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Helical focusers
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Poster: hottr6 (see all of this user's photos)
Description: Specifications include: Manufacturer/size/weight (grams)/min height (mm)/max height (mm)/lift-per-turn (mm)

1) Novak/2”/205g/37mm/56mm/2.4mm
A vintage rotating focuser. The base is cast aluminum, and the eyepiece holder is machined plastic (delrin?). The disparate chemistry of the two sliding parts entail considerable roughness and noise when focusing. This can be alleviated by using a lubricant. Classic details using brass screws for clamping the eyepiece, but nylon screw to adjust friction.

2) KineOptics HC-1/1.25”/86g/30mm/45mm/7mm
Rotating, uses Crayford bearings. A modern design that allows easy focusing with non-parfocal eyepieces, but suffers from all the problems of the Crayford design (bearing surfaces must be kept extremely clean or rough focusing occurs). The optional machined nylon base for this focuser weighs 24g.

3) Antares FOCH/2”/182g/51mm/105mm/3.2mm
Rotating. This is a sweet focuser that works extremely well. However, the clearance between the hole in the OTA and the mounting points on the base are extremely tight, necessitating that this focuser must be mounted on a metal plate. This is my second-favorite.

4) Orion fine-focusing adapter/1.25”/106g/18mm/28mm/5.0mm
Not a stand-alone focuser, rather this slips into a standard 2” focuser. Two versions of this focuser have been offered, one with a coarse and one with a fine thread count. I have used both and prefer the coarse (this version) over the fine version as it is a lot smoother.

5) Unknown (maybe Edmund??)/1.25”/112g/45mm/88mm/1.4mm
Rotating. Has the smoothest and finest adjustment of all tested. This is my favorite. Also has a spot to mount a single-arm secondary holder. Includes a nylon eyepiece clamping screw.

6) Baader T2 microfocuser/1.25”/45g/29mm/33mm/3.0mm
Rotating. A specialty focuser with an extremely small lift range (4mm), often found in SCTs with mirror shift issues or AP rigs. Baader and Borg offer similar units in non-rotating designs as well. Includes a brass compression ring, a nice touch for such a low weight.

7) Towa/0.965”/149g/55mm/82mm/5.7mm
Non-rotating, found on 1960s reflectors. No clamping mechanism for the eyepiece. This uses a sliding pin design, and is a lot smoother and quieter if lubricant is used. Base is curved for a 5.5” diameter tube.

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