SVBony
SVBony SV905C Guide Camera
The other half of a guide scope. A 1.2 megapixel sensor that never takes a photograph you keep, and without which none of your photographs are sharp.
86/ 100
Camera Type
GuidingImaging
This is a guiding sensor and very little else. It will show you the Moon and it will run a planetary capture in a pinch, but 1.2 megapixels with no cooling is not a camera you build an astrophotography plan around.
Type
Monochrome guiding
Cooling
None
Pixel Size
3.75µm
Read noise
4.0 e⁻
Resolution
1.2 MP · 1280×960
Sensor
Sony IMX225 · 1/3 inch
From$119.99
Price tracked by PolarisNew to trackingTracking since Sep 2026
01What it's good atWhat it's best at — and the trade-offs.
Every guide scope page on this site ends with the same sentence: it needs a guide camera, sold separately. This is the one that fits, at a price that does…
01What it's good at
What it's best at — and the trade-offs.
Every guide scope page on this site ends with the same sentence: it needs a guide camera, sold separately. This is the one that fits, at a price that does…
Best at
✓Every guide scope page on this site ends with the same sentence: it needs a guide camera, sold separately. This is the one that fits, at a price that does not distort the budget of the rig it serves.
✓The 12.5 mm back focus is the depth the mini guide scopes are built around, so it threads on and reaches focus without an adapter or a spacer hunt.
✓One USB-C cable carries both data and power, which on a rig that already has too many leads is a real convenience rather than a specification.
✓Roughly 80% peak quantum efficiency means it converts most of what the guide scope delivers, so guide exposures stay at one or two seconds and drift gets caught while it is still small.
Trade-offs
!1/3 inch sensor, so the patch of sky it sees is small and sparse fields can take a moment to yield a star.
!No cooling, which is irrelevant for one second exposures and would matter for anything longer.
!USB 2.0 caps the frame rate at 39 fps, fine for guiding and slow for planetary work.
!Rolling shutter and 12-bit readout, both entirely adequate here and both below what an imaging camera offers.
02In plain EnglishThe numbers, in plain English.
Sony IMX225 · 1.2MP · 3.75µm · None
02In plain English
The numbers, in plain English.
Sony IMX225 · 1.2MP · 3.75µm · None
Pixel sizeStandard
3.75 µm
This is the number that decides how finely the camera measures drift, together with your guide scope's focal length. At 3.75 microns it samples at 6.5 arcseconds per pixel behind a 120 mm mini guider and 3.2 arcseconds behind a 240 mm guide scope. Software locates a star's centre to roughly a tenth of a pixel, so even the coarser of those measures drift to well under an arcsecond.
Read noiseFine for guiding
4.0 e⁻
Read noise is what the camera adds every time it empties the sensor, and a guide camera empties it constantly. Four electrons would be mediocre in a deep-sky camera and is unimportant here, because a guide star is bright by definition: you are not trying to detect faint signal, only to locate a bright point accurately.
Sensor sizeSmall
4.8 × 3.6 mm
This is the specification most likely to frustrate you. A 1/3 inch sensor behind a 190 mm guide scope sees roughly 1.4 by 1.1 degrees of sky. In most of the sky that contains several usable guide stars. Near the galactic poles, where stars genuinely thin out, it can leave you nudging the mount to find one, and a larger guide scope helps more than a larger sensor would.
Back focusStandard
12.5 mm
Twelve and a half millimetres is the depth the mini guide scopes are designed around, which is why this threads on and reaches focus without an adapter. It is also exactly the body thickness of the SV238 off-axis guider, so the same camera moves between a guide scope and an off-axis guider without re-spacing anything.
Peak QEHigh
About 80%
Quantum efficiency is the fraction of arriving photons the sensor actually records. Eighty percent is close to the practical ceiling and is the reason a small elderly sensor still guides well: it converts most of what the guide scope delivers, so you can keep exposures down to a second or two and catch drift while it is still small.
InterfaceConvenient
USB-C, USB 2.0
USB 2.0 sounds dated and is entirely sufficient: guiding sends one small frame every second or two, not a video stream. The connector matters more than the standard. One USB-C cable carries both data and power, so a guide camera adds no power lead to a rig that already has too many.
03Build your imaging rigEverything you'd actually buy.
Look through · Correct · Run it
03Build your imaging rig
Everything you'd actually buy.
