@Robodot wrote:I did check for a back focus issue when i purchased it and recently. both times it shows a very slight back focus but I do not know if thats a big problem (both 70-300 showed the same thing here is a recent test:
I really do not see a problem with the DOF in this shot. Take a look at the illustrations near the bottom the page at this link.
http://www.dofmaster.com/doftable.html
The plane of focus does not fall in middle of the depth of field. One third of the area of acceptable focus should fall in front of the focus plane, [with] roughly twice that distance in acceptable focus behind the focus plane.
You should always perform your [AFMA] focusing tests at maximum aperture, because this is the aperture setting that the AF system in the camera uses. The whole point is that you want to see what the camera is seeing. Test shots taken at stopped down apertures are simply put, not very useful. The idea is to take a number of shots and come up with a working average.
The type of lighting used can affect the focusing system, too, so keep that in mind. I have taken test shots indoors with artificial lighting, and gotten inconsistent results from one shot to the next. When I moved everything outside into bright sunshine, my results were suddenly very consistent. Sunlight has a broad spectrum, while artificial lighting generally does not.
There is a very good video on YouTube called “Dot Tune Method”. It takes a lot of the guess work out of AFMA testing.
