SVBony

SVBony SV106 50mm Guide Scope

50 mm f/3.8 achromatic guide scope · 190 mm focal length · F9177A

The 50 mm guide scope that most astrophotographers should own. Enough focal length for almost any amateur imaging rig, and it arrives with tube rings and a dovetail rail rather than a finder shoe.

88/ 100

Polaris Score

Our default pick for guiding almost any amateur rig

From$97.99

Where to buy

SVBONYPartnerBest price$97.99→

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What problem does this solve?

Fifty millimetres is where guide scopes stop having caveats.

The mini guiders are genuinely good, and their limits are real: short focal length that samples the sky coarsely, a small objective that occasionally cannot find a star in a barren field, and a mounting foot that flexes. Each of those is survivable on a short refractor. Stack them on a 1500 mm scope and guiding becomes a thing you fight rather than a thing you set up.

A 50 mm objective at 190 mm of focal length removes all three at once. It samples at roughly three to four arcseconds per camera pixel, gathers well over twice the light of a 30 mm, and comes with proper tube rings on a dovetail rail so the whole assembly bolts down instead of perching. It is the size the hobby settled on for good reasons, and this is the inexpensive version of it.

You need one if

You need this size once your imaging scope passes about 1300 mm, or as soon as you would rather buy the guide scope once than climb the ladder a rung at a time.

You can skip it if

Skip it if you image at 600 mm or less and carry your rig up stairs, where a mini guider saves real weight, or if you shoot the Moon and planets, where nothing is guiding anything.

How it actually works

What the setup looks like.

The tube contains no electronics. It becomes a guiding system when a camera and software join it:

Bolt the rings and rail to the main scope

Tube rings on a dovetail rail come in the box, so the guider clamps to a spare dovetail or a saddle rather than balancing in a finder shoe. Tighten the ring screws evenly.

Thread a guide camera into the back

The rear takes a 1.25 inch guide camera directly. An ASI120MM Mini, an SV905C or a QHY5L-II all drop in.

Focus with the helical barrel

Eight millimetres of helical travel, which sounds small and is ample: you are only ever moving between one camera's sensor depth and another's. Lock the thumbscrew once the stars are tight.

Let the software do the arithmetic

PHD2, N.I.N.A. or an ASIAIR picks a star, measures its drift several times a minute and corrects the mount before the error reaches your exposure.

The eight millimetres of helical travel is the one number to check against your camera. It is enough for any bare guide camera and will not absorb a stack of adapters, so keep the optical train short.

01Will it fit my setup

Compatibility.

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

Any main telescope with a spare dovetail or saddle spaceZWO, QHY, Player One and SVBony guide cameras1.25 inch camera connectionPHD2, N.I.N.A., ASIAIR and EkosMain scopes from roughly 800 mm to 2000 mm focal length

Note✕Needs a guide camera, sold separately✕Achromatic doublet, so it guides well and photographs badly✕Eight millimetres of focus travel does not absorb long adapter stacks✕Heavier and longer than a mini guider, which matters on a small mount✕Will not reach focus with a star diagonal fitted

02The numbers

What These Numbers Mean

5 numbers in plain English · full specifications

Focal lengthGenerous

190 mm

With the 2.9 to 3.75 micron pixels of a common guide camera, 190 mm samples the sky at roughly three to four arcseconds per pixel. Since guiding software finds a star's centre to about a tenth of a pixel, the drift measurement lands within a few tenths of an arcsecond. That is enough resolution to guide an imaging scope out to roughly 2000 mm, which covers almost everything an amateur owns.

ApertureComfortable

50 mm

Fifty millimetres gathers nearly three times the light of a 30 mm mini guider, which changes the experience in one specific way: you stop hunting for guide stars. In the sparse fields near the galactic poles, where a small guider can leave you slewing around looking for anything usable, a 50 mm simply finds one.

Focal ratioFast

f/3.8

A fast objective lets the guide camera expose for a second or two rather than four. That matters more than it sounds: short guide exposures let the software see a drift developing and cancel it, instead of measuring an error that has already been recorded in the photograph you are taking.

Focus travelShort but sufficient

8 mm helical

Eight millimetres is a narrow range and an entirely adequate one, because a guide scope only ever needs to bridge the difference between one camera's sensor depth and another's. What it will not do is swallow a filter, an extended nosepiece and a spacer all at once. Keep the train short and this is a non-issue.

MountingRigid

Rings and dovetail rail

This is the specification that separates a 50 mm guider from the mini ones, and it does more for your images than the glass does. Any flex between guide scope and main tube makes the software push the mount the wrong way. Rings clamping the tube along its length and bolting to a rail remove that path almost entirely.

Optical

Aperture50 mm

Focal length190 mm

Focal ratiof/3.8

LensAchromatic refractor, fully multi-coated

Physical

FocuserHelical, 8 mm of travel

Camera connection1.25 inch

Tube diameter54.5 mm

Total length240 mm

MountingTube rings and dovetail rail included

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.

This is the size to buy if you buy once.

The 30 mm and 40 mm guiders are correct for short refractors and save weight. The 50 mm is correct for nearly everything, which makes it the cheapest way to stop thinking about guide scopes altogether.

It will not take pictures.

The objective is an achromatic doublet, not an ED lens. Bright stars carry a violet halo that guiding software ignores completely and a photograph does not. If you want a guider that doubles as a small imaging telescope, an ED design like the EvoGuide 50DX is the one to compare against.

Weigh it before you hang it.

Rings, rail and 240 mm of aluminium tube add real mass to the front of a main scope. On a small mount already near its payload, a mini guider is the wiser answer even if it resolves less.

Keep the optical train short.

Eight millimetres of helical travel is enough for a bare camera and not much more. Adding a filter or a long adapter is the usual reason a guide scope refuses to reach focus.

Editor’s Take

Guide scope choice is one of the few places in this hobby where the popular answer is also the correct one. Fifty millimetres at around 200 mm of focal length has been the default for two decades because it is where the compromises stop biting: enough resolution for any amateur focal length, enough aperture to always find a star, and a mounting scheme rigid enough that flexure stops being a suspect. The ED versions cost two to three times as much and guide the same. Buy this, put the difference toward the mount, and never read a guide scope comparison again.

— The Skynocular verdict

88/ 100

SVBony SV106 50mm Guide Scope

50 mm f/3.8 achromatic guide scope · 190 mm focal length · F9177A · $97.99

The 50 mm guide scope that most astrophotographers should own. Enough focal length for almost any amateur imaging rig, and it arrives with tube rings and a dovetail rail rather than a finder shoe.

SVBONYPartnerBest price$97.99→

SVBony SV106 50mm Guide Scope

Fifty millimetres is where guide scopes stop having caveats.

What the setup looks like.

Compatibility.

What These Numbers Mean

Good to know.

Related accessories.