to do with developed slide film cutoffs
Ice scratch repair
The Infrared Process
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.
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
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
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
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
How Digital ICE works
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.
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.
HOME SCHMIDT GALAXIES EMISSION NEBS REFLECTION NEBS COMETS
GLOBULARS OPEN CLUST PLANETARIES LINKS
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
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.