| CliveKoopa wrote:|
I am moving house in a couple of months and I have decided to start using my telescope. My specification is:
Objective Diameter: 600mm (2.36")
Focal Length: 700mm
Eyepieces: 12.5mm, 4mm
Erecting Eyepiece: 1.5X
Maximum Magnification: 525X
Accessories: Diaganal, 5X24mm Finderscope
I would like to know what does the Barlow and Erecting eyepieces do?
What will I be able to see with this specification?
What does the finderscope do?
I am sure you meant 60mm objective diameter (aperture) rather than 600mm. that would be nice however.
And I can assure you that you will not achieve 525x magnification with that telescope.
50x to 60x per inch of aperture. Or 2x per millimeter. Generally magnification is also restricted to about 300x to 350x magnification maximum even in much larger telescopes by the Earths atmosphere. However, larger aperture is still better even at equal magnifications. More aperture equals higher resolving power.
Divide the focal length of the telescope by the focal length of the eyepiece to calculate the magnification you will be using
for example this telescope has a 700mm focal length and has a 12.5mm EP and a 4mm EP
700 / 12.5 = 56x magnification
700 / 4 = 175x magnification. (exceeding the limits of the telescopes aperture)
Include the 3xBarlow into those equations then with the 12.5mm EP you would have 168x magnification (again exceeding the limits of the aperture.) With the 4mm EP and 3xBarlow you would get 525x magnification, which is by far exceeding the limitation of a 60mm telescope. You wouldn't see anything but a black or at best a dark faint blur. Just because the combination of eyepieces, Barlow and telescopes focal length equal to a certain number doesn't mean you can use it.
If that is what they are telling you then it is time to look elsewhere to shop for your telescope. Did you read my long post on getting started into amateur astronomy? I seriously recommend you review that before you continue any further. Scroll down to the part about magnification. Please read through it. That will give you a greater understanding of what to look for. http://www.astronomy.com/ASY/CS/forums/291288/ShowPost.aspx
What does a barlow do?
A barlow lens multiplies the focal length of the telescope effectively multiplying the magnification with whatever eyepiece you are using it with. If it is a 3xBarlow then it will multiply the magnification by 3. If you are using a eyepiece the will yeild 100x magnification with your telescope, then when you include a 3xbarlow you would double the effective magnification to 300x. Far beyond the capabilities of that telescope
An errecting eyepiece corrects the orientation of the image so it appears in the eyepiece as it would if you were to look at it with the naked eye. Generally used for terrestrial observing such as birdwatching.
When you look through a telescope otherwise, the object will be be oriented quite differently than you are used to. For example without getting too deep into the details of how optics work, a Reflector will project the image sort of inverted and reversed. A refractor will project the image inverted and reversed if you were to use the eyepiece straight through. If you were to use the eyepiece with a star diagonal it would only appear reversed. However, you can also get a correct image star diagonal. IMHO those work better than errecting image eyepieces. Especially those included with entry level telescopes.
What does the finderscope do?
It is essentially a small version of a refractor telescope in most circumstances. It is used to aim the telescope in the general area of the object you are looking for. You have to first align it to the telescope so they will be looking at the same thing.
Some objects are bright enough to be seen in the finderscope. However, many times you will only be able to use it to aim on a star or formation of stars (Astrism) to get you in close proximity of the object you are hunting.
What can you expect to see?
To be totaly honest, I get the feeling it won't be as much as you would like. Unless you are in pristine clear very dark skies not much other than the moon. You will be able to identify and locate the larger planets and some other deep sky objects. But the amount of detail will be very little and very plain. The planets will be very small and pretty much featureless. You should still be able to see and distinguish the rings around Saturn and some of the darker banding around Jupiter. You will be able to see some of the brighter and or large deep sky objects. The Orion Nebula, The Andromeda Galaxy and a few other smaller but brighter galaxies, open clusters and a few of the more dense globular clusters. However, they will leave a lot up to your imagination than you will actually be able to view. You will be limited to a maximum useful magnification of only around 120x. The planets such as Saturn and Jupiter don't really start resolving much detail until you reach 200x and higher.
Have A Nice __________