Tube rings

[wookie1965]

What size tube rings would I need for a Meade LXD55 127" Refractor the OTA circumference is 41cm.

[Waldemar]

cicumference = diameter x 3,14 (Pi), so diameter is circumference : Pi = 41 : 3,14 = 13 cm.

[wookie1965]

So I would need 130mm rings is that correct.

 

[Astro-Geek]

32 minutes ago, wookie1965 said:

So I would need 130mm rings is that correct.

 

As Waldemar calculated, 130mm is the exact diameter, but be careful of rings advertised as "130 rings" because they would probably be approx 159mm internal diameter.

That's becuase the usual naming convention is for the diameter of the mirror or object lens of the telescope that they fit, which is usually smaller than the OTA tube diameter.

For example, I use Celestron "130" rings for my deforked Meade ETX 125, which has an outside diameter of 147mm, and the 130 rings are about 159mm internal diameter (the nearest I could get).

[wookie1965]

so I can get 140mm rings and pad them out if need be. Daft this should be able put circumference of OTA in and the supplier tells you what rings to get rather than guessing.

[Alan64]

The diameter of your OTA is 130.6mm, so yes, go with the 140mm.  You may need the thicker felt, green or red in colour, and the thickness used within pianos...

https://www.fletcher-newman.co.uk/index.php?l=product_detail&p=399

...for example.

[Astro-Geek]

As Alan said, yes, on that list, 140 would be the nearest.

However, when I googled "tube rings", I came across this page https://www.365astronomy.com/SkyWatcher-120mm-Refractor-Tube-Mounting-Rings-WHITE.html

...which lists a set with a 130 inside diameter, but then frustratingly doesn't individually show them..  ?

Maybe worth ringing a few suppliers or further google searching, just in case they are available, as they would presumably fit nicely without any extra packing.

[Waldemar]

3 hours ago, Astro-Geek said:

As Alan said, yes, on that list, 140 would be the nearest.

However, when I googled "tube rings", I came across this page https://www.365astronomy.com/SkyWatcher-120mm-Refractor-Tube-Mounting-Rings-WHITE.html

...which lists a set with a 130 inside diameter, but then frustratingly doesn't individually show them..  ?

Maybe worth ringing a few suppliers or further google searching, just in case they are available, as they would presumably fit nicely without any extra packing.

Yes that is the correct one, 130mm

[wookie1965]

Thanks everyone much appreciated.

[Geoff Lister]

22 hours ago, Astro-Geek said:

For example, I use Celestron "130" rings for my deforked Meade ETX 125, which has an outside diameter of 147mm, and the 130 rings are about 159mm internal diameter (the nearest I could get).

A little while ago, I bought a spare set of rings for my Star Travel 120 refractor. The main tube of the OTA required 116mm rings.

[Waldemar]

26 minutes ago, Geoff Lister said:

A little while ago, I bought a spare set of rings for my Star Travel 120 refractor. The main tube of the OTA required 116mm rings.

Yes, rings for a refractor are normally smaller then the objective, because of the smaller main tube, where the rings are mounted.
but for a reflector, the rings are always larger then the mirror, because the tube where the mirror is mounted in has to be bigger, logically.