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.
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.
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Re: Bushnell 18-1560 Telescope
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.
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
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Put the diagonal into the rear focuser-- then put the eyepiece into the diagonal. DO NOT use the 2 x barlow if you have one. AND the 4mm may also be too much magnification for this size telescope.
So-- put the eyepiece with the largest number written on it into the diagonal and practice focusing on a distant object during the daytime. DO NOT POINT the scope at the sun! You will be instantly blinded!
A telescope like that has a very narrow depth-of-field, so you need to focus very, very slowly to be able to see any image. Try focusing on something bigger (like a spot on the moon) and adjust the crosshair accordingly. The two eyepieces gives different magnification.
Is this your telescope? http://www.binocularsdirect.com/Bushnell_Telescopes/dptsmzmyqcq.html
Can you try replacing the eyepieces on the side with the one on the back. Also if you "slightly" slide the eyepiece OUT does it come to focus?
I must tell you this is a very unusual design with a turrent AND another eyepiece on the back. Has the rotary eyepiece module become loose from the back of the tube? Can you push it in closer to the tube?
Other than forward or backward adjustment that's all the focuser will do.
The FOCUSER end should be pointed UP the mirror end is toward the ground. Turn the scope around and put the eyepiece with the largest number written on it into the telescope. DO NOT use the 2x barlow if you have one.
Go outside during the day time and practice focusing on a distant object.