Discussion in 'Astronomy, Exobiology, & Cosmology' started by Tristan, Dec 7, 2001.
What do you think?
Log in or Sign up to hide all adverts.
I'm kind of wondering how you mean?
I guess you mean some form of telescopic lense for either of these methods, Reflection or refraction.
Of course just looking at what each entails gives you an idea (I can only put that forwards because I'm not sure if this is even the correct type of response.)
Reflection is light being rebound with the exact same degree as it hit and object. (This is depended on taking an angle of the lights path with a perpendicular point and then mirroring this angle to work out the lights trajectory.) Reflection is also dependant on the composite of the surface in it's shineyness and what spectrum it reflects.
Refraction usually occurs in clear (or near clear) liquids and prisms (crystals etc) light is reflected but only partially and depending on the substances depends again on how the spectrum is reflected throughout the object or liquid. Of course in liquids the reflected light from an object will make the object seem distorted.
(refraction relies upon reflection)
Reflectors are good for seeing deep space objects as they are usually of a larger aperture(aperture = width of the primary mirror in reflectors or the primary lens of a refractor).
The larger aperture gathers more light, but is directly related to cost, so the bigger the aperture the more money needed.
If I were buying a scope, and being realistic as to what I could afford, it would be a 150-200mm (6-8") reflector, with a German Equatorial mount. This would set me back about $1500 Australian ($750US).
Don't buy a cheap telescope, you will only be frustrated and the joy of observing will be lost.
I prefer a refractor for my own:
First of all because I live in a town with quite a lot light-pollution, deep-sky is not an option for me, so a reflector won't give me good sights.
Though refractor objects like planets are visible too with much light-pollution.
So, what's your interest? What's your location? What can you afford?
refractor vs. reflector
well i live in suburbs. So i dont have access to really dark skys but i can get darker by driving a little farther away. I put my self on a list for the new meade reflector 10". Its a Schmidth-Newtonian.
Its 879.00 US. But with shipping and tax, just a hint over $1000.00.
You may think the Schmidth newtonian is not possible, that it is one or the other well check out this:
I will definetlay save up for some good astrophotography modifications and for a few summer trips to Montana. Thats where the REALLY dark sky sites are. Anyway thanks
Refractor's are better suited to observing the sun, moon and planets -- bright objects with detail.
Refractors are typically of greater focal ratio -- ratio of the diameter of the imaging lens/mirror to the focal length -- than reflectors and require less magnification to produce an image scale where details can become obvious (iow, refractors at low magnification can see things that reflectors can see only with greater magnification).
On the other hand, reflectors typically gather much more light than refractors and can see many more things -- dim things far outnumber visually bright things -- than refractors can see.
In years passed, I used, among others, a 36" reflector with a 6" refractor as a guide scope. The view of Saturn, for instance, through the guide scope was better than through the 36", although not nearly as bright.
To me, globular clusters were a visual toss up -- resolution versus visible numbers -- and, of course, galaxies where way cooler in the 36.
In urban settings, refractors afford better contrast because the light-polluted night sky looks blacker than when seen through a reflector (through which the background sky looks bright gray).
Large diameter refractors are also better than reflectors for visual binary/multiple star work, as well as for asteroid occultation work.
If you need resolution go refractor. If you need image intensity go reflector. Schmidt-Cassegrains are a reflector-refractor hybrid compromise.
I haven't actually read anything about Schmidt-Newtonians but I presume thay are smaller focal-ratio instruments, thus wider angular field of view instruments that the 'cats.
Hey, I am tryin gto buy a telescope
I know that refractors have better clarity over reflectors. But, how big is the difference? Is the clarity only really needed for pictures, or if I got a reflector would I be constatly reminded of the low clarity?
All large telescopes are Reflectors (I have a 8in Dobsonian) its the only viable solution for larger scopes, reflectors just get to long as the diameter increases.
