SBIG CFW-8a and Tru-Technology for 1.25" Astrodon Filters
Most customers will order 1.25" Astrodon filters mounted in screw-in holders compatible with SBIG CFW8a filter wheels. Simply screw them into these filters wheels. This includes the Tru-Tech CFWs, as well.
Astrodon 1.25" filters come mounted unless otherwise indicated. Astrodon 50 mm filters always come unmounted. This document has links to show how to install unmounted Astrodon filters into several filter wheels from various suppliers.
FINGER LAKES CFW-2 for 1.25" and CFW-7 for 50 mm Astrodon Filters
Finger Lakes Instruments (FLI) makes several color filter wheels (CFW) that require unmounted filters, including the CFW-2 with 8 1.25" positions and the newer CFW-7 with 7 50 mm filter positions. For these FLI CFWs, Astrodon supplies viton o-rings (022 1" x 1 1/8"; McMaster-Carr #9464K76 for CFW-2 and 133 1 13/16: x 2" McMaster-Carr #9464K133 for CFW-7) that are placed into each position as a spacer that brings the surface of the Astrodon filter to the surface of the filter carousel. The filter is then secured into place with the FLI-provided washers and metric, metal cap screws. PLEASE NOTE THAT THE O-RINGS PROVIDED BY FLI MAY NOT WORK WITH ASTRODON FILTERS. The link provided here shows the procedure for the 1.25" FLI CFW-2, but the procedure is identical for the larger CFW-7 using larger o-rings supplied by Astrodon.
Remove the two cap screws and washers.
Place the o-ring into the filter position and tap down with a tool such as an allen wrench.
Place the Astrodon 1.25" filter on top of the o-ring.
Orientation does not matter, Gen 1 filters had a "^" marked on the edge. Gen 2 LRGB, photometric filters and narrowband filters do not. This is a recognition that orientation does not matter in terms of spectral performance. It is widely believed that facing the shinier side of the filter toward the incoming light, i.e. the telescope, somehow eliminates or minimizes reflections between the highly reflective CCD and the filter, but no evidence has been provided. That would be akin saying that there is a significant reflection difference between a first surface (reflective coating on the front surface) and second surface (cotaing on the back side) mirror. Although there may be minor differences, if you have an optical problem with one, you'll likely have an optical problem with the other. In imaging, it is a system property of your scope, f/ratio, location of the filters in the light path, how far off axis the light is and the distance to the detector, etc. So, until data are put forth that demonstrate an effect, we will continue to advocate that orientation does not matter. However, for the sake of consistency during troubleshooting, you may consider mounting all filter one way or the other regarding the most reflective side.
Secure the filter with the washers and cap screws, blow off with a puffer or compressed air and replace the cover to the CFW.
SANTA BARBARA INSTRUMENT GROUP (SBIG) STL for 50 mm Astrodon Filters
SBIG's STL CCDs have internal filter wheels with 5 positions for 50 mm or 2" filters. The unmounted 3 mm thick Astrodon filters, being 49.7 mm in diameter, do not fit as snuggly as the slightly larger SBIG filters. Both SBIG and Astrodon sell filters that are 3 mm thick. Astrodon supplies hard rubber washers with all 50 mm filter orders that fit under the SBIG-supplied thumbscrews that provide a secure fit for the filters.
The washers supplied are now typically red or grey in color, 0.031" thick and 3/8 O.D. The provide sufficient overlap with the filter to make a secure hold. Just remove the cap screw, put the supplied wide washer down first, the narrower SBIG-supplied washer over it and then tighten them down.
Please place the arrow ^ on the side of the filter toward the telescope (facing down in the above view.
Make sure you handle the filter only by the edges. If you get a fingerprint on the filter, use a lintless cloth, like a Kimwipe, and isopropyl alcohol or methanol with just a drop or two (not saturated) and lightly wipe the filter in one direction. You'll want to blow off the surface first to remove any loose dirt or particles before wiping.
The other issue is what sequence of filters to use and where to put them. This took some time to figure out. Adjacent to each filter hole is a stamped label, e.g. 1/R. Position 1 is the "home" position, which is assumed to be red, because Maxim and CCDOPS have this default built in. The Optec wheel is different. This label is centered between the two holes and refers to the position on the opposite side of the wheel. So, whatever filter you put into the hole immediately adjacent to 1/R becomes the top slot when you define it in your software. Let's say you put Red, Green Blue, Luminance and H-a into 1/R, 2/G, 3/B, 4/C and 5/L, respectively. If you use Maxim, your Filter Wheel Setup Screen should look like:
The Optec IFW has removable "carousels" as shown above. The filter slots are numbered across from the filter. In this picture, red is #1, green is #2, blue is #3, and so on.