• Wondering which camera, gear, computer, or software to buy? Ask in our Gear Guide.

Focusing...

How come it is that you can focus on two different people of objects which are each different distance from the camera...?
And how do you keep the focus on a person that is constantly moving distance from the camera?
 
Last edited:
Search for my definition of depth of field elsewhere on this list for a more detailed explanation of DOF.

The way you get more things in focus (near to far) at once is by closing your iris (aperture) -- smaller openings are larger numbers and let in less light.

The way you follow a moving subject takes practice and planning. Some cameras have a built in feature to pan the focus between two points in a specified amount of time. If you don't have such a feature, or you can't use it in your situation, you just need to get good at adjusting your focus on the fly, or, prefocus, have the subject move a little, refocus and have the move again. Then shoot one or more additional angles so you can edit the movement into a smooth move (cutting from one angle to another) that doesn't reveal the stops.

If you're shooting someone on a motorcycle or something, you'll just have to practice, do several takes and use the best one. Shooting with a smaller iris for more depth of field will also help a lot.

Doug
 
Last edited:
On larger format cameras, this can be more difficult as they naturally have a shorter DoF. A split-diopter lens will allow to have two separate distances in focus at the same time (see the beginning of reservoir dogs when they get to the warehouse for an example of it). There will be a slight blurry bit in the middle though as it's two separate lens halves fused together down the middle.

close the iris as OSPV stated in the previous post, or shoot the two separately and composite them together (see Citizen Kane, the scene with the blurry lady in bed and the background and foreground elements in crisp focus). Like a split screen effect.
 
Hmmmm ... didn't even think of that. I guess I need to watch more movies.

One more thing to add, I suppose, is that if you are further from your subject, it will be easier to maintain focus, as DOF also increases as you move away from the camera.
 
Lets not, and say we did. I keep getting in trouble for mathematical illustrations.

I do think it is virtually impossible to do a perfect follow focus on a subject 2 feet away, given you'd have 3 mm of DOF. By the same token, if the subject is 10 feet away, at f8 with a typical prosumer video cam, you'd have enough DOF that following should be doable with practice.

Have you noticed that the XH-A1 only stops down to f9.5? They never tell you the smallest aperture, only the widest. At least it has a couple of built in ND filters.
 
Back
Top