Everything About Telescopes

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

  1. Tristan Leave your World Behind Valued Senior Member

    Messages:
    1,358
    My mind hasn't "clicked" yet as far as AFOV and FOV. What is the difference?



    Later,
    T

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  3. cjmowery Registered Senior Member

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    Apparent FOV vs True FOV

    That is a good question, I'm glad you asked that. It's kind of an abstract idea but I'll do my best to clarify.

    The apparent field of view, is what your eye perceives when looking through an eyepiece regardless of magnification. Lets say you have a Plossel eyepiece in your telescope, it has an apparant FOV of 50º by design, thats just how the lenses are engineered. When you look through it, to see everything in the FOV, you have to look 25º to the left, 25º to the right, up and down, etc. Its a 50º circle FOV that you are looking at. They make some special eyepieces that are called wide-angle, some go as large as 85º. When you look through one of them, its like you are sitting in space, it really is an amazing view. Now that you understand apparent field of view, lets talk about the true field of view. True field of view is the actual size of the sky you are seeing in the eyepiece, it still APPEARS 50º in size, but the image you are looking at is magnified. If I have a 50º eyepiece, and the part of the sky I can see at say, 10x magnification, will be 5º of the sky spread acrossed a 50º viewable area in the eyepiece. True FOV is simply a function of magnification and Apparent FOV of the eyepiece. I hope this helps.

    Clear Skies
    CJ
     
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  5. mjf Registered Member

    Messages:
    3
    Thanks Bachus!


    We live in a still unpolluted (beautiful clear dark sky) area in northern Wisconsin, and I purchased what will be our first telescope before I found this site. It's not out of the box yet, so I'm looking for info. It is a reflector (I think this is better than refractor since the skies are clear and bright??), Meade ETX90 with starfinder and tripod--$500. We have not used telescopes before, so we are amateurs but we want a good (not cheap, not the best) piece that will last and keep us interested. Any thoughts beyond all other good stuff in this thread? Thank you.
     
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  7. cjmowery Registered Senior Member

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    37
    Wisconsin

    I'm from Wisconsin too, unfortunately I'm near Milwaukee... BAAAAAD light pollution. Have to drive pretty far to get some decent skies. Good luck with your new scope, hope you enjoy it!

    Clear skies!
     
  8. Xevious Truth Beyond Logic Registered Senior Member

    Messages:
    964
  9. TXShay85 Guest

    what brand of telescope do you'all guy prefer. I'm looking into buying one soon. I wanna see deep space objects and dunno where to start at. please, i need some feedback

    thanks
     
  10. shoelessjoe20 Registered Member

    Messages:
    18
    answer to your request

    I see many people recommending the spaceprobe 3, which had a 700mm focal length and a 76mm primary mirror diameter which sucks up roughly 7 sq inches of light. Now thats a decent telescope for lets say my 12 year old brother with a decent price of $129

    But the best buy i see and the one i would have to recommend AGAIN! Is the SpaceProbe 130 EQ Reflector. This baby has a nice little 900mm focal length. A primary mirror of 130mm which intakes about 20.6 sq. inches of light. Now normally this scope is about $230. But if you buy this scope online it only costs $179 at www.telescopes.com i think. ne ways orion makes it. thats what i would recommend
     
  11. Xevious Truth Beyond Logic Registered Senior Member

    Messages:
    964
    The Spaceprobe 130 is far better suited for a beginner who is very enthused about learning about Astronomy. If one is merely curious, the Spaceprobe 3" is a better option. You don't want to spend around $200 on a telescope you might rarely use.

    Yes, the Spaceprobe 3" doesn't have the light grasp that a 130 has, but that is no reason to knock it. It has just as wave accurate a mirror and thus the same overall image quality as the 130. Sure it's not as suited to the deep sky, but just about all the deep sky objects a beginner would look up are well in the grasp of the Spaceprobe 3". It can track down most of the Messier catalog for example.
     
  12. shoelessjoe20 Registered Member

    Messages:
    18
    You are right Xevious the SpaceProbe 3 is good for someone quite new and who really just wants a look at the stars and not go bankrupt but i like the 130 especially now mainly because its on sale for $179
     
  13. Nova1021 Registered Senior Member

    Messages:
    168
    I'm looking at getting the SpaceProbe™ 130 EQ Reflector from Orion, but I don't want to jump the gun. Does anyone have any experience with this scope? I noticed many people reccomending Orion, are they a well repected company? Will I be getting a quality scope? I ask because the price seems almost too low. Not that I'm arguing, but I don't want to end up with bad optics.

    Thanks!
     
