About Telescopes

[FrostyBoy]

I'm looking at getting one, but I want to know what the ACTUAL image looks like at their zoom levels.

And how do I know exactly how far it can see (clearly) by looking at its number of zooms.

For example, if its a 25x telescope, how far can I see and how clear will the image be? (if I maxed it out).


I need a telescope that can see about 1 mile, with crystal clarity.

Also, are there telescopes out there that I can plug into my computer and see the image relayed onto the monitor?

[alva]

Reds will be along soon to bore tell you all about them.

[Tattila the Hun]

Depends, whether your looking at stars, or dormroom windows.

[FrostyBoy]

um.. no.. more like sceneries.. such as from mountains.. etc...

[reds4ever]

Originally posted by alva
Reds will be along soon to bore tell you all about them.

Ahem!

A decent scope "maxes out" at around 50x per inch of aperture. So a 3 inch scope will give clear views upto around 150 maginification.

Most people who want to look at scenery etc go for an apochomatic refractor in the 66mm to 80mm f5-f7 range and then buy a decent zoom eyepiece. It's more flexible than getting a scope with fixed zooms.

A cheaper option is a 90mm Makutzov/Cassegrain telescope which are cheaper but will have a narrower field of view than the apo refractors.

Both are around the same size/weight is portability is important to you and they'll both "see" for a mile easily (depending on how small the objects you want to look at are) The refractors cost around $300 - $600, the Mak/Cass about $150-$200.

As for the monitor question, the easiest way to do it is to but a $20 adaptor and plug a webcam into the eyepiece socket, you can get some surpisingly good results like that.

I don't want to bore Alva, but how much do you know about focal lenght, focal ratio and their effect on the field of view and the magnification? You'll need to look into these in order to make an informed choice.

[alva]

I don't want to bore Alva,

Ohh, touchy, are we?

England won, remember?

[reds4ever]

Originally posted by alva

I don't want to bore Alva,

Ohh, touchy, are we?

England won, remember?

[Proteus_MST]

If you buy a telescope which is originally meant for astronomical observations, you should, of course, also think of buying an inverter lense to convert the inverted image from the astronomical telescope into an upright image.

[FrostyBoy]

Originally posted by reds4ever


Ahem!

A decent scope "maxes out" at around 50x per inch of aperture. So a 3 inch scope will give clear views upto around 150 maginification.

Most people who want to look at scenery etc go for an apochomatic refractor in the 66mm to 80mm f5-f7 range and then buy a decent zoom eyepiece. It's more flexible than getting a scope with fixed zooms.

A cheaper option is a 90mm Makutzov/Cassegrain telescope which are cheaper but will have a narrower field of view than the apo refractors.

Both are around the same size/weight is portability is important to you and they'll both "see" for a mile easily (depending on how small the objects you want to look at are) The refractors cost around $300 - $600, the Mak/Cass about $150-$200.

As for the monitor question, the easiest way to do it is to but a $20 adaptor and plug a webcam into the eyepiece socket, you can get some surpisingly good results like that.

I don't want to bore Alva, but how much do you know about focal lenght, focal ratio and their effect on the field of view and the magnification? You'll need to look into these in order to make an informed choice.

wow thanks for the info!

I know jack all about telescopes. I basically want to get one for general use. One that I can use for viewing into space and also for long distances (such as open scenery). I am returning to New Zealand this year and would like to carry it back home from Singapore, I figure it is cheaper to get one here than in New Zealand.

I'm going down soon to have a look at some.

[reds4ever]

Most scopes you see advertised will have two numbers, the aperture and the focal ratio multiplying the two gives the focal length which in turn gives the you magnification and the field of view the scope will give (more mag = less FOV obviously).

So a 80mm f6 scope has a focal length of 480mm, using a mid-range eyepiece (say, 25mm) this gives a magification of x19 (480/25) and a field of view of 2.6 degrees (50/19, don't ask!). As you can see, by altering the either the scopes focal length or the size of the eyepiece we can either have more magnification and less FOV or vice-versa.

If you want to look at scenery I'd guess you'd want a wide FOV, so it'd be better to buy a scope with a focal length of less than 600mm, it'll also make it easier to transport. Don't skimp on the tripod/mount, a lot of cheaper scopes do this to cut costs but theres nothing more frustrating (or pointless) than a wobbly telescope.

The bottom line (as always! ) is how much you want to pay, the apochromatics I mentioned are nice scopes but they are pretty expensive if you just want something to use once in a while. Cheaper versions are called achromatic refractors the compromise with these are that some of the light is not focussed at the same point as it passes through the lens, so bright objects sometimes have a slight purple or yellow fringe to them (the apochromatics have an extra lens system or different glass to correct for this) it's nothing too bad but it is there, some people find it more annoying than others. It's not as bad as I've probably made it sound, but some people are a fussy over their optics and don't mind spending a lot of money to get small improvements.

I'd recommend something like a 66-80mm scope in the f 5-7 range, or maybe even a 100mm f5 (esp. for the astro side of things). The trade off is resolution (how small an object you'll be able to effectively magnify, the bigger the aperture the better) against portability, if you want to use it for looking at the night sky then 80mm is the minimum TBH. The physical size/weight of a scope increases very quickly as you increase the aperture and the f#, a 100mm f5 is about a foot long and can be easily carried in one hand, a 120mm f8 is a bit of a beast!

Some brands to search for are:

Expensive:
Williams Optics
Televue
Takahashi

Other:
Skywatcher
Orion
Synta
Celestron
Meade

I've tried to be as general as possible, and the maths side holds for any telescope, but the above will have an astronomy bias (esp. the 100mm f5 recommendation) and there may be other options as regard brands or dedicated terrestrial spotting scopes that I havn't mentioned. Your best bet might be to find an astronomy/ birdwatching forum based in Singapore (or NZ) and ask whats availiable and where, they'll need to know how much money you want to spend, what targets you intend looking at and how portable it needs to be.

Any other questions, just ask


(and you alva)

[Provost Harrison]

Would you like me to tell you about my 8 inch refractor?

[Fake Boris]

8 inches with magnification?

[SpencerH]

Red, are you an amateur or professional astronomer?

[reds4ever]

Originally posted by SpencerH
Red, are you an amateur or professional astronomer?

Unfortuneatly I do it for nothing.

[SpencerH]

IIRC some big time discoveries have been made by amateurs. Maybe you'll be the first to see the asteroid/comet on a path to destroy the earth.