what telescope lens should i use?
Thursday, May 20th, 2010 at
11:46 am
I recently aquired a telescope with accessories from my brother that he wasnt using and the instruction manual for this thing would be more useful in the bottom of a hamster cage. My question is, when looking at the moon, should i use celestial or terrestrial lenses (barlow lens or the mirror attachment)
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US $1.00
By definition, terrestrial means the earth, celestial means everywhere else (like the moon).
If its a cheap refractor ’scope, I hope your hamsters like it.
By mirror attachment I assume you mean the diagonal. Use it. What other eyepieces do you have with your scope, and can you name or describe it?
The cream-of-the-crop is the “Nagler” eyepeice (marketed by “Televue”), but it is also the most expensive. At the bottom of the barrel is the “Huygens” configuration -no redeeming qualities- usually sold with “toy” telescopes. In my experience,
“Plossl” eyepieces are ideal with long focal lengths. And the
“Orthoscopic” is excellent for “near” targets (like the Moon and planets), and is a good all-around performer at a moderate price. You may also consider getting a “lunar filter”
(if your scope has an aperture of 4″ (100mm) or more), as
this orange filter enhances the contrast range of lunar features, making crater rims, and other small details easier to see. “Barlows” shouldn’t be needed with the Moon (I rarely use them at all). Using an erecting prism or diagonal is mostly a matter of personal taste. Experiment to find the configuration you like best for the target you happen to be viewing at the time.
For the Moon, a magnification of 40-50X will give the best
“full disc” views. And 4 days before, or 3 days after a full moon, the views of the lunar surface are especially nice. Good Luck and have fun.
definatly not a barlow lens while looking at the moon, that only distorts it so bad you can not even focus in on it at all, Be sure to use a filter while looking at the moon also so your eyes are protected, Most scopes come with a tinted filter you can insert over the eyepiece just for that purpose,, happy skywatching,
Astronomers use the word “lens” only to refer to the main lens at the front end of the telescope. Your scope probably came with one to three eyepieces, a Barlow lens, and a mirror diagonal. It may have come with an erecting system for terrestrial viewing.
For astronomical viewing, you will almost always use just the diagonal and an eyepiece. The Barlow lenses supplied with scopes like this are generally very poor quality. The best eyepiece to use is generally the one with the largest number (focal length) on it, usually 25mm or 20mm. The other eyepieces are also likely to be of poor quality.