Filter Cartridges

Have been working lately on the filter cartridge design, since it affects the position and design of the focusers.

Filters are a pain to use on a dark night. They are delicate, fragile, and easy to smudge, scrape, or drop. So you keep them in cases that snap or screw tightly, which are difficult to open. Once the case is open, you have to determine whether you put the filter in the case threads-up or threads-down by thumbing both sides, being careful not to touch the glass. Then you have to remove your eyepiece from the scope, hold one in each hand, and carefully screw on the filter so as not to strip the threads on either.

Doing this twice on a binoscope is half the fun. And the Russ Rule reminds us that when basic tasks require two hands, they need to be improved.

Filter wheels make this much easier on monoscopes, but they are not a great fit for binoscope design. We have three mirrors rather than two, and a small 45mm filter placed between the secondary and tertiary is going to block light. The filter needs to be between the tertiary and the eyepiece.

So for the Drifter I am doing cartridges you can pop in and out, like a Nintendo. Filters stay screwed into the cartridge at all times. It will be quick. The filter will be better-protected from fingers since it will be recessed into the cartridge. Orientation will be easy to determine and largely irrelevant. You’ll be able to tell each filter in the dark by the feel of the cartridge.

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