Sony A57 vs A65 noise

Hi, he means when the image is viewed at the same size.

24MP sensors produce approx images with pixel dimensions of 6000 x 4000

16MP sensors produce approx images with pixel dimensions of 4900 x 3200

So when people say 'view them at the same size' they mean either so they take the same space up on your monitor, or you could analogise it to printing both images out at A4 size and viewing them side by side..

It turns out that actually image noise (the noise present in the entire image) is actually mainly down to the size of the sensor, so a 24MP sensor and a 16MP sensor should (everything else being equal, and sensors of the same generation) have almost identical image noise..

It's probably best to just take DPReviews word on it from the A77 review (same 24MP sensor as the A65) when it compared it to the 16MP of the A55..

http://www.dpreview.com/reviews/sonyslta77/19

But, to answer your original question, all Sony DSLRs are slightly disadvantaged at high ISO because they have a translucent mirror permanently in the light path which take approx 30% of the light away from the sensor..

This means both the K30 and D5200 will have better ISO performance (The D5200 being especially good from what I've seen).. However, they obviously can't hold a candle to the other features of the A65 (EVF, PDAF focus in video, high FPS, Mutli-Frame Noise reduction) etc..

All camera's are compromises.. and these days, all perform quite well at high ISO if you know how to get the most out of them.. if you want to trade features for a few more percent improvement at high ISO (an even moving goal post), then you have to decide what's best for you.