Dwarflab Dwarf 3 external filter holder and dew heater

The built-in duo filter bandpass is stated as 15nm for Ha and 30nm for O3, both +-3nm. Here's a holder and heater to allow use of tighter bandpass 2" third party filters or neutral glass for dew control only. In the case of NB filters, halos aren't created as the filter is in front of the objective.

Please excuse the 3D print quality but draft mode get's the job done sooo much quicker.

A 65Ω polyimide heating strip provides 2.2W at 12V and 0.4W at 5V. I suspect 5V is good enough as the Dwarf itself warms noticeably.

The filter is an Optolong L-Extreme which the manufacturer says is tuned for incident rays between 85° and 90° to the filter surface. The holder surface the filter rests on is tilted by 2.5° so incidence is 87.5°. I haven't been able to test if it makes much difference yet but it seemed sensible to go for the middle.

A spacer corrects the filter inclination so that the screw-in dew shield seats properly.

Use of the filter holder is limited by OTA rotation but as it's held in place by magnets it just gets knocked off, rather than jamming, if the limits are exceeded.