Astronomy Specialist

WILLIAM OPTICS GUIDESTAR 61 F/5.9 APO

$799.00 AUD
SKU: WO-M-GS61-GD

William Optics

Apochromatic doublet

61 mm

f/5.9

360 mm

1.44 kg


Color: Gold

 

The William Optics GuideStar 61 is an apochromatic guide scope with a focal ratio of f/5.9 and a focal length of 360mm. Utilizing FPL-53 synthetic fluorite glass, the GuideStar 61 provides excellent aberration correction.

The GuideStar 61 is compatible with QHY, ZWO and many other guide cameras (Note: some guide cameras may require an extra 2" extension tube to reach focus). The locking dew shield focuser allows you to easily reach the correct focus point. An extension tube is included to help reach focus with different cameras. The CNC-machined finder-style dovetail base is compatible with all William Optics saddle handles.

The GuideStar 61 can also be used as a widefield imaging telescope with the optional Flat61A field flattener.

Note: As the Flat61 an adjustable flattener, you must adjust the distance for your specific telescope. See the Instructions tab above.

 

Optical design

Apochromatic with FPL-53 lens

Objective diameter

61 mm

Focal length

360 mm

Focal ratio

f/5.9

Compatible flattener

William Optics Flat61A

Mount attachment

Vixen-style sliding-base

Focuser

Screw-type focuser

Camera connection

M54 x 0.75, 2"

Tube weight

1.44 kg

SKU

WO-M-GS61-GD (Gold), WO-M-GS61-RD (Red)

 

 

  • GuideStar 61
  • Finder sliding-base
  • M54 to 2" adapter
  • Extension tube
  • Soft carry case

 

Note: Once you have unscrewed the rear adapter to the appropriate value in the table below, the remaining backfocus distance to make up will be 55mm from the rear M48 thread.  

Distance adjustment needed for correct backfocus

Zenithstar 61 12.9 mm
Guidestar 61 12.9 mm

 

Customer Reviews

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P
Paul Lloyd
A nice guidescope for those longer focal length OTAs

This is a very nicely made guidescope, as you would expect for a William Optics refractor. It's focusing adjustments feel solid and they tighten up without any flexure in the light train. The image quality (mine with a ASI120MM camera) is good without noticeable flare or fringing. With my configuration, PHD guiding is regularly reporting 0.5 arcsec errors in average seeing conditions. Getting a good focus with the camera was drama-free, fine-adjusting with the front helical focuser which moved easily (with the usual caveat that the focuser needs to be locked in place each time it is adjusted to take up the backlash in its thread).

The only issue I had with this g.s. is that it seems to be designed for the visual astronomy. To get a focus with the ASI120MM I found it necessary to insert a 35mm extension tube between the rear focuser, and the camera. Even with this extension tube, I have the rear drawer tube at 57mm and the front helical focuser at 4mm. This leaves the rear drawer tube with a small amount of adjustment, but there is still plenty of adjustment in the helical focuser. (A 50mm extension tube would probably win back 15mm in the drawer tube extension.) Even at these extensions, the 'scope is quite rigid. A 2"-to-1.25" adapter is required to mount the ASI120MM.

I have no hesitation in recommending this guidescope, especially where you are operating a longer focal length telescope (>= 500mm?).

Paul.