Focusing through water surface

[EastLelandDavid]

When shooting fish in the pond I am uncertain on focusing situations.  The camera is auto-focusing when I ask it to do so, but upon what is it focusing?  Is the image of the fish on the surface that is in focus, or is it the actual fish under water?  Some shots have good, clear, sharp focus while others do not.  There are many factors involved, but the fact that an image ( a reflection of such ) and the real thing are not one-in-the-same makes me wonder just what other factors there may be.  Upon what is the camera system focusing, a reflection or the real thing?  The camera in question is a 1 Dx and lenses used vary, but include the EF 135mm f/2.0 L, EF 17-40mm f/4.0L,  EF 24-105mm f/4.0L, and EF 24mm f/1.4L.

[ScottyP]

If you are seeing a reflection on the surface of the water, it will probably be the reflected image of the sky or trees or whatever is above the water, not of the fish under it. The AF does not know what you want to focus on, and may alternately try for either the fish or the reflected sky.

If you want the fish, try a circular polarizing filter. It lets you shoot through glass windows, water surface, etc., without seeing (or focusing on) the reflections.

[EastLelandDavid]

Scott, this isn't a case of a reflection on the surface.  As you point out a polizar could eliminate that.  My question invovles exactly where or on what does the camera focus?  Water plays havoc with vision.  I am tyring to focus through it and am encountering varied results concerning that focusing.  

[ebiggs1]

The camera focus' on whatever has the highest contrast.  That is what it looks for.  If it is the fish that is what it will focus on.  If it is a reflection off the water it may focus on that.

A circular polarizer may or may not help.  You will need to try one.  But if it does, this is one of the few cases where a filter is better than Photoshop if it works.