  14. Tristan Leave your World Behind Valued Senior Member

    Messages:
    1,358
    Orion is not a bad company at all. The price is low because the cost is low. Since these are big companies, they can pump thousands of these things out. Not to mention, that prices go up exponentially because of the mirror. See a 4" mirror is about 20 times easier to grind, polish, and aluminize than a 8" mirror. and then 8" mirror is about 20 easier to grind, polish and aluminize than a 12" mirror, etc.

    Im not saying its crap, but you seriously need to evaluate two things: Location, and what you want to see. Im severly hampered with a 10" because I live in the burbs. I can see alot, but could see 10x more somewhere else. A 4" in dark sites performs about as well as my 10" does in and around the city. So if your in the city and not a burb that has low light pollution, you are not going to see much at all.

    Just my quarter worth. And remember, eyepieces are about just as important as the mirror. Crappy EP's and a great mirror won't neccarily give you great results... and vice versa.

    Later
    T

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  15. Xevious Truth Beyond Logic Registered Senior Member

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    964
    Tristan has a good point here - aperture isn't going to do as much for you in high amounts of light pollution, so the "aperture is king" rule might not nessassarily be a constant truth. The best urban telescopes are actually anything smaller than a 6" - not that the extra ligtht grasp won't give you some help with some things, but the light pollution will drown out most of the deep sky objects anyhow.

    Urban Astronomers like me know that the dimmer deep sky objects are a waste, so I focus on bright clusters, planets, the moon, and the sun. For this, you don't need much.
     
  16. cjmowery Registered Senior Member

    Messages:
    37
    scopes

    In my opinion, the old saying buy the biggest aperature you can afford is the worst thing a person new to telescopes can do. Do yourself a favor and buy something small you can set up easily, simple to operate and easy to transport. Sometimes, the best first instrument you can buy is a pair of binoculars. www.bigbinoculars.com has some great prices on decent pairs, 11x70 or 15x70 will give you specatular views of many objects. But if they aren't for you, maybe settle on something with a middle of the road focal length, because you will undoubtly start out looking at brighter objects, like planets, moons, star cluster, double starts, etc. Which also, aren't affected as much by light pollution. In most cases, you get what you pay for in telescopes, but I've always enjoyed dealing with Orion. And they've always been above par in price and quality. I don't have much experience with the Spaceprobe 130, but all the other users on here have nothing but praise for it. If you've had some prior experience with scopes, it may be a good one for the price. One of there small refractors on an Alt-Azimuth mount might be a good scope too.

    Cheers
     
  17. -iLluSiON- Registered Senior Member

    Messages:
    151
    my telescope isn't alligned right... i go to trace the star i want, then when i look through the actual telescope, it's not where it should be. it'a s little to the left (considering space is huge, this "little" can result in millions of miles difference hehe). what can i do to fix it?
     
  18. Tristan Leave your World Behind Valued Senior Member

    Messages:
    1,358
    Most likely, your problem sounds like you finder isnt aligned right with your scope. Simply center a bright star in your telescope eyepiece than look through your finder and, without moving the telescope, adjust the finder so that the bright star is in the center. And you should be all set.

    Later
    T
     
  19. Red Devil Born Again Athiest Registered Senior Member

    Messages:
    1,996
    I dont own one but wish I did, as we get some good skies around where I live, cloud allowing. I would tell anyone buying or considering buying a telescope - get the biggest aperture you can! I had a telescope when a kid and the aperture was so bloody small I was chasing the moon across the sky. No sooner did I focus on a particular region or crater, it had moved!
     
  20. Tristan Leave your World Behind Valued Senior Member

    Messages:
    1,358
    Aperture is related to the amount of light that the telescope can accomodate. More likely, your problem is that you had too much magnification. Simply, I different eye piece which allowed a lower magnification would have solved your problem.

    If your commited to getting some good sights and doing whatever it takes to use a scope, then get a big aperture. A smaller apeture is only going to let you see the bright planets and the brightest of the bright deep sky objects (speaking reflectors... refractors are a whole other story.)


    Later
    T
     
  21. cjmowery Registered Senior Member

    Messages:
    37
    telescopes

    If your chasing around objects in the sky, its more than likely your magnification is quite high rather than your aperature being too small. You can get small aperatures with some pretty big field of views, and also, you can get some huge aperature scopes on the order of 16" Mak-Cass's that have enormous focal lengths (big magnifications). Long focal length and wide angle eyepieces and a motorized mount will help you in that department also.

    Cheers!
    CJ

    Oops, just realized I said exactly what TRISTAN just wrote above, we must of been typing at the same time

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  22. Red Devil Born Again Athiest Registered Senior Member

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    1,996
    Well, you know what they say:

    "Great minds think alike"

    Just wondering who was using yours

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  23. howeman Registered Member

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    20
    I own the spaceprobe 130, and in the information, it said that you could se the rings of saturn.

    So, my question is, how good should I be able to see mars? I went out the other day, and it just looked llike an enlarges star even with the 90x magnification.
     

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