Bino questions

[Neil H]

Hi all last night I tried my binos in my refractor 127/1200 using the 1.6 Barlow I got focus on the moon using earpieces from 32 mm down  to a 9 mm all looked ok . I had about 1 to2 mm back focus left

Staying with the 20mm WO eyepiece I can't focus with the x2 WO Barlow but can with my bst x2 full size Barlow waited for Saturn now this is were my problem started I could not merge the images with 1.6 nose Barlow? No matter what combination of Barlow could I merge the image 

So is the bino ok or me not doing some thing right . I know Jupiter was low so seeing may have been poor but 2 images  too and no detail at all ? 

Edited July 2, 2022 by Neil H
Typo

[Neil H]

How do you get more back focus . I have 2 extensions  I use when a camera is fitted to this telescope do I need to use them with the binoviewer  any ideas any one 

 

 

[bosun21]

12 minutes ago, Neil H said:

How do you get more back focus . I have 2 extensions  I use when a camera is fitted to this telescope do I need to use them with the binoviewer  any ideas any one 

 

 

I am just about to buy myself a new binoviewer so regarding the dual images not merging i can’t comment. Regarding the back focus , you don’t want any extension and it’s actually in focus travel that is the issue with binoviewers. This is why a barlow is required to reach focus ie: the binoviewer needs to be nearer the focuser and because this is not possible a barlow is used.

[Louis D]

You need to remove length from the OTA if you run out of in-focus.  Some refractors come with rear sections that can be unscrewed and removed to shorten the overall tube length.

Before blaming BV alignment, try checking that neither eyepiece is tipped in its holder due to undercuts.  Next, rotate the diopter adjusters to see if the images demerge due to lack of concentricity in the adjusters.

[MalcolmM]

I sometimes have to loosen off the retaining screw of one of the eyepieces (usually the right hand eyepiece) in order to merge. Removing the tension must allow the eyepiece to centralise itself. Doing this has allowed me to merge even with 7.5mm eyepieces. I do find I can sometimes merge easily and sometimes it takes a bit of fiddling! Rotating an eyepiece can sometimes help merging. Making sure each eyepiece is in good focus is important too.

Malcolm 

[Neil H]

Ok I can't shorten  the refractor with out cutting it down may be I need a different one 

 I will have another go when the clouds go away 

If any one of a refractor the bino will work in fully can they post a link please 

[MalcolmM]

I can reach focus (Tak 100DC + WO Binoviewers) with the WO 1.6x GPC attached to the telescope end of my diagonal. To reach focus without any GPC I have to remove all the extensions from the scope, in effect reducing the OTA length by about 9 cm.

Malcolm 

[Space Hopper]

Generally any refractor that is optimised for imaging with a big, large travel focuser will work ok.

With Baader viewers for example, the focusing distance focusing with no gpc, to  focusing with the 1.25x, 1.7x and 2.6 gpc's in situ is a little under 70mm.

[Louis D]

I've recommended it many times before, but here it goes again.  Look for a used, vintage Meade 140 2x Barlow to use as an OCS/OCA/GPC.  They regularly go for between $40 and $65 over here on our astro classifieds.

The nosepiece is a three element, filter threaded unit that can be screwed onto the front of a WO/Arcturus/etc. BV.  It operates right at 3x in that configuration and is insanely sharp.  I have no trouble reaching focus in my Dob that has a low profile focuser and 20mm of in-focus left with eyepieces that focus at the shoulder.  It also works great in refractors to avoid having to rack the focus in from its normal focus position.  Since I only view planetary sized objects with BVs, the 3x magnification is a plus.

[WJC]

The higher the magnification, the more prominent collimation error.

[Louis D]

@WJC Is that true regardless of where the magnification originates?  If a BV is used with the same eyepieces in a 400mm versus a 2000mm telescope, will collimation error be 5 times more obvious in the 2000mm telescope?