Kiddy Astronomy -- which lenses?

Hello :)

Out of the following lenses:

   • 20mm -- 45x
   • 12.5mm -- 72x
   • 4mm -- 225x

And a 3x Barlow Lens.

(Telescope: DIA. = 76mm, F = 900mm)

Which combination would you recommend for the following:

   • Mars
   • Saturn

On a 'typical' night...

I've found that the following have been pretty good for the brighter stars of the night sky:

   3x Barlow + 20mm [45x] = 135x


I've yet to have a clear night where I can see anything other than sirius, and a few stars from orion however. :-(

But when I get the opportunity to gaze at the moon, mars, and saturn, I'd like to know which lenses I should try first... because obviously, I could be perfectly lined up on something, but not see it, because my mag is all wrong.

So, any guesses? Around about 135x?

(Also, while we're at it: any other star-gazing tips? Unfortunately, my telescope has an absolutely rubbish Alt-Azimuth Mount, so it's a little frustrating...)

Thanks! :D
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InteractiveMindAsked:
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grg99Commented:
LIke they say in auto racing, there's no substitute for cubic inches.

In astronomy , there's no substitute for square inches, as in the size of the main lens or mirror.

A few years ago I stumbled onto an awesome telescope at a thrift shop, with a 7 inch mirror.

You wouldnt beleive the number of stars that are out there when you have a 7-inch mirror to gather the light!

Many many many times more than you can see with your little .3-inch pupils!

As for magnification, that's not very important-- you're not going to see any more detail in the stars anyway.



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ozoCommented:
The moon spans half a degree.   135x would span 67 degrees, which your telescope probably won't let you see all at once.
If you can't see more than sirius and orion with naked eyes, you'll want to find a better viewing location.
If you don't have a finder scope, it's probably better to line up with lower magnification before switching to larger magnification.
45x = 900mm/20mm
InteractiveMindAuthor Commented:
>> A few years ago I stumbled onto an awesome telescope at a thrift shop, with a 7 inch mirror.
Wow, that is pretty damn incredible. *envy*

>> 135x would span 67 degrees
How do you calculate the fovy based on the mag?

>> If you can't see more than sirius and orion with naked eyes, you'll want to find a better viewing location
Yeah, it's terrible light polution round here--and with all the christmas lights being up, it doesn't particularly help :-(
It's also been quite cloudy lately (we've had some snow).. but when we get a clear night, my dad's going to drive me out of town :-) So I'm hoping to be prepared by then..

>> If you don't have a finder scope
Yeah, I've got a finderscope--mind you, I've yet to actually adjust it, such that it's parallel to the main body. :-\

On the subject of adjusting finderscopes (my documentation is pretty rubbish): Do I in fact just need to get them as parallel as I can? Or, does the finderscope need to be pointed downwards *ever so slightly* ?


>> As for magnification, that's not very important-- you're not going to see any more detail in the stars anyway
lol, that's true. But I'm more interested in the planets.. To the naked (and perhaps, untrained ;-)) eye, they appear like stars, correct?


Also, are the any 'standards' for Alt-Azimuth Mount's? Such that I could buy a new one, that would fit with my telescope? Because, whilst my telescope itself is reasonably good, the stand is absolutely terrible.. it wobbles about.. and also, doesn't have any knobs to allow me to turn it a tiny amount in a certain direction--instead, it's a case of placing my hand on the back of it, and very very gently shifting it..


Cheers
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aburrCommented:
"Yeah, I've got a finderscope--mind you, I've yet to actually adjust it, such that it's parallel to the main body. :-\

On the subject of adjusting finderscopes (my documentation is pretty rubbish): Do I in fact just need to get them as parallel as I can? Or, does the finderscope need to be pointed downwards *ever so slightly* ?
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You can adjust the finder scope in the daytime. Center a clear object as far away as posssible inthe telescope. Adjust the finder scope until that object is in the center of the finder scope view.

Planets are good objects to look at. Usually the smaller magnifications are best. Much depends on you optics. Look at the moon with all your combinations. Pick as your standard the one which gives the clearest view (most detail). That will work for planets and stars. For particular objects on the moon you might want a bit more magnification if it does not reduce the clarity much.

Venus is particularly interesting right now. I do not know where you are located so I cannot tell you when to look for it, but it is about the brightest "star" in the sky now. The real interesting part is that through your telescope you can see that it is not completely illuminated. In fact, only about 30% of what you can see is in the sunshine now. You can follow the phases in time if you want.
InteractiveMindAuthor Commented:
> Venus is particularly interesting right now. I do not know where you are located so I cannot tell you when to look for it,
> but it is about the brightest "star" in the sky now

I'm in Milton Keynes, England (a little north of London).

As it goes, I could see a bright star earlier (around about 5 PM GMT I think).. so, interested in what it was, I loaded up my sky map software--from which it appeared to be venus.. (Unfortunately, it was still quite bright outside, so I didn't bother setting up my telescope.)

It appeared in the West, for me..

:-)

Cheers for the tips on the finderscope, also.
David_FongCommented:
Have you considered moving to a country where it isn't cloudy all the time and where there isn't so much light pollution?
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