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 THE TELESCOPE'S F/NUMBER - Loron Knowlen

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loron_knowlen2011



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PostSubject: THE TELESCOPE'S F/NUMBER - Loron Knowlen   Wed May 18, 2011 12:28 pm

The f/number (focal ratio) of any telescope tells two things about the telescope and that is it's intended purpose and it's photographic performance. The brightness of a star depends on the telescope's aperture not the telescope's f/number. All telescopes of the same aperture at any magnification will show the same visual brightness. There are many that insist their long focal ratio telescope gets higher contrast, this is not correct. A refracting telescope does have more contrast than any other because of it's optical system not because of the f/ratio. You can see that when you are comparing very well made and very well corrected refractors, you will see there is no gain in contrast regardless of the f/ratio of each telescope. Even if a reflecting telescope is well made and has the same size secondary mirror obstruction as another, it will have the same contrast regardless of the f/number of each telescope. All of the confusion and there is much on this issue, is because of the photographic use of the f/number. A faster f/ratio does mean brighter images on film but not in a telescope. Aperture not f/ratio is the important factor with a telescope. Some photographers have a great deal of trouble with this concept. The f/number of any objective lens or a mirror of a telescope has nothing to do with the visual brightness of an image, the bigger the aperture the better.
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PostSubject: Re: THE TELESCOPE'S F/NUMBER - Loron Knowlen   Wed May 18, 2011 12:29 pm

Not that one again. lol!
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Roy Toshima

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PostSubject: Re: THE TELESCOPE'S F/NUMBER - Loron Knowlen   Wed May 18, 2011 12:43 pm

Most of what you've put there Loron is correct but there are some variations as to the concept but the statement still can stand.
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Astrowizz



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PostSubject: Re: THE TELESCOPE'S F/NUMBER - Loron Knowlen   Thu May 19, 2011 10:56 am

Well I have some issues with that but not to violate terms I won't paste here but refer you to a link to the information as to the f/number continuing.
http://en.wikipedia.org/wiki/F-number

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John Koestlerman
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loron_knowlen2011



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PostSubject: Re: THE TELESCOPE'S F/NUMBER - Loron Knowlen   Fri May 20, 2011 5:41 pm

Too much fun jocolor
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Mark Smith

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PostSubject: Re: THE TELESCOPE'S F/NUMBER - Loron Knowlen   Mon May 23, 2011 10:49 pm

2nd Not this one again, zzzzzzzzzz
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