Re: crazy OOF shape


Paul Furman wrote:
> bjw@xxxxxxxxxxxxxxxxx wrote:

> > That's what an iris diaphragm looks like when the leaves get
> > slightly offset from where they are supposed to be. The "notch"
> > in the gear is the end/corner of the leaf, which normally
> > should be overlapped by the next leaf over.
>
> So it's a broken lens, like they tried to stop it up wider than the lens
> was designed for. Those are really huge OOF circles too. I might guess
> the faster the lens, the larger the OOF circles?

It's not really broken, but the diaphragm is a little out of
adjustment. That's more common than you might think. I'm a
little surprised to see it in a movie, but perhaps not if it
was a low budget production (that is, a high budget production
would probably use high dollar rented equipment that was more
throughly checked out). It's most likely to show up about one
stop down from wide open. Wide open you don't see the iris leaves.

The out of focus circles (circles of confusion) are proportional
to the physical diameter of the aperture (e.g. 25mm for a 100mm
lens at f/4), when distances of subject and background are fixed.
This is probably in the Lens FAQ if that's still around. A long
and fast lens produces more blur in the background, this is a
well known effect.

.

Relevant Pages

  • Re: Tthe aperture hexagon
    ... between leaves would take on the shape of the crescent sun. ... the shadow of a tree usually looks like a tree. ... is light that hasn't been brought to a focus properly by the lens. ... The iris diaphragm of the lens is ideally put ...
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  • Re: Lens system design help needed
    ... glass" or frosted glass or acrylic. ... Adjust iris diaphragm diameter as you vary the lens distance. ...
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