Confused about magnifications

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  • Member since
    November, 2013
Confused about magnifications
Posted by turboslim on Saturday, November 09, 2013 3:13 PM

Trying to make a long story short:

My scope came with a 15mm and 6 mm lens.  I was looking at the 2x shorty Barlow eyepiece and it said: "The Orion Shorty 2x Barlow Lens doubles the magnifying power of any 1.25 inch eyepiece, essentially dividing the eyepiece's focal length by a factor of 2--using a 25mm eyepiece in the Shorty 2x Barlow provides the same magnification a 12.5mm eyepiece would normally exhibit (25 / 2 = 12.5)".  In my other research of eyepieces, the bigger the #mm the more magnification.  So this statement sounds contradictory to me and I feel like there is something I'm missing. Clearly I'm new to the world of using telescopes to view the night sky although I've been staring up there all my life.  Thanks in advance for any help!

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Posted by DaveMitsky on Saturday, November 09, 2013 3:53 PM

In my other research of eyepieces, the bigger the #mm the more magnification.

It's actually the reverse.  The longer the focal length of an eyepiece of the same optical design, the less magnification, and consequently a larger true field of view, it produces in a given telescope.  Dividing the focal length of the telescope objective by the focal length of the eyepiece yields magnification.

http://www.saguaroastro.org/content/formulas.htm

http://www.chuckhawks.com/telescope_formulas.htm

See http://www.stargazing.net/naa/scopemath.htm and http://www.telescope-simulator.com/index.php?option=com_content&view=article&id=45  for some handy calculators.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

  • Member since
    November, 2013
Posted by turboslim on Saturday, November 09, 2013 6:16 PM

Thanks for your quick reply! The links were great and explained where the variables were coming from for each equation.  That info is going to help a lot in my future purchases!

 

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  • Member since
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  • From: PA, USA, Earth Moderator
Posted by DaveMitsky on Saturday, November 09, 2013 6:42 PM

You're welcome.  

What's the aperture (diameter) and focal ratio of your telescope?

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

  • Member since
    November, 2013
Posted by turboslim on Monday, November 11, 2013 1:13 PM

Focal ratio: f/3.9

aperture: 4.5 inches 

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  • Member since
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  • From: PA, USA, Earth Moderator
Posted by DaveMitsky on Monday, November 11, 2013 3:23 PM

You may also want to consider obtaining a 25 to 27mm eyepiece to maximize your scope's true field of view.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

  • Member since
    November, 2013
Posted by turboslim on Monday, November 11, 2013 6:48 PM

Oh ok. I will do that. I always thought telescopes were all about magnification but now that I have my own I find myself less interested to zoom extra close and more interested in exploring.  I would love to experience that "lost in space" effect. Thanks for your help!

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