ElPelado wrote:Hi again. i have an other question now: i know there are eyepicies with different diammeters, 1.25" and 0.9" are the most common i think. my telescope has a 1.25" hole for the eyepice, but i can also put the 0.9" ones that came with the telescope. someone told me that i should buy 1.25" because those are better.
Can someone told me what's the diference between the diameter of the eyepice???
Thanks.
ElPelado,
the standard eyepiece diameters for 'more serious' telescopes are 1.25 " and 2" (for deep sky wide field). The 0.9" is a size that came originally from Japan and is still to be found in cheaper telescopes (department stores) like yours.
In principle, you could have excellent eyepieces for any size.
Yet, if you want to cover a
very large field, you obviously need a large diameter, like 2"! In general, the optical design of an eyepiece is characterized by the name of its inventor, like
Huygens (cheapest, non-achromatic, 45deg),
Ramsden (similar, but exists also with one achromatic lens),
Kellner (one acromatic lense, field lens non-achromatic)
Othoscopic (fully acromatic, 4 lenses)
Ploessl (very good symmetrical design, 4 lenses, 50 deg),
Erfle (5-6 lenses, wide field ~65 deg),
Nagler (super expensive 82 deg field)...
...
just to name a few. The prices vary tremendously among the different kinds.
The 0.9" ones are typically Huygens, Ramsden or perhaps Kellner designs.
The field that is specified for an eyepiece is the so-called
apparent field of view. You must divide it by your magnification to get the
true field.
Suppose you have an eyepiece with 50degs apparent field and 100 times magnification then the full moon (30 mins= 1/2 deg) just fits into your view...
Bye Fridger