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Forum index » Science and Technology » Physics
Optics: need help understanding lens flare/smear effect
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tadchem
science forum Guru


Joined: 03 May 2005
Posts: 1348

PostPosted: Wed May 17, 2006 10:48 pm    Post subject: Re: Optics: need help understanding lens flare/smear effect Reply with quote

Gert wrote:
Quote:
Hello,

I'm having a hard time to understand what is causing a certain lens
flare/smear effect I'm seeing.

The setup is a bright halogen lightbulb, a PAL composite video camera
with optical zoom lens and a TFT monitor. Pointing the camera at the
lamp, the image shows horizontal, vertical, and diagonal lightrays,
"shooting away" from the lightbulb. A popular effect when photographing
christmastrees. (what is the offical term for this, flare, smear, or
something else ? )

Sounds like you are describing something like this:
http://www.crystalpixels.com/gallery/lensflare1.jpg

True lens flare is a spot 'halo' (or a set of them in a line) with no
apparent source:
http://www.clavius.org/lensflare.html
usually seen with lighting from a single intense source that is both in
front of the plane of the lens and (usually) outside the field of view.

The optical artifacts you are describing are usually obtained when
shooting a small but very high contrast light source directly:
http://www.nasbydalskolan.taby.se/Projekt/quiz7.htm

IIRC, the effect results from diffraction of the light around the edges
of the iris elements, which is why there are variable numbers of rays
seen, depending on the camera used.

Quote:
I have made a photograph of the resulting image on the TFT display, see
the first picture on :

http://zevv.nl/div/flare.jpg

Your link is broken.

Quote:
Now the strange part: when I rotate the camera, I would exepect the lens
flaring to rotate as well, together with the picture. However, it
doesn't. Rotating the camera or the lightbulb doesn't affect the
orientation of the flaring!

Rotating the camera also rotates the film. The rays will always point
in the same direction *relative to the film edges*.

Quote:
So my questions are: Why is the flaring not
rotating together with the camera ? Is it caused by the lens, or
something else ? What's so special about those 90 and 45 degrees angles
I'm seeing ?

My quess is that your iris has 8 elements.

HTH

Tom Davidson
Richmond, VA
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Gert
science forum beginner


Joined: 17 May 2006
Posts: 1

PostPosted: Wed May 17, 2006 9:22 am    Post subject: Optics: need help understanding lens flare/smear effect Reply with quote

Hello,

I'm having a hard time to understand what is causing a certain lens
flare/smear effect I'm seeing.

The setup is a bright halogen lightbulb, a PAL composite video camera
with optical zoom lens and a TFT monitor. Pointing the camera at the
lamp, the image shows horizontal, vertical, and diagonal lightrays,
"shooting away" from the lightbulb. A popular effect when photographing
christmastrees. (what is the offical term for this, flare, smear, or
something else ? )

I have made a photograph of the resulting image on the TFT display, see
the first picture on :

http://zevv.nl/div/flare.jpg

Now the strange part: when I rotate the camera, I would exepect the lens
flaring to rotate as well, together with the picture. However, it
doesn't. Rotating the camera or the lightbulb doesn't affect the
orientation of the flaring! So my questions are: Why is the flaring not
rotating together with the camera ? Is it caused by the lens, or
something else ? What's so special about those 90 and 45 degrees angles
I'm seeing ?

Thank you very much,
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