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Focusers

Focusers secure the imaging sensor to the telescope itself.  Various adapters are generally involved in accomplishing this attachmenet, depending on the imaging sensor and other assessories involved (e.g. Off-Axis Guiders, filter wheels).  

Because telescopes components often consists of metal, they are prone to expansion and contraction due to temperature changes.   These changes influence the focus over long exposures, so computerized focusers are used to automate maintaining focus relative to temperature changes.

Many telescopes come with suitable focusers for eye-pieces, since most eye-pieces are generally not as heavy as cameras and associated equipment.  Therefore for astrophotography, generally most focusers will need to be upgraded.

For my focuser, I was recommended to go with the FTF2515HD from Starlight Instruments as a replacement to the stock Vixen VC200L focuser.   While the Vixen focuser is Rack and Pinion and "pretty good", it will still "sag" with heavy payloads and is not motorized.  Motorized focusers allow the setup of automated focusing routines.   The "sag" on a focuser causes star-halos to be off-center and other imaging defects.

Starlight Instruments provides an "adapter plate" for the FTF2515HD to the Vixen scope, as well as Celestron C11/C14 and other scopes.  This adapter however adds length, which for me required adjusting the secondary mirror (by inserting a nut behind it).

To motorize the focuser, Starlight Instruments provides a FeatherTouch system.  While fairly expensive, it is an extremely rugged set of equipment (meaning the focuser provides smooth auto-focus operation and sustains quite a bit of weight without sagging).

Starlight Instruments FTF2515HD (FTF2515HD---Feather Touch® 2.5" Diameter Dual Speed Focuser 1.5" Draw tube travel, and Brake)
http://starlightinstruments.com/store/index.php?route=product/product&path=37_54&product_id=63

Starlight Instruments MKIT30  (MKIT30---Micro Touch Focusing System - 2 Piece Kit(hub/hand control and motor) for Control of 2.5", 3.0" Feather Touch® and 2.7" Astro-Physics Focusers - WIRED)
http://starlightinstruments.com/store/index.php?route=product/product&path=41&product_id=83

PreciseParts.com is extremely helpful at building the necessary adapters to connect various focuser/reducer/camera components together.  Here is a inventory of adapters that I have ordered from them...


5C1C608D (12/13/2016)
Custom adapter, FeatherTouch 2515/2525/2535 without end cap to Vixen VC2xxL f/6.4 reducer, L=22.0 mm
(M48x0.75 filter thread inserted on focuser side)

5C1CA322 (12/9/2016)
Custom adapter, FeatherTouch 2515/2525/2535 without end cap to Vixen VC2xxL f/6.4 reducer, L=22.0 mm
Add-on M48x0.75 Filter Thread: (12/9/2016)
[clearence issue; filter fits extension on reducer before threads can engage]

54CC60F3 (11/22/2016)
Custom adapter, Vixen VC2xxL f/6.4 reducer (60 mm) to extension tube, L=42.0 mm

5B45BF12 (11/11/2016)
Custom adapter, Vixen VC2xxL f/6.4 reducer (60 mm) to extension tube, L=49.5 mm

4EE94E7D (11/11/2016)
Custom adapter, Vixen VC2xxL f/6.4 reducer (60 mm) to ZWO ASI1600 Series CCD Camera, L=7.5 mm
Add-on M48x0.75 filter thread (11/11/2016)

3D7ED4F9 (7/12/2016)
Custom adapter, FeatherTouch 2515/2525/2535 without end cap to Vixen VC2xxL f/6.4 reducer, L=7.5 mm
Add-on M48x0.75 Filter Thread for 3D7ED4F9 Adapter (7/12/2016)
[clearence issue; insert for filter does not allow this adapter to fit on back of the reducer]

3D7E48A4 (6/14/2016)
Custom adapter, FeatherTouch 2515/2525/2535 without end cap to Vixen VC2xxL f/6.4 reducer, L=7.5 mm
[allows attachment of the reducer to the focuser, without filter]

497DE91C Custom adapter, Vixen VC2xxL f/6.4 reducer (60 mm) to extension tube, L=40.0 mm (11/10/2016) [cancelled - replaced with 54CC60F3]

77AA6AD7 Custom adapter, Vixen VC2xxL f/6.4 reducer (60 mm) to ZWO ASI1600 Series CCD Camera, L=20.0 mm (11/10/2016) [cancelled - replaced with 4EE94E7D]