Autofocus w/big lenses at short distances

This one is a bit specialized. I regularly shoot birds in flight with a 600 and a 600 with a 1.4 converter, sometimes using an extension tube to get closer to marsh wren sized birds. Does anyone have experience with the newer autofocus 600's with N90s and/or F5? Distances for a Forsters Tern are between 20 to 45 feet and the birds don't fly in straight lines but zig zag, double back, sudden dives into the water & some hovering. Cliff swallows are more rythmic but pretty quick, especially at these distances for frame filling images. Avocets feed with a side to side motion and close ups leave only a few millimeters to centimeters of depth for accurate focus. A slight turn of the head & the eye is no longer sharp & the "bulls eye" autofocus I've tried definately inhibits composition as one can't focus, hold a button & recompose on a moving subject as it goes back & forth. I am looking for info on what really works at these close distances when the motion isn't quite predictive. Thanks.

Dan asked me this very same question a week or so ago when we met at the Bear River NWR and he noticed I was using Canon AF gear.

 

<p>

 

I'll expound on my brief comments to him, and am curious as to what others think.

 

<p>

 

My only experience with the F5 and AF-S lenses was very brief, last fall, when I got to play with an F5+400/2.8 AF-S combo. Very impressive, but I suspect my experience with Canon AF would hold true with this new system from Nikon. I'll speak from my experience with Canon gear. Perhaps someone out there with AF-S lenses can tell us if Nikon's made a great leap in this area (oops, just gave away my answer!)

 

<p>

 

In essence, Dan's described exactly the kind of situation that AF does NOT work well, at least for me. Canon's 1N helps the situation a bit, with the camera able to track moving subjects with 5 focus indicators. This allows one to track, say, an avocets eye near the edge of the frame rather than the center. However, Canon's AF sensors are horizontally lined up in the middle of the viewing area so this still limits composition. Any configuration would.

 

<p>

 

Whatever the compositional limits imposed by such a configuration, you're still faced with trying to keep the bird's eye covered by a sensor (any sensor, but, still, a sensor!) and as Dan notes, avocet swing their heads rapidly side-to-side. Even keeping their pretty, but skinny and quickly-flexing, necks near their eye covered by an AF sensor is a trick, at least in my experience.

 

<p>

 

AF with hovering terns works if you're quick, as Forster's terns at least tend to hover for a few seconds before either plunge-diving or moving to another spot. I don't think it works better than MF, though, in this specialized case and the fluttering wings are likely to confuse AF unless the bird is head-on. I lucked out during my visit to Bear River NWR when a tern hovered just feet from my car window, just above eye-level, directly opposite. My other attempts to shoot them while hovering were not that successful, I'm afraid, though perhaps when I get my film processed tomorrow I'll be happily surprised!

 

<p>

 

Anyway, I find AF a useful tool in many cases, but the situations you describe are ones where I find follow-focusing by hand a useful skill to retain. AF works much better for birds flying steadily, say an avocet when it's flying at you trying to drive you away from its nest or chicks. The camera's ability to calculate the bird's actual speed and compensate for it when it flies steadily is a big win, then.

for several years now i have been using an eos 70-300 and an a2

 

<p>

 

muonted on a gunstock which i modified especially for flight

 

<p>

 

shots. i find canon,s track focus to be good but i have a cable

 

<p>

 

release built into the stock so i can control it with my left

 

<p>

 

hand which is right there at the forward stock. the camera is

 

<p>

 

right at my eye and my right hand can adjust exposure(which i

 

<p>

 

usually preset) so i can manually focus often better than the

 

<p>

 

auto focus can. i have been very successful with skimmers, ospreys

 

<p>

 

and most shore and wading birds. some of little wrens, warblers

 

<p>

 

and others are a real challenge if not impossible for me without

 

<p>

 

trippers or other high speed equipment. jeff hallett FL