Binoviewers & "in focus travel" - advice please!

[Muddy Rutter]

Hi All,

Prompted by another thread I am interested in the Revelation binoviewers sold by Telescope House.

Their Website says: "The use of a Barlow helps achieve focus with Newtonian telescopes and refractors with less than 100mm of focus in-travel."

I have a Celestron Omni XLT120 refractor which is f8.3 and has a focal length of 1000mm - does anyone know if I will need a Barlow, and can you explain what 'in-focus travel' is please?

I did ask the nice man at Telescope House but he wasn't too sure.

Many thanks,

Nick

PS: The Revelation kit comes with two 26mm 'premium' Meade Possls, does anybody know which model they are?

[GazOC]

Hi Nick,

Your refractor will come to focus at a certain point so that when a diagonal is used the image come to focus in the eyepiece, with the binovewiers added to the setup the eyepiece is pushed further away from the diagonal and the point of focus so the focuser cannnot reach focus when fully racked in towards the lens (in focus travel).

Adding a barlow lens to a telescope pushes the point of focus outwards and will (hopefully) allow room for the binos to "fit in" .

HTHs

Gaz

[step_hen]

I have these binoviewers and the skywatcher evostar version of the 120. they will not reach focus without a barlow between the diagonal and the binos. I'd recommend the Tal 2x barlow- you can use it as supplied or for less magnification you can unscrew the element from the barlow and screw it directly into the bino nosepiece.

This scope and bino viewer makes a great combo for lunar and planetary viewing.

Stephen