Jump to content

290128050_ConstellationBanner.jpg.6eb5d1fe82e0853d4c3b80a745d12d74.jpg

Fun with a largish newtonian


Recommended Posts

I was having a few peeks and a play with one of these last night. It's a JMI NGT 18" newtonian. Interesting design that was on sale during the early 1990's I believe. Compact and innovative equatorial mount design that tracks, when the motors are working (not last night !). Quite a handful to actually use and the eyepiece height is not friendly unless a small set of steps is at hand although the upper tube assembly does rotate to move the focuser and finders to the best position. I only managed to see the moon and Jupiter last night because of cloud cover but the views were quite impressive. The scope belongs to my society so I will hopefully get some more opportunities to observe with it under darker skies :icon_biggrin:

NGT-18.jpg.bde2c0db911cef844ddea266cdea084e.jpg

JMI did a 25" scope as well :grin:

rtmc_01_jb2.jpg

  • Like 12
Link to comment
Share on other sites

42 minutes ago, cloudsweeper said:

Very interesting design that, John.  I like the idea of the rotating secondary assembly, but just wondered whether it might impact unfavourably on collimation.  Any thoughts or experience on that?

Doug.

I haven't had enough time using the scope as yet but I have read reports that the rotating upper tube assembly can affect collimation. Apparently while the rotation mechanism works, it's none too precise and adjustments to collimation can be required after rotation.

 

 

 

  • Like 1
Link to comment
Share on other sites

Just now, John said:

I haven't had enough time using the scope as yet but I have read reports that the rotating upper tube assembly can affect collimation. Apparently while the rotation mechanism works, it's none to precise.

 

Glad you said that John.  It shows I'm getting to grips with this fabulous pastime!  ?

Doug.

  • Like 1
Link to comment
Share on other sites

2 minutes ago, 25585 said:

BAS must be quite large and well funded.

I was a member in the early 80s and it was quite big then. We met in the HH Wills Physics Laboratory at the University. Happy days!

  • Like 1
Link to comment
Share on other sites

Cool!

I remember seeing that Skywatcher were developing prototypes with that kind of mount for 10"-14" newts a few years back, around the same time that the stargate structure was also being prototyped for larger apertures, but then shelved it.

While an interesting design (allowing astro photography?), the SW mounts did look possibly heavy/cumbersome imho.  The JMI looks more streamlined!

  • Like 1
Link to comment
Share on other sites

21 hours ago, 25585 said:

BAS must be quite large and well funded. Does it have its own private dark site, or special access to one away from public access?

It's about average now in terms of membership numbers, compared with other societies. Not particularly well funded. The observatory site we have is a small piece of land rented from a farmer at a "peppercorn" rent. Darker than if you live in Bristol but not as dark as we would ideally like. We have a 4m "homebrew" dome with an interesting old 12" newtonian in it and the 18" NGT in a massive roll off shed type structure. We are in the process of updating all this but it will take time. 

We do get some excellent speakers (Prof Chandra Wickramasinghe last week) and do quite a bit of outreach which I really enjoy :smiley:

 

 

  • Like 2
Link to comment
Share on other sites

23 hours ago, John said:

Sir Patrick Moore's 15" Fullerscopes newtonian has a rotatable upper tube section as well but I suspect that was a little better engineered:

 

spm15.jpg

Shows well how big an aperture 15" is, for anyone considering over 12. My dodgy shoulder twinges at the thought. 

  • Like 1
Link to comment
Share on other sites

3 hours ago, 25585 said:

Shows well how big an aperture 15" is, for anyone considering over 12. My dodgy shoulder twinges at the thought. 

I'm pleased to be able to use the BAS 18" from time to time. 12" is the largest I can manage at home and that has to be an Orion Optics based dob to keep the weight manageable. It's my knees with me :rolleyes2:

  • Like 1
Link to comment
Share on other sites

6 hours ago, JeremyS said:

Too much praying for clear skies, John?

:grin:

Begging to be allowed to keep 6 telescopes when I'm supposed to have a 3 scope limit more likely ..... :rolleyes2:

  • Haha 2
Link to comment
Share on other sites

On 24/05/2018 at 18:28, cloudsweeper said:

Very interesting design that, John.  I like the idea of the rotating secondary assembly, but just wondered whether it might impact unfavourably on collimation.  Any thoughts or experience on that?

Doug.

I've built large reflectors with rotating upper assemblies and it is indeed tricky to engineer them with minimal collimation effect in use. I subsequently made them with just the secondary mirror rotating. Four focusers, three visual and one photographic were used, the diagonal shaft had click stops for accurate rotation and each focus mount was collimated to suit its position. Seemed to work ok.   ?

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.