A900/850 vs A700 AF

[DennisT]

Noting that the ff versions have 9 point auto focus and the a700 an 11 point system raises the question - is the 700 more effective in a wildlife / sport environment due to a "wider" AF range. Having owned both the 700 (now sold:cryin: ) and the 900 I do detect less agility in the 900 - it seems less able to hold focus on birds in flight when panning, with the consequence that the camera loses focus and fails to fire continuously. This was significantly less noticeable with the 700. Am I being daft or is there some validity to this observation?

[Canuck935]

I've never handled an a900 so I can't say for sure, but it does make sense that less AF points would have a harder time tracking moving objects. Hopefully someone else that has both camera's can give a go and chime in on this..

[Anbesol]

I generally use spot focus for everything, even on continuous tracking mode. It would seem that the A900's brighter pentaprism would allow the AF points to find focus quicker, albeit marginally. Do you use all 9 points? I almost never use anything but spot - so the number of points hasn't ever really been an issue for me.

With continuous tracking mode - you should generally wait till an AF point signals focus detection before releasing the shutter anyway. I'm a bit confused as to what you mean, you say that the camera fails to fire continuously, but in continuous mode the shutter would release even without focus detection. Are you panning those birds with continuous AF engaged, or single AF? Or do you actually have some sort of focus shutter lock on continuous AF mode??

[DennisT]

Thanks Anbesol, for the response. I only use spot metering when the subject is in the bushes or amongst the reeds because I find that the auto focus in wide mode gets confused - hunts so badly that the bird more often than not flies before I can get focus.
I use only wide auto focus when panning, which includes all nine focus points. I have tried spot but find that when the focus area loses the subject the camera, set to continuous, stops firing and if I get the subject back into the focus area it fires again - all within the same "pan". This also occurs in wide mode but it is easier to get the subject back within focus - possibly due to the focus area being wider. The a900 offers ten additional supplementary focus points that are active only in the wide mode which is why I am so uncertain as to the reason it stops firing - it loses focus during the pan and then regains it. I experienced this only occasionally with the 700 and put it down to "pilot error" but, with the 900, it happens too frequently to be ignored. :mad2: