Briefly, I'm on a shoestring budget, but I really want to start shooting with a DSLR. My primary use for a camera is aviation photography, be it 787s taking off and landing out here in Seattle or warbirds at EAA AirVenture, so the vast majority of my subjects are distant (1/8 mile to 1/2 mile) and fast-moving (60mph to 500mph), but well-lit in a sunny sky. I shoot about equal parts photos and videos.
I'm looking at getting a Canon T2i body and kit lens for general shooting, and then using the old Pentax SMC 100-300mm f4.7-5.8 (silver) (
Pentax Lens Review and Specification Database - 100-300mm F4.7-5.8) lens via an adapter with AF confirmation circuitry as my "airshow lens". I like that it is lightweight, but even more I like that the majority of owners say it is extremely sharp, especially on an APS-C sized camera. I'm a little worried that squeezing 18 megapixels out of it might soften it up a bit, but I can always shrink/sharpen the photos.
So my primary question is this: Do you think I will have any trouble with this lens/body combination at an airshow? I'm assuming that in the morning I'll be able to zoom in to 300mm or so, set the aperture wide open, focus on infinity, stop down the aperture for the lighting conditions, set the camera in Av mode, and then just be able to shoot airplanes, without having to constantly refocus (aside from some minor tweaks now and then)?
The action at an airshow can get fast and furious, so if I would need to open up the aperture, refocus, close down the aperture, and then shoot each time my subject changes, then that would pretty much be a deal breaker. Likely/unlikely?
Thanks very much for your help