What is a Guide Camera in Astrophotography

In simple terms, a guide camera is a small, dedicated camera used in astrophotography, especially in deep-sky photography, to help keep your main imaging camera precisely pointed at the target object in the sky. It works alongside guiding software and the telescope mount to make tiny, precise adjustments to the mount’s position, ensuring the camera stays locked onto the target object in the sky.

 

Why People are Using Guide Cameras

Improved Image Quality

The primary reason people use guide cameras is to improve image quality. Long-exposure astrophotography is all about capturing as much light as possible from faint celestial objects. With a guide camera ensuring that the target remains in the frame and in focus, you can take longer exposures without worrying about blurring. This allows you to capture more light and fine details, resulting in sharper images, deeper colors, and greater overall clarity.

Enabling Longer Exposures

Without a guide camera, the maximum exposure time you can use is limited by the Earth’s rotation. As the Earth is constantly rotating, this rotation causes celestial objects to appear to move across the sky. When you’re taking long-exposure images, even the slightest movement can result in blurry images. A guide camera helps stabilize the movement caused by the Earth's rotation, ensuring your target stays in focus. It continuously tracks a star in the field of view and sends real-time corrections to the mount, ensuring your main camera stays perfectly aligned with the target throughout the exposure. You can extend your exposure times to minutes or even hours with a guide camera. This enables the capture of more light and uncovers details that would otherwise remain hidden.

More Opportunities for Complex Images

Guide cameras also allow you to explore more complex astrophotography shots, such as wide-field panoramas and deep-sky composites. These techniques help you capture the full grandeur of the night sky, taking your astrophotography to the next level. You can attempt wide-field panoramas, deep-sky composites, and other advanced techniques. These types of shots often require long exposures and precise tracking, which a guide camera can provide.

 

How to Choose the Most Suitable Guide Camera

Sensor Size and Resolution

The sensor size and resolution of a guide camera are important factors to consider. A larger sensor has a larger FOV (field of view), which is beneficial in finding stars. Higher resolution sensors can provide more detailed information about the position of the guiding star, allowing for more precise adjustments.

For beginners, a sensor size of at least 1/3 inch is a good starting point. And a resolution of around 1-2 megapixels should be sufficient for most guiding tasks. However, if you plan to do more advanced astrophotography or guide on very faint objects, you might want to consider a camera with a larger sensor and higher resolution.

Sensitivity

Sensitivity is another crucial factor. A more sensitive camera can detect fainter targets, which is essential for precise tracking, especially when working with dim objects in the night sky. Hence, you need to aim for a camera with a high quantum efficiency (QE). Quantum efficiency is the percentage of photons that are converted into electrons by the sensor. So a higher QE means that the camera can capture more light and is more sensitive, especially when you use small aperture guide scopes, shooting with short exposure times, or in high-pollution areas. With a high QE sensor, you can track even the faintest celestial objects, ensuring that your astrophotography is always clear and precise, even in areas with light pollution. Guide cameras with QE higher than 70% are generally recommended for astrophotography beginners. In addition, you should choose higher QE sensors when using OAG (off-axis guider), as less light will be captured.

Readout Noise

Read Noise is the electronic noise (in electrons, e⁻) introduced when the sensor’s signal is read out. It directly influences the detection of faint stars. In short exposures (e.g., 0.1s-1s), read noise can drown out weak guide star signals, causing failed star detection or false tracking (noise mistaken for stars). Readout noise also has a direct impact on SNR (signal-to-noise ratio). A low read noise (e.g., 1 e⁻) maximizes SNR, especially in short exposures. Moreover, low readout noise allows shorter exposures without SNR loss, improving the corrective response speed of mounts.

Thus, when choosing a guide camera, you need to select cameras with readout noise ≤3 e⁻ (ideal ≤1–2 e⁻). Also, you can consider some brands with “Low-Noise Mode” which enables high conversion gain to effectively reduce the readout noise. Lastly, for short exposures (<0.5s), readout noise becomes more significant than thermal noise (dark current), making cameras with lower readout noise essential for clear star tracking in these conditions. For long exposures (>1s), you may need a guide camera with a cooling function, as dark current thermal noise will dominate. The cooling function will help to reduce the noise caused by dark current.

