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Old 22-03-2019, 03:03 PM
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Allan_L (Allan)
Member > 10year club

Allan_L is offline
Join Date: Mar 2008
Location: Central Coast NSW
Posts: 3,206
Aperture and focal length and magnification

Welcome Mario to IceInSpace
So the highest theoretical magnification is often regarded as being twice the aperture (in mm). So a 125mm (5") scope could produce magnification upto 250 times. (subject to atmospheric conditions etc). Note we rarely get to the theoretical max due to crappy seeing conditions.

The magnification you can get is a function of the focal length and the eyepiece. Eg: a telescope with 650 mm focal length and using a 10mm eyepiece will produce a magnification of (650 / 10) 65 times. A 25mm eyepiece with the same scope will give 26 times.

Planets are relatively small, so you need a high magnification to get a pleasing view (people often suggest around 100-150 magnification).

DSO's are normally much larger so much smaller magnification is usually better viewing. But these are distant and dimmer, so the more light (bigger aperture) the better.

Hope this helps as a starter.

Feel free to ask lots of questions.

Oh, and re priority 4: astronomic scopes are not normally much good for terrestrial viewing due to image inversion and/or reversal (depending on type of scope).

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