A200- AF accuracy.

[bfitzgerald]

I am starting to have some serious doubts as to the accuracy of the A200 autofocus in low light conditions, even sometimes in not so low light too.
No questions in better light, that the A200 is notably faster than the Km5d, I have not yet really had much chance to test things for tracking, I don't often do shots like this.
Also, I don't believe the body I have is showing any major problems with FF/BF, rather that it makes mistakes at times that I would not expect it to. I even have had some wa shots (20mm at non fast apertures) where it's decided to confirm focus and give me a nice sharp background, ignoring the main subject. I took both to do some horse jumping shots indoors, and the 5d consistently gave more accurate AF in these conditions with a variety of lenses. In the end I bagged the A200 and used the KM for the rest of the shots. I know there have been examples of the 50mm primes giving problems, and that obviously it's better to have double cross sensors aka A700, film 7. But even with the 50mm..AF accuracy is better with the 5d, and having been on a bit of a 35mm rampage of late, the film 60 is also proving to be accurate even in low light conditions without any AF assist..with the 50mm as well.

This does not happen all the time with the A200, but maybe more than I would expect, it can get the accuracy at times.

I wonder if the specs for the AF make any difference, both the 5d and 60 have EV-1 for AF, the A200 is I think EV 0.

It's not all bad news A200 wise, the flash metering is good..consistent, though I remain convinced the metering is a bit off (5d was a bit over in some cases, the A200 is mostly under..half way between the 2 would be ideal!) A200 is pretty nice on colours..better than I expected. Shame that I don't feel confident with the AF at times. Anyone got any thoughts on this at all?? Even with other bodies etc.

[David Kilpatrick]

I have not noticed the A200 being any worse than the 5D, A100 or A350 but there is a quantum leap from that to the A700 and A900 of course.

The A200 offers, I think, fast AF only where the A700 (which has the same power of focus motor) gives a choice between fast and slow. The idea is that slow is more accurate (it is not there to cope with tricky lens drives etc, it is there to give a choice between speed and accuracy at the expense of speed). The A200 does not offer this choice, it is full speed only.

Secondly, there is a deliberate 'bug' which can confuse you with the A200 (etc). When WIDE AREA focus is selected, the central focus spot is ALWAYS used to confirm focus and light up - even if ANOTHER sensor is the actual one which has locked the focus! This is quite misleading, as you would assume the central spot has been chosen by the camera and fail to realise that in wide mode, no other spot will ever light up when focus is confirmed. So you can be focused on an entirely different part of the scene, like the background, but the centre AF spot will light when the focus is acquired. See the manual, first footnote, bottom of page 71. It is very badly written.

To avoid this, you must use local selection or centre spot focus only. These are the two settings where the point of focus is always correctly shown by what lights up on screen.

David

[bfitzgerald]

I never use wide area AF, always selection..and in low light I of course tend to use the central point.

I was wondering, this was mentioned in a few threads before. About the size of the AF sensor being much larger than is indicated in the VF. Someone suggested it could cause some issues with "what" the sensor locks onto, and that it can lock on to something not exactly in the middle area.

[Javelin]

on my A200 I found the centre point is a lot bigger than you expect. popping up the flash helps but once I addded my 36AM flash with the AF assist lamp focus was of course fast and precise. not so much wih the pop up flash assist.

[Brad Smith]

My A300 lights up the correct AF light when focusing in the wide mode. I thoguth the A200 and A300 were basically the same bar Live View?

[David Kilpatrick]

Same sensor, but the body is different and so is the whole mirror/AF thing - different transmission ratio for the AF lightpath, in order to make LV work better. On the A350 (same as the A300 in these respects) the different sensors light up in wide view AF, depending on which is being used.

I can not remember tha A200 behaving otherwise, but I generally did not use wide mode, and the instruction manual says only the centre spot lights regardless of where the focus is.

David

[bfitzgerald]

I just tried the A200 on "wide AF", never done so before. And it lights up not just on the middle but the others.

As for the Sony user manual, I think you would really have to sit down and hunt someone to write a worse one, I found the KM manuals vastly superior and easier to grasp. The Sony ones are poorly written, and confusing for new users.

[David Kilpatrick]

I've sussed it out - the footnote actually refers only to manual focusing, and means that if you select Wide Area focus and then use manual, the centre area focus is used; if you select local point focus, the selected point is used. Sorry, I've confused this issue and would not have done so with an A200 still to hand (all I have left is a spare manual). But it's very badly written and laid out, and ambiguous in meaning.

David

[Brad Smith]

Oh well, we got there in the end!