How to improve the focuser on my 150PL?

[RobertI]

My 150PL is a really good all rounder and great for doubles, but it’s really hard to focus at high power. This is partly due to the long tube - every touch induces a wobble - and partly due to the agricultural single speed focuser. I want to add a motorised focuser but the focus wheels are stuck on and will not come off - I’ve tried. The alternative is to replace the focuser with a nice two speed unit but I don’t believe there is one off the shelf that will fit. Does anyone have any experience or advice on this? Thanks. 

[johninderby]

Using the TS baseplate you can fit a few different crayfords to the 150 although a bit of surgery is required. The hole in the tube is too small for a 2” focuser so you will have to enlarge the hole and drill new mounting holes.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p3701_Base-for-Newtonian-focusers-for-tubes-with-D--160-205mm.html

You could also fit the SW replacement crayford but again would have to enlarge the hole in the tube.

https://www.firstlightoptics.com/skywatcher-focusers/dual-speed-crayford-1252-inch-focuser-for-skywatcher-explorer.html

I did fit a crayford to a 150PL using the TS base plate.

 

Edited December 18, 2021 by johninderby

[RobertI]

Thanks John, looks like you did a great mod there (as always! ) and that focuser (Long Pern?) suits the scope really well. I'm not sure about my abilities to enlarge the hole though - I'd be interested to know how you did it? 

You got me thinking though - whilst looking at you suggestion I came across this alternative - it's only 1.25" but I'm thinking that wouldn't be an issue as I use it for mostly doubles anyway, and means I wouldn't need to enlarge the hole, although it does mention an "oversize drawtube" which might be too big for the existing hole. Although single speed, it would allow a motorised focuser to be fitted as the knobs seem removable. What do you think?

[johninderby]

The focuser was the old SW crayford. Same design as the SW refractor crayford which is still available. 

Not that hard a job to fit the TS baseplate. Just need an electric drill. Put masking tape on the tube. Position the baseplate on the tube and drill the new mounting holes then  with the mounting bolts in place draw a circle on the tube to match the hole in the plate. Remove the baseplate. Then comes the tedious bit. Drill holes using a 3mm drill bit along the circle. Lots of holes.Then by wiggling the drill bit join up the holes. Not difficult but just tedious as mentioned 😁 Then file the hole so it looks neat and tidy.

The TS 1.25” crayford looks interesting. Wonder what the mounting hole spacing is? Perhaps ask TS to confirm the spacing to see if it would  be a bolt on. The worry I would have is if the base is smaller than the stock SW one.

[RobertI]

Many thanks for your thoughts John. I've looked at the measurements of the TS focuser and measured the 150PL and it might be ok, although the TS focuser is about 1cm shorter across the tube - presumaby the issue there is the old holes will be exposed? I've pinged a message to TS and I'll let you know what they say.

[johninderby]

Yes exposed holes was my concern although not a deal breaker. Just fill the exposed holes with some black button head bolts.