Why is the EM5 so much more popular than the GH3?

The OM-D has been available since May. It was very hyped up because it was the first MFT camera that serious hobbyists, and some pros, said was good enough to wrest their DSLR's from them for a lot of shooting situations. which did, and does, make it a special camera no matter what side of the format fence you are on.

The GH-3 was released 8 months later but is barely available. It's also noticeably bigger and you know how we are as a marketing driven society.

As others have mentioned, besides the size difference the IBIS is a serious advantage of the OM-D unless you are already invested in numerous panny OIS lenses. Otherwise it's really a toss-up between the two. If you want to shoot more video, GH3 hands down. IBIS you get an Oly. Perhaps better ergonomics at the expense of size, probably GH3. Etc. Etc...

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