Anyway, if the other way of saying "pushing the limits" is "doing something crazy", this might actually apply. Historically and practically the best focal length for bird photography in terms of a small APO refractor or spotting scope is usually about 300-500mm focal length. Same generally goes for lenses. Steve Owen, a great bird photographer, works from a marvelous Canon L lens, the 100-400mm zoom. That makes a lot of sense to me. Any focal length above this is generally reserved for the catadioptric style optical tube. That makes sense too as it is compact to handle such a longer focal length.
And so goes the thinking until I tried this...
Outdoor Bird Cannon?
Now, before you start thinking I've lost it (or is it too late for that?) let's take a look at that set up. That's a 127ED Explore Scientific 5" APO with a 952mm focal length on the SkyWatcher AZ4 mount head and a standard tripod. This set up is not too heavy and not too heavy to transport for a short walk. Yes, a SHORT walk. I wouldn't want to hike it. Attached is my Canon 30D DSLR producing a crop factor of 1.6 making the effective focal length 1523mm and you might be surprised about the results. With that sort of focal length getting close to 500 metres or more is possible. But is it practical? Yes and no. I found there were a lot of gremlins working together. First, there was a lot of infrared around as it was bright and sunny and of course that equates to poor seeing at such a distance. Second, I was set up on a wood boardwalk like structure affecting the stability, perhaps that had an effect. Probably the hardest thing was to get focus on moving objects. Birds just don't sit around too long, so that was really tough. The auto-focus 400mm lens has a big advantage over this set up.
Have a look at some of the results...
One thing that I did learn in the two hours at Rattray Marsh here in Mississauga, is that birds-in-flight is almost next to impossible. It can be done, but there is a lot of blood, sweat and tears to get it. I'd rather leave that to the 400mm crowd.
In the end, with some more practice, this could be a very nice, stationary set up to work from to compliment my 480mm Tele Vue 76. But there are limits. I would only want to walk a short distance and at the end of this particular session, I had to walk up hill with it. Not fun :) M