Frame Rate

The frame rate of a guide camera, measured in FPS (frames per second), determines how often it can take and process images. In the autoguiding workflow, the camera captures star position, and the software (e.g., PHD2) calculates star drifts and then sends correction commands to the mount. Hence, with a higher frame rate, the latency in this loop is reduced, enabling faster closed-loop corrections and more precise tracking. High FPS requires very short exposures (e.g., 0.05s), risking low SNR if the camera has poor QE or high read noise. In this case, you can use guide cameras with high QE (≥80%) and low read noise (≤2e⁻).

Cost

Cost is always a consideration, especially for beginners. Guide cameras are available at a range of price points, and you don’t need to spend a fortune to find a high-quality option.

Brand	Series	Retail Price Range (US$)
ToupTek Astro	GPM & GPCMOS Series	99-379
ZWO	ASI Series	149-399
QHYCCD	QHY5III Series	199-659
Player One	Dwarf Planet Series	149-399

The above prices are from the official websites of each brand on 23^rd April 2025. These prices may vary in the future.

 

Introducing ToupTek Astro’s Guide Cameras

ToupTek Astro offers GPM and GPCMOS series guide cameras that are suitable for astrophotography beginners as well as more experienced astrophotographers. The GPM series includes GPM462M/C, GPCMOS02000KMA/KPA, GPCMOS01200KPF, and the new release GPM174M. This series is ideal for guiding with an Off-Axis Guider (OAG) and for use with short focal length guide scopes. This series has a 1.25” front-end outer diameter and can accommodate a standard 1.25” interface.

Sensor

The GPM series features high-quality Sony sensors. See the specifications below for more details:

Model	GPM174M	GPM462M GPM462C	GPMCMOS02000KMA GPMCMOS02000KPA	GPCMOS01200KPF
Sensor	IMX 249 (M)	IMX 462 (M/C)	IMX 290 (M/C)	IMX 225 (C)
Size	1/1.2”	1/2.8”	1/2.8”	1/3”
Resolution	1920*1200	1920*1080	1920*1080	1280*960
Pixel Size (µm)	5.89	2.9	2.9	3.75

 

Especially, the new arrival GPM174M stands out with the largest sensor size and the highest resolution among the other guide cameras of the GPM and GPCMOS series cameras. The sensor G Sensitivity of GPM174M is 825 mV with 1/30s. Its spectral sensitivity is shown in the figure below. The sensitivity is measured with an excitation LED light source with a color temperature of 3200 K. An IR cut filter CM500(t =1.0 mm) is placed between the LED light source and the sensor receiving surface to irradiate substantially parallel light.

QE Peak

Model	GPM174M	GPM462M GPM462C	GPMCMOS02000KMA GPMCMOS02000KPA	GPCMOS01200KPF
Sensor	IMX 249 (M)	IMX 462 (M/C)	IMX 290 (M/C)	IMX 225 (C)
QE	>89%	>89%	>81%	>75%

The QE peak of GPM and GPCMOS guide cameras are all above 75% and can satisfy the different needs of amateur astrophotographers and professionals.

Frame Buffer

A frame buffer in astrophotography serves as a temporary storage solution for images captured by a camera. Different from other brands, the ToupTek Astro GPM and GPCMOS series guide cameras have a built-in frame buffer, which helps maintain the stability of data transmission and effectively reduces the amp-glow caused by image data that can be temporarily buffered without being sent hastily to the receiver. This feature ensures stable operation and allows the camera to achieve its maximum frame rate, even when operating alongside multiple other cameras. This makes it easier to detect faint stars, improving guiding accuracy in challenging conditions. Moreover, the buffer is necessary for continuous frame capture in video mode, which is more effective for guiding than still images. It ensures that the guide camera can provide a steady stream of data for tracking.

Conclusion

In conclusion, a guide camera is an essential piece of equipment for astrophotography. It helps improve image quality, enables longer exposures, and opens up more opportunities for complex shots. When choosing a guide camera, consider factors such as sensor size, resolution, sensitivity, readout noise, frame rate, and cost.

ToupTek Astro’s affordable guide cameras are a great choice for beginners. We offer excellent product specifications, including high-quality sensors, good sensitivity, low readout noise, and high frame rates. There is always one option that meets your requirements. By choosing a ToupTek Astro camera, you’re not just investing in a tool but you’re joining a community of passionate astrophotographers who are dedicated to capturing the universe’s hidden wonders. Whether you're a beginner or an expert, you’ll be part of a global network of explorers who share your love for stargazing and discovery.

 

Explore Our Guide Cameras Now!

Shop Here: www.touptekastro.com/collections/guide-cameras