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ATM Filter Wheel



Pre-mounted eyepiece filters can be used in many ways.  Sometimes you, while observing you want to switch back an forth between two filters.  This is best done using a filter wheel. 

I wanted a wheel to create color planetary images using my monochrome video camera.  I purchased an inexpensive set of parfocal filter (4) 1 1/4" filters from B&H having an IR, and RGB filters.  A set of parfocal filters allows you to switch from one filter to the next, without the need to refocus the objects.  A "must-have" when using a wheel for planetary imaging. 

Rather than buy a wheel I decided to make my own.   

 00 Meade Filters
 01 Filter Wheel Plan The first step was to make a plan for construction.  If you have read some of my other build articles, you know by now, this is how I like to work.  I chose materials I already had in the shop.  Some scrap pine and a few square feet of 3mm luan I had left over for my Schiefspiegler project.
I cut two 4.5" diameter luan discs.  These were made together and match marked to form two matching sides.  I bored only 1/3 the way through with a 1 1/4" hole saw. Using the center hole made by the hole saw I then bored all the way through the 3mm luan with a 1 1/8" spade bit. This made a nice counter sunk hole to retain the pre-mounted filters. 02 WHEELS CUT
 03 Wheels Coated  I sanded the discs and coated them with a black "Polyshade" one step polyurethane finish.
 Next I built, sanded and finished the case and its front plate.  I used a section of 1 1/4" sink drain PVC pipe which happens to be the exact outside diameter of an 1 1/4" eyepiece assuring a good fit in my 1 1/4" later.  The case has a hole in the back for the nose of the my Imaging Source video camera.  The case and front plate were finished using a one step polyurethane finish matching the Schiefspiegler OTA. 
 04 Filter Wheel Case
 05 Filters Installed  Four filters were installed between the two halves forming the assembled filter wheel leaving one space open.  Filters included Red, Green, Blue and IR.  The central bolt holds the two halves together and also acts as the axle for the wheel once installed in the case.
 The wheel fit nicely into the case with a small hole drilled in the case and the front plate to accept the wheel's axle.  The wheel protrudes beyond the case on one side.  This allows the wheel to be turned by hand.  The inside of the case and front cover were blacken using a black polyurethane finish.  06 Wheel Installed in Case
 07 Front Done Several stainless steel screws were used to hold the front plate in place.  This view clearly shows the 1 1/4" PVC drain pipe nose piece.

The back side of the filter wheel assembly with Imaging Source monochrome camera attached is shown to the right.  

The color wheel will allow imaging the brighter planets, Jupiter, Saturn and Mars, in color using a monochrome camera.  To do so, the planet is imaged with each color filter separately.  First Red, then Green and the Blue.  This image is then combined in Photo Shop to reconstruct a color image.

 Saturn 3 IR  Here are three images of Saturn all captured the same night.  The upper left is a color image created by combining three separate Red, Green and Blue videos.  The upper right and lower left are monochrome images captured using only the IR filter.