Here is a little
            photographic demonstration on an interesting property of Ektachrome
            film. We all have those cut off ends of developed film laying
            around, left over from developing those hard earned astro photos.
            Films such as Elite chrome, or Provia are developed E6, and the
            unexposed frames are always jet black, letting little light through.
            But here's a nifty fact you may not have been aware of: These
            pieces of black cut off ends make very good deep infrared filters,
            that can be used to photograph daytime scenes an reveal the hidden
            beauty of a deep IR shot. They are actually black till about
            800nm, then they become optically transparent. With the right
            web cam, or digital camera, you can take dramatic infrared images.

            
This article is broken
            up into two parts:

            
1. The infrared process
            and sample daytime images

            
2. How this technology
            is used in scanning your astro films in slide scanners that use
            Digital ICE for scratch removal.
 

The Infrared Process


            


            
LEFT: Using a Phillips
            TU Cam, this shows that the infrared remote from my television
            which transmits at 910nm can be easily picked up as a bluish
            white bright source. This is the difinitive test to see if your
            web cam or digital camera will work with IR imaging.

            
RIGHT: A jet black piece
            of Elite chrome 100 slide film that has been developed but unexposed
            allows nearly 100 percent of the 910nm light through, but no
            visible.



            


            
LEFT: When we take the
            camera outside, a typical scene toward the snow covered Colorado
            Plateau is seen with pines in the foreground seen here in normal
            visible wavelengths.

            
RIGHT: Through the film
            chip, the auto gain of the camera boosts up and yields this bizarre
            scene. The trees and plants are pure white as chlorophyll has
            a very high IR reflectivity. The clouds become more dramatic
            in contrast.



            


            
LEFT: Normal scene from
            my balcony looking over the pine trees toward the town of Payson.

            
RIGHT: Through the film
            chip, the scene looks like a snowy winter shot in far IR.



            


            
LEFT: Blades of green grass
            (I need to mow my lawn!) with a tree in the background. 

            
RIGHT: In deep IR the grass
            is pure white and shows contrasts and details unseen in  white
            light.



            


            
LEFT: Final image, a prickly
            pear cactus in my back yard sitting in the sun, normal spectrum.

            
RIGHT: Even the common
            cactus takes on a very strange and eerie appearance in deep IR.

How Digital ICE works

            
 About half the scanners
            today have whats called "Digital ICE" for removing
            scratches from negatives and slides scanned. When you put that
            astro photo into the scanner, every scratch will show up in the
            final image because of the high contrasts we stretch our images
            to when we process. Using ICE can optically remove the scratches
            WITHOUT degrading the fine detail of an image. But HOW it does
            this has always been a mystery to most people. 

            
How it works.

            
A normal slide scan consists
            of three passes on the image, one for Red, one for Green and
            one for Blue. When ICE is activated, a fourth scan is done in
            infrared light. You'll see below why this works.



            


            
The LEFT image is a normal
            visible light shot with my Philips camera of a schmidt camera
            slide taken back when the sky was clear long ago. Behind it is
            a star chart printed out with my ink jet printer using Megastar.
            There are a few penciled in areas of interest on the chart as
            well.

            
RIGHT: In infrared using
            the film chip as a filter, something very strange happens to
            both the slide and star chart print ! The slide is now totally
            transparent and you would be able to easily see any scratches
            on the film without interference from the actual image. Digital
            ICE corrects ONLY those areas by an algorithm that lightens them
            to match the background of the image. But look though the side
            and you can see on my chart one of the penciled in regions showing
            where the Fox Fur nebula is located. The word "Cone"
            is at bottom too.

            
Where are the stars on
            the chart? They are invisible in infrared! Only the graphite
            pencil line notes and sketches I made are seen. 

            
I hope you've enjoyed this
            write up, write me if you found it interesting.



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