Problem with my Meade LX Quartz Drive optical tube.

[Oddsocks]

Hi Zade,

Just an idea, since you can not see any hint of a prime focus projected image, I'm wondering if the secondary adjustment is miles off axis and projecting the image into the side of the central baffle tube?

During the last time you used the scope and it was working, or since then, did you try adjusting the secondary collimation?

I looked again at your through-the-rear-cell images on Imjur and enhanced and zoomed them in photoshop and noticed that the outer ring and inner ring images were not aligned.

Try this and see if you improve things:

With no eyepiece fitted and no diagonal fitted look by eye alone through the rear cell of the telescope and adjust the pointing of the telescope so that you align the distant mountain / sky horizon so that as exactly as possible it runs through the middle of the outer ring image, i.e. exactly half the image is mountain and half the image is sky, lock the clutches so that the tube can not move.

Now check first of all that the three secondary adjustment screws are tight and that the secondary holder is not loose on the front corrector plate.

If all is ok then gradually loosen and tighten the opposing secondary adjuster screws until the distant mountain horizon appears to follow in a straight line from the outer ring, through the inner ring to line up again with the outer ring.

The outer ring is you looking at the distant horizon around the edge of the secondary support and straight through the corrector plate, the inner ring is you looking at the distant image reflected in the mirror, as long as the distant horizon exactly dissects the corrector through the middle then the same horizon should line up with the reflected image making one continuous line across the entire field of view (ignoring the black rings).

The next part is going to be difficult to achieve but you need to find something far enough away that is as near vertical as possible and fills the entire field of view from top to bottom, edge of a building or telephone pole perhaps, point the telescope at this vertical object and now align the telescope so that the object exactly dissects the field of view by a half as seen in the outer ring, the vertical object appears to make a straight line running from top to bottom through the centre line of the telescope, lock the clutches again, now adjust the secondary screws again so that the image moves from side to side until the vertical object can be seen to align perfectly from the outer ring, through the inner ring and back through the outer ring again.

You will need to swap back and forward several times between the horizontal and vertical adjustment until whenever the telescope points to a vertical or horizontal object that object can be seen to pass exactly through the centre line of both the outer and inner images as seen directly by eye when looking through the rear cell opening.

Now, try with the eyepiece, with luck this may have solved the problem and you will be able to see a focussed image again but you will need to make a final fine collimation adjustment on a de-focussed star as normal if this has been successful.

William.

[Quirq]

Hey William,

I got that all sorted, horizontal collimation looked fine, vertical fine too. But I inserted the diagonal, and eyepiece, to no avail. It still looked like it did at the start.

I'm seriously questioning this telescope!

Thanks for the reply,

Kind Regards,

Zade.

[Oddsocks]

Hi Zade,

It seems then that we have arrived back at the beginning, either the eyepiece is defective or the focuser mirror support arm is bent or loose.

The only way forward is to take the rear cell off and check the focuser arm is straight and tightly attached to the mirror so that the mirror moves far enough up the OTA towards the corrector plate, and/or borrow another eyepiece to test.

Unless the eyepiece was dropped or the lens retainer rings are loose (happens sometimes when cleaning with a circular motion that the lens retainers unscrew) which should be easily seen, then I would suspect the focuser mechanism because of the age of the telescope and the fact that you can't make a prime focus projected image when the eyepiece is not fitted.

Really can't think of anything else...

William.

[Quirq]

Hey William,

I have the eyepiece with me, it's a Meade Super Plossl 20mm 'multi-coated'.

I did at one stage take it apart to clean, I may not have inserted the lenses in correctly when I put it back together, do you know anything about the lenses for eyepieces?

Kind Regards,

Zade.

[Oddsocks]

Hi Zade,

The Plossl lens has two sets of doublets, two lens back to back touching each other, one side of each doublet pair is flat, this side points outwards towards the viewer and towards the telescope.

the other side of each doublet is convex, curved outwards and the curved side of each doublet face each other in the barrel of the eyepiece.

There is a good description of eyepiece lenses on Wikipedia with diagrams of the lens groups and how they relate to each other.

In the Wikipedia drawings the thin element shown at the front of each eyepiece is a diaphragm (looks like a washer) called a field stop, this is not present in all makes of Plossl so your eyepiece may just have the two lens groups.

If you took your Plossl to pieces you could have reassembled with the doublets facing the wrong way, outwards instead of inwards, or one group facing out and one group facing in etc.

Here is a link to the Wikipedia page:

http://en.wikipedia....ssl#Pl.C3.B6ssl

William.

[Quirq]

Hi William,

Just went out (It's about 10.45PM)

Tried looking at the stars, and even city lights with the newly aligned telescope and maintained eyepiece, but in the sky, I see nothing but blackness even when perfectly aligned at a star, city lights looks like an orange tinted blackness.

Kind Regards,

Zade.