4.5" newtonian reflector

[Jimmyboy]

I have just recently bought a 4.5 inch newtonian reflector telescope, and i feel alittle let down with it. I tried to look at venus at dusk in london with it and it still looks like a star. I am sure what i was looking at was venus as it was really bright and in the right part of the sky at the right time, you could even see mercury along side it. I have 20mm, 10mm and 6mm eyepieces and X2 barlow lense, surely venus should look bigger than a star??? My daughter loves saturn, have i got any chance of seeing the rings?? i know i wont see too much of the rings due to the time of the year. Light pollution wouldnt effect the size of the object you are viewing surely?? i would have thought it would just effect the detail???

Any help would be appreciated

 

[MeteorWayne]

Re: 4.5" newtonain reflector

Well, other than being fairly bright, Venus isn't much to look at right now. It's off to the side of the sun, about 88% illuminated (so looks like a ball) and is fairly small right now. By July it will be much better; larger, becoming crescent shaped, etc...IOW, something you can see in a telecope.

Another question is, have you collimated your scope since you got it? Without proper alignment of the optical elements, fuzzy stars look just like fuzzy planets.

Yes, definately take a look at Saturn. While the rings are thin right now, due to the alignment, they are visible, and the moon Titan is always easily seen nearby. Some of the other moons can be seen as well.

 

[Jimmyboy]

Re: 4.5" newtonain reflector

Thanks meteor. I havent done anything with the telescope, i just put the barlow lense then the eyepiece in, i thought it would be that easy!!! I dont know what collimating the telescope is?? will that make the images bigger??

 

[MeteorWayne]

Re: 4.5" newtonain reflector

No, collimating will make the images focus correctly. I'm sure some advice came with the telescope as to how to do it. There's also a link that I'll dig up later describing the why and how of the process. Every reflector needs to have it done periodically.

My first advice is to not use the barlow. Use the eyepieces without it, for 90% of the objects you might look at, it will provide a much better, brighter, and clearer view.

 

[Jimmyboy]

Re: 4.5" newtonain reflector

Well I was looking at the moon last month, and it looked focused, but the moon is quite near obviously. As I said in the previous post when i looked at venus it looked like a fussy star, just makes me think i got no hope of seeing saturn!!!

 

[MeteorWayne]

Re: 4.5" newtonain reflector

Saturn is currently almost twice the size of Venus, and the rings are twice that, so it's a much easier and more distnctive target.

 

[crazyeddie]

Re: 4.5" newtonain reflector

Thanks meteor. I havent done anything with the telescope, i just put the barlow lense then the eyepiece in, i thought it would be that easy!!! I dont know what collimating the telescope is?? will that make the images bigger??

Here's the best website I know of on how to collimate a newtonian:

http://www.andysshotglass.com/Collimating.html

You will need a collimation cap or a cheshire eyepiece to do a decent job of it, though.

One point that new telescope owners are usually not aware of is that you will use low and medium magnification much more than high magnification. A 4.5" telescope has a useful magnification range of 25x to 175x, tops. Since you didn't give any details about what specific telescope you purchased, only it's aperture, I can't estimate the magnifications you can get without knowing the focal length of your mirror. Assuming it is about 900mm (which is typical in scopes this size), your 25mm eyepiece will give you about 36x magnification....perfect for viewing the moon's face and low-power sweeping. The 10mm will give you 90x, good for Jupiter, Saturn, star clusters, close-ups of the moon, etc. Your 6mm will give you about 150x, which is the the practical maximum for a scope this size. You might be able to push it a little higher if you have perfect collimation and a night of steady seeing, but in any case, you have no real need of the barlow lens, since the eyepieces supplied will give you all the magnification you need. One question, though: do you need to wear glasses to correct for astigmatism? If so, you need eyepieces with good eye relief, and a barlow can be useful in such instances, since it preserves the eye relief of lower-power eyepieces while boosting their magnification potential.

 

[Jimmyboy]

The focal length is 500mm, so the 6mm with a barlow would give approx X166 mag. No i dont wear glasses so eye relief isnt a problem. So even if the scope isnt collimated properly I should still be able to see saturn as quite a large fuzzy ball with fuzzy rings??? The light pollution is a real problem though, it is hard to make out the constallations when half the stars are missing!!

brilliant link by the way!

 

[crazyeddie]

The focal length is 500mm, so the 6mm with a barlow would give approx X166 mag. No i dont wear glasses so eye relief isnt a problem. So even if the scope isnt collimated properly I should still be able to see saturn as quite a large fuzzy ball with fuzzy rings??? The light pollution is a real problem though, it is hard to make out the constallations when half the stars are missing!!

What is the specific make and model of your telescope? With a focal length of 500mm, that would make it's focal ratio F/4.5, or what we call a "fast" newtonian reflector. These scopes are better suited for low-power, wide-field viewing, and not so good for viewing planets, which need high magnification. Such scopes can be tricky to collimate. But once you get all the mirrors properly aligned, you should get reasonably sharp views, although things may start getting a bit fuzzy at 166x. This scope just wasn't designed for such magnifications.

 

[Jimmyboy]

It is a skywatcher skyhawk 4.5" F/500. So i have no hope of seeing the planets with any real detail then?? They have cheaper scopes with a bigger focal length too!

 

[crazyeddie]

It is a skywatcher skyhawk 4.5" F/500. So i have no hope of seeing the planets with any real detail then?? They have cheaper scopes with a bigger focal length too!

I think a better choice would be a dobsonian reflector, preferably a 6" F/8, like this:

http://www.telescope.com/control/telesc ... -telescope

or, if you need something slightly less expensive, a 4.5" F/8:

http://www.telescope.com/control/telesc ... -telescope

These types of telescopes are ideal for beginners and are well-suited for viewing the planets. They are also easier to collimate and very transportable. The 6" F/8 has a focal length of 1200mm, which makes it capable of high-power views without having to resort to the use of a barlow.

 

[Jimmyboy]

thanks crazy edd, ill see if the shop guy will part exchange or something, he knew what i was looking for and it was a professional shop (well ment to have been)!