D3100 Manual Focus

jaydeaner

Hello,

I have a question regarding using manual focus with the D3100, or rather what could be causing trouble when I am fully focused on manual. I am wondering if there is a back focus that could be thrown or something electronic that does not respond from the manual focus to the image sensor. I can take the same picture twice with full manual focus and get different results; blurry and in focus. Any help or theory as to why I am getting thrown focus would be appreciated!

Thanks,
Jay Dean

ohyeahar

There are 2 reasons I can come up with.

1. Your blurry shot is not from missing focus. It’s from motion blur, either the camera or the subject.

2. Your blurry shot is from missing focus because either your camera moved since the first shot or your subject moved. This happens often if you’re shooting wide open at f/1.8 with the subject relatively close to you. This means that your depth of field is very shallow and unforgiving. Even the slightest shift will move your subject out of the plane of focus.