Williams Optics Binoviewers - can't achieve focus on 5" Celestron Newtonian

[StarGazingSiouxsie]

Hi,

I bought some Williams Optics Binoviewers. They appear very nice quality but I cannot achieve foucus with them on a 5" Celestron Newtonian, FL = 650MM fr = f5. 

I have not used binoviwers before today and I bought them primarily for my new telescope which hasn't arrived yet, a Celestron 9.25 CST. 

I wanted to try the binoviwers out on the 5" today but could not achieve focus. I also tried using the 1.5 x Barlow that came with them.

Is there a reason they won't focus? Do you think they will be OK on my bigger scope?

Thanks. 

Edited July 11, 2020 by StarGazingSiouxsie

[Ricochet]

The binoviewers have a light path that is approximately 110mm long, so to get them to focus with no barlow or corrector you would need to wind the focuser inwards by 110mm. With a Newtonian this is not possible, and so you have to add a barlow or corrector to the nose piece which reduces the amount of in focus required. A 1.5x corrector is not much of a change, so it is unlikely to reduce the required in focus enough for it to be within the limited focus travel typically found on a Newtonian focuser. If you were to attach the nose piece from a 2x barlow to the front of the binoviewer, you would likely find that it acts like a 3x barlow, and might allow you to focus the binoviewers in the Newtonian (might!). 

The C9.25 is a completely different telescope. Unlike your Newtonian, it focuses by moving the primary mirror itself. This means it has a large range of focus travel, enough that you should be able to focus the binoviewers with no barlow/corrextor attached. However, moving the mirror so much will introduce aberations, and the narrower the light cone, the better the binoviewer will perform, so you will get a better image by using some sort of corrector, even in the new scope. 

[StarGazingSiouxsie]

Thanks Richoet  

[StarGazingSiouxsie]

Just as an update in case it helps anyone out down the line............

I was able to achieve focus by using a 2X Barlow lens with the binoviewers in Cassie, my 5" Newtonian

I was able to achieve focus in Celeste Bubble,  my new 8" SCT without using any magnification at all, just using the binoviewers as is.