130P-DS - shorten Focus tube

[Stub Mandrel]

I want to shorten the focus tube on a 130P-DS, as a good 1/2 - 3/4" pokes into the tube.

How do I remove it? Which screws remove the focusser and will bits fall out?

I have a well equipped workshop to do a neat job of the shortening.

[Peter Drew]

Neil. Removal of the four screws at the corners of the radiused mounting plate should release the whole focuser assembly without any further dismantling. There will be nuts and washers and maybe even a stiffning plate inside so place the tube horizontally. You might be able to shorten the tube in situ.

[Stub Mandrel]

Thanks Peter,

I'm hoping to part off the end of the tube in the lathe, so I need to get it right out really.

Is there an exploded diagram 'out there'?

[nightfisher]

If you remove the focus bar assembly, again four little hex bolts and lift this of the draw tube will all but fall out, you need to be careful that draw tube does not fall into the secondary and there might be little rubber washers under the focus housing

[Uranium235]

Yes, those tiny rubber washers - dont lose em!

 

[Stub Mandrel]

Thanks Both.

[alacant]

Hi. Sorry to come back to this but I'm having the same problem of focuser tube ingress into the light path, but only when using the -what I think is- skywatcher coma corrector[1] where the focus point is further toward the telescope. Could anyone confirm that the cc is responsible for the move of the focal plane? TIA.

[1] it's an unbranded cheepo from AliExpress but looks exactly the same.

Sorry. Just one more thing. Does this cause 'D' shaped stars on one side of the image?

[Skyline]

I recently bought a 130PDS, the SW coma corrector has a .9x reducing factor which mean the focal ratio of the scope changes from f5 to f4.5, now the funny thing is SW have made a few changes to the scope.

1. the primary collimation thumbscrews have changed design.

 2. I believe they might have changed the length of drawtube. As I am using the SW CC but I am not getting any bite marks shown in my stars. Even when I am using a low profile collar which is half of the thickness of the original collar supplied on the drawtube, usually there is still a small bite mark shape present. Which leads me to believe they might have modified the drawtube as well.

It would be nice if someone who has bought a recent 130PDS can confirm this also.

[spaceboy]

Personally I would refrain from shortening the focuser tube as it will almost certainly render the focuser unusable for visual in the future. Sure you can use extension tubes to reach focus but the problem is....... if it is intruding in to the light path as far as your saying it is then there is a good chance your going to end up cutting of the pinion stop on the draw tube which will in turn mean when you rack the focuser out, the draw tube it will simply just wind all the way until it drops on the ground. There is the possibility of putting a very small socket screw in to the draw tube to prevent this from happening but there really isn't a lot of meat for the screw to thread in to.

I would consider if there is a way of lengthening the primary screw and springs so that you have a longer travel on the primary mirror. I'm not 100% but I think TS in Germany do these kits ? I know scope and skies used to.

[alacant]

1 hour ago, Skyline said:

a .9x reducing factor

Hi. Could you confirm that this brings focus closer inward with the cc than without? IOW, I focus normally without the cc. I put in the cc; i now have to rack in the focuser to achieve focus. TIA

A frame with D shaped stars. (to the left). Not a 130pds admittedly. I've tried a separate thread but could not resolve the issue. Apologies for off topic.

[Skyline]

When the supplied standard collar is used the focus is closer inward, when your using a low profile collar, you do not have to rack the tube inward that much. Maybe a guess estimate would be around 5-8mm less inward focus then a standard collar fitted. HTH

Have you checked your primary clips on your mirror ?

[Stub Mandrel]

2 hours ago, spaceboy said:

There is the possibility of putting a very small socket screw in to the draw tube to prevent this from happening but there really isn't a lot of meat for the screw to thread in to.

I would consider if there is a way of lengthening the primary screw and springs so that you have a longer travel on the primary mirror. I'm not 100% but I think TS in Germany do these kits ? I know scope and skies used to.

 

I chopped my draw tube, but superglued a small square of brass on the end of the flat to stop the tube falling out.

I can't say I had bitten stars, but the flare around bigger stars was uneven - less pronounced on one side.

As for visual, I suppose I ought to try looking through the damn thing one day...