Quote:
Originally Posted by strummer4
This is probably a dumb question but
why would I buy a 13mm eyepiece when I could just use my 26mm with a x2 Barlow? Is there any difference? Instead of buying say 4 eyepieces could I not buy 2 and use a Barlow?
Steve
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Not a dumb question at all.
As a basic principle, the fewer pieces of glass you put between yourself and the starlight, the better; every optical element will result in
some loss of transmission. So, all other things being equal, it's better to go with the EP.
However, all other things are most definitely
not equal. For starters, a 26mm EP will usually have a wider exit pupil and give more eye relief. Many observers find it's more comfortable to observe through a 26mm with a 2.5x Barlow than through say a 9mm EP, especially a cheap one. Not all EPs and Barlows are equal. If you can afford a
2.5x Televue Powermate, for instance, you'll be effectively doubling the size of your EP collection; with, say, a 32mm and a 20mm EP and a 2.5x Barlow you'll be giving yourself the equivalent of a 12mm and 8mm and I'd find it hard to imagine an observing situation that you wouldn't have covered.
Everyone here will you that the absolute best thing to do when selecting EPs is to get along to an astronomy club and try out other people's kit. Have a look at what the difference is between a 12mm EP and a 26mm + 2x Barlow. There is a whole world of different EP designs, some of which cost about half what you paid for your telescope :-) Everyone's eyes and preferences really are different - for instance I have astigmatism, so finding EPs that allow me to observe with my glasses is important.
Just one word of caution. With your scope, I wouldn't go for a Barlow above 2.5x. That will give your an effective focal ration of f/25 which is about as high as you want even looking at Jupiter and Saturn. The guys with the really fast scopes like the f/5 Newtonians or the short tube refractors need