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Aperture comparison

andynpage

By andynpage
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nmoushon

nmoushon

Posted
Posted

In terms of pure light gathering then there is only one thing to consider and that is the central obstruction that is in reflectors. (This holds the secondary) Refractors though have color abberation where reflectors do not. This is more prelevant in cheaper optics and in Achromatic lenses. You can get Apochromatic refractors that deal with it to varient degrees and pretty much eleminate is all together. They are more expensive than Achros though and some of the higher quality Achros deal with CA quite well.

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ronin

ronin

Posted
Posted

Just consider it a 1:1 match.

There are so many factors to take into account that really it is not worth it.

If they are both 100mm across then both collect 100mm worth.

It generally ends up in a difference of opinion and really is not worth the trouble.

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Paul73

Paul73

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Posted

Hi and welcome to the lounge, light gathering depends on aperture and the more aperture the better, then it comes down to the size of your wallet.

Yes. Your wallet. And, your ability to move the beast to garden/observing spot. The bigger the apature, the heavier and more cumbersome they become!

Paul

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glowjet

glowjet

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Hi Andy and welcome to SGL. Light gathering is related to the size of aperture, as already pointed out, but where there will be a difference, with a quality APO refractor, is in the resolution of the subject under observation :)

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Alien 13

Alien 13

Posted
Posted

Hi and welcome to the lounge i have asked myself the same question many times, in the old days of either silver or aluminised coatings it was often said that a 3-4" frac would have the same light gathering as a 6" newt but with modern coatings i have no idea or how much the reflectivity drops off with age or dust for that matter.

Alan

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John

John

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Hi and welcome to the lounge i have asked myself the same question many times, in the old days of either silver or aluminised coatings it was often said that a 3-4" frac would have the same light gathering as a 6" newt but with modern coatings i have no idea or how much the reflectivity drops off with age or dust for that matter.

Alan

Thats a fair point. The coatings on mirrors will loose a small degree of reflectivity each year whereas a refractor will maintain it's light grasp at the original level provided the lenses don't pick up any fungus or blooming and their coatings remain in good condition. Of course many people use a mirror diagonal with their refractor so I guess that will get less effective over time as well.

I have seen approximate figures on the annual loss of mirror reflectivity but I can't recall what they were. 

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Vanilla

Vanilla

Posted
Posted

Speaking for myself>>>If portability is an issue, and it can be,  if you want something to take on vacation or to a minor outing, a small inexpensive Maksutov-Cassegrina if hard to beat. 

I have an Orion Mak-Ca that's 90mm, 1250 ff  and will just about fit in a shoe box. As far as light gathering power, it is superior to anything it's size....and for 200 dollars (US). I'm very happy with it. 

I'm not hawking Orion as there are other brands also.  :)

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Umbraldot

Umbraldot

Posted
Posted

'Twas always said a 3 inch refractor was equal to a 6 inch reflector. Probably not the case today with all the refinements of modern telescopes. It's more important to work out what you want to observe and then what type of telescope/aperture will suit your observing needs. Welcome to the forum.

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