Wed Oct 23, 2013 8:53 pm
You mentioned you already own the BMPCC, so you can definitely make it work. The sensor size isn't the issue- in fact like you've discovered, the crop is a plus for reach.
The most difficult thing to do with a long lens, other than stability, is initial focus acquisition. Forget about follow focus and framing the subject properly for now, and say you spot a bird in a tree. With the BMPCC you will have to locate the subject, manually focus on it accurately and quickly. Quite frankly I just don't see how you could do this consistently well enough with the focus peaking or 1:1 modes on that screen, which is hard enough to use outdoors on still subjects. Manually focusing a long lens is hard enough. Not saying you can't, just saying that reliability and consistency will be an issue. You would be better off prefocusing and waiting for the subject to come into view.
A good, sharp EVF will be a plus if you have the budget. At any rate, these are limitations to be aware of. On a super tight hobbyist budget for wildlife (you mentioned nature docs but seems more specifically you want to shoot wildlife), I would think the GH3 would be the best option. You can set the camera to do one shot AF which will help you acquire focus quickly at the onset. Built in EVF will be super helpful outdoors. Coupled with the 100-300 I think one could pull off some wildlife shoots quite consistently. Plus, if you need stills it's right there. But unless you can switch cams at this point this is all moot. The IQ of the BMP camera and codec is hard to beat, but it really is better suited to more static or controlled environments where you aren't trying to follow something around, focus on it, operate the camera all at the same time. Bottom line is, learn to use the equipment, and be realistic with your expected results, or what you can/can't shoot (big difference between filming an elephant vs a hummingbird) especially given a hobbyist budget. I'm sure you can make it work, you will have to find workarounds, be patient, and just enjoy working.
Sheen Yen