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barlow before or after diagonal, magnification

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#1 moynihan

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Posted 21 August 2003 - 05:04 PM

Howdy,
Does any one know if their is a standard "rule of thumb" for the effect on magnification if you put a barlow in front of your diagonal as opposed to putting it between the eyepiece and diagonal mirror?
I would imagine optical design of all the light path elements would govern it (and whether it can be done at all), and that the rating (2x, 1.6x etc) of the barlow is with it directly infront of the eyepiece?

jay

#2 Gary BEAL

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Posted 21 August 2003 - 05:43 PM

Don't quote me on this, but I always understood a rough rule of the stated magnification if the eyepiece was in the barlow, and more if the diagonal separated them. A 2x would becopme about 3x if the diagonal was in between.
Gary

#3 Charles

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Posted 22 August 2003 - 11:22 PM

I don't know about you'll, but I can not bring my TAO to focus with the Barlow in front of diaganol. I have to always put the Barlow after the diagonal. I guess I need to buy more extensions.
Charles

#4 Mike Sandy

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Posted 05 September 2003 - 12:44 AM

The further away from the barlow lens you move the eyepiece - the more magnification you get. The formula is (I think this is correct): Magnification = 1 + (d/FL), where "FL" is the focal length of the barlow and "d" is the distance to the eyepiece. If you put it before the diagonal (and can reach focus) you get more magnification. Does this help?


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