af servo mode

[jason5]

ive been practicing with my digital rebel lately and ive been messing with af mode which leads me to my question how to gegt a picture of something moving thats in focus while the background is not do i just put it on a tripod and try and follow the object as good as possible? do i keep it on bulb mode or do i time it like 6 seconds or something?

 

[tr0gd0o0r]

I'm not quite sure exactly what you're going after here. There are two different ways to get the background "blurry". The question is do you simply want the background to be out of focus or do you want to have motion blur in the background?

Since your description seems to imply the latter, I'll explain it first. You need to set a slower shutter speed (I haven't done a lot so I'm not sure how slow, experimenting seems best, but it'll be at least 1/15 i'd imagine). Focus on the moving subject and follow it through its motion, but the camera has to move at the same "speed" at the object. (You have to keep it in the same place in the frame). A tripod may or may not help here, my inclination is that it would be difficult to move the camera fluidly enough, but i've never tried, i'm sure someone with experience will let you know shortly though.

In regards to the title of your post, the af servo mode isn't going to help with this. What that mode does it maintains focus between shots. The idea is when you're firing off shots of someone running at you at 5 fps, it will refocus b/t each shot.

Now, if you just want a blurry background, all that takes is a big aperture (small number) with a long lens. (and being closer helps to)