Coleman CDB804AZ3, Инструкция и руководство пользователя

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6) Calculating the field of View
The size of the view that you see through your telescope is called the true (or actual) field of
view and it is determined by the design of the eyepiece. Every eyepiece has a value, called
the apparent field of view, which is supplied by the manufacturer. Field of view is usually
measured in degrees and/or arc-minutes (there are 60 arc-minutes in a degree). The true
field of view produced by your telescope is calculated by dividing the eyepiece's apparent
field of view by the magnification that you previously calculated for the combination. Using
the figures in the previous magnification example, if your 10mm eyepiece has an apparent
field of view of 52 degrees, then the true field of view is 0.65 degrees or 39 arc-minutes.
To put this in perspective, the moon is about 0.5° or 30 arc-minutes in diameter, so this
combination would be fine for viewing the whole moon with a little room to spare.
Remember, too much magnification and too small a field of view can make it very hard to
find things. It is usually best to start at a lower magnification with its wider field and then
increase the magnification when you have found what you are looking for. First find the
moon then look at the shadows in the craters!
7) Calculating the exit pupil
The Exit Pupil is the diameter (in mm) of the narrowest point of the cone of light leaving your
telescope. Knowing this value for a telescope-eyepiece combination tells you whether your
eye is receiving all of the light that your primary lens or mirror is providing. The average
person has a fully dilated pupil diameter of about 7mm. This value varies a bit from person
to person, is less until your eyes become fully dark adapted and decreases as you get older.
To determine an exit pupil, you divide the diameter of the primary of your telescope (in mm)
by the magnification.
For example, a 200mm f/5 telescope with a 40mm eyepiece produces a magnification of 25x
and an exit pupil of 8mm. This combination can probably be used by a young person but
would not be of much value to a senior citizen. The same telescope used with a 32mm
eyepiece gives a magnification of about 31x and an exit pupil of 6.4mm which should be fine
for most dark adapted eyes. In contrast, a 200mm f/10 telescope with the 40mm eyepiece
gives a magnification of 50x and an exit pupil of 4mm, which is fine for everyone.
True Field of View = = = 0.65
Apparent Feild of View
Magnification
52
80x
Exit Pupil =
Diameter of Primary mirror in mm
Magnification