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Old June 1st, 2004, 08:17 PM   #1
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filming thru a screen?

just wondering if anyone else has experienced this...

the other day when i was testing out my new tele adapter (sony 1.7x) on my gl2 in my bedroom i started freaking out because i thought the glass was bad and causing my images to smear on the screen. turns out it wasnt the lens but it seems it was the screen that is in front of my window which i was shooting out of that was causing this smearing effect.
when i moved to the other side of the window without a screen the image i was looking at thru the window (a patio chair by a pool about 15 yards away) wasnt smeared and looked fine.

has anybody seen/heard of this before? i am wondering if i need to send my cam in for work..
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Old June 1st, 2004, 08:33 PM   #2
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It's called Depth of Field (DOF). when you were far away the DOF increased and the screen was in focus and obscured the scene. The closer you got to the screen, DOF was reduced and became out of focus. A complete description can be found here.
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Old June 1st, 2004, 08:55 PM   #3
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Might I suggest that light defraction from the sun was your problem. Try it again at the same time of day, in the same light conditions, to attempt to dublicate the situation.
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Old June 1st, 2004, 09:50 PM   #4
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Maybe I'm misreading the post (complete sentences are a big help). If you are wondering why shooting through a screen causes a softening of the image, it is called diffusion. If your wondering why the screen is in focus or out of focus, it's DOF. If you are wondering why shooting into (towards) the sun causes the image to go soft, lose contrast, it is diffraction (as Robert suggests) and lens flair. You can read about these optical defects and more on the DV Info site, in our articles section.
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Old June 13th, 2004, 09:28 PM   #5
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sorry ive been away from the comp....

i know what DOF is and understand how to control it and its effects on my images, this is not the case however. nor is the sun - i tried shooting through the screen again yesterday when the sun was shining onto the chair outside and the same effect was the result again. it is not a softening so much as it is a smearing. the best example i could give would be that it looks similar to when you shoot at a low shutter speed and the images trail across the screen; except in this case there is not motion inside the frame, just a "smeared" image of a chair...

PS i shot this with my f stop all the way open and stopped all the way down and the effect did not change.

any ideas?
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Old June 14th, 2004, 12:44 PM   #6
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Nothing to be alarmed. The window screen is acting like a net placed in front of the lens to cause diffusion. You are using it in an extreme position by having the screen a distance from the lens and shooting with a very long lens. What you are doing is exaggerating the diffusion effect. Move the camera till the lens is just about against the screen, and you will probably get a different version of the effect. It's not unlike shooting with a number three diffusion filter: on a wide shot it looks quite acceptable, but zoom in close to full tite, and the picture becomes ridiculously soft.

Screens have been used quite often to soften backgrounds in shots. Place the screen between the subject and the background, and keep the light off the screen. There is a company that sells a device which is basically what I have just described.

Wayne Orr, SOC
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Old June 14th, 2004, 02:45 PM   #7
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Most homemade netting type diffusion systems (silk stockings, toulle etc.) will cause a similar type of "smearing" to the image...its caused by the pattern of the cloth...an effect that is similar to "star" filters witch have tiny lines etched into the glass, except that the weave will typically cause a streak in one direction, or perhaps two directions than may not be at right angles. The screen in your situation is diffusing the situation in several ways....one of which is most likely light (not direct sunlight, but rather the light that forms the image of the chair) striking the edges of the screen fibers, and reflecting into the lens in a semi-regular, imprecise fashion...thus a smeared, or streaked image placed on top of the diffused, but otherwise clear image coming through the holes in the screen. This effect will probably be most visible in contrasty situations like when the subject is in full sun.

Enjoy your new cool effect!

Barry
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