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WO BV barlow position

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#1 Ice Cube

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Posted 18 March 2023 - 09:48 AM

i've recently acquired from CN classified a WO BV set which included the WO 1.6 barlow nose piece.

 

i've used it with two scopes (C8 EDGEHD and an AT102ED) with a stock 1.25 prism diagonal that came with the C8.

 

no problems achieving focus on the C8, but the AT102ED is more challenging.

 

with the 1.6 attached to the nose of the BV, most of the time i can achieve focus

before the focus bumps up against it's most inward travel.

 

yesterday in the daylight i took the time to 'dial' in the diopter of both eyepieces by focusing on top of a radio tower about 3 or 4 miles away.

 

last night, i couldn't get infinity focus even at the most inward focuser position and rotating the eyepiece diopters to either limit.

 

in frustation, i moved the 1.6 barlow in front of the celestron diagonal instead of after.

with that change, i achieved infinity focus and seem to have much more latitude in focuser position.

 

what am i giving up by moving the barlow forward of the diagonal?

 

is the effective FL of the AT102ED different with the barlow forward instead of aft of the diagonal?

 

 

 



#2 Alrakis

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Posted 18 March 2023 - 10:25 AM

With the barlow attached to the diagonal it is intercepting the light earlier and in a sense expands the image earlier. This is why it provided the ability to achieve focus. The downside is that this increases the barlow's magnification which decreases the true field of view.

 

Chris 


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#3 junomike

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Posted 18 March 2023 - 05:20 PM

Also, the SCT should reach Focus without the 1.6X Barlow



#4 Ice Cube

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Posted 18 March 2023 - 05:44 PM

Also, the SCT should reach Focus without the 1.6X Barlow

it does, not a problem!


Edited by Ice Cube, 18 March 2023 - 05:45 PM.


#5 doug mc

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Posted 18 March 2023 - 07:13 PM

I use the William Optics 1.6x OCS mainly in the nose piece of my 1.25 inch diagonal, even though I own maksutovs. In this position the total magnification comes to around 1.8x to 1.9x. It also projects the focal plane the full distance of my 1.25 diagonal. It is not a standard barlow. It has a separated two group optical system. I prefer to use it that way as it allows the maksutov and schmidt cassegrain scopes to operate near their optimal back focus position. 



#6 jprideaux

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Posted 24 March 2023 - 07:58 PM

Yes the magnification of the WO OCS is dependent on the light-path length after it.  When placed on the nose-piece of the WO BV, it works as 1.6x.  When placed where after it the light goes through both the diagonal AND the BV, with that longer light-path it functions as more than 1.6x.  Perhaps, depending on diagonal up around 1.9x or so (+/- a bit).  I use my WO OCS so the diagonal comes after it in order to be able to reach focus with my refractor.  Otherwise, I cannot reach focus.  Yes, with it working as a higher magnification OCS, the field-of-view is smaller.    




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