BOONER's Blog

Adventures, Photography, And more

The problem with sheep (aka, autofocus problems) part 1

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On my way to work I often see sheep outside grazing on a farm. Each time I passed I wanted to take a picture so I started carrying to work my camera with the telephoto lens attached.

Now my telephoto lens is not anything special. It is a Pentax FA 80-320 F4.5-5.6 that has a reputation for being fairly sharp between 80-200 and very soft 200-320mm. I have been very disappointed trying to get my telephoto lens to be sharp at the long range since switching to digital.

Back to the sheep. I stop on my way to work and take some pictures of the sheep. When I put the pictures on the computer I am very disappointed that none of my sheep are sharp, but after careful inspection of the picture below I see that the grass & leaves behind the sheep is what is in focus.

Back Focus Example Photo

Classic Back Focus - The grass just behind the sheep's legs are in focus.

I know that I had the focus point on the head of sheep that is on the right. Then it occurred to me why so many of my pictures may be “soft”. My camera has a back focusing problem where the auto focus system focuses behind the subject with my telephoto lens attached. My other lens I regularly use does not appear to have this problem. Now that I know the problem I have to find a solution.

Check back later in the week for part 2 where I try to correct the back focus problem.

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