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Forum: Pentax SLR Lens Discussion
02-17-2009, 10:46 PM
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I used the A* 400 f2.8 and 1.7x quite a bit for bird photography in the past. The combination worked very well and sharpness is great.
The AF range is very narrow – like a matter of inches. The teleconverter does snap the image into focus after you pre-focus to its working range. As you probably know, the 1.7x AF adapter only uses the center AF sensor – so that is another limitation.
The A*400 f2.8 is a sweet lens with incredible sharpness. The only complaint I’d register is that the Bokeh can be really harsh under some circumstances. A few years ago a photo I took with the A*400 was bandied about on a Leica forum as an example or a really horrible bokeh. It was pretty embarrassing but they were right about the bokeh.
To test the bokeh I focused on a stalk of grass and then slowly focused to a closer point. The idea was to see how an object would look as it moved into the background. I found that as I defocused , the sharp image split into two – like seeing double – and that these two images then quickly went soft. That’s what can make the bokeh bad – things that are at the distance where the double image is present make for a distracting background. Get a bird on a branch with nothing behind it for a few feet, and the bokeh is great. Get a bird in a field with grass stalks behind it, and the bokeh is not so great.
Nonetheless – I’ve managed to get pretty good bird shots with this lens. One advantage with it is that it has a fairly close minimum focusing distance, and even with a 400mm plus a 1.7x converter, you need to get pretty close to small birds.
HTH –
MCC
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