SVBony SV165 30mm Guide Scope — image 1
SVBony

SVBony SV165 30mm Guide Scope

30 mm f/4 achromatic mini guide scope · 120 mm focal length

The cheapest way to stop your long exposures from smearing. A 30 mm tube that rides on top of your main scope, watches one star, and lets software keep the mount honest.

83/ 100
Polaris Score
Our budget pick for guiding a short to medium focal length rig
From$49.13
Where to buy
Affiliate link — we earn a commission, you pay the same. We rank on fit, not payout.
What problem does this solve?

Your mount drifts. This is the cheapest thing that notices.

A deep sky photo is a stack of exposures that each run for one to five minutes. No mount tracks perfectly for that long. Periodic error in the drive gears, a slightly imperfect polar alignment, a gust of wind: any of it moves the target a few arcseconds, and a few arcseconds is the difference between round stars and short streaks.

Autoguiding closes the loop. A second, small telescope rides piggyback on the main one with a cheap camera in the back. Software watches one star through it several times a minute, measures how far it has wandered, and sends a correction to the mount before the drift becomes visible. The SV165 is the smallest honest version of that second telescope: 30 mm of glass, 120 mm of focal length, a helical focuser, and a finder shoe foot.

You need one if
You need one the first night you try exposures longer than about 60 seconds on a tracking equatorial mount and find your stars have turned into commas.
You can skip it if
You can skip it if you shoot the Moon and planets, work in short unguided subframes, use a smart telescope that handles tracking internally, or already own a 50 mm guide scope.
How it actually works

What the setup looks like.

The SV165 has no electronics at all. It is a tube, a lens and a focuser. It becomes a guiding system when you add two cheap pieces:

The SV165 has no electronics at all. It is a tube, a lens and a focuser. It becomes a guiding system when you add two cheap pieces:

1
Clamp it to the main scope
The base drops into a standard Synta or Vixen style finder shoe, or onto a spare dovetail. Nothing plugs into the telescope.
2
Thread a guide camera into the back
The 1.25 inch nosepiece and M42 thread take any small mono guide camera. An ASI120MM Mini, an SV905C or a QHY5L-II all fit.
3
Focus by twisting the tube
There is no focus knob. You rotate the front section through its 45 mm of travel until stars are tight, then lock the thumbscrew and leave it alone for the rest of the season.
4
Let PHD2 do the arithmetic
Free software picks a star, measures its drift several times a minute, and pushes correction pulses to the mount through the guide port or the ASIAIR.

Do not put a star diagonal in the light path. The SV165 has only 45 mm of back focus and will not reach focus with a diagonal in the way. It is also not meant for visual use, though a reticle eyepiece will focus in it if you want to use it as a finder.

01Will it fit my setup

Compatibility.

What this accessory works with — check the fit before you check the price.

What this accessory works with — check the fit before you check the price.

Any main telescope with a finder shoe or spare dovetailZWO, QHY, Player One and SVBony guide cameras1.25 inch and M42 x 0.75 camera connectionsPHD2, N.I.N.A., ASIAIR and EkosMain scopes up to roughly 1000 mm focal length
Note✕Needs a guide camera, sold separately✕120 mm focal length is short for guiding a long SCT✕Achromatic doublet, so it is a guider and not a photographic lens✕Will not reach focus with a star diagonal fitted
02The numbers

What These Numbers Mean

5 numbers in plain English · full specifications

5 numbers in plain English · full specifications

Focal lengthCoarse sampling
120 mm
This is the number that decides whether the SV165 suits your rig. A guide scope measures drift in proportion to its focal length, and 120 mm with the 2.9 to 3.75 micron pixels of a typical mini guide camera samples the sky at roughly 5 to 6.5 arcseconds per pixel. That sounds hopeless until you know that guiding software locates a star's centre of brightness to about a tenth of a pixel, which brings the real precision to well under an arcsecond. Plenty for an imaging refractor between 400 and 1000 mm, and thin for a 2000 mm SCT where the main camera resolves detail the guider cannot see.
ApertureModest
30 mm
Thirty millimetres reaches to roughly ninth magnitude in a one second exposure, which is enough to find a usable guide star in most fields but not all of them. Near the galactic poles you will occasionally hunt. A 50 mm guider roughly doubles the number of candidate stars in any given field.
Focal ratioFast
f/4
Fast optics let the guide camera work at one and two second exposures instead of four. Short guide exposures let the software see a drift and cancel it while it is still small, rather than reporting it after the error has already been recorded in your image.
Optical designFine for guiding
Achromatic doublet
An achromat brings red and blue to slightly different focus, which puts a faint violet halo around bright stars. Guiding software measures a star's centre of brightness and is untroubled by this. Photography is not, which is why this tube guides well and photographs badly.
Back focusSet and forget
45 mm of helical travel
Enough range to reach focus with any common guide camera, and short enough that a star diagonal will never work in this scope. Once you have focus, the helical barrel locks and holds it through car journeys and cold nights, which is exactly what you want from a component you never want to think about again.
Optical
Aperture30 mm
Focal length120 mm
Focal ratiof/4
LensFully multi-coated achromatic doublet
Physical
FocuserHelical, 45 mm of travel
Camera connection1.25 inch and M42 x 0.75
MountingTube rings with nylon tipped screws, finder shoe base
BuildCNC machined aluminium
03Before you buy

Good to know.

The honest caveats — the things that save you a return, a bad first night, or a second purchase you didn't need.

The honest caveats — the things that save you a return, a bad first night, or a second purchase you didn't need.

The focal length sets the ceiling.
The usual rule of thumb is that a guide scope should be within about a quarter of the main scope's focal length. At 120 mm the SV165 comfortably guides a 400 to 1000 mm imaging refractor. Above that, on a long SCT or a big Newtonian, move to a 50 mm guide scope or an off-axis guider.
You focus it once and then forget it.
The helical focuser has no knob and no drawtube to sag. Get the stars tight on the first clear night, lock the thumbscrew, and it holds through transport for months.
It will not take pictures.
The 30 mm objective is an achromatic doublet, not an ED or apochromatic lens. Bright stars show a violet halo. That is irrelevant to guiding software, which only needs a centroid, and disqualifying for photography. If you want a guide scope that doubles as a small imaging telescope, buy a 50 mm ED guider instead.
Rigidity matters more than optics here.
Any flex between the guide scope and the main tube produces drift that the software corrects in the wrong direction. Tighten the rings evenly, keep the cables from hanging on it, and prefer a dovetail mount over a plastic finder shoe if your scope offers one.
Editor’s Take

Most of the money in astrophotography goes to the mount and the camera, and guiding is where people are tempted to economise badly. The SV165 is the rare case where economising is correct. Above about 1000 mm of main scope focal length it runs out of resolution and you should buy a 50 mm guider. Below that, spending four times as much buys you a tube that guides no better, and the difference is far better spent on the mount that is actually causing the drift.

— The Skynocular verdict
83/ 100
SVBony SV165 30mm Guide Scope
30 mm f/4 achromatic mini guide scope · 120 mm focal length · $49.13

The cheapest way to stop your long exposures from smearing. A 30 mm tube that rides on top of your main scope, watches one star, and lets software keep the mount honest.