2007-06-04 00:49:44 · 7 answers · asked by Dave 1 in Science & Mathematics ➔ Astronomy & Space
No.
However, it's true that a refractor will collect more light than a reflector of the same size. It typically offers more contrast as well.
How much more light the refractor collects depends. Reflectors (and catadioptrics) have a secondary mirror which is in the middle of the front of the tube, directly in the path of light. This secondary mirror, being an obstruction, reduces the amount of light than can enter the tube. It's not uncommon for the size of the secondary mirror to present as much as a 33% obstruction. The refractor of the same aperture of this telescope will collect a little more light, but not twice as much.
The deal with refractors is this though. Refractors suffer from something called chromatic aberration. This means it causes each color of light to focus to a slightly different point. You can think of it a bit like a prism. It makes things have color glares. Some refractors have special coatings and extra lenses that reduce this. They're called achromatic. Other refractors have extra lenses made out of special materials, such as fluorite, which eliminate chromatic aberration, and these are called apochromatic refractors.
Lenses are expensive to make and the larger they are, the more difficult it is to make them flawless. Since apochromatic refractors have a lot of lenses, they're very very expensive.
If you can afford a 4" apochromatic refractor, it will deffinately outperform a 4" reflector, but for a primary telescope under $1000, you'd be better off buying a reflector than a refractor.
Here's a website that talks about this in a little more depth:
http://legault.club.fr/obstruction.html
He has a comparison table.
2007-06-04 17:52:08 · answer #1 · answered by minuteblue 6 · 0⤊ 0⤋
Given equal optical quality, a 120mm reflector will be much better than a 60mm refractor in every way: both light gathering power and resolution.
True, the secondary mirror in Newtonians and Cassegrains introduces diffraction and lowers contrast, but the result is roughly equivalent to a telescope whose aperture is equal to the diameter of the primary mirror minus the diameter of the secondary mirror. Note that its the diameter that's significant, not the area.
2007-06-04 02:50:58 · answer #2 · answered by GeoffG 7 · 1⤊ 0⤋
If you have a reflector and refractor of the same diameter, the refractor would be preferred because the relfector's central obstruction causes a slight increase in diffraction (and decrease in image quality).
But when you're talking about a 2-to-1 ratio in aperture, the bigger telescope will most definitely be better.
2007-06-04 03:53:22 · answer #3 · answered by Keith P 7 · 0⤊ 0⤋
No. Depending on the quality of the mirror and lenses, of course. The 120mm mirror will capture more light and has the potential for greater magnification.
2007-06-04 02:25:33 · answer #4 · answered by Anonymous · 2⤊ 0⤋
No, in fact it may be just the opposite.
Reflectors can take in much more light mm for mm than refractors can, and depending on the quality of the unit can have better resolution.
2007-06-04 02:40:08 · answer #5 · answered by Lorenzo Steed 7 · 0⤊ 3⤋
no no !!!!
the telescopes light gathering power is determined only by the aperture , u may feel its the same ( maybe the rates making u feel so)
but no they are not the same .
2007-06-04 04:14:20 · answer #6 · answered by Anonymous · 0⤊ 0⤋
i don't think so.
2007-06-04 00:54:22 · answer #7 · answered by neutron 2 · 0⤊ 0⤋