Choosing a suitable astronomical camera certainly requires considering many factors, such as budget, the quality of the camera, and the compatibility between the camera and the main telescope, etc. Among them, how to make the camera adapt to the resolution of the telescope is a rather complex issue.
Focal Length and Aperture are the most basic optical parameters no matter for a refracting, reflecting, or catadioptric telescope. For beginners with limited experience and little understanding of various formulas, we can start by using Stellarium, a free and open-source software, to simulate our entire system. This can help us roughly determine the visual representation of the target we want to photograph in the system we intend to build, considering factors such as focal length and aperture.
Here are the specific steps: Open Stellarium, and select any common deep sky or planetary target, such as M31. Click on the wrench icon in the top right corner to enter the “Oculars” interface. Here, we need to input some information, mainly about the Camera’s Sensor and Telescope, such as chip size, effective resolution, as well as the focal length and aperture of the telescope.
Then, return to the view simulation interface, clicking the “Image Sensor Frame” option will display the camera and telescope parameters that were inputted earlier. This allows us to visualize the size of celestial objects in the camera frame. This tool aids users in gaining a basic understanding of the size and proportions of the image frame produced by the equipment combination, allowing them to select suitable equipment before making a purchase.
After the imaging telescope and camera are determined, we can proceed to select other equipment, such as a mount with an appropriate load capacity, filters and a filter wheel that match the main camera.
Guide Camera/OAG Combinations
Different Guide Ways: Guiding Camera VS. OAG
At present, there are two main guide approaches in amateur astrophotography.
One approach involves the combination of a guide camera and a guide scope.
In the era of highly sensitive and small-pixel cameras, there is no longer a need for large and heavy guide scopes. Occasionally, in some astronomy magazines or forums, one may come across individuals who have been involved in astrophotography for many years still using refractors with apertures of 60mm or even 70mm for guiding. These scopes are now comparable to some small main telescopes used for wide-field observations. However, this is actually a legacy of the CCD guiding era. In the era of small-pixel CMOS, the pixel density has significantly increased, and it is no longer necessary to have a very long focal-length telescope to detect the movement of stars effectively. With improved sensitivity, larger aperture telescopes are also not required, especially as shorter focal lengths result in a larger field of view, providing more guide stars within the frame. Therefore, if choosing a guide scope, it is recommended to use a mini guide scope. Guide scopes that are too large or heavy may potentially cause optical distortions in the main telescope. Additionally, some users may be concerned about the alignment of the guide scope with the main telescope. Typically, mini guide scopes have short focal lengths and much larger fields of view than the main telescope, as long as the installation is done as per standards, there is no need to overly insist on extremely precise alignment.
The other approach involves the combination of a guide camera and an OAG (Off-Axis Guider). With an OAG, the guide camera and the main camera can share the field of view of the main telescope. Compared to guide scopes, the OAG guiding structure is more compact and the counterweight distribution on medium to large-sized setups is more reasonable. OAG is more widely used in backyard observatories and remote observatories.
Recommended Combination for an Guide Camera+OAG
The size of the guide camera primarily depends on the field of view of the main telescope. The sensor size of the guide camera determines whether a larger OAG prism should be chosen, and the size of the camera/filter wheel determines what diameter of OAG would be more convenient.
For general medium to small aperture, medium focal length guide telescopes, such as refractors around 70mm f/5 or reflectors around 150mm f/5, it is typically sufficient to use a standard-sized prism with a medium-sized sensor guide camera. Among the currently available planetary guide cameras, we recommend the QHY5III462M and QHY5III200M. Since guiding does not require color data, using a monochrome camera provides higher sensitivity.
If the main telescope has a long focal length (e.g., above 1000mm) and the observing conditions are somewhat challenging, there may be fewer stars visible in the field. In such cases, using guide cameras with larger sensor sizes, such as the QHY5III174M and QHY5III585C, can present an image size approximately 2-4 times that of standard guide cameras. This naturally allows for the detection of more stars, effectively addressing issues of insufficient or sparse guide stars in the field. To fully leverage the capabilities of large sensor guide cameras, a larger prism is needed to transmit more light. In such situations, it is recommended to use the new OAG Pro series with a larger prism, which is ideally suited for large sensor guide cameras.
Recommended Combinations for Camera+Filter Wheel+OAG+Filters
The following are the combinations we recommend. They have been tested by astronomy enthusiasts worldwide and are considered ideal choices in terms of optical quality, structural stability, and other aspects. Our new adapter design is also specifically tailored to these recommended combinations.
Recommended Combinations for Mono Cameras
The full-frame mono camera is available in two models: QHY600M-PH (Standard Version) and QHY600M-PH SBFL (Shorter Back Focal Length Version). It is recommended to use them with CFW3L+OAGM. If you have specific requirements for the back focal length of your optical system, such as 55mm/56mm or when using a DSLR lens, it is advised to choose the QHY600M-PH SBFL (Shorter Back Focal Length Version). Additionally, some users have reported possible vignetting when using QHY600 with M48 MPCC. For better optical performance, it is suggested to connect full-frame cameras like QHY600 to telescopes using M54 or larger openings.
The APS-C mono camera QHY268M supports two types of filters: a 2-inch mounted filter using CFW3L, or a 36mm unmounted filter using CFW3M-SR 7*36mm version. According to our estimation, the 36mm filter can be used when the focal ratio of the main scope is greater than f/4. If you are using a telescope with a small focal ratio, such as f/2.8, it is recommended to use the 2-inch mounted filter. Additionally, if you choose to use unmounted filters with filter masks, it is recommended to use the thicker SR version to provide more space inside the filter wheel.
For cameras with a 3/4-inch sensor, like QHY294, it is recommended to use CFW3M-SR+OAGM. For cameras with a 1-inch or smaller sensor, like QHY533, it is recommended to use CFW3S-SR+OAGS.
2” Mounted or 50mm Round
2” Mounted or 50mm Round
2” Mounted or 51mm Round
2” Mounted or 52mm Round
2” Mounted or 36mm Round
Recommended Combinations for Color Cameras
Color cameras usually do not need to be paired with a filter wheel. There is no need to switch filters, or only a few filter changes are necessary using a filter drawer. If a filter wheel is required for special reasons, refer to the combination recommendations for the corresponding mono model of the camera.