Oly is just as sharp or sharper without having to stop down as much, which would make both lenses close to equally fast if sharpness is important to you. It is, for me - I don't have much use for a long telephoto that's overly soft. Might as well use a sharper, shorter lens and crop.

Same can be said for ISO with a lens like this. I find that I need to keep the ISO way down in order to have sharp enough images when zoomed into the longer end of this lens in order to have acceptably sharp images. In effect, both lenses are really only going to excel in excellent light, where a half stop or so of aperture won't much make of a difference, and if you have to stop the faster lens down more, anyway, the difference in speed disappears completely.

I'll wait for the reviews on this Mk II, but if it reviews as well as the Mk I, I will try to sell my 100-300mm (it's in like-new condition) and buy the Olympus, instead.

One other point that I have heard from others who've owned or compared both lenses in person, but have not experienced, myself, is that the build-quality of the Olympus lens seems better than that of the Panasonic. Having said that, I'll say that my Panasonic doesn't "wiggle" like some models seem to do, and I find the zoom ring smooth and easy to operate, unlike other owners of this lens. I'm A-OK with the performance and build quality of my 100-300mm, so far, but if I can buy an alternative that's lighter and smaller with a wider range of focal lengths, (perhaps) better build quality and (perhaps) better optical quality (sharpness) for approximately the same price, that seems like a pretty good deal to me.

Lastly, I will point out that none of the info I have shared in this post is new, in any way. It's all been discussed, in detail, many, many, many times on this forum.

tex