jonhd wrote:..........If he sees this thread, MikeOxon may be able to offer better-informed opinion.
I've seen this thread!
I find the Panasonic/Leica 100-400 lens is very good indeed for both bird and butterfly photography. I often start at the 400mm end but, if the subject is amenable, I try to move closer and shorten the focal length. On the other hand, with birds in flight, it is often easier to 'pick up' the bird at the shorter end of the zoom and then zoom-in for the optimum shot. When I bought the lens, I had already bought an Olympus E-M1, which has phase-detection AF, as well as the more usual contrast-detect AF.
I started my use of micro 4/3 cameras, however, with an Olympus E-M5 (the original version).
In response to a query on this forum, I did a very basic comparison of the two cameras and found that the 100-400mm captured focus more quickly and more reliably with the E-M1 than with the E-M5. I don't know for certain but I suspect that the difference may be to do with the phase-detect capability of the E-M1.
Very recently, I bought the E-M1 Mk.ii and, with this camera, I have found that the Tracking-AF is a huge improvement over the previous model. This camera, with the 100-400 lens, really can follow a bird-in-flight, in conditions where the E-M1 struggled (and usually failed).
I have not used Panasonic bodies but, from what I have read, it looks as though the E-M1 Mk.ii is the 'state of the art', as far as Tracking AF is concerned (Panasonic seem to target video users more than still photographers). If tracking matters to you, then the very expensive E-M1 Mk.ii can deliver results that the cheaper models cannot. If you are happy with static subjects and, possibly, a slight hesitation in the AF, then any micro 4/3 camera body should do the job.
I am consistently impressed by the optical quality of the 100-400 lens and it works well for me on Olympus bodies - stabilisation (IS) for example seems fine on the E-M1, even though the lens stabilisation does not co-operate with an Olympus body - I select IS lens priority.
In the last few days, I have been photographing Hawfinches, which are very difficult to approach, and I am very pleased with the results I've got. When I see the massive lenses and tripods that other birders use, I am very glad to have the light weight and general flexibility of the Olympus -Panasonic combination
Mike