Focus Tube Slop

[johnrt]

I've been struggling with star shapes again - I thought the collimation was dropping out very easily on my RC, until I discovered the amount of movement in the focus draw tube.

The issue here is you have to unlock the focuser after you have slewed to a star to focus, the draw tube then drops under gravity and you tighten up a misaligned focuser tube.

Clearly the cause of the odd stars with the light point offset to the side I posted a picture of earlier this month.

I've made a quick video of the movement in the draw tube. All the movement in the video is the focus tube wobbling from side to side - the OTA was wedged in place against a wall.

Does anyone have any thoughts on where to go from here?

http://www.flickr.com/photos/skywatcher150/7005265539/

[spacemouses]

Thin metal shim slipped into the gap and can be held in place in one of various ways. It is possible to buy small sheets of brass shim in just about any thickness you want. (soft drink tin can be used if thickness is ok- can be cut with scissors)

David

[johnrt]

Hi David.

I suppose a shim of some description would solve the problem. But I'm a little pained to do this as the scope is only 6 weeks old, should I really be going to all that trouble to fix an item that wasn't fit for sale in the first place?

[Dave Smith]

I have some self adhesive teflon tape that may be of use, I did use it on my ST80 guide scope to stop flop (since sold on). If you would like some PM your address and I will stick some in the post.

Just seen your reply, if you would still like some, let me know.

Dave

[johnrt]

Hi Dave.

Thats a very kind offer thank you. To be honest I'm in two minds what to do at the moment. No sure whether to return the scope or battle on. If I decide to keep it I will take you up on your offer. Thank you!

I have some self adhesive teflon tape that may be of use, I did use it on my ST80 guide scope to stop flop (since sold on). If you would like some PM your address and I will stick some in the post.

Just seen your reply, if you would still like some, let me know.

Dave

[perfrej]

There is always the "buy a proper focuser" route... I bit the bullet and replaced the focuser on both my active scopes, the FLT-98 and the EdgeHD 9.25. Both now have motorized Feathertouch focusers (Microtouch in the case of the HD).

/per

[johnrt]

Yeas there is that argument, but a 600 euro focuser on a 400 euro scope doesn't add up to me!

There is always the "buy a proper focuser" route... I bit the bullet and replaced the focuser on both my active scopes, the FLT-98 and the EdgeHD 9.25. Both now have motorized Feathertouch focusers (Microtouch in the case of the HD).

/per

[DaveS]

That really is unacceptibly poor engineering John, and in 'Trading Standards Speak' not fit for purpose. I would be inclined to return it under warrantee,

I had problem with the DDG focuser on my WO FLT110, albeit there was no 'splop' in it, it just couldn't handle the weight of my imaging gear.

The focuser has been changed for a Moonlite, and this is fine, albeit only just, as far a weight handling goes.

As Per says, the Feathertouch' is the focuser of quality, but at a ridiculous price.

Dave

[perfrej]

Yeas there is that argument, but a 600 euro focuser on a 400 euro scope doesn't add up to me!

Oops! Never checked the price level of the scope

/per

[johnrt]

There might be a light at the end of the tunnel yet.

I thought I would try a quick poke around inside the Altair focuser before I condemned the whole scope. Removing the four allen screws and the housing shown in the top picture exposed 4 small phillips head screws.

These were so loose that as I waggled the draw tube they almost popped out of the holes. A quick tighten and the draw tube is now very sturdy without any lateral movement.

The focuser and draw tube now feel like a solid unit, no slop or play at all.

[DaveS]

That sounds promising John, and hopefully the problem is resolved.

However, it doesn't excuse the fact, that the scope should not have been supplied in that condition.

Dave

[Dennis]

I figured that might be the problem but not knowing anything about that scope I kept quiet. I guess the screws can work loose with temp changes and fair wear and tear. A little thread lock might benefit but not so much that you cannot re-adjust as the supports wear out.

Dennis

[jcm]

Better check the screws on mine ( 8" RC) but the focuser feels OK.

John

[johnrt]

Well after a lengthy test run last night where conditions were awful for real imaging but good enough for some testing I'm disappointed to report the problem still remains. Elongated stars with their central points offset to the left. It seems all I have done is locked down a crooked focuser.

Not sure there is anywhere left to go with this other that to either return the scope or pay out a further £250 for a moonlight unit.

[DaveS]

Not sure there is anywhere left to go with this other that to either return the scope or pay out a further £250 for a moonlight uni

Unlikely John, but you could pay out for another focuser, only to find that the problem lies elsewhere. In the Optics perhaps?

I think you have every justification to return it, as not fit for purpose.

Dave