Everything About Telescopes

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Tristan, May 10, 2003.

  1. howeman Registered Member

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    Hey, I am also looking for a scope. I got a bush of B-=Day money $_$ so I have about 250-300 to spend. I am a beginner,; but I don't want a crappy scope (obviously) I want to be able to see everything, not just planets/deep space etc. On the other board, I had the Spaceprobe 130 reccomended, but I would love to hear other thoughts/recommendations.

    Also, what are the benefits/downfalls of a shortscope versus a longscope?
     
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  3. howeman Registered Member

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    20
    oh, and what are opinions about dobsonian telescopes. For example, the Sky Quest XT4.5 versus the spaceprobe 130 or the Short Tube 4.5 EQ
     
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  5. howeman Registered Member

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    okay, and i know I'm thick in this area, but could someone please explain to me the benefits/ downfalls of fast, slow, and medium focal ratios?

    for example the SpaceProbe™ 130 EQ Reflector and the SpaceProbe™ 130ST EQ are virtually the same scope, except one has f/6.9 and the other f/5.0, how would I choose between the two?
     
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  7. cjmowery Registered Senior Member

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    Telescope F/ratios

    A telescope's F/number is the ratio of its aperature to its focal length. The focal length is the length (usually in mm) from the lens or mirror to the point where all the light is focused to a single point. For example, an 80mm refractor with a 1200mm focal length with have an f-ratio of F/15. (1200/80=15). A relatively FAST scope will be around F/8 or lower. The benefits of a fast scope is you have a wider field of view. This is great for viewing constellations or deep sky objects such as Nebula or faint galaxies. The draw backs of a fast refractor is (unless you spend lots of $$$$ for an apochromatic) is the inherent chromatic aberations. Bright objects such as the moon or planets will have this purple hue or halo around them. It is caused by trying to refract light at a high angle, and each color we see in the spectrum bends (or refracts) at a slightly different angle. What you end up seeing is the violet part of the spectrum slightly out of focus with the rest of the light. Reflectors on the other hand do not have this problem and are better suited for the wide angle stuff. They too can suffer from other types of abberations, such as spherical abberation where the mirror doesnt quite focus all the light right an exact point. Mirrors in reflectors are actually the shape of a parabola. Now for slow scopes, (F/10 or higher), your field of view is generally much narrower but is much better at splitting double stars, viewing the moon and planets. And the abberations in fast scopes are not as much as a problem. So to sum it up, if your after seeing the Ring Nebula, faint galaxies or viewing open star clusters, you can't beat a larger aperature fast reflector scope. If you want to look at the planets, study the moon and have fun splitting close double stars, you probably want to lean towards a slow refractor or newtonian reflector. Also, one last tidbit of info. Generally with a slow scope, you can obtain higher magifications than with a fast scope. Hope I helped, If you have any specific questions, give me a hollar.

    Cheers and Clear Skys!

    PS here is a good informative site on telescope optics
    http://lyra.colorado.edu/sbo/astroinfo/scopes/scopes.html
     
    Last edited: Aug 4, 2003
  8. Bachus Registered Senior Member

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    1,271
    I also have a question:

    Is there any way to get a prisma on a scope? And for a 70mm refractor will i actually see different collers?
     
  9. howeman Registered Member

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    thank you CJ, that helped alot! And so if I want to view everything, you would recommend a focal ration of around 6 or 8, so its not to far on either side?
     
  10. cjmowery Registered Senior Member

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    First Scope

    In my own humble opinion, if somebody is buying a first scope, they tend to want to look at easier things. Such as planets and the moon, the sun (WITH A FILTER!!) maybe look at some of the brighter deep sky objects. I would say look for a decent refractor like this one:

    http://www.telescope.com/shopping/p...PRODUCT&iMainCat=4&iSubCat=13&iProductID=5154

    Or these nice Mak-Cass scopes (actually made by Synta)

    http://www.telescope.com/shopping/p...=PRODUCT&iMainCat=4&iSubCat=10&iProductID=368

    Meade and Celestron also make some decent affordable first scopes, but tend to be a bit pricer (you get what you pay for though)

