Here’s everything you need to know about astrophotography in December 2024: ...

Figure 2.8: An afocal attachment can be placed in front of another system to change its focal length, power, or field. Shown here is a galilean afocal which, in the upper sketch, increases the focal ...

An afocal system is one which images an infinitely distant object at infinity. It is called afocal because it has no focal length (or an infinite one; either concept can be a nuisance). Telescopes, ...