07-11-2018 11:17 AM - edited 07-11-2018 11:32 AM
You haven't made it clear if you have tried Single-point SPOT AF.
Single-point SPOT AF covers an even smaller area than the center AF point and will make it easier to isolate the subject form the surrounding foliage.
Here is a detailed explanation of the difference between Single-point AF and Single-point SPOT AF: An inside look at Spot AF
While it’s not necessarily the go-to AF Area setting for every situation, Spot AF gives the experienced DSLR shooter a means to work even more carefully with his or her AF and place the sharpest focus even more precisely on the subject where it’s wanted. If you own a camera with this feature, it’s worth experimenting with and learning where it can be of benefit to you. Simply keeping in mind the actual area covered (see the graphics, above, in this article) goes a long way toward truly maximizing Spot AF’s potential. And, equally important, is awareness of where the other AF Area options display their benefits.
07-11-2018 12:02 PM
Keep in mind Single-point SPOT AF is not an option if you are in Auto mode. You shouldn't be any way but just to be clear.
Av is the best choice.
07-11-2018 01:01 PM
Thank you. I did not know there is a difference betwen Single-point AF and Single-point SPOT AF. I don't recall seeing thay fact anywhere before.
Also, I am astonished to see your blue and red rectangles. I assumed single spot meant -- single spot. Duh. Evidently not.
07-11-2018 01:23 PM
No it does mean just a single more tiny single point. You will not see anything additional in the viewfinder just a smaller square. The colored example just indicates coverage you can expect.
I would not use it as a first option. Let's get the basic settings a good try first. When things don't go as expected it's always best to start off at the beginning. The walk before you run thingy.
07-11-2018 07:42 PM
The 5D III (and IV, and 1D X, 1D X II, 7D II, etc.) are all very "technical" cameras. They are very powerful... but they have loads of options that other cameras don't have.
You really want to take the time to go through the manual and learn the features.
Also, download and read Canon's 47 page PDF guide on the 5D III auto-focus system (this entire 47 page document is dedicated to JUST the focus system on your camera ... the number of pages alone should give you some idea that this camera has a LOT of options when it comes to focus.)
"Spot AF" is not the same as "Single Point AF". Spot AF reduces the AF point to the smallest size possible to avoid possibility that another object will interfere with your subject and confuse focus. But also... when you are in AI Servo mode, all the "case" settings (you'll read about those in the document) come into play. You can tune the behavior of the camera as to whether it should ignore obstacles that momentarily block your subject ... or if should immediately snap the focus to that new subject.
A downside of "Spot AF" is that since the point is much smaller, it needs to be something wtih good contrast (to help the camera lock focus). "Single Point AF" has a more generous area so that's more opportunity to find contrast to lock focus. There's also "AF Point Expansion" that uses four additional AF points (above/below/left & right of your chosen AF ... these points "extend" the range of the single AF point. There's also an AF Point Expansion that uses all 8 surrounding points (again... same behavior. It wants to use the center but borrows the other points to "expand" the area in an effort to increase the area to search for good contrast.) The risk is... as you expand the area it can search for good contrast... it might find good contrast on a tree branch or leaf and NOT on your subject.)
If you have a fast moving subject free of distracting obstacles, the camera can often work better (focus faster) if you give it a larger area. Basically use more when you can. When you realize there are competing obstacles... reduce the area so the camera HAS to use the tiny little spot you picked out to lock focus.
07-12-2018 10:54 AM
Thanks for all the replies.
A perched bird is basically an ellipse for the body, an ellipse for the head, and a rectangular shape for a tail. There may be a branch interesecting one of these. Nonetheless, I don't see why software can't be written to search for a bird near the center of the field of view. I say this as a mathematician and computer programmer.
This would establish a "perched bird mode". It's more complicated for a flying bird, but I've not had trouble photographing them. Usually there is no competing foliage.
07-12-2018 11:31 AM
Remember camera sensors only see luminosity. They can not distinguish a limb from a bird since it is just lighter or darker.
07-12-2018 11:46 AM
That might work in live view, but through the view finder you only have at most 60 widely separated pixels.
And you might want a perched-bird focus mode, but I want a bee focus mode.
How many modes should canon add?
07-12-2018 12:10 PM
<<Select a fairly high ISO 800 to 1600.>>
ebiggs1.... Can you elaborate on this a little just for my own knowledge? Does that ISO range somehow improve AF sensor capabilities?
07-12-2018 12:22 PM - edited 07-12-2018 12:23 PM
Nonetheless, I don't see why software can't be written to search for a bird near the center of the field of view. I say this as a mathematician and computer programmer.
Sorry if this is a bit of a diversion from topic... but I am in tech as well, so your comment caught my eye. Google is doing quite a lot with its AI platform wrt photography. In this  case, they worked on using AI to sift through "street view" images and basically work out which clips would make "good" photographs. They've also been doing well in competitions against human photographers where people "vote" on images. And here  is an example where they are doing more with short video clips that are determined worthy of capture with their AI. I suspect that phones will be the faster adopters of AI technology for photography and professional-grade cameras will lag a bit due to the use cases being somewhat different.