Eyepiece calculator

magnification = 34× exit pupil = 3 mm field: 1° 28' apparent field of view: 50°  

Fast search on database
Use the search field in the upper right and type in brand, construction design and focal length, for example: Pentax XW 40 mm

eyepieces in stock: 692
New: TS Plössl Fadenkreuz 23 mm

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Explanation:

V_max = maximum useful magnification,
V_opt = primal magnification on 3 mm exit pupil
V_min = minimum magnification on 7 mm exit pupil

Exit pupil: if the eye is adapted to darkness the diameter of the exit pupil is 7 to 8 mm. If the beam of rays (exit pupil) is bigger than the pupil of the eye light will disappear, if the beam is less than 0.5 mm no more details will be visible and the image loses sharpness. Brightness and definition of the calculators image adapting to the combination of telescope and eyepiece.

Resolving power: minimum distance of two objects, which can theo­reticaly seen as resolved. This depends on the scope aperture. Example: Double star ε¹ Lyrae: distance 2,8" - the scope -Ø should have a minimum of 60 mm, in practice 70 mm.

Eyepiece design: The bigger the apparent field of view (diameter of the graphic above), the more complex is the eyepiece construction.
Extreme example: design Huygens = 30°, design Ethos = 100°.
Apparently beautiful fields of view:
The real values and the specifications given from the manufacturers are often very diverging. For some eyepieces in the database the values were measured with the star transit method on different telescopes. This eyepieces are marked with an asterisk in the column Design. All measured eyepieces can be found by typing in an asterisk and choosing "Design" as a search option.

20mm Huygens (left) und 21mm Ethos

Eyepiece Calculator download (only German): 480 KB ZIP