Fitting a Meade De-Rotator - Help !

[slug]

Help! – I have a Meade LX200 8” F10 ACF with zero shift micro focuser and have just acquired a Meade field de-rotator. Following the manual, the installation is as follows: -

http://www.meade.com/manuals/TelescopeManuals/LXseries/LX200-ACF_manual.pdf

(page 70).

From the rear of the scope, screw on the de-rotator, then add the focuser unit adaptor ring onto the thread on the rear of the de-rotator. The instructions then say ‘back off the adaptor ring 1 turn’ – presumably to allow the casing of the focuser to rotate when the shaft it’s connected to rotates as designed to. Connecting everything up this way means that you can manually rotate the focuser. My concern is that what may happen is the shaft will turn but the focuser will stay in the same orientation, either screwing or unscrewing the adaptor ring it’s attached to.

Has anyone else had this problem? I guess I could just get hold of a small threaded ring to tighten up against the focuser adaptor ring but surely Meade should have though of that???

Any advice would be gratefully received.

Dave

[Merlin66]

I used one of these on a 12" Lx many years ago...

From memory the "Key" if you escuse the pun, is to lock the focuser with the grub screws to the de-rotator. This then locks the focuser and prevents it from turning

(From page 70 middle)

Place the microfocuser over the ring with the “hump” of the microfocuser in the

12:00 position as shown in Fig. 61.

3. Using the provided hex key, tighten to a firm feel one of the three microfocuser hex

screws (Fig. 8, K) up against the adapter ring as shown in Fig. 62. Take care not

to tighten or loosen the adapter ring as you position and tighten the microfocuser

in place.

4. Tighten to a firm feel the other two microfocuser hex screws.

[slug]

Many thanks merlin66.

Any use of the adaptor ring - as shown in the diagram - when its unscrewed 1 turn from being a tight fit to the derotator, results in the screw turning (screwing in or out) regardless of how tight the grub screws are connecting the focuser to the adaptor ring. As a result the whole focuser and eyepiece assembly is loose.

Did you mean dispense with the adaptor ring and connect the focuser (via the grub screws) directly to the thread coming out of the derotator? - because that might work provided the grub screws are long enough.

Cheers - Dave

[Merlin66]

I thought the focuser was just screwed (and held with grub screws) to the rear thread of the derotator.

Can't remember an adaptor sleeve...let me revisit the manual.

EDIT:

Fig 5.4a on page 14 shows the locating slot to lock the adaptor ring.....

[slug]

Merlin66 - thanks for the reply - The problem is actually at the other end of the focuser - Its where item B on the photo screws to the derotator rather than the back of the scope. Whereas on the back of the scope, you can tighten it so it cant undo, on the derotator, you have to back it off by 1 turn (to allow the threaded shaft to turn) - as such, the whole focusser assemble is loose on the tread. Seem like a flawed set of instructions unless I'm missing something ! Cheer, Dave

[Merlin66]

Hmmm

You may be right!

I only wish I could remember the set-up I used.

Just checked the #1209 focuser and the holding grub screws only retain the Ring B, not go through to "lock" it to the SCT thread....

Have you tried without backing the adaptor off the de-rotator?

There may be some info over on the MAPUG site??

[slug]

Merlin66 - Its a mystery to me ! - I can't screw the Ring B tight to the derotator as it will interfere with the derotation - (the screwed shaft rotates relative to the housing). I think the only way is to get another Ring B, and tighten them together, backed off from the housing of the derotator. This way the focuser will have a secure fixing. Thanks for your help though Merlin66. cheers, Dave