A-99 and understanding the auto focus ?

Started Dec 29, 2012 | Discussions thread
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copejorg1 Senior Member • Posts: 1,626
Re: A-99 and understanding the auto focus ?

Trevor_S wrote:

So my A-99 has just arrived, not had a lot of time to play with it but I am struggling to understand what it is doing. Yes I have read bits of the manual but thought I might ask here in the hope of some elucidation.

I came across from Nikon, where I had my older D300 set up in AF-C, AF release priority with AF set to the rear AF button and multi shot. I kept my thumb mashed on the rear AF and it was always in focus under the selected sensor, then I just clicked the shutter release front button to take a pic when I wanted to, or kept it down to fire a group of shots. If I wanted to recompose I just took my thumb off the rear AF button and pushed the front shutter release button. This workflow worked superbly for me and I liked it, not sure if I should try and bring that across to the Sony or explore the other focus features more eg DMF and AF-D modes ?

Struggling to get my head 'round it all on the A99, that and the AF is more "advanced" (# of sensors is the only real complaint here). Face detection is off. All's sorts of squares appear in front of the AF sensors on the EVF Green ones and grey ones mainly ! The shutter release button seems to want to AF as well, something I don't want it doing, how do I turn this off ?

I have the drive in slow, which seems to work ok, fast seems a little "touchy" ?

I am loving the EVF and focus peeking is an outstading feature (high/yellow) but I am struggling to connect how that works with the selected focus mode and in relation to the sensors ?

I have to say, this is one superb camera.

Only lens so far is the SCZ 24-70 2.8 (865 is on the way and looking for a 70-200)

Hi Trevor (and Welcome),

I'm getting in on this discussion kind of late, so you've already received replies confirming that you can indeed set up your A99 with "Back-Button AF" combined with Continuous AF, the way you did with your Nikon D300.  But I"m going to mention another approach, as well, because you made specific note about how much you like the focus peaking feature ...

The default setup for the Sony cameras in this class (those having an AF/MF button on the rear) is for AF to be activated by the shutter button, and for the AF/MF button to be set to "Hold".  So, for example, if you have AF set to "Continuous", holding down the shutter button half-pressed or fully-pressed gives continuous AF tracking, and pressing the AF/MF button (even with the shutter button being pressed at the same time) switches the camera to Manual Focus.

Note that in that last sentence above, I didn't say that pressing the AF/MF button in that situation simply deactivates AF, but that it switches the camera to MF.  That's an important distinction, for a couple of reasons:

First of all, the fact that pressing the AF/MF button switches the camera to MF means that you can then fine-tune focus manually even with the camera's AF switch set to on of the AF modes -- even with an older screw-driven AF lens.  That wouldn't be true with the "AF-On" methodology a la Canon or Nikon, in which the AF is simply deactivated (but the camera is not actually switched to MF) when the AF-On button is released.  That difference isn't such a big deal if you happen to be using a lens equipped with an ultrasonic AF motor having full-time MF override capability even when set to AF ("SSM" in the Minolta/Sony nomenclature).  But with a "screw-driven" AF lens (such as many current Sony models, and nearly all legacy Minolta Maxxum or Dynax AF lenses), use of the AF/MF button and shutter buttons in their default configurations allows you to achieve that portion of an SSM lens's capability, even when using continuous AF.

The second incentive to give the default configuration a try is because of the focus peaking feature.  Same story as for screw-driven lenses above -- the camera needs to actually be in a Manual Focus mode (with the AF drive disengaged) in order for focus peaking to work.  And since releasing the "AF-On" button (AF/MF or other button configured that way) doesn't actually put the camera into MF mode -- it simply prevents AF from engaging -- focus peaking can't be used in combination with "AF-On" and Continuous AF configuration.

At this point, someone undoubtedly will point out that you can achieve the combination of "AF-On" (along with deactivated AF on the shutter button), manual focus touch-up even with screw-driven AF lenses and focus peaking (both after AF'ing), by using the DMF (Direct Manual Focus) setting in the camera's AF options.  That's true.  But DMF only gives you Single-Shot AF capability before switching to MF -- not Continuous AF.

Using the camera in the default configuration will definitely seem "backwards" to someone such as yourself who has become accustomed to the Canon/Nikon paradigm of back-button autofocusing, since you have to put up with AF on the shutter button half-press, and press two buttons simultaneously to not AF (whereas the Canikon AF-On methodology forces you to shoot with those two buttons simultaneously pressed if you do want to shoot with AF).  But it's not inherently more difficult -- just different -- and does provide you with a couple of additional capabilities if you use older AF lenses and/or want to utilize focus peaking while the camera is set to Continuous AF.  Something to think about, anyway ...



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