As Secretary of the Astronomy Club on the campus, I recently came into possession of a Bausch & Lomb Criterion 4000. It is a Schmidt-Cassegrain telescope, with a 4" aperture, 1200mm focal length. A cassegrain reflector uses a combination of a primary concave mirror and a secondary convex mirror to form the image, thus giving the telescope its name. A schematic diagram of the telescope is given here.
Hugely popular when it first came, because of its portability, this model hasn't been in production for some time now. A good model for use in homes by amateurs, on terraces and gardens, it doesn't really qualify as too useful in outdoor conditions, with its table top stand and small size. However, because of lack of funds (ours is a new club), we think it is good enough for our use.
So the first time we take it out on an observation session, we notice that whatever we do, we can't see anymore than just a white blob (yeah, we started with the moon). We figured it was a problem with focussing knob as it seemed too loose. When I googled about it, I found that its focussing knob was a common problem.
That was when we decided to open it.
Ideally, an instrument such as a telescope should be handled by experts, especially on repair jobs. But, then, such is youth!
So we, Co-ordinator of the club and myself, sat down to work with a couple of large pliers, a set of screw-drivers and a cutter, just in case. It does seem like too heavy duty equipment for an object so delicate, but trust me, we had use them all. After detaching the tube from its mount, we first unscrewed the focussing knob. It was mounted on a screw which had apparently disengaged from the mechanism inside it. We dismantled the tube. It was essentially made up of 3 parts, the tube, the primary mirror with the focus mechanism and the eyepiece. The screw of the focussing knob is used to rotate a shaft, which in turn rotates another screw, thus moving the primary concave mirror forward or backward. This adjustment of the mirror distances helps in focussing.
After re-engaging the mechanism, there was a slight problem of aligning all parts as before. A small tip would be to keep taking photographs of he arrangements in the telescope during opening it.
Finally, we tested it out, and got sharp image of the full moon. Only problem is stray reflections from the glass front of the tube, which I suppose is something we will have to live with.
And this way, I have a perfect gift for the club for the General Body Meeting tomorrow!
Hugely popular when it first came, because of its portability, this model hasn't been in production for some time now. A good model for use in homes by amateurs, on terraces and gardens, it doesn't really qualify as too useful in outdoor conditions, with its table top stand and small size. However, because of lack of funds (ours is a new club), we think it is good enough for our use.
So the first time we take it out on an observation session, we notice that whatever we do, we can't see anymore than just a white blob (yeah, we started with the moon). We figured it was a problem with focussing knob as it seemed too loose. When I googled about it, I found that its focussing knob was a common problem.
That was when we decided to open it.
Ideally, an instrument such as a telescope should be handled by experts, especially on repair jobs. But, then, such is youth!
So we, Co-ordinator of the club and myself, sat down to work with a couple of large pliers, a set of screw-drivers and a cutter, just in case. It does seem like too heavy duty equipment for an object so delicate, but trust me, we had use them all. After detaching the tube from its mount, we first unscrewed the focussing knob. It was mounted on a screw which had apparently disengaged from the mechanism inside it. We dismantled the tube. It was essentially made up of 3 parts, the tube, the primary mirror with the focus mechanism and the eyepiece. The screw of the focussing knob is used to rotate a shaft, which in turn rotates another screw, thus moving the primary concave mirror forward or backward. This adjustment of the mirror distances helps in focussing.
After re-engaging the mechanism, there was a slight problem of aligning all parts as before. A small tip would be to keep taking photographs of he arrangements in the telescope during opening it.
Finally, we tested it out, and got sharp image of the full moon. Only problem is stray reflections from the glass front of the tube, which I suppose is something we will have to live with.
And this way, I have a perfect gift for the club for the General Body Meeting tomorrow!
