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Light Box Flats



OK, you all have beat me up enough.  I dug out the light box and fired it 
up.  It was designed with green LEDs so I just tried it.  Nothing out.

I then cut a hole in the side and stuck in a night light (5 watt bulb like 
a Christmas tree light).  This gave a very nice flat on the V camera with a 
50 second exposure.  This was 35000 counts on what is about a 45000 count 
full scale.  Possibly I want to shorten the exposure.  Until I rebuild the 
box with an aperture, it is a compromise between shutter and saturation 
problems.  Since the shutter takes about .2 second to open, there is a 0.8% 
shutter effect.  This may be small compared to the quality of the light box.

For the I camera, the signal was saturated at even a 0.4 second 
exposure.  So I guess you all know where most of the energy goes when put 
into incandescent light bulbs.

I will have to build an addition on the light box to allow closing down the 
aperture to the night light.  Other than that, I should be able to start 
making better flats.

Looking at the V flat, it has the same structure as the V flat made from 
object frames.  This looks a lot different from the I flat made the same 
way.  I take this as a good sign.  The V flat looks like a V flat.

For those that have not followed this, the light box consists of a light 
bulb shining on a white paper screen in a black tube.  This screen is 
separated by several inches from a pair of white screens in a white 
tube.  The lens then looks at the far side of the white box.

It goes:

bulb
space in black tube
white screen
space in black tube
white screen
space in white tube
white screen
space in black tube
lens

This from a suggestion from Norman Mulhant long ago.  The idea is that the 
white screen illuminates the white box.  Light bounces around in the white 
box many times so that the light tends to be uniform on the far face of the 
white box that the lens sees.

As soon as I get the box modified, I will take flats and send out a data 
set for study.

Tom Droege