Skywatcher Collimatable Focuser

[John]

I notice that the stock simple single speed crayford type focuser on my Skywatcher 200P dobsonian has a push-pull collimation bolt system fitted which allows the tilt of the focuser to be adjusted.

Has anyone ever used this facility to adjust the tilt of the focuser ?

Personally, I have not found a reason to adjust focuser tilt with this scope. It would be a very useful facility on some of the Skywatcher refractors that I have owned but, sadly, the focusers on those scopes did not have the feature 😒

It seems quite an advanced feature to have on what is otherwise a rather simple and sometimes rather criticised focuser.

 

Edited October 12, 2023 by John

[Barry Fitz-Gerald]

This sounds like the same system as on the SW250PDS I have, and it is quite useful. It is surprising how far off the focuser can be, but this allows quite precise alignment with the OTA. I bought a handfull of those small magnetic bubble spirit levels to get the OTA completely level by mounting them along the tube and on the horizintally orientated spider vanes, then used a tightly fitting blanking cap in the focuser with a circular bubble level on top of that. In this way I could ensure everything was level, and usually confirmed it by using a plumb line dangled down through a hole in the blanking cap to check if it was lined up with the vertically orientated spider vanes. Keeping the polystyrene cradles included with the packing helps as this provides a good base to hold the tube horizontal. Fancy for a fairly basic focuser.

[John]

1 hour ago, Barry Fitz-Gerald said:

....Fancy for a fairly basic focuser.

Yes, that is what I'm thinking. I wish they incorporated it in their refractors. 

[Split Zygote2]

Hello John think I bought a HEQ5 black version (non go-to) from you a few years ago.

I have realigned the focuser using this adjustment on my SkyWatcher solid tube 250 dob  fitted with the single speed basic focuser.  

In essence I flocked the tube, which involved removing all the optical components, then  having put it all back together again I squared the focuser to the tube and  re-centered  the secondary, I also replaced the bearings, added adjustable counterweights, fitted rudimentary but effective setting circles and wheels.  THEN I bought the latest greatest collimation device and destroyed  the already pretty good collimation ... it takes a while getting this back - then (some people take longer to learn than others) I went  and  bought  the newest latest greatest collimation device v. 2.0 and repeated the process  ... and so it goes ad infinitum. Nowadays I just use the pole star!

Apropos the focuser Why it's got a bad press I just don't know? Sample variation?  Mine albeit single speed on a fast focal ratio scope is very precise (easy to find focus) and can hold a paracorr and Nagler 31 most adequately albeit not vertically as would sometimes be the case with a refractor. (minus the paracorr of course) The focuser on my Tak 130 NFB the 4 inch diameter drawer-tubed, huge ginormous one (bought new)  racked out under its own weight and a 2inch diagonal ... not a little creep but an accelerating mass that hit the stops with a thunk that vibrated the whole scope and made you fear for the collimation. My Tak FC - 100DZ focuser didn't rack out but was so stiff that turning the focuser moved the scope off target. Both these issues took not a little time to resolve. So I am a BIIIG fan of this SW focuser. My SW 130PDS has the 2 speed version and that too has  been hassle free and a joy to use - Roger Vine if memory serves commented on this focuser by saying "It is a gem" (as fitted to his 16 inch go to SW Dob). Note however that I did true up the flat bearing surface that interfaces with the focuser pinion (on the dob) by hand using a perfectly flat Japanese waterstone . Note also that for me the 10 inch Dob will outperform the 5 inch Tak (as it should) but only on a night of near perfect seeing otherwise it's pretty much of a draw. The Tak will however give me a better aesthetic experience - way better contrast, no light scatter,  no diffraction spikes etc ....... or so I keep telling myself.  

Sorry gone off topic a bit!

Just thought my 120 Equinox has a similar focuser and that has also been exceptional holding binoviewers equipped with dual  morpheus  eyepieces very well. No image shift or backlash is apparent in any of my examples of these  SW focusers 

 

Michael

[Spile]

I check the focuser is square with a pair of compasses. It always is so like you, I have no need to adjust it.

[John]

Thanks for the responses folks 🙂

I'm happy with the focuser tilt on my scope so I won't be adjusting it. 

I find that the stock single speed crayford seems to do it's job quite well, even with monster eyepieces. 

 

Edited October 12, 2023 by John

[bomberbaz]

24 minutes ago, John said:

Thanks for the responses folks 🙂

I'm happy with the focuser tilt on my scope so I won't be adjusting it. 

I find that the stock single speed crayford seems to do it's job quite well, even with monster eyepieces. 

 

I think that much of the basic equipment provided to astronomers is more than up to the job John. How easy a whistle and flashing light can and does change how we view things even though it's basic function remains the same.

I used to have no zooms and I think about 25-30 ish fixed length EP's. Personally I now carry less fixed focal lengths EP's than I do variables (4 zooms, I could manage with 2). How times change!

[wookie1965]

On 12/10/2023 at 21:43, Spile said:

I check the focuser is square with a pair of compasses. It always is so like you, I have no need to adjust it.

Can you explain how please I would like to check the focuser on my 10" 

[Spile]

3 hours ago, wookie1965 said:

Can you explain how please I would like to check the focuser on my 10" 

I open the compasses to the length of one side and check it against the opposite side. See initial check part of https://astro.catshill.com/collimation-guide/

[wookie1965]

10 hours ago, Spile said:

I open the compasses to the length of one side and check it against the opposite side. See initial check part of https://astro.catshill.com/collimation-guide/

Thank you so much I had not come across that guide and I have probably all links to collimation you can think of.