Hi ManintheMoon & All,
Quote:
Originally Posted by ManintheMoon
Yesterday my Dad bought me The Australian Sky and Telescope magazine and Mum has also got me a subscription with the free moon phase map and CD. (YAY ME!  ) It is so interesting! It has also taught me a few words that you use a lot although I am wondering what a Barlow lens does (and do I need one?) I have been looking at the moon and stars with my little binoculars but can't wait to buy a 8" dobsonian like you said (but I have to save up yet) |
Thanks very much for your kind comments about Australian Sky & Telescope. I'm glad you found it interesting and useful. You'll also find this place (IIS) is brilliant to find help on a whole range of topics to do with your binoculars and what to look at and when the time comes, a 'scope.
Don't forget to ask lots of questions, you won't go long without some sort of an answer here.
In basic terms, you should think of a Barlow as being a bit like a "pre-amp". It goes into the focuser in front of the eyepiece. The eyepiece then slips into the back of the barlow. Many, if not most barlow lenses provide a x2 amplification so an eyepiece that normally gives x100 magnification with a given telescope, will now give x200. Some specialised barlows give x3, x4 and x5. There is a down-side though. That increase in magnification means the size of the field (the sky you see inside the eyepiece) will halve in diameter (or quarter in area) with a x2 barlow.
But remember this: magnification isn't everything. It actually describes very little about how a telescope is performing. The true "power" of a telescope is the diameter of the main mirror (primary mirror) or lens collecting the light. Never buy a telescope based on how much magnification it can give. You can make any telescope magnify any amount just by changing the eyepiece or eyepiece/barlow combination. There is a
practical limit to how much magnification a particular size telescope can handle. To calculate it, for most purposes, it is the aperture in inches x40. So with an 8" the
practical limit is 40 x 8 = x320 (or thereabouts).
Most of us do most of our observing at low and medium magnifications. High power (magnifications) is reserved for really small bright objects like planets and planetary nebulae etc.
Barlow lenses are a good accessory to own because they make each eyepiece in your collection do double duty -- but it is important to get a quality barlow because a poor one will degrade the image quality greatly.
Hope you have a good time here and keep saving for that 'scope! (Christmas isn't that far away) If you have an astronomical society nearby, it is a very good idea to join up where you can meet other amateur astronomers and look through lots of telescopes. There is a listing of amateur societies on this site somewhere but I'm too tired to look for it at the moment ...
Best,
Les D
New Mag!
)
and I will be reading a lot!
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I can’t wait till I get the next issue soon!
