Jeremy Nixon wrote:

Erick wrote:

In terms of getting the maximum power together with the maximum usable
details and sharpness from a particular telelens, I wonder which option
gives the best results for a particular purpose: let's say: get the max.
amount of details of a bird on a 1600x1200 display.

A full frame SLR (EOS 5D 12 megapixels) combined with a top class CANON
400mm
or
a EOS 20D (crop factor = 1.6x but only 8 megapixels)) combined with the same
lens as above

You're talking about the same lens from the same distance, so, whichever
camera has smaller pixels will give higher resolution. The larger sensor
will only create a wider field of view around the subject.

From a general point of view and at equal sensor resoultion, does a smaller
CMOS provide any advantage in terms of power and resolving small details if
using the same lens?

No. The sensor size has no bearing on it. Pixel size does, but of course
smaller pixels come with other baggage as well.

What will be the best buy for widelife photography: EOS5D with Canon 400mm
or NIKON 200D with Nikon 400mm

The Nikon.

10 megapixel + 1.5x or 12 megapixel FF

Pixel count and resolution are very low on the list of things that are going
to make your pictures better. You're falling into the marketing trap.

I agree. Good advice. Some of the other things you need to look at a
camera speed: speed to turn on, speed to wake up from sleep, shutter lag
time, frames per second, buffer size when writing raw, write speed to
empty buffer, autofocus precision and speed. All the pixels in the world
will not help if you don't have good specs listed above. Most wildlife
or sports photographers would not choose the 5D. The Nikon isn't out yet,
and I haven't studied the specs, but if it competes with the 5D I would
bet wildlife and sports photographers would choose a faster camera
with lower megapixels, than more megapixels but slower.

Which gives a better image: 300 mm f/2.8 on an 8-megapixel camera, hand held
at 3 meters versus 500mm f/4 IS on an 8-megapixel camera at 5 meters,
also hand held?
I tested this today at Bosque Del Apache while photographing a road runner.
Answer: the IS lens produced perfect images, while the non-IS were blurred
due to shake, despite faster shutter speeds. (There was no time for a tripod,
and my window mount wasn't within reach.)

Roger