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

Stargazing What am I doing wrong? - Telescope Trouble

  1. Jun 23, 2005 #1
    I decided to dust off my old telescope to see what I could see. I was looking at the moon and messing around, but I could only get a sharp image with the eyepiece removed. Without the eyepiece, I can focus in a good image with my glasses on or off, but with it in it is only a blob of white light. I cleaned it off, but no change. Any Ideas?
  2. jcsd
  3. Jun 23, 2005 #2


    User Avatar
    Science Advisor
    Gold Member

    It sounds like an alignment problem. Fidget with your mirror adjustment screws and see if that helps.
  4. Jun 23, 2005 #3


    User Avatar
    Gold Member

    What type of telescope are you using? The fact that you can get a good usable image without an eyepiece inserted suggests that you already have some kind of secondary lens installed in the light-path. Do you have other accessory lenses, such as field-flattener, barlow, compressor?
  5. Jun 23, 2005 #4
    yea there is a barlow x3 before the eyepiece. its a refractor telescope.
  6. Jun 23, 2005 #5
    is the barlow made to use with that scope??
    try removing the barlow and see if you get normal focus with an eyepiece

    I suppect the barlow is toooo long to get a good focus with your scope
    or is in backwards or other non proper mounting [not all the way in place]
    making the distance too long
  7. Jun 23, 2005 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I agree, get rid of the barlow and see if the focuser has enough travel without it.

    - Warren
  8. Jun 25, 2005 #7
    I took the barlow out and it works pretty good now. Not a perfect image, but it's cloudy tonight so it seems to be working good. Which eyepieces are for higher magnification - long or short focal length?
  9. Jun 25, 2005 #8


    User Avatar
    Gold Member

    High magnification = short focal length. Shorter-f/l oculars often give you a narrower field of view and less eye relief, so the longer f/l oculars are more comfortable to use, especially with an unguided scope. If you're going to let people look through your 'scope who are not used to using one, you may want to stick to the longer f/l oculars for this reason. Long f/l oculars teamed up with a high-quality Barlow can be a good combo. Often the short f/l oculars bundled w/ commercially-available 'scopes are unrealistically short, delivering magnifications that are unusable, given the small aperture and poor optical quality of the primary.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook