Opticstar AR80S GOLD GUIDE-SCOPE, Руководство пользователя

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© Opticstar Ltd 2011
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APPENDIX A
Appendix A outlines the most important aspects of a telescope in terms of its focal
length and focal ratio. These values are important as they dictate magnification,
exposure times when imaging and fields of view.
Practical Magnification
The focal length of a telescope can be calculated by multiplying the focal ratio of the
telescope with its aperture i.e. an f5 refractor with 80mm of aperture will have a
focal length of 400mm (5x80=400).
In a telescope, magnification is the number of times an object appears larger to the
observer when compared to what the observer can see with the naked eye. There is
no real limit to the amount of magnification possible in a telescope, but practical
magnification is limited by the optical system and is normally around 30-40 times
per inch, and around 50-70 times per inch of aperture for high quality apo-chromatic
refractors. Experienced observers using high quality telescopes may push these
figures even higher under favourable conditions.
Please keep in mind that the maximum useful magnification from a suburban yard
using any telescope will be around x30 – x35 per inch of aperture, this is due to light
pollution (sodium lights in particular), thermal currents and other environmental
factors. Expect higher magnification from dark sites and when transparency is good.
Eyepieces and Magnification
The actual magnification
capability of a telescope will vary
depending
on the eyepiece
attached to the telescope.
Magnification can be changed by
simply exchanging eyepieces.
Magnification depends on two factors. The focal length of the telescope and the
focal length of the eyepiece used. To calculate the magnifying power an eyepiece
gives, simply divide the focal length of the eyepiece into the focal length of the
telescope.
Magnification = telescope’s focal length / eyepiece’s focal length = F/f
For example a telescope with a focal length of 400mm and an eyepiece with a focal
length of 5mm will magnify its target 80 times (400/5=80).
Barlow lenses can be employed in conjunction with an eyepiece to increase
magnification. To calculate the magnifying power an eyepiece gives in conjunction
O
fl
F