    To give you an idea of the prices on higher end scopes, here is a Televue Apochromatic. These scopes do not suffer from the Chromatic Abberation that I spoke about in my earlier post because they use multiple front lens (two, three even four) to focus all the spectrum of light better. And this is just the OTA (Optical Tube Assembly), you still need a tripod. Talk about an EXPENSIVE hobby! Wait until you start wanting to get into CCD astrophography.

    http://www.telescopehome.com/televuetelescopes-102mm.html

    Cheers
     
    Last edited: Jun 26, 2003
  11. howeman Registered Member

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    20
    Just asking, but why would you reccomend a refractor versus a reflector? And is there anything you would say against the SpaceProbe™ 130 EQ?
     
  12. Xevious Truth Beyond Logic Registered Senior Member

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    964
    Bachus, I found you a spectroscope for your telescope. It is produced by a small company called "Rainbow Optics" and is available at least here in the United States, from a company called: ADIRONDACK VIDEO ASTRONOMY.

    Here is a link to the product desciption:
    http://www.astrovid.com/STARSPEC.HTM
    Here is a link to the company's website:
    http://www.astrovid.com/default.htm

    I personally don't have the money to buy one, but I found your question to be interesting so I went to see at least if anyone made one. I don't know how well it performs, honestly. It is here in the US, but if you need help obtaining it somehow, you are welcome to get a hold of me.
     
    Last edited: Jun 27, 2003
  13. cjmowery Registered Senior Member

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    Refractor vs Reflector

    For a beginner, I dont think it really matters much what you start out with (refractor or reflector). Alot of people say, buy the most aperature you can afford. As that may seem like a good idea, I dont think that should apply for a person just getting into using telescopes. From experience, the amount of times you use your scope will be inversely proportional to its size. Lugging around a 10" 40 pound Newtonian Reflector every other day gets old real fast. My first optics for viewing the sky was a pair of 8x50 Binculars. I thought they were the greatest thing, just grab and go. It would take you years to see everything in the sky with just those. I dont have any experience with the optics in a SpaceProbe 130EQ, but for the price of $179 you really can't go wrong, seems like a good deal to me. You will be able to look at alot of sky objects with that.

    Clear skys!
     
  14. shoelessjoe20 Registered Member

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    review: fact or fraud

    I just purchased the spaceprobe 130 EQ reflector, and i read a review on it, and a guy said that the andromeda gallaxy filled up the whole eyepiece, now is he lying, or telling the truth

    When i had an old bushnell refractor 700mm focal length and it only sucked up 4.4 sq in of light, andromeda appeared only small in size, and i could barely tell it was a galaxy.

    Will my new scope make much of a diff
     
  15. cjmowery Registered Senior Member

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    Re: review: fact or fraud


    Andromeda Galaxy (M31) is actually quite a large object to view, its size is approximately 178x63 (arc min). Believe it or not, thats much larger than a full moon. The moon (and the sun) is about 30 arc minutes, that makes the Andromeda galaxy (length wise) 6 times the size of a full moon! The only problem is, is that it is also quite diffuse. Its quite hard NOT to fill your eyepiece completely with it, you really need a wide angle (short focal length) or a very large wide angle eyepiece (expensive!). I have a pair of 15x70 Bincoulars, and Andromeda fills the enter view. Andromeda can actually be seen with the naked eye as a fuzzy patch in the sky if your at a dark location. With most telescopes, you will only see the center bright area of the galaxy which makes it appear smaller than it really is. All those fancy photos you see of the Andromeda Galaxy are time exposed photos at a very low magnifications, probably no more than 10 times. To answer your question directly, YES, you will definately fill up your eyepiece with the lowest magnifcation. BUT, you will just be seeing part of the brighter nucleous of Andromeda, which is what most of us will only be able to see anyways. The wispy arms are all but invisible without a camera or a HUGE aperature telescope.

    http://www.seds.org/messier/Jpg/m31.jpg

    Cheers!
     
  16. howeman Registered Member

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    shoelessjoe how do you like it? I am seriously considering buying it, do you recommend it?
     
