Guide scopes
A light 60 mm guider, or a longer 70 mm one for a long main telescope?
Both guide a main telescope and double as finders. The SV106 is a 60 mm with a non-rotating helical focuser and a focal length only implied by its listing. The GS70 is a 70 mm at 400 mm, the longest guide scope on its shelf, with 90 mm of focus range.
| Compared on | SV106 60 mm | GS70 70 mm |
|---|---|---|
| Aperture | 60 mm (2.36 in) | 70 mm (2.76 in), fully multi-coated |
| Focal length | Implied as 240 mm (9.6x with a 25 mm eyepiece) | 400 mm (15.7 in), stated |
| Focuser type | Non-rotating helical, 8 mm · drawtube up to 35 mm more · compression ring | Double helical with brass compression ring · 90 mm range |
| Back focus | Not published · up to 35 mm of back-travel, male T-threads | Not published · takes 1.25 in eyepieces |
| Weight | 790 g (1.7 lb) in Amazon’s item data | 1.13 kg (2.5 lb) in Amazon’s item data |
| Listed on amazon.com | Yes | Yes |
A tick means one listing published something the other did not, or published a better figure. It does not mean the product is better, and the column is not a score out of anything: a maker who says less loses lines here without losing a comparison. The two verdicts below are where the page is settled.
The light one. At about 790 g it suits a small mount, its focuser keeps the guide field from rotating, and male T-threads take a guide camera directly. Its 240 mm focal length suits mains up to about 1000 mm.
The long one. 400 mm resolves smaller guiding errors, which matters behind a long main telescope, and 90 mm of focus range covers almost any camera. It weighs about 1.4 times as much; check the mount’s payload.
A common rule is at least a fifth of the main telescope’s focal length with a typical guide camera: 240 mm suits up to about 1200 mm, 400 mm suits longer.
If the camera rotates while focusing, the guide star field turns and guiding must be recalibrated. Both of these use helical focusers that move straight in and out.
Yes, with a 1.25-inch eyepiece in the focuser.
60 mm (2.36 in) · non-rotating helical focuser · 8 mm helical plus 35 mm drawtube travel · compression ring · male T-thread
SVBONY's SV106 60 mm guide scope: a non-rotating helical focuser with 8 mm of travel plus up to 35 mm on the drawtube, a compression-ring fitting, male T-threads, and use as a 9.6x60 finder with a 25 mm eyepiece.
Best for: A guide scope that will spend half its life as a finder
≈ $95
70 mm (2.76 in) · 400 mm (15.7 in) focal length · helical focuser with brass ring · 90 mm focus range · takes 1.25 in eyepieces
Astromania's GS70 deluxe guide scope: 70 mm aperture and 400 mm focal length, a double helical focuser with brass compression ring and 90 mm of range, pipe clamps, a Synta-style plate and a balance weight.
Best for: Guiding a longer main telescope, where a short guide scope would not resolve the correction
≈ $156
Any figure written into the body of this page was true on the day it was written. The amount shown next to each instrument is requested from the retailer as the page loads, and it is that amount, not the text, that stands.
