Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Stargazing Magnification of telescope

  1. Jan 29, 2008 #1

    I am slightly confused... Many books and website says that your telescope's useful magnification ranges from 20X per inch to 100X per inch according to the optic quality. How do i find out the optic quality and useful magnification for my own telescope? (p.s. i am using a Orion Skyview Pro 6")
  2. jcsd
  3. Jan 29, 2008 #2
    Most things I've read say about 50 times per inch of aperture for a high-quality telescope or about 2 per millimeter. So yours would probably be about 300. I don't know how to find optic quality as it's not something you can measure, just collimate the scope to the best of your abilities and read up on some reviews to get an idea. I think it would be about 50 times per inch though.
  4. Jan 29, 2008 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The majority of amateur astronomy is done at fairly low powers, yet, for some reason, many newbies are obsessed with magnification, and think the point of a telescope is to magnify as much as possible. The real purpose of a telescope is to gather more light; magnification is a side-effect and is sometimes not even desired at all.

    The realistic limit for most telescopes is indeed about 50x per inch of aperture, as NerfMonkey said. Only in particularly good circumstances will it be sensible or useful to go for higher powers. Always start with the low power first, and work your way up when conditions permit.

    - Warren
  5. Jan 29, 2008 #4
    Thanks for the reply.

    However, Saturn looks awfully small on 300X... Does this mean that I should push against the max limit slightly or should I just leave it at 300X?

    Heres an attachment of saturn... I took it just putting my digital camera next to the lens. I used a 6" Orion newtonian, 750mm focus length and at 300X

    Sorry about asking newbie questions... :redface:

    Attached Files:

  6. Jan 29, 2008 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    From the look of it, the telescope is very poorly collimated (the rings appear to be blurred out up and to the left) and the eyepiece is of low quality or Saturn was unreasonably low on the horizon (the separation of red and blue light).

    You should be able to get much better views of Saturn out of a 6" scope. Do you know how to collimate your telescope, or can you find an astronomy club in your area that would offer some assistance?

    - Warren
  7. Jan 29, 2008 #6


    User Avatar

    Staff: Mentor

    Tough to really know if that is collimation or just a handheld camera that wasn't lined-up right. Regardless, it is something to check.

    Saturn won't be big at 300x (it'll be smaller than that pic), but it should be relatively sharp if it is more than 30 degrees or so above the horizon on a still night. Your eyes can do the rest.

    Btw, if you have a webcam, you can very easily take high quality pics of it by removing the lens and mounting the webcam directly on the scope without the eyepiece.
  8. Jan 29, 2008 #7


    User Avatar
    Gold Member

    Yes, as chroot points out, it's not about mag, it's about light-gathering.

    If you look at your own image, you can see that simply making it larger will not improve what you see, it will just be a larger, fuzzy image. The low amount of discernable detail in your image could just as easily be captured in a much smaller picture.

    What you want increase is how much light it gathers. More light means more contrast.

    http://spacsun.rice.edu/~has/images/ES_SaturnPhotoReg3_1_26s.jpg"'s a much smaller image of Saturn with excellent contrast.

    I agree again with chroot that a good collimation would help you too.
    Last edited by a moderator: Apr 23, 2017
  9. Jan 29, 2008 #8


    User Avatar

    Staff: Mentor

    That pic is a good size to compare with what you might see through a scope - the contrast is much better than you can actually see, though.
  10. Jan 30, 2008 #9
    Thanks for the help.

    I'll collimate my telescope again sometime, maybe it may help with the fuzz... (P.S. my telscope guy says i collimate by looking into the place where you stick your eye piece but that seems quite approximate; is there a more accurate way without buying fancy stuff?)

    I would also like to ask if the builtin webcams for laptops are OK for photography?
    Last edited: Jan 30, 2008
  11. Jan 30, 2008 #10
    I will agree with the presents posts and the bad collimation that it is said. However a ''good'' observation has a lot of factors that can influence it. I believe most important of all when you observe a planet is the seeing of the sky in which you observe as it is said.The reason of a ''bad seeing'' is atmospheric abnormalities or because the planet is found in low height therefore is interfered more atmosphere between the observer and the region of the planet at the sky. When the seeing is bad the image will have less contrast and sharpness. in addition when you try to photograph the planet the image will be very Blur.
  12. Jan 30, 2008 #11
    NO the only thing that you will need for the collimation proses is a 35mm film box with a very tiny whole in the centrer of the cylinder. The further proses of collimation is the same as you probably know.

    Of course you can photograph with a laptop webcam but you have to replace the lens of the webcam with a special adapter instead in order to adjust the webcam to the telescope.
  13. Jan 30, 2008 #12
    Sorry about the newbie question.

    Can you give me some more detail about the 35mm film box thing, the only way i know is to visually look into the hole where you put the eyepiece without any aid. I can only collimate to a rough estimate with this method...
  14. Jan 30, 2008 #13
    Last edited by a moderator: Apr 23, 2017
  15. Jan 31, 2008 #14
    I'll add one more collimating instructional site site. This one has a short video using both standard and laser methods.
    One thing to remember with your scope(s) is the larger the aperture and shorter the focal length the more important collimation is.

    My 6 inch is collimated approximately every 6 months. However, I collimate my 10 inch f5 just about every time I use it.


  16. Feb 3, 2008 #15
    Thanks for the replies.

    Those websites are GREAT!!! the websites and guides i used before are in no way as good as these websites...

    I'll try out my collimated telescope someday when the weather is better.
  17. Feb 4, 2008 #16
    What do i need to adjust for this situation? The primary or secondary mirror or the eyepiece?

    Thank You.

    Attached Files:

  18. Feb 4, 2008 #17
    Here i got the actual picture of what i can see after collimation: I would like to ask if i did it correctly? (im asking because its quite hard to determine to middle point)

    I would like to state that you can't my eye in the picture, but my eye is centered within the smaller circle.

    Attached Files:

    Last edited: Feb 4, 2008
  19. Feb 5, 2008 #18
    Thank you for the help. My previous question is no longer valid since i got myself a laser collimator (for around USD$40)

    Thank you for all the replies and help.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook