Extension tubes?

[Mamsoth]

Hi all, I've just about scrimped enough together for a crayford to replace the dodgy focuser on my Celestron omni 120, I'm fairly sure I'll need an extension tube and am wondering if there's any real difference between a more expensive one (say the Televue one for £65) and the bog standard ones for around £15. Surely there can't be much difference at all in practical terms?

[jgs001]

I'm using the cheap ones, and they are working nicely for me. I can't comment on the Televue one though.

[Doc]

Most of the difference will be in the name. The finish should be better but as it's only an extention tube with no glass I wouldn't say the difference is huge.

[Moonshane]

when using a SW dual speed crayford on my OMNI 120mm and with a 2" diagonal I didn't need an extension - try it first you probably wont.

I'd agree with the others, the £18 one from FLO is great quality.

[Astro_Baby]

I have a WO one. As far as I can see the only different in most tubes is what the compresision fittings are like. The WO one has a tri knob compression like a Moonlite so its a bit slicker but if its in use the whole time it probably makes little difference.

You dont say what focuser your replacing with but if its a Moonlite you can probably specify how long the drawtube is which would make an extension redundant (possibly).

[Mamsoth]

Thanks a lot for the help guys.

Clear skies to you

[John]

I use the Revelation ones which don't cost much but have a brass compression ring fitting which seems more secure.

[johninderby]

Besides overall better fit and finish it's the compression ring that is the main difference. The cheaper extensions use a thinner gauge and softer brass for the compression ring and the recess for the ring isn't as accurately machined. This can cause some eyepieces to hang up on the compression ring and also when tightening the ring the eyepiece (or eyepiece adaptor) can be pulled a bit off centre.

The best one I've ever had is the Baader which uses a bronze ring. The Moonlite was my least favourite extension as the three screws had to be carefully tightened, each one a bit at a time, to keep the eyepiece centered. The Televue worked very well but was overpriced.

I had two of the Revelation type, and while one worked OK the other was a real pig to use as the brass ring kept slipping out of position and eyepieces were always hanging up when trying to insert or remove them. Quality control is more variable with the cheaper extensions I suppose

John

[daneel]

I need one too as my DMK 21AU04.AS coupled with a StarTravel 80 can't quite focus. I'm going to try this one from SCS Astro:

Orion Eyepiece Extension Tubes - SCS Astro

I need a 1.25" extender but there wasn't one on FLO .

[johninderby]

The only problem I can see with the Orion extensions is that they don't seem to have compression rings but just locking screws.

Opticstar does a 1.25" extension tube.

http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Telescopes-Ascension.asp?p=0_10_5_1_1_67

John

[Mamsoth]

As I'm spending all the money I have on the focuser (the SW dual speed) I think I'm going to go for the cheapest model of ET I can and hope for the best. Thanks alot for all the help.

Cheers

Matt