Modest focuser upgrade for SW 250px

[tooth_dr]

Anyone recommend a modest upgrade for this scope?  I also don’t like the way the whole imaging kit is held on by just a couple of thumbscrews.  I’m not sure how much back focus I have, maybe a Baader clicklock would be an option?

[tooth_dr]

[paul mc c]

I have a clicklock on my sct and it is a cracking piece of kit,really clamps what ever goes into it....cheaper and less hassle than changing focusers,just my thoughts.

[discardedastro]

I think on the 250 you'd struggle with backfocus. I upgraded my 200PDS focuser to a Baader Steeltrak Diamond and it's night and day - well worth the investment. But I also got a Clicklock clamp with it, which does work, but takes up a lot of backfocus so my "focus in" remaining at prime focus was very minimal. Fine for imaging but not great for observing, so I ended up swapping back to the supplied clamping ring w/ three screws. The Clicklocks are good and would probably be awesome on an SCT/Frac with tons of backfocus to play with.

I spent quite a bit of time trying to make the Skywatcher dual-speed focuser "better" but fundamentally it's pretty much as good as you're likely to get out of it because of the materials, construction methods etc. The Baader focuser is about 1.5 times the weight and has completely different feel to what I was able to achieve with the SW one.

Common "mod" suggestions are to really flatten the friction plate on the drawtube and replacing the bearings but for my money I'd just save and invest in a replacement.

[Dinglem]

I totally agree with @discardedastro I changed my 200p focuser to a Baader Diamond Steeltrack and the difference in feel, quality etc. was very noticable, I also tried the clicklock with it and had to remove it due to issues with inward focus.

[tooth_dr]

On 25/01/2020 at 23:24, paul mc c said:

I have a clicklock on my sct and it is a cracking piece of kit,really clamps what ever goes into it....cheaper and less hassle than changing focusers,just my thoughts.

Hi Paul

I got a clicklock today, so that should do the trick.

 

Adam

[tooth_dr]

On 26/01/2020 at 10:58, discardedastro said:

I think on the 250 you'd struggle with backfocus.

With a DSLR I couldn't have done it, but the photo below shows how much focus travel I have to spare, this is with CCD and EFW2

[discardedastro]

4 hours ago, tooth_dr said:

With a DSLR I couldn't have done it, but the photo below shows how much focus travel I have to spare, this is with CCD and EFW2

 

Ah, no coma corrector? If you get a Paracorr they have a modest Barlow effect to push the backfocus out - but more affordable ones won't, so you lose some travel to that. With a Clicklock on the Baader diamond steeltrack and a MPCC Mk3, EFW and CMOS (ASI183MM) I had about 10mm of inward travel left.

[tooth_dr]

25 minutes ago, discardedastro said:

Ah, no coma corrector? If you get a Paracorr they have a modest Barlow effect to push the backfocus out - but more affordable ones won't, so you lose some travel to that. With a Clicklock on the Baader diamond steeltrack and a MPCC Mk3, EFW and CMOS (ASI183MM) I had about 10mm of inward travel left.

I’ll need to check again as Ive maybe got this wrong, but I thought I was using my MPCC here.  Otherwise I’m not sure how my EFW fitted into the focuser. 

[tooth_dr]

44 minutes ago, discardedastro said:

Ah, no coma corrector? If you get a Paracorr they have a modest Barlow effect to push the backfocus out - but more affordable ones won't, so you lose some travel to that. With a Clicklock on the Baader diamond steeltrack and a MPCC Mk3, EFW and CMOS (ASI183MM) I had about 10mm of inward travel left.

Yes 100% was using a CC. I found a photo of the setup. I have a spacer between the CC and the EFW.  This let me insert it further into the focuser and also now explains why I used longer screws because the 10mm spacer has a smaller diameter. 

Edited January 31, 2020 by tooth_dr

[discardedastro]

5 minutes ago, tooth_dr said:

Yes 100% was using a CC. I found a photo of the setup. I have a spacer between the CC and the EFW.  This let me insert it further into the focuser and also now explains why I used longer screws because the 10mm spacer has a smaller diameter. 

Ahh, that makes more sense! I couldn't see the MPCC ring in the photo but yes you can remove that and insert it further. Not a bad idea to get some more backfocus!

With the Clicklock you'll just need to make sure it's actually gripping on the CC rather than on the spacer, as otherwise you might not end up with the kit held straight in the focuser. The Clicklock will do a great job of bringing things on-axis consistently if you've got it gripping onto the CC - I don't think it'd make good contact on the spacer.

[tooth_dr]

7 hours ago, discardedastro said:

Ahh, that makes more sense! I couldn't see the MPCC ring in the photo but yes you can remove that and insert it further. Not a bad idea to get some more backfocus!

With the Clicklock you'll just need to make sure it's actually gripping on the CC rather than on the spacer, as otherwise you might not end up with the kit held straight in the focuser. The Clicklock will do a great job of bringing things on-axis consistently if you've got it gripping onto the CC - I don't think it'd make good contact on the spacer.

Ah ok yes as it stands that wouldn’t be any good.  Looks like I’ve used an m48-m42 reducer then an m42 spacer.  I’ll try it differently 

[tooth_dr]

Quick update - I’ve been playing around this evening and I think I’m there now. The back focus is very very tight.

Ive rearranged spacers, and turned the M54-M42 adapters inside out on the EFW2 (sitting flush with the surface) to get me the right spacing with as much of the kit actually inside the focuser as possible.

I also moved the mirror up as far as it could go and recollimated it.

I now have 1mm focuser travel to spare, when focusing on a light about 2 miles away.  How this will translate to infinity I don’t know but hopefully it will be close. I can get another 1mm if I really needed it by taking a little lip off the clicklock but hopefully I don’t have to go that!

I also tried out using a newly purchased phone adapter, to help check collimation, via camera.

 

Some pictures: