I sold my lens already together w/ my 450D. I have tried them both actualy. I can't tell much of a difference that's why I am concerned w/ the reviews I read. I really love how fast a700 AF but reviews say that d90's noise/iso performance is way better than a700.
Probably I am in a good position to advise a bit since I got the chance to own both cameras for brief period. I did an intensive comparison 2 months ago to see which cam should I keep.
I just concentrate on these 2 points since it was the decisive factor for me.
Noise:
- Yes, you are right, many reviews do say D90 do better in noise control and I also agree with that. But it will only be obvious when it's ISO1600 and above. Anything lower is the same.
- However, do note that at ISO1600 and ISO3200, the colour rendition of A700 is still superior and vibrant as per it's ISO800 and below. While D90, the colours start to become a little dull and lose some details at shadow areas due to noise reduction.
- For dark areas like shadows, D90 has no noise even at ISO1600 and slight noise at ISO3200. A700 does have some visible colour noise at shadow areas for ISO1600 and above but it's only visible when you view the picture 100% on PC. If you print, you won't notice them.
- For bright area like white surfaces, A700 is still noiseless even at ISO3200 while D90 has some sparkles of noise visible.
So you must take note of this, whether you like the noise to be at dark area or bright area. A rough gauge is D90 is roughly 1/2 stop better than A700 in terms of noise at dark areas only.
AF Speed:
- D90 has good AF speed and accurate. However only for still objects or things that doesn't move suddenly. I have used the 18-105 kit and 35/1.8G lens and I can only get about 10-20% sharp images of my moving son as D90 did not AF fast enough for slight movement or sudden change of directions of my son.
- A700, couple with it's eye-start feature, capture 70-80% sharp images of my son, while only using the 18-250 lens which many claimed to be slow in AF. So I guess it's the AF function of A700 that was fast enough to do slight adjustments to cater to my son's movement.
Summary:
So in the end, it's really what you want to shoot with the camera. If you shoot mostly still objects (landscape/portraits) and in low light condition, then D90 might be good. However, take note of the details in shadow areas and slight sparkles of noise in bright areas.
If you normally shoot fast moving objects (kids/sports) in moderate light, then A700 will do better.
Don't be too overly concerned about the lens variety. Though Sony does not have as much lenses as the others, it is well equipped by 3rd party ones. And since you are going for Tamron 17-50, then it is not much concerned for you anyway.
I mostly use 3rd party lenses like Tamron 17-50 and Sigma 30 as I find them more affordable and meet my needs better.
In fact, even if the manufacturer has 200 lenses in their arsenal, I dun think you will buy all of them anyway. And not all their lenses are good though, only some are legendary...and legendary lenses comes with a high price...
