Thread: White BIF
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Old 16th November 2013
photo_owl photo_owl is offline
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Re: White BIF

Originally Posted by Ross the fiddler View Post
OK, my description about the cross hairs is probably not correct (I just thought I remember hearing it that way from someone), but the smaller area, however it is done can lower the chances of getting focus lock than the default larger area in a number of situations. The smaller area would be more ideal to pinpoint a particular focus point when the surroundings are likely to be focussed on instead of the intended subject. An example could be a stationary bird that is filling most of the frame & focus on the eye is the key area of intended focus, then the small focus point might be an advantage or any other situation where the focus point is critical. I would think BIF would be more reliable with the AF Sensitivity being set at Normal.

To quote from the E-5 manual:
You can set the range of the AF target for focusing when [AF AREA] is set to M. It is
available when shooting with the phase difference AF (when shooting using the view finder).

[NORMAL] The camera focuses using a range that is somewhat larger than the selected
AF target.
[SMALL] The camera focuses only within the selected AF target. When [SMALL] is
selected, the setting display for [AF AREA] becomes o.

(Italics details were not included in the E-30 manual)
well if the E5 is the same as the other 2 then the issue of which to use comes down to a very simple equation - relationship between the target size and the effective AF area.

if there's only one bird and a clear sky, subject to sufficient dof that focus on any part of the bird will ensure an appropriate lock - all points will be the easiest way to get an AF hit, diamond pattern will normally be the fastest way to get the fastest AF lock and shot.

after that it becomes a simple matter of the relationship between the target and the appropriate target area. as you go on to say the example of a small bird hiding amongst branches is normally the best example of this in the context of birds.

on the specific question IainMacd asked, my understanding (based on the engine in the 3/30) is that there's no effective difference in focus speed between N and S single point on the basis that they are covering the same relative subject; and based on the fastest AF speed being based on use of Diamond pattern, it suggests that AF processing isn't the critical element in the overall AF process.

the relationship between the AF target marks in the viewfinder and the N and S focus points (which is what I think the latter part of the manual entry you quote is trying to get over) is shown here -

effectively the (s) AF points are well represented by the small squares in terms of the active area and Normal are approximately 25 times the (s) area (which is why the difference is so clearly noticable in practice)
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Ross the fiddler (16th November 2013)