Multiple focus points ! How does that work ?

[BADGER.BRAD]

Multiple focus points is something I just cannot understand, coming from a film back ground and using manual cameras/lenses you manually set the focus on the part of the image you are interested in and off you go. So how can the lens be set on multiple points at the same time ? Is this a software thing ? Another quick question having never used a auto focus changeable lens camera is can you hold the camera by the lens or would this stop it being able to focus just a thought after speaking to a guy with a camera with a very large lens.

 

[sirch]

Two things. For AF it allows you to select which part of the frame the AF will focus on, you pick the point and the AF uses that as the focus point.

Secondly, multiple parts of an image may fall on the focal plane and some cameras will indicate which parts are in focus. Suppose you are photographing a group of flowers, in the simple case of the film plane square-on to the flowers, all flowers that are the same distance from the camera will be in focus. If the camera is at an angle to the subjects then the focal plane will be at an angle but multiple parts of the frame may still be in focus.

This is nothing to do with digital, lots of film cameras have multiple focus points. The Canon EOS 3 film camera has 45 focus points (IIRC) and eye detection to track what you are looking at in the view finder and focus on that AF point

 

[d00d]

I guess 'Multiple focus points' should be renamed 'Multiple potential focus point possibilities', or something like that.

There's only ever one focus point. But hang on, we now have cameras that allow you to select the focus point after you've taken the shot, in-camera focus stacking, cameras with multiple lenses.

 

[Nod]

we now have cameras that allow you to select the focus point after you've taken the shot,

I know that some cheat that - they shoot a slab of 4K video, shifting the focus point from front to back (or back to front) of the scene so, IF the precise timing of the shot is important, it might be missed by a fraction of a second.

 

[BADGER.BRAD]

Thanks everyone , that makes total sense that multiple parts of the photo would be in focus, I had thought that in software the image was being made up out of multiple shots with all the various points being added together to get an image that was all in focus.

 

[Andy Into The Wild]

Thanks everyone , that makes total sense that multiple parts of the photo would be in focus, I had thought that in software the image was being made up out of multiple shots with all the various points being added together to get an image that was all in focus.

This is called focus stacking and is possible both manually (taking shots at difference focal points and blending in post processing) or automatically on cameras that have it (the camera automatically takes multiple shots at different focus points and stitches them for you).

Welcome to the future