Photoclubalpha

After reading DP review's A77 description, I tried to shoot birds using low iso on my A77

Mark, all I could see from the EXIF, is that you were shooting at 400mm with 1/60s !
What lens? Is it the 70-400 G?

Yes. In fact I　was quite happy this time with my photographers around me, and all were using similar grade cameras and lenses....D7, 50D, E5, D300s and Tamron 200-500, Canon 300/4 + 1.4x, Olympus 300/2.8 with 2.0x and me, 70-400G with 1.4x. My a77 was tripod mounted and connected to shutter release cable.
The most controversial is the shutter speed used. I may try faster next time and challenging iso 640. The thing is, while chroma noise is most obvious in a850 iamges, this is not the case in a77

Lovely Kingfishers Mark K.
Greg

Mark K wrote: The thing is, while chroma noise is most obvious in a850 iamges, this is not the case in a77

That's only to be expected with the smaller denser sensels. The data between adjacent sensels gets more correlated since the wavefront is broken into individual registered photons over closer positions of the incident wavefront. Ideally, had the sensels been spaced by no more than the wavelength, we'd get the lowest apparent noise from that source phenomenon.

You may also observe the same effect looking at a very deeply defocused blurred image - that bokeh always shows lower apparent noise than the well-focused detailed areas because different parts of that blur were originally represented as very close areas in the original wavefront, so registering a photon from a given point on the wavefront in a given direction on the sensor lowers the probability of sending another one in the same direction - the photons are thus spread more evenly in the blurred areas.

Thanks for the detailed information