Look through · Correct · Run it
Look through
What the camera watches the star through
SVBony SV165 30mm Guide Scope
The cheapest pairing. 120 mm of focal length samples at 6.5 arcseconds per pixel with this sensor, which suits a main scope under about 1000 mm.
SVBony SV106 50mm Guide Scope
The pairing we would pick. 190 mm samples at about 4 arcseconds per pixel and the 50 mm objective removes most guide-star hunting.
SVBony SV238 Off-Axis Guider
For long Schmidt-Cassegrains. Same 12.5 mm back focus, so this camera moves straight over with no re-spacing.
Correct
What the guiding actually fixes
A tracking equatorial mount
Guiding sends correction pulses to the mount. Without a mount that accepts them, the camera is only watching the drift, not fixing it.
Run it
The software that closes the loop
PHD2
Free, and the reference implementation. Picks a star, measures its wander several times a minute and pushes corrections.
N.I.N.A., Ekos or an ASIAIR
All three see this camera without a driver hunt and will run the guiding alongside your imaging sequence.
04The Polaris ScoreHow it scores, and why.
86/100 · #1 of 1 guide cameras
04The Polaris Score
How it scores, and why.
86/100 · #1 of 1 guide cameras
86/ 100
SVBony SV905C Guide Camera
#1 of 1 guide cameras
Scored as a guide camera, not as an imaging camera. Judged on whether it finds a star and reports its centre reliably, the IMX225 is close to the ceiling of what matters. Judged on sensor size, cooling or resolution, it would score poorly, and those axes are irrelevant to the job.
Image quality76
Low-light sensitivity83
Ease of use88
Value94
Polaris weighs how well the camera does the job it was designed for — image quality, sensitivity, versatility and value — never list price or brand.
05Who it's forAn honest fit check.
Anyone who has just bought a guide scope and discovered the camera is not in the box.
05Who it's for
An honest fit check.
Anyone who has just bought a guide scope and discovered the camera is not in the box.
Buy it if you
✓Anyone who has just bought a guide scope and discovered the camera is not in the box.
✓Deep-sky imagers running exposures longer than about 60 seconds on a tracking equatorial mount.
✓Someone assembling a first guided rig who wants the cheapest component that will not be the weak link.
Look elsewhere if you
!Anyone hoping to take pictures with it. 1.2 megapixels, no cooling, and a sensor 4.8 mm across is a measuring instrument, not a camera.
!Planetary imagers, who want a fast modern sensor running hundreds of frames per second rather than 39.
!Owners of a long Schmidt-Cassegrain using an off-axis guider with a small pick-off prism, where a more sensitive sensor genuinely helps find a star.
!Anyone without a mount that accepts guide corrections, because a guide camera with nothing to correct is just an expensive finder.
06The numbersFull specifications.
22 measured and stated values
06The numbers
Full specifications.
22 measured and stated values
Sensor
ModelSony IMX225
TypeCMOS · 1/3 inch
Megapixels1.2
Pixel Size3.75µm
Bit depth12-bit ADC
Noise & sensitivity
Read noise4.0 e⁻
Full well13,000 e⁻
Peak QE~80%
Cooling
CoolingNone
Connectivity & fit
InterfaceUSB-C, USB 2.0
Weight0.23 kg
More
back focus12.5 mm (8.5 mm without the 1.25 inch nosepiece)
barrel1.25 inch
cooledfalse
exposure range64 µs to 20 s
max frame rate39 fps at full resolution
powerBus powered over USB
Sensor Height3.6mm
Sensor Width4.8mm
Editor’s Take
There is a particular disappointment that comes with unboxing a guide scope and discovering it is an empty tube. This is the part that goes in the back, and the interesting thing about it is how little the specification matters. A guide camera is not trying to make a picture. It is trying to answer one question several times a minute: where is the centre of that star now, compared with a moment ago. An eleven year old 1.2 megapixel sensor answers that as well as anything modern, because the star is bright and the maths is subpixel. Spend the money you did not spend here on the guide scope in front of it, which is the component that actually limits how well the answer comes out.
— The Skynocular verdict
07AlternativesFor a different goal, start here.
2 alternatives, each mapped to the goal it wins at
07Alternatives
For a different goal, start here.
2 alternatives, each mapped to the goal it wins at
ZWO ASI120MM Mini
A larger guide scope