I'm not looking for a big telescope. I'm going to need to move it around. I was just wondering how much image quality was lost on reflectors. If you only really need a refractor for astrophotography that is one thing, but if you can't tell saturn is saturn from a refletor than that is another
I don't notice any image loss at all! Of course my First telescope was a 60mm refractor. What kind of price range are you looking for howeman? What do you want to do with it, find a comet, take photos, just look at stars and planets? Are you looking for something you can upgrade as you go along?
For about $200 I would advice this:
Damn, $1000 is not much for that one here it costs $ 2200 Please Register or Log in to view the hidden image!
Please Register or Log in to view the hidden image!
In the whole Refactor vs. Reflector argument, one must first ask the question: What are you going to do with it? What are you shooting for, Tristan?
This will be my first telescope. I am not planning on photograpy, I am probably aiming more at casual use. I'm not wuite sure of my price range, it depends on my birthday money. So not alot (alot not defined in telescope terms probably 500 max) but I don't want a piece of junk either. I am looking for a nice telescope that will give me good views.
So you say that you didn't notice a loss in image quality, and for my casual use you would recommend a reflector for more numberous (a.ka. deep sky) viewing capabilities
I would guess that an upgradeable one would be good, so I can start cheap(er) and build up to a better scope, but whatever
oh, and could someone explain to me what a faster and/or longer focal length does? I know faster ones are better for photography, but what else?
Its changes the length of the scope and also the width of vision (how wide you eye piece can see)
I would recommend the above one because you can upgrade it, you can start casual and then buy attachments like motors and a camera adapter, so forth, This thing will last you forever! You could have your kids use it! No matter what I recommend an equatorial mount.
My strongest recommendation for general use Astronomy is a Reflecting telescope between 4" and 6" in aperture. It's big enough to give you nice views of the brighter deep sky objects, and beautiful for close-up lunar and planetary studies. Refractors in my opinion, are more specialized and it sounds like you wants something very general.
Wellcooked's suggestion is a winner, though Orion has a 5.1 inch telescope for a little more. It might be worth the price difference to you.
wellcooked could you expand on your def? I'm still confused
- the length of the telescope is a function of the focal length.
- How many degrees you can see of the sky per eyepiece is also a function of the focal length. Like wide or short field cameras
These are a reprint of my notes on the subject when I used to tutor Astronomy. I hope they help!
Magnification and Focal Ratios
Everything in Astronomy is based on ratios... that is, a proportion between two things. The focal length of a telescope determines how much magnification it gives a certain eyepiece, and thus, how wide the field of view is on the telescope. In other words, the more magnification you have, the narrower the field of view. The less your magnification is, the more of the sky you can see in your field of view.
The mathmatical formula for magnificaiton is as follows:
Focal Length (divided by) the eyepiece mm = the magnification of the image.
Example - "Slow Ratios"
My 3" Spaceprobe telescope has a focal length of 700mm. If I was to use my 25mm Kellner eyepiece with it, I would get a magnification of 28x. At 28x, I could see the entire moon in my eyepiece. Let's say I now replaced my 25mm Kellner with my 10mm Kellner. With this eyepiece, the magnification is now 70x. At 70x, I can see much of the moon in my eyepiece, but I cannot see all of it at one time. Craters and ejecta from the craters are now really visible. But, I am now looking at a smaller area of the sky as I was before. Thus, I am looking through a narrower field of view than I was when I was looking through the 25mm Kellner.
Example - "Fast Ratios"
My friend Jenny's 70mm Refractor she build has a focal ratio of only 300mm. If I was to use my 25mm Kellner on her telescope, the magnifcation would be 12x - which is less than HALF the amount of magnification I would get on my own telescope! The moon would be only half the size in her telescope's field of view as it would be in mine if it was useing the same eyepiece! Similarly, if I was plug in my 10mm Kellner, the mangification would be 30x - almost what it was in my telescope with the 25mm eyepiece! Thus, the 70mm Refractor with a short 300mm focal length gives a far wider field of view compared to my reflector when useing the same eyepieces.
Separate names with a comma.