Reassemble.IT – Meade 6×30 Finder Scope

Six months ago, I bought a second hand Meade LXD55 SN-6 telescope. The LXD55 is a computerized mount that is capable of slewing to any object in its database. The SN-6 is a 6-inch Schmidt-Newtonian telescope. I noticed at the time that the Meade 6x30mm finder scope was mounted backwards. The finder scope is a small telescope so usually the big end points to the sky and we look through the little end, however they were looking through the big end – strange.

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Yesterday, I was reminded about this finder scope, so decided to have a closer look. I looked through the finder scope and realized why they used it this way. When viewing through the eyepiece, everything was blurry – a case of not being in focus. To focus the finder scope we have to move the eyepiece section and front lens apart, i.e. move the eyepiece in and out of the tube. Or move the main lens in and out, but no matter what I did, it would not focus. After taking the eyepiece out, I worked out that the tube was about half an inch too short. How is this possible?

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A search through google mentions that some Meade finder scopes also had this problem, and the solution was that the supplier would replace it. This telescope was first released in 2002, so now it was way past its warranty. The only solution now is to work out what was wrong with it.

The eyepiece appeared strange, so I decided to take it apart, noting in which order the pieces came out.

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It was strange – the piece on the right end is obviously for the crosshair reticle, which should be in the middle.

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Both eyepiece lenses are half-convex and judging by the thickness, they should be arranged as a standard Kellner eyepiece.  A Kellner would have the two lenses separated by the small spacer with the thicker lens on the right, with the curved surfaces facing inwards.

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This lens arrangement would then be on the right.  In the middle would be another spacer, then the crosshair ring – which didn’t have crosshairs, and the final piece on the left.  Once I “reassembled.IT“, this is what the eyepiece looks like – quite different from the original which must have come apart and then the owner didn’t know how to put it back together.

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Once the finder scope was fully assembled, it was able to be focused on short distance by moving the eyepiece outwards, and to focus on long distance by screwing the eyepiece inwards. Another thing fixed.

P.S. The crosshair reticle, if it had one, would be at the focal point of the lens arrangement, which can be worked out by looking through to see at which point the image is sharp and focused.  I just need to find some very fine wire or hair and glue them to that piece. Alternatively, use a piece of clear plastic of the same diameter and scribe or draw a couple of fine lines on it.

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