## Explanations

### Diameter (Ø)

The diameter of the primary objective (in millimeters or inches).

### Focal length (f)

The distance (from the center of) the objective to the point where the light comes together (in milimeters).

### Focal ratio (f/)

The ratio between the focal length and the diameter (in millimeters).

**Calculation:** Ø / f telescope.

### Focal length eyepiece (f)

The focal length of the eyepiece.

### AFOV (apparent field of wiew)

The apparent field of view of the eyepiece. This is the field of view of the eyepiece in degrees (°) at a magnification of 1.

### Barlow/reducer (x)

Is used to alter the focal length of the eyepiece and can thus be used to lengthen or shorten it.

### Limiting magnitude location (m)

The weakest visible star from the location in the zenith.

### Exit pupil (mm)

The maximum diameter of the pupil in diameters. This differs per age and person, but is usually between the 6mm and 7mm.

### Maximum magnification (x)

The theoretical maximum magnification (with excellent optics and circumstances).

**Calculation:** Ø in milimeters * 2

### Resolving power (′)

The theoretical resolving power of a telescope is the distance in arcminutes (&prima;) between 2 points that can be split by the telescope.

**Calculation:** 116 / Ø (Dawes' limit)

### Limiting magnitude (m)

The theoretical magnitude of the weakest object that can be seen with this telescope at the given location and with the given maximum pupil diameter.

**Calculation:** 5 * log10(objective diameter / pupil diameter)

### Surface area objective (cm2)

The total surface area of the objective in square centimers.

**Calculation:** Pi * (Ø / 2) * (Ø / 2)

### Magnification (x)

The amount at which the object is magnifide in apparent diameter.

**Calculation:** f telescope / f eyepiece

### Exit pupil (mm)

Diameter (in milimeters) of the sharp image that is given by the telescope and eyepiece.

**Calculation:** f eyepiece / magnification

### FOV (field of view)

The (true) field of view is the diameter of the view in degrees (°) or arcminutes (′).

**Calculation:** afov eyepiece / magnification

### Transition (min/sec)

The duration in minutes or seconds that one point in the ecliptic needs to travel the full width of the field of view in a telescope that is not following.

**Calculation:** 240 x tfov