Difficulties in deep space photography

Defocus lens and F/2 system are two different things.

The defocusing ratio of an defocusing lens is generally 0.5~0.63, which means that the Zeca's defocusing ratio can be increased by 1 times, and the lens barrel does not need to be replaced when in use. The focal ratio of C8 system is about F/ 10, and the focal length is about 2m. With a defocus lens of 0.63, it will only become F/6.3, with a focal length of1.25m. ..

The F/2 system will completely replace the Zeca secondary mirror. For example, the famous HyperStar equipment is a set of complicated transmission correction mirrors. When in use, the original secondary mirror needs to be detached from the Zeca corrector, so that the light reflected by the primary mirror can directly enter, and after various aberrations are corrected by HyperStar, it can be directly imaged on the CCD, and the focal ratio of the system can reach F/ 1.9~2.2. In this way, the brightness of the view image can be improved by more than 30 times, and the shooting time can be shortened by several times, which greatly improves the deep space photography ability of Zeca.

Having said that, you may have understood that the function of defocusing mirror is only to shorten the focal length of the main mirror, which is a dual-purpose equipment for vision and shooting; F/2 is a pure deep space photography device, which requires a high level of users.