  17. shoelessjoe20 Registered Member

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    Yes

    Howeman

    I do recommend the sp 130 from Orion, but be sure to order it online for only 179, its 229 if you order it by direct mail... but yeah its well worth the money, but get the astrotrack to go with it, or some other drive engine, so that objects dont drift out of view
     
  18. Xevious Truth Beyond Logic Registered Senior Member

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    Their is another possibility to get a wider field of view - get a lower powered eyepiece. The 25mm Kellner that Spaceprobe came with might mangnify too much. Look for a 30mm - 35mm Plossl eyepiece somewhere.

    It is also possible the city is drowning it out. When I look at the Orion Nebula on my Spaceprobe here in the city, all I see is a fuzz patch in the middle of Orion's dagger which is only a few degrees wide. This is because I can only see the brightest center of the Nebula. The rest is drowned out in Light Pollution. When I took my Spaceprobe out to a friends place outside of town, the Nebula filled most of my field of view. When I took it out to West Texas, I could not fit the whole nebula in my eyepiece! This is all with the 25mm Explorer II.
     
  19. shoelessjoe20 Registered Member

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    you say that a 25mm will likely fill up my entire eyepiece.
    Well what would happen if i used a 5mm eyepiece. would i be able to see aliens picking their noses, or would it be a giant fuzz ball?
     
  20. Xevious Truth Beyond Logic Registered Senior Member

    Messages:
    964
    A 5mm would increase the magnification of the telescope, yes. If you were looking at Andromeda through a 5mm eyepiece, you would only see a small part of the Andromeda Galaxy.
     
  21. shoelessjoe20 Registered Member

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    but would it still be possible that i will have a clear image, at whatever point i would be looking at? with the 5mm
     
  22. cjmowery Registered Senior Member

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    When you magnify an image, you are spreading the same amount of light over a larger part of your eye. This causes the image to be dimmer and have less detail, but IT IS larger. The best way to look at deep sky objects is with low magnifications, especially if your scope is smaller than say 8 inches. They will appear brighter and more detailed. Now planets and the moon are an entire differenct ball game, they are so bright you can magnify them many hunderd of times without much detail or light degradation. If your Spaceprobe comes with a 25mm Kellner, Andromeda will completely fill your field of view plus some. If you can get a nice Plossel eyepiece (maybe a 32mm), they have a wider field of view than a Kellner at the same focal length. I think Kellner's are 40º and Plossels are 50º. Somebody correct me if I am wrong. Also, if you people are stuck in a city with bright lights like myself, they make a special filter that blocks the the wavelengths produced by common city street lights. I know Orion, Meade and Lumicon sell them. They really help the contrast of deep sky objects stand out against the city light washed out night sky.

    Ok, one last thing, if you know how large an object is in the sky, For example, the Moon is 30 arc minutes arossed. You can easily figure out how big it will "appear" in your eyepiece. To do this, first you need to find out the APPARENT FOV of the eyepiece you are going to use. A Plossel eyepiece has a FOV of 50º, other types of eyepieces will have less or more, check the manufacturer for this information. Next, you need to calculare the magnification that eyepiece will have with your scope. Divide the focal length of your scope with the focal length of the eyepiece. For example, a 1000mm Scope and a 10mm eyepiece will yield a 100x magnification of the image. With a 10mm Plossel, your field of view looking through a telescope of 1000mm focal length, will be (APPARENT FOV/MAGNIFICATION=TRUE FOV). Therefore, 50º/100 = 30 arc minutes. Tada! Which is exactly the same diameter as a full moon.

    http://www.telescope.com/shopping/p...=PRODUCT&iMainCat=6&iSubCat=22&iProductID=103

    Cheers.
     
    Last edited: Jul 8, 2003
  23. cjmowery Registered Senior Member

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    What will I see?

    I found this website, thought you guys on here might like it.

    If you ever were wondering what exactly something will look like in your certain scope with a certain eyepiece, check this Telescope Simulator out, kind of neat.

    http://www.stic.net/mattwier/

    Cheers!
     

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