Rapala
Well-known member
It seems that my copy of a Sigma 100-300 f/4 has some serious focusing issues. After suspecting the lens was front focusing, I printed off a test chart and conducted the test. The test itself was pretty simple, requiring the test chart propped up at about a 45 degree angle and shooting straight at it from a tripod. I aligned the center focus point with the center line on the chart and shot with a 10sec timer to reduce shake. The results I got are much worse than I had expected. The first photo attached shows the chart from about 7ft @ 300mm, 1/2000 f/4 ISO 100. Right about near the number 1 seems to be the perfect focus, showing prominent front focus. The second photo below is from about 12ft away @ 300mm, 1/1600 f/4 ISO 100. This one looks even worse, with focus around the number 2. BTW, both photos have been cropped to the center of each frame.
To show what this equates to in the field, the third photo would have been a nice photo of a young chickadee. The photo is uncropped, so the center focus point was directly on the bird's head. Instead I came away with a detailed photo of the Chickadee's alula and primary feathers. (Okay, maybe I looked up alula ) This is very frustrating since it would have otherwise been a great photo. In this thread I am looking for guidance since I have never had this issue before. I assume that my lens requires micro adjusting to fix this issue, but I am not sure. I also don't know how or where to get it micro adjusted if that is the case. Any help here is much appreciated.
To show what this equates to in the field, the third photo would have been a nice photo of a young chickadee. The photo is uncropped, so the center focus point was directly on the bird's head. Instead I came away with a detailed photo of the Chickadee's alula and primary feathers. (Okay, maybe I looked up alula ) This is very frustrating since it would have otherwise been a great photo. In this thread I am looking for guidance since I have never had this issue before. I assume that my lens requires micro adjusting to fix this issue, but I am not sure. I also don't know how or where to get it micro adjusted if that is the case. Any help here is much appreciated.