Thread: Down the Coast
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Old 18-05-2009, 03:01 PM
Wavytone
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Join Date: Jul 2008
Location: Killara, Sydney
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An"erecting prism" is what you want

A nice spotting scope would be best, by far, however you could use a smallish refractor and an erecting prism. You can get an erecting prism 90 degree diagonal, like this, but they're for refractors:

http://www.scopestuff.com/ss_diag6.htm or

What's different is that these have a roof prism inside so light going through is reflected off two surfaces, and hence the image is right-way up and left-right orientation is also correct.

There is a second type that use a pair of wedge-shaped prisms to achieve the same but deviate the light path by 30, 45 or 60 degrees, more comfortable for terrestrial viewing:

http://www.astronomics.com/main/Imag...E38XSE1/Page/1

Putting an erecting prism into a Newt with a low-profile focusser, you may be unable to focus. The solution is to move the primary up the tube a couple of cm. Refractors may also be unable to focus if the drawtube doesn't have enough travel inwards.

Personally i would suggest a spotting scope or a small refractor would be the best option.
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