I recently purchased a new 100-400mm IS II lens and love it! I have run into a small issue and not really sure of the cause.
I have been using the same Canon 6D for 4 years with 70-300mm IS and have not had this issue before.
For some reason I am randomly getting shots that are not in focus, I have tried using just center point only,(which is what I have done primarily for the last 4 years) and also all points active. I have tried single shot, AI Focus and AI Servo mode.
I have attached 2 images taken back to back to show what I am seeing..
1 ACCEPTED SOLUTION
I don't think there is anything wrong with your lens. I think you are discovering the nature of AF points, and depth of field. The AF points are actually la bit larger than the the little squares that you see in the viewfinder, and in this diagnostic display. Your depth of field is approximately just over one meter. Your AF point is covering two subjects, the bird and the tree trunk, that are at distances that are significantly different when compared to the distance to the lens. The camera seems to have alternated between the two subjects under the AF point.
Because of the bird under the lit Af point, I assume the top photo is the one "in focus" and the bottom photo is not. Both photos are reporting distance to the focused subject. The top photo is reporting the shorter distance, and seems to be focused on the bird on the branch. The bottom photo is reporting a slightly longer distance to the subject, and seems to be focused on the main tree trunk behind the bird. Notice how the reported distance to the subject, or bird, in the top photo falls outside of the reported depth of field in the bottom photo.
In the top photo, the bird seems to be within the DOF. In the bottom photo, the bird seems to be outside of the DOF. These differences in focusing should have been visible through the viewfinder. Do you wear eyeglasses? If so, you may wish to adjust your diopter. I wear eyeglasses and find need to adjust mine from the default setting of "zero".
In the below photo, I could not focus on the bird, because of the branch between the bird and the lens. When focused on that branch the bird was nearly sharp, but not razor sharp, because of the DOF. Instead, I focused on the high contrast branch, upon which the bird was perched. Also, I used "ONE SHOT" mode, and the manually selected center AF ointment, which seems to be the best way to use the 6D for precise focusing.
Picking out a bird amongst tree branches is a tricky task. I have had my best success doing it by using BBF, back button focus.. Once I have locked focus on the bird, I don't want the camera to try to refocus when I press the shutter button. Your shutter speed also seems to be on the slow side, too. Generally, you want to use a SS that is at least as fast as being equivalent to 1//FL, or one over your focal length.
Overall, I think your lens seems to be functioning as it should. You just need more practice with the lens, and with the camera's AF points behaviors. Keep in mind that AF points are significantly larger than the tiny targets you see in the viewfinder, and nearly overlap. I use the same camera and lens combination.
When I first began using my 100-400mm lens, my keeper rate seemed to drop significantly. Of course, I suspected the lens was a lemon. But, I decided to give the lens a fair trial, and over time I began to quickly realize how the focusing distance adjustment switches and the image stabilization mode switches can impact how well my photos turned out.
