130PDS drawtube protrusion

[Devonshire]

Hi!

I've searched on this and found quite a few hits, but some of the responses are conflicting and I'm having a bit of trouble figuring out what's what.  

Sorry if this is old ground...  

Given a 130PDS + Baader MPCC III, T-ring and filter + DSLR, did you experience drawtube protrusion into the light path, or not?  

If you did, and you corrected it, how much length did you need to cut off the drawtube, or alternately, how much did you have to move the primary up?

Thanks!

[bottletopburly]

Wind out draw tube until it hits stop  now look in ota the protruding tube is the max to cut off it’s only about 10mm to much and tube will run on rollers supporting drawtube  before it hits drawtube stop  .

[Devonshire]

Thanks, but I'm waiting for my PDS to arrive, so I'm trying to determine the probable necessity of this kind of mod in my situation, not potential 'Max'.

Restated, with better precision:  Given a 130PDS + Baader MPCC III, T-ring and filter + DSLR, did you experience drawtube protrusion into the light path, while in focus and imaging?  

 

[edarter]

14 hours ago, Devonshire said:

Restated, with better precision:  Given a 130PDS + Baader MPCC III, T-ring and filter + DSLR, did you experience drawtube protrusion into the light path, while in focus and imaging?  

 

Yes you do get protrusion unfortunately. I have exactly the same setup as you and the tube does indeed show when everything is focused. Can't recall offhand how much. However, I've not done anything about it myself as I think I have other priorities to nail down first like getting better at post processing and sorting out the bl&*#y mpcc spacing so the stars are not egg shaped in the corners. 

Hth

Edited December 28, 2020 by edarter

[bottletopburly]

14 hours ago, Devonshire said:

Thanks, but I'm waiting for my PDS to arrive, so I'm trying to determine the probable necessity of this kind of mod in my situation, not potential 'Max'.

Restated, with better precision:  Given a 130PDS + Baader MPCC III, T-ring and filter + DSLR, did you experience drawtube protrusion into the light path, while in focus and imaging?  

 

I acquired a 130pds in a deal which unfortunately had too much chopped off I fixed it by supergluing 6mm of tube to the end of drawtube  and fitting a grub screw to the flat surface on draw tube slightly in front of the stop to act as a new stop so drawtube can’t fall off support  rollers .

[Whistlin Bob]

I use a Skywatcher Coma corrector, but I'm sure the same principle applies. When I realised I was getting Pacman stars, I focused it on a distant church spire in daytime, locked the focus and marked the tube- it was about 6 mm.  Solved the problem nicely 😀

Still bugs me that you need to do this, but then again it's a £170 scope that's astonishingly capable so I'll stop my whinging!

[Devonshire]

Thank you!  Good to know. 

Asking because the Scope's not here yet and I want to get the mods list sorted out before it gets here.  

I have the Skywatcher electric focuser on order as well.  I've seen the videos and it's a bit of a fiddle to adapt it - the crayford gets taken off, disassembled, focus motor installed, and then reinstalled with the base turned 180, so the motor points to the rear.  And hopefully it's all square when it's done.  So that's the time to cut the drawtube if it needs to be done, then blacken as needed, etc., etc...    

Re: MPCC spacing... yeah... I'm expecting some fiddle on that score.  I do have the various Baader shims, from wrestling with field flatteners for the refractor I'm retiring.  But my T-ring is a Baader as well, so maybe it'll work first time.  But if it does, I'm buying a lottery ticket!