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Build A Light Box



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This is the one I followed a few years back... but I did not put foil in, with the white foam board it is not needed and added little to no value imo.





I built mine based on this general design that Guylain mentions.  I too didn't use the foil because it didn't seem necessary and I thought it would cause too many reflections.  I preferred to let the white foam core diffuse the light.  Instead of vellum, I used a piece of double-matte mylar (used in drafting the old school way).  I also placed the lamps on the outside of the ring which holds the mylar next to the rim of the telescope so that no light shines directly at the mylar screen (hard to explain).  I used 12v grain of wheat bulbs and hooked up a switched circuit to power the lightbox from the accessories port on the mount (no worries about dying batteries).  See the NexStar site for the circuit if you have a Celestron with an Acc port.  Only problem with the foam core board is it is susceptible to moisture issues from dew and eventually the box is going to fall apart.  


So I don't have the dew issues or have to carry the awkward box with me, I set up a gray screen PDF that I show in full screen mode on the laptop.  I then hold the screen up to the telescope while BYE does it's work.  I was surprised how well it worked.  Just make sure you are about to pack up and nobody else is around because it'll kill your night vision and make enemies of fellow astronomers.  The laptop also gets heavy real quick if your doing exposures that take longer than a minute or two to complete the series.  Cables also can be a problem since you still need to maintain your connection to the camera from BYE (unless you have two laptops, of course).

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I have an 8" RC, and normally use the white t-shirt method to take flats during the day. I have an astrozap dew shield, and use that to stretch the t-shirt over the scope so it is wrinkle free.


To take flats at night, I do the same but add a 12v LED light source by taping it to my bahtinov mask and putting that on the sky end of the dew shield.


I can dig up the source for the LED light if anyone is interested. It's an array of LEDs in a circle, about 2 or 3 inches across.

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To take flats at night, I do the same but add a 12v LED light source by taping it to my bahtinov mask and putting that on the sky end of the dew shield.

That seems to be a recipe for NON-GRADIENT-FREE lighting.


With the Light Source so close to the Baht Mask, its veins should be producing a shadow onto the Optics.  With the Light Source so much smaller than the Scope Aperture, that should be producing a rather strong Gradient - even through the T-shirt.


The T-shirt Flat taken at Dusk or Dawn works because the Scope is pointed at an evenly diffuse portion of the Sky.  A Light Box with LED Light Sources works because of multiple layers of Diffusing Material - Tracing Paper, Velum, Acrylic, etc - between the Light and the Optics.


Have you inspected one of your LED/Baht-Mask/T-shirt Flats, and compared it to what you are producing with Dawn/T-shirt ??

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The bat mask is just to hold the light. the light in on the inside of mask, facing down the dew shield towards the t-shirt, which is on the other end of dew shield, stretched over the scope.


I have not used any software to evaluate the quality of the flats in that case, just looked at them by eye and used them in stacking. I haven't taken flats at night in a long time. My scope is pretty stationary in the yard these days, so doing it the next morning is more convenient than using any light/box etc. . 

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