telescope

rmudgway@xtra.co.nz · Guest

whats a spec like this

mirror dai 130mm
focal len 1000mm
eye len ma20mm(low power)
ma10mm med power
sr4mm hi power
Barlow; 3x
Max mod 750x

opticsplanet.com · Posted: Thu Mar 31, 2005 10:03 am Post subject:

Hi

These specs tell you exactly what to expect from your telescope.

The first spec, 130mm mirror, is the most important. The word mirror tells you that you have a reflector telescope. The 130mm tells you this is a 5 inch mirror. The size of the mirror (or lens in other telescope designs) is the single most important factor on telescope performance. The larger the mirror, the more objects it will be able to detect and the better the image quality, assuming you have reasonable quality.

Focal length, 1000mm, is the length of the optical system, which, in this case, also translates into the length of the telescope tube. In this telescope the tube will be about 3.5 ft long. The focal length will also be used to determine the magnification with any given eyepiece and it will also influence optical performance with accessories.

The next three are eyepieces ma20mm(low power), ma10mm (med power) sr4mm (hi power). The numbers are the focal length of the eyepiece, not the magnification. The letters describe the design of the eyepiece. To determine the actual magnifcation these, divide the number into the focal length of your telescope - 1000mm. This gives you a magnification of 50x with the 20mm, 100x with the 10mm, and 250x with the 4mm.

A barlow is something you add to the eyepiece to increase the magnification. With a 3x barlow, each of the above magnifications is tripled. The 750x is the magnification yoiu would get when adding the barlow to the 4mm (250x) eyepiece.

Be warned, however, that there is a huge difference between the magnification you can get from your telescope and the magnification that you will actually be able to use. Figure 30-50x per inch of mirror size, depending on atmospheric condition which vary from night ot night. Thus maximum useable magnification on most nights will be about 150x in this telescope. Anything more will produce images of such low quality as to be useless.

You might also want to read our articles on telescopes, http://www.opticsplanet.net/how-to-buy-a-telescope.html and http://www.opticsplanet.net/telescope-faq.html for lots of helpful information.

And, of course, you can always call me (Joanie) if you have more questions.
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