Panasonic AG-DVX200 Tech Brief - Volume 5 - Page 2

Focusing and 4K, °e Confusing Circle Of Confusion, Bigger Sensors Require Bigger Glass - digital video camera

Get Panasonic AG-DVX200 PDF manuals and user guides View all Panasonic AG-DVX200 manuals
Add to My Manuals
Save this manual to your list of manuals

Page 2 highlights

Focusing and 4K Focus is one of those things that video shooters generally take for granted; a er all, it's a fundamental task for any use of a video camera. But consider for a moment the implications of 4K -- with much higher resolution than ever before, now focus becomes more critical than ever. If you miss focus by even just a little bit, you may end up losing all the bene t of having chosen 4K (or UHD) as your shooting format. Slightly misfocused 4K may end up resolving no more detail than properly-focused HD, for example. It's de nitely easier to achieve proper focus in HD (or standard-def) than it is to focus 4K (or UHD). e Confusing Circle Of Confusion Perhaps some clarity can come from exploring what we mean by "achieving proper focus." A lens is only ever truly focused on one speci c plane in space. Technically speaking, anything that is in front of that plane, or behind it, will be out of focus -- although in practice, we're not necessarily so strict. Generally we can say that there will be a certain range in front of and behind the focused plane that will be considered "acceptably sharp" or "in focus"; we refer to that range as the "depth of eld." So what does "acceptably sharp" mean? Generally, it means that the size of any given unfocused point is within a tolerable level. Consider that when a point is focused sharply, it will be rendered at the smallest possible size. If the point is not focused perfectly sharply, it will be rendered as more of a "spot" or "disc". e more out-of-focus that point is, the larger the disc will be. So long as that disc is rendered smaller than our "acceptably sharp" de nition, it will still appear to be properly focused; once the size of that disc exceeds the limit at which we consider it to be "acceptably sharp", it crosses over to being de ned as "out of focus." e Circle of Confusion is a way to de ne that size limit; when a point is rendered larger than the Circle of Confusion, it's considered to be out of focus. Why is this important? Because the higher-resolution sensors used in 4K cameras can resolve so much more detail that a point that might have been considered "acceptably sharp" on an HD camera, would now be considered "out of focus" on a 4K camera. In other words, the Circle of Confusion is smaller for a 4K camera, and the tolerance for out-of-focus errors is tighter. e standards are higher, and the job of achieving proper critical focus becomes harder when using a higher-resolution camera. Bigger Sensors Require Bigger Glass Larger sensor cameras generally need larger lenses to properly cover them, and especially when one is talking about a zoom lens. Digital camera (SLR) lenses typically o er only about 2

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
Focusing and 4K
Focus is one of those things that video shooters generally take for granted; aſter all, it’s a fun-
damental task for any use of a video camera.
But consider for a moment the implications of
4K -- with much higher resolution than ever before, now focus becomes more critical than
ever.
If you miss focus by even just a little bit, you may end up losing all the benefit of having
chosen 4K (or UHD) as your shooting format.
Slightly misfocused 4K may end up resolving
no more detail than properly-focused HD, for example.
It’s definitely easier to achieve proper
focus in HD (or standard-def) than it is to focus 4K (or UHD).
°e Confusing Circle Of Confusion
Perhaps some clarity can come from exploring what we mean by “achieving proper focus.”
A
lens is only ever truly focused on one specific plane in space.
Technically speaking, anything
that is in front of that plane, or behind it, will be out of focus -- although in practice, we’re not
necessarily so strict.
Generally we can say that there will be a certain range in front of and
behind the focused plane that will be considered “acceptably sharp” or “in focus”; we refer to
that range as the “depth of field.”
So what does “acceptably sharp” mean?
Generally, it means that the size of any given unfo-
cused point is within a tolerable level.
Consider that when a point is focused sharply, it will
be rendered at the smallest possible size.
If the point is not focused perfectly sharply, it will
be rendered as more of a “spot” or “disc”.
°e more out-of-focus that point is, the larger the
disc will be.
So long as that disc is rendered smaller than our “acceptably sharp” definition,
it will still appear to be properly focused; once the size of that disc exceeds the limit at which
we consider it to be “acceptably sharp”, it crosses over to being defined as “out of focus.”
°e
Circle of Confusion is a way to define that size limit; when a point is rendered larger than the
Circle of Confusion, it’s considered to be out of focus.
Why is this important?
Because the higher-resolution
sensors used in 4K cameras can resolve so much
more detail that a point that might have been con-
sidered “acceptably sharp” on an HD camera, would
now be considered “out of focus” on a 4K camera.
In
other words, the Circle of Confusion is smaller for a
4K camera, and the tolerance for out-of-focus errors
is tighter.
°e standards are higher, and the job of
achieving proper critical focus becomes harder when using a higher-resolution camera.
Bigger Sensors Require Bigger Glass
Larger sensor cameras generally need larger lenses to properly cover them, and especially
when one is talking about a zoom lens.
Digital camera (SLR) lenses typically offer only about
2