Baader Diamond Steeltrack 2" Focuser for SC/HD Telescopes

The Diamond Steeltrack Drive

True diamonds form its micro-geared, high-precision drive, and in comparison to conventional Crayford or rack-and-pinion drives this movement has zero backlash, zero cogging and zero flexure. The bearing system uses unbreakable instrument-grade roller bearings instead of simpler ball bearings, with no Teflon pads anywhere, running on ultra-hard subzero-coated bearing races that are precision milled and much harder than anodizing or stainless steel.

The 1:10 stainless-steel fine-focus mechanism moves the drawtube about 2 mm per turn of the fine knob, against about 22 mm per turn of the coarse knob. The detachable drive block is reversible for right- or left-hand fine-focus operation: remove the four marked screws with a 2.5 mm Allen wrench, rotate the block by 180°, refit the screws carefully, then check the alignment and that the focuser runs as smoothly as before.

30 mm Travel and Load Setting

The BDS-SC has 30 mm of focus travel and an engraved index scale from 0 to 30 mm in 1 mm steps. By factory default the pressure screw, which sets the contact pressure between the diamond-coated axis and the steel plate, holds up to 6 kg of lifting force; Baader chose this setting for photographic use. You can tighten it further, but the focuser will then run less smoothly, or loosen it for visual use to make it run even more smoothly. Baader adds that the focusers are rigid and slip-proof without a locking screw pressing on the tube or drive plate, so motor focusers can be used at any time without tipping the image plane, and the zero-shift locking knob stops any movement without affecting the optical axis adjustment.

The focuser is rotatable.

Telescope Side: 2" and 3.3" Adapters

The focuser includes an adapter for 2" UNF threads, such as Celestron SC/HD or Meade telescopes, and an adapter for Celestron 3.3" threads (84.2 mm), such as the C11 and C14; to use the 3.3" thread, the 2" adapter is removed. The two adapters fit all C14, C11, C9¼, C8, C6 and C5 OTAs. When used via the 3.3" thread, all lengths are reduced by 12 mm, the screw-in depth of the thread. Behind the adapters sits an 88 x 6 mm dovetail for other telescope adapters, reached by loosening six M5 screws.

One example of imaging without mirror shifting is the BDS-SC on a Celestron 8" EdgeHD with built-in mirror lock: with the primary mirror locked, focusing is done with the Diamond Steeltrack.

Eyepiece Connection: 2" Clamp, S58 Dovetail, and M55 Thread

The business end of the focuser offers a versatile connection system for your imaging train. The 2" eyepiece clamp with hardened bronze clamp ring (12.5 mm long) is included as standard. The S58 dovetail ring clamp built into the focusing tube accepts optional T-2, M48, M68 and other S58 direct-thread adapters, so accessories and cameras can be threaded on without the 2" clamp, and Baader offers an optional 2" S58 ClickLock clamp (#2956258), which adds 16 mm.

The integrated 2" clamp comes off after loosening its six M2.5 headless set screws with the included 1.3 mm Allen wrench; the BDS T-2 (#2957202), M48 (#2957204) or M68 adapters, or the S58 ClickLock clamp (#2956258), then fit the S58 dovetail. M55 is also among the eyepiece-side inner connections.

Height, Clear Diameter and Weight

The minimum height is 93 mm as supplied with the 2" clamp, 80 mm with an optional S58 to M68/M68i/M48/T-2 direct adapter (82 mm in Baader's description), and 112 mm with the optional S58 ClickLock clamp; on the 3.3" thread all lengths are 12 mm shorter. The net weight is 1.07 kg.

The oversized 55 mm clear inner diameter has anti-reflection knife-edge baffles to prevent vignetting.

Optional Steeldrive II Motor Focuser

All Diamond Steeltrack focusers carry a dovetail for the optional temperature-compensating Baader Steeldrive II motor focuser with controller (#2957165); a mounting instruction is included with each Steeldrive II. Because the drive needs no locking screw pressing on the tube or drive plate, motor focusers can be used at any time without tipping the image plane.

Aligning the Drawtube

BDS focusers are unique in that they can be fine-aligned (collimated), so critical users can square the focuser to the optical axis; this is particularly useful for imagers who need sharp stars out to all corners. Every BDS is aligned at the factory to be square to its mounting base, and most users will find this sufficient with most commercially produced telescopes, particularly visual observers, for whom the procedure is not recommended. The adjustment works through bearing adjustment screws around a pivot point on the bearing block; read the instructions completely first, make only small adjustments, and attach no heavy accessories during the first attempt, since the drawtube is loose and could slip. Critical SCT users will also find this useful for aligning the focuser axis to the centre of the secondary mirror.

Fitting and Care

Unscrew the visual back from the telescope and screw on the BDS-SC with the 2" UNF adapter, or remove the 2" adapter to use the Celestron 3.3" thread.

The focusers need very little maintenance: keep them clean so dust does not accumulate on the tracks, and if the tracks are dirty, clean them with a soft cloth and isopropyl alcohol. The focuser is greased permanently and needs no re-greasing; do not apply grease to the roller track or the diamond pressure plate, and do not expose the focuser to temperatures above 80°C, the limit of the grease used. Protect the anodizing from years of strong UV exposure as well, such as behind a south-facing window.