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| The purpose of a filter wheel is to be able to change filter without taking the camera off the telescope. This is my filter wheel from Astro Engineering. It comes with an eyepiece plug on one side and an eyepiece socket an the other with T-threads and also with a male-male T-thread adaptor. I chose it for two basic reasons: 1. It was on offer at <£100, 2. You do not have to dismantle the case to replace filters. It does, however, have a few snags. 1. It is not motorised (it would be a lot more expensive if it was) so care has to be taken when changing filters not to disturb the orientation. No big deal! 2. It is so narrow that thicker filters (the type where you can screw one filter onto another) are a tight squeeze. I managed to ease the parts apart slightly so that they will go round without scraping but an extra couple of millimetres would have made all the difference. 3. The filters are not well protected when the wheel is taken off, but that is why it is easy to change them without dismantling the case - you can't have it both ways. 4. The wheel has no marks on it to tell you which filter is in place. I have put numbers on the wheel with Tippex. 5. The sides are thin, so that a standard T-threaded device has so much sticking through the casing that the filters hit it and won't go past it. Hence the rather crude cardboard washer shown in the picture. 6. None of the threads are particularly smooth and I have had some difficulty unscrewing, particularly, filters. 7. It carries only 5 filters. To be fair I don't know of one that holds more, but 5 is the minimum you need - four for LRGB and a blank for dark frames (you can manage without the latter by using a half-way position but blank is handy). I have both the Astronomik LRGB set and also the three common narrow-band filters for Hα, OIII, and SII. Maybe I need two wheels. Apart from these small niggles, it works well. |
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