Question about Bushnell Deep Space 18-1560 (150 x 53mm) Telescope

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Bushnell 18-1560 Telescope

Hi I received the above model as a gift. My problem is that I cannot focus on any object when using the 4mm eyepiece. I can focus 100% when using the 20mm eyepiece. What am i doing wrong or is my 4mm faulty. Regards Gary

Posted by Gary Mengel on

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Anonymous

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Hello,
What you have is called a refractor-type telescope with the primary lenses (the Objective) at the top of the tube and the only other lenses in the system are your selection of eyepieces, probably a barlow lens (2X magnification of any eyepiece used), and a diagonal (in line mirror so that you cand see into the telescope from the side.). As the focal lenth of the eyepiece decreases, so does the distance away from the Objective Lens. I believe that you are using the telescope with a diagonal mirror which makes the optical path longer. The fact that your longer focal lenght eyepiece can focus and not your short one would be only if you didn't have the diagonal or the eyepiece all the way in tight to allow the focus mechanism (rack and pinioin) to get compressed enough to focus. Look at the Moon, if the image gets smaller then bigger as you focus, but not sharp, then I would have to tell you that your eyepeice lenses are not in the right order. Someoner may have taken it apart and didn.t put them back in the correct order. The lenese could just be very dirty also. Barrow a short focal lenght eyepice from a friend and see if it works in your system. Then you will know for sure.

Posted on May 31, 2010

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Ginko

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Hi.

A refractor is a very simple telescope, with only two sets of lens (objective and eyepiece) and a small aperture.

Remove the prism (the diagonal adapter before eyepiece). Check status of the objective lens. Ensure that the lens is steadily incorporated into the objective.
Ensure the eyepiece is properly screwed to the telescope.

If all the rest is fine, and the 20mm is working, then replace the 4mm. If the objective or the eyepiece is not well in place, that may cause the telescope not focusing on the 4mm eyepiece.

Posted on May 31, 2010

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mark york

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Hi there koosie when using the 4mm eye piece you have to be looking at something at quite a distance hence the power with a 20mm eye piece you can focus closer objects and dont need so much light as the 4mm the more power the more light and furthur away the least power(20mm)the least light and closer you cant focus close with a 4mm eye piece but can with a 20mm

Posted on Jul 17, 2007

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