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Author Topic: Another Question For John Pytlak
Will Kutler
Phenomenal Film Handler

Posts: 1506
From: Tucson, AZ, USA
Registered: Feb 2001


 - posted 07-13-2001 12:32 PM      Profile for Will Kutler   Email Will Kutler   Send New Private Message       Edit/Delete Post 
Can you please explain why and how lens elements invert the projected image? Thanks.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 07-13-2001 01:45 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
If one were to do a simple double convex lens and cut it in half top to bottom and then draw a line from a point to the centre of the lens.
Now when the light hits that point it will exit as a mirror of it and after the second focal point it will be reversed ie on the other side.
That is a very oversimplified explanation as lens are not that simple anymore

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 07-17-2001 04:06 PM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
There's some good tutorial information on lenses and optics on-line:
http://208.154.71.60/bcom/eb/article/printable/5/0,5722,115155,00.html
http://www3.cerritos.edu/henriques/physics/raytrace.htm
http://www.abdn.ac.uk/physics/streamb/fin26www/

The simplest "lens" is a pinhole, as in a pinhole camera. If you do a ray trace using a pinhole "lens", you will see how the image is inverted.

When the original negative is exposed in a camera, the emulsion faces the lens. The image formed is inverted, and "reads" correctly through the base side of the processed negative. When a contact print is made of the negative, the image is inverted again, and the image "reads" correctly through the emulsion side of the print. A 35mm contact print is projected with the emulsion side toward the lamp, and the base side toward the lens. The analog soundtrack is on the "outboard" side of the projector (towards the operator), but ends up being on the left side of the projected image on the screen. The image on the print must be upside-down in the gate to be projected upright on the screen.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion


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