AF and sharpness

  • From: Mark Bohrer <lurchl@xxxxxxxxxxxxx>
  • To: leica@xxxxxxxxxxxxx
  • Date: Fri, 05 Sep 2008 11:22:22 -0700

Good focus with digital AF SLRs depends on choosing the focus point and
placing it on the right spot on your subject. Perfect focus with fast-moving subjects is challenging with either manual or AF.

I prefer my Canon EOS 1D mk II's 45 AF sensor locations to the EOS 20D's
9 locations, but I use the same procedure with either camera. I see a
shot I want, choose the point of focus for the composition, then track
moving subjects and shoot when I like what I see.

I used that procedure in both of these wildlife images. The originals
are very sharp at the eyes and the feathers. Images were made with EF
500mm f/4L IS (robin snarfing berries) and EF 400mm f/4 DO IS (snowy
egret in the pink):
http://tinyurl.com/3zoq6
http://tinyurl.com/4fner

It works for sports too, like in these shots of pro mountain bike racers:
http://tinyurl.com/4o2j2
http://tinyurl.com/yc6x2f

While the 400mm DO IS was in the shop awhile back, I used my backup
400mm f/6.8 Telyt. Here's a manual-focus shot made with the 20D and
400mm Telyt:
http://tinyurl.com/y2ub5j

(I use a Katz Eye focusing screen with split-image focusing aid in the 20D. The split stays bright at f/6.8.)

In the original image, this young Cooper's hawk's feathers are sharp.
The eye is very slightly soft, from my (mis)focusing. It may also be the
limitations in a two-element achromat showing up in a digital image. The
sharpest feathers in this Telyt image don't look as individual-feather
sharp as those in the robin image from the 500mm f/4L IS.

With manual or auto focus, you can anticipate subject placement and
choose photo situations to give the composition you're after. Sometimes anticipation isn't possible, like in David Young's rodeo shot. It's still a great shot.

Will you lose a few shots due to not getting the sensor on your subject
where you want it?

Probably.

With a manual focus lens like the 400mm f/6.8 Telyt, will you lose a few
shots due to not focusing fast enough on the part of the subject you
want to be sharp? Maybe due also to vision problems?

Again, probably.

But perfect sharpness isn't necessary when the image tells the story well.

Mark Bohrer
Mountain and Desert Photography
www.mountain-and-desert.com
Wildlife on the urban edge


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