Has anyone ever animated a camera lens aperture? I've got part of it done,
but I can't seem to figure out what the correct pivot point should be for
the blades. And I can't figure out how to get the correct overlapping
pattern, or a good 3D effect. How do those darned things work, anyway?

-Dave

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Attachments:
Download 'Test.mpg' (74 KB)

"Dave Blandston" <gra### [at] earthlinknet> wrote in message
news:39729613@news.povray.org...
| How do those darned things work, anyway?

A little more complex than you might think at first.  They are semicircle
leaves pivoting on both an anchor point and a sliding point.  The sliding
points are moved by a control which has notches to allow the sliding pivots to
go both inward and outward and also turn around the iris axis.  It's the
turning that makes it open and close, the sliding pivots allow for small
non-linear changes as they are moved.  And the leaves overlap in a screw type
way, only one end under the next leaf, not one on top of the other like a
regular layering.  That's how the iris on a old Kodak bellows camera I have
operates near as I can see anyhow.  I can't look from the other side without
tearing it apart completely because the shutter iris is broken.
If I can manage to make a rendering to show better I will, but don't count on
it.

Bob

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> Has anyone ever animated a camera lens aperture? I've got part of it done,
> but I can't seem to figure out what the correct pivot point should be for
> the blades. And I can't figure out how to get the correct overlapping
> pattern, or a good 3D effect. How do those darned things work, anyway?

seee if you can borrow a lense from a regular 35mm camera, you should be
able to see the blades inside move as you adjust the settings, might give
you a better idea.

either that or try looking at one of the camera manu sites - eg kodak.com
they do have a history of photograpy

Rick

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Well, I have rendered one now, animated too.  Like to see?  I hesitate to show
either the mpeg or the pov script since you might want to be going it alone
there as much as possible.  For right now I can say that I found translating a
disc with a wide opening over to one radius and rotating partway around then
translating back again does work.  Just needed to also rotate a slight bit in
the x and y first thing in order to get a good overlap later.  Then it's only a
matter of applying a specified amount (multiplied by clock) of rotation again
to turn the whole thing opposite the first rotation (which was also done with
clock aside from the while loop amount) so it acts like the aperture I have
here.  Not exactly, but pretty close to it.
There was a bit more to it than this but it wasn't trigonometry either.
I won't blame you if you need to see some actual code, it's one of those
flip-flop kind of things to reason out for me anyway.

Bob

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I've taken apart many a diaphragm from different microscopes (damn things
break too often!) which work on the same principle.  To me, it looks like
you've got the overlapping just fine.  For a pivot point, if you're looking at
each
piece as a triangle with it's upper tip at the centre of the circle, you
should use
the bottom left corner as the pivot point and let all the pieces fall to the
right.

hope this helps,

Ph_Rob


Dave Blandston wrote:

> Has anyone ever animated a camera lens aperture? I've got part of it done,
> but I can't seem to figure out what the correct pivot point should be for
> the blades. And I can't figure out how to get the correct overlapping
> pattern, or a good 3D effect. How do those darned things work, anyway?
>
> -Dave
>
>                Name: Test.mpg
>    Test.mpg    Type: MPEG Video (video/mpeg)
>            Encoding: x-uuencode

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That was my impression too, after examining my wife's camera lens, but it
only worked for the first few frames.

-Dave

"rsibbald" <rsi### [at] julianuwoca> wrote in message
news:39730F01.7F831C1F@julian.uwo.ca...
> I've taken apart many a diaphragm from different microscopes (damn things
> break too often!) which work on the same principle.  To me, it looks like
> you've got the overlapping just fine.  For a pivot point, if you're
looking at
> each
> piece as a triangle with it's upper tip at the centre of the circle, you
> should use
> the bottom left corner as the pivot point and let all the pieces fall to
the
> right.
>
> hope this helps,
>
> Ph_Rob
>
>
> Dave Blandston wrote:
>
> > Has anyone ever animated a camera lens aperture? I've got part of it
done,
> > but I can't seem to figure out what the correct pivot point should be
for
> > the blades. And I can't figure out how to get the correct overlapping
> > pattern, or a good 3D effect. How do those darned things work, anyway?
> >
> > -Dave
> >
> >                Name: Test.mpg
> >    Test.mpg    Type: MPEG Video (video/mpeg)
> >            Encoding: x-uuencode
>

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I'm not sure I follow all that. You describe the blades as "semicircle,"
while the ones in my wife's camera (which I'm trying to duplicate) are more
like shark fin shapes (I think, anyway, I can only see part of them). I also
tried twisting the blades a little to get the overlap, but that just caused
other problems. I was starting to think that there needed to be some
sliding, you're certainly correct that it's more complicated than it first
appears!

May I see your code? I'm amazed that you were able to succeed so quickly...

Thanks for taking the time (again!) to take a look at this.

Regards,
Dave

"Bob Hughes" <per### [at] aolcom?subject=PoV-News:> wrote in message
news:3972e411@news.povray.org...
> Well, I have rendered one now, animated too.  Like to see?  I hesitate to
show
> either the mpeg or the pov script since you might want to be going it
alone
> there as much as possible.  For right now I can say that I found
translating a
> disc with a wide opening over to one radius and rotating partway around
then
> translating back again does work.  Just needed to also rotate a slight bit
in
> the x and y first thing in order to get a good overlap later.  Then it's
only a
> matter of applying a specified amount (multiplied by clock) of rotation
again
> to turn the whole thing opposite the first rotation (which was also done
with
> clock aside from the while loop amount) so it acts like the aperture I
have
> here.  Not exactly, but pretty close to it.
> There was a bit more to it than this but it wasn't trigonometry either.
> I won't blame you if you need to see some actual code, it's one of those
> flip-flop kind of things to reason out for me anyway.
>
> Bob
>
>
>

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"Dave Blandston" <gra### [at] earthlinknet> wrote in message
news:39732ddc@news.povray.org...
| I'm not sure I follow all that. You describe the blades as "semicircle,"
| while the ones in my wife's camera (which I'm trying to duplicate) are more
| like shark fin shapes (I think, anyway, I can only see part of them). I also
| tried twisting the blades a little to get the overlap, but that just caused
| other problems.
|
| May I see your code? I'm amazed that you were able to succeed so quickly...

Sure thing.  It didn't take long to get the basic idea modeled and rendered.
I've been away from the PC much of the day so sorry about the delayed reply
back.
You're describing what the shutter looks like on this old camera here.  It is
shark or dolphin fin shaped "petals".  I'm fairly sure most any apertures
though are open semicircles more or less anchored at one end (still a guess
because I never found a decent diagram of one and it could be totally wrong)
and a sliding pivot at the other.
I'll post these two animations I have which show very well how it operates,
even has the varying pivot slide as it goes inward then back out slightly and
in again.  I think people would be interested to see it.
What's wrong with it mostly is there needs to be at least some S-shaped
curvature to the leaves, or petals, as they weave together as you realized
already.  Without that it is hardly flat and even intersects at certain times.
I'll post the still sloppy pov script to povray.text.scene-files.

Bob

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(16.5 years later - beware of the Evil Thread Necromancer!)

Hi(gh)!

On 17.07.2000 07:12, Dave Blandston wrote:
> Has anyone ever animated a camera lens aperture? I've got part of it done,
> but I can't seem to figure out what the correct pivot point should be for
> the blades. And I can't figure out how to get the correct overlapping
> pattern, or a good 3D effect. How do those darned things work, anyway?

Sweet little snippet - not even 100 kilobytes! May I Commodore64ize 
and/or AtariSTize and re-post it? Credits of course will go to you!

See you in Khyberspace!

Yadgar

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