canon 300 f/4 is

Do not attempt a micro adjust before you get all the basics down on using a telephoto lens. Only after eliminating all the common mistakes made by a new user do you look any further. Until we see your photos with the problem can we make a suggestion.

jingler wrote in post #12654231
hi
i have a 50d

The 50D does have micro adjust capability, it's a great camera, I gave mine away when I got my 7D and I miss it. Lenses can have the focus slightly off which will make the subject fuzzy. Mine was WAY off, so I sent it to cannon; they got it much closer to focusing correctly but it's still +7 off. With micro adjustment you can tell the camera to focus slight behind or infront of the object to compensate for slight front or back focus. Mine is now crazy sharp, I love the pics that it takes. It's my most consistent lens (other than the 70-200).

The post above warning to make sure you're doing everything else correctly before micro adjusting is great advice. The main thing with a long prime is shutter speed; keep it above 1/400 for still objects and over 1/800 (minimum) for moving subjects (ensure your using servo mode for moving subjects.

mrgooch wrote in post #12651885
Usi Motro
Other than posting the photos what do we learn from them? We all know that it is a great lens.

It seems that Jingler is not absolutely sure that his lens is working properly or even that it is a great lens. It seems to me that showing some good results from that lens might just narrow Jingler's problem down to either an abberant individual copy or bad technique.

Most of the problems with long lenses can often be attributed to several problems or a combination of those problems. The problems are not mutually exclusive. You can have more than one anomality. Sometimes these are additive and compound the focus problem and sometimes, they are subtractive and cancel each other out.

1. Too slow a shutter speed for the photographer's hand holding capability - which can vary greatly between photographers and even between different days for the same photographer. The 1/focal length x crop factor shutter speed is a recommendation, not a firm rule. Some of us need faster shutter speeds to get sharp imagery. I cannot hand hold my camera/lens as well at 71 years old as I could at 41 or 51 years...

2. Incorrect focus either the camera chose the wrong focus point or the photographer selected the focus point and used focus lock - then either the subject or the camere moved. It doesn't take much to throw off the focus of a 300mm lens.

3. The lens is front or back focusing...