ICEINSPACE
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Moon Phase
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Waning Gibbous 90.1%
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31-10-2016, 01:20 PM
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Registered User
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Join Date: Apr 2012
Location: Adelaide, Australia
Posts: 224
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Basic optics question
I am curious to know, if I have a 12 inch newt and a 6 inch newt and used the same eyepiece, would the view be the same size but just a lot clearer and more detailed, or does mirror size also affect magnification? I am aware that the bigger the mirror the more light gets in and that without a decent aperture you cannot get the detail, what has the bigger affect in magnification?
mirror diameter or mirror focal length or just eyepiece size??
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31-10-2016, 01:25 PM
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amateur
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Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 7,101
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Magnification is defined as FL (mirror) / FL (eyepiece)
The size of the mirror determines the resolution and brightness of the image.
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31-10-2016, 03:00 PM
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Registered User
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Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,927
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If both mirrors had the same focal length - 12" f5 (60" FL) and 6" f10 (60"FL) then the magnification with the same eyepiece would be the same ie a 1" (25mm) eyepiece would give x60 in each scope.
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31-10-2016, 06:18 PM
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Registered User
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Join Date: Apr 2012
Location: Adelaide, Australia
Posts: 224
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is the focal length of the mirror determined by the depth of the mirror.?
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31-10-2016, 06:20 PM
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Registered User
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Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,927
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Peter,
Generally, yes.
A deeper mirror infers a shorter focal length.
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31-10-2016, 08:47 PM
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Registered User
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Join Date: Jul 2008
Location: Killara, Sydney
Posts: 4,147
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31-10-2016, 10:49 PM
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Registered User
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Join Date: Apr 2012
Location: Adelaide, Australia
Posts: 224
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Thank you all, I will try to decipher wavytone's link into some legible english and look forward to some serious study on the matter.
Peter
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12-11-2016, 08:01 AM
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Registered User
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Join Date: Mar 2016
Location: Long Island, New York, USA
Posts: 372
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Generally the focal length is provided by the manufactuer.
I have a 1200 mm FL scope and a 400 mm FL scope.
A 20 mm eyepiece would give me 1200/20 - 60X
Same eyepiece in the 400 mm FL scope would give me 400/20 = 20X
It is a simple ratio. The aperture has nothing to do with the magnification. Aperture tells you the relative amount of light the scopes will gather. It is based on the area of the lens/mirror.
Area = Pi R squared. Since Pi is the same in each calculation we can ignore it.
12" scope R-6 6 squared = 36
6" scope R=3 3 squared in 9
36/9 = 4
The 12" scope gathers 4x the light of the 4" scope so you can see dimmer objects and you can apply more magnification when using the bigger scope up to the point that atmosphere limits magnification.
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