I am thinking of buying an affordable tele lens (600mm+ equivalent) for my panasonic Lumix G5. I have read about adapting 400mm f5.6 EDIF
a) For wildlife/bird pictures, would it be too much of trouble? I assume setting up and focusing and waiting may not be always practical. Is this only advisable for shots when you have ample time to set-up?
b) Are there any other similar affordable tele lenses which could be adapted (any popular combinations)?
As someone who occasionally indulges in bird photography, shoots micro four-thirds, and has adapted manual lenses to her Canon dSLRs, I'd say don't do it. The lens will be disproportionately big and heavy compared to your G5, and the lack of autofocus (and EXIF, and aperture control from the body unless the lens has an aperture ring) will probably be more frustration than it's worth, unless you "grew up" in the era of manual film cameras.
Getting bird-in-flight shots with my G3 and autofocusing PL 45-200 has already been a serious exercise in frustration, and my GX-7 doesn't seem to have improved matters much; I stick with my Canon 50D and EF 400/5.6L USM for birding. I couldn't imagine trying to do that with a manual focus lens.
But. If I just want to go zoo shooting or get perched bird/wildlife shots, I'm perfectly happy with my Panasonic Lumix G Vario 45-200 f/4-5.6 OIS. It's regularly trash-talked on mft boards, but it's hecka better, as consumer telephoto zooms go, than my old EF 75-300 III. And you can find a used copy for <US$200. Most pixel-peepers would point you to the 45-175 or 100-300 as sharper prospects, but they're more expensive, and it's not like the 45-200 is terrible. It just requires decent telephoto handholding/support technique and working knowledge of the 1/focal_length (x crop factor) rule of thumb. Micro four-thirds shooters seem to have a lot of folks who don't know supertele technique or how an eye-level viewfinder can make a big difference is stabilizing a long lens vs. arms-length LCD composition technique.
I've been a professional long-lens bird/nature shooter since the 80's. I used to use very big and pricey dedicated video cameras/lenses, but now have found the wonderful micro-4/3 world and love it. I've gotten some amazing shots, both video and stills, by adapting older long telephoto lenses to my Panasonic G6 and GH3, as well as my Olympus E-PL5 and E-M5 Mark II.
For convenience and smallish carry-along lens, the Panasonic Lumix 100-300mm does a good to very-good job as long as you learn how to use it and shoot with good technique, but for my super long tele shots, I found a Canon FD 500mm f4.5 lens (built in 1989 - big and in pristine condition, it's very good glass and cost $1300) which adapts very easily to micro 4/3 cameras, but requires you to focus manually and learn to use the focus assist built into the cameras.
If you are serious about getting great telephoto shots, there are lots of Canon, Nikon and other telephoto lenses which can be adapted for manual use on these small micro 4/3 wonder-cameras. Keep in mind, none of these options, including the Panasonic 100-300, is going to give you high percentage focus accuracy for moving bird/critter for stills, but will, with practice, allow good focus when shooting video. You have to have a camera with a good viewfinder or a focus device on the rear LCD, regardless.
Olympus is supposed to be releasing a 300mm f4 in the early part of 2016 which should focus faster than any other super-telephoto now available and be very sharp, too. Supposedly Panasonic will be offering a 100-400mm in 2016, as well, which is said to be a better lens than the 100-300 now available.
A 600mm lens on m4/3 gives a 1200mm equivalent. That's an incredibly narrow field of view, probably too narrow for most subjects. Also, I'd want that absolutely locked on the steadiest tripod and head I could find (and mounting to the lens rather than the body), and firing via a remote release. Anything else would be an exercise in frustration and camera shake.
That said, I still wouldn't do it.
I've got the Panasonic 45-200 for general use which I like, but I'm not chasing birds with it very often :-) I'd take a look at any of the x-300 lenses available that were built for m4/3 - you should get enough reach for most realistic subjects, but with better performance and handling.
