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Novice Challenge

William Optics Barlows?.

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You are indeed both correct,
but if you don’t have the binos new, how do you tell them apart? 

It’s the identity after purchase that I am asking about, are the differing in length or something perhaps?

Perhaps a question for @FLO via email

Edited by Alan White
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  • 2 weeks later...

I have both of them.

I have no trouble telling them apart - they are different lengths for one thing - the 2x being the shorter one, but the main difference is that if you hold them up in front of your face a few inches away and look at (e.g.) some nearby trees, the 2x will have the wider view. 

If you are in the dark and want to know which one you have in your hand, with experience you can hold it up to the sky and tell by the aperture which one it is - the 2x having the larger aperture by some margin. 

Edited by great_bear
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An easy way to determine the focal length of a Barlow lens is to draw a circle to twice the size of the lens and then focus the Sun  through it.  Draw the lens away until the image fills the circle and the distance between the lens and the image is the focal length.  Perhaps not so easy in the UK!       😀

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5 hours ago, Alan White said:

I can now work out the magnifications being used.

Will you do this be by coomparing (e.g.) star distances with a known eyepiece?

That's what I had to do with my Mak + binoviewer. The mirror shift required for a revised focal plane that includes the binoviewer, changes the magnification on a mak. in a manner that I knew would be tough to calculate, so I recorded the change in spacing between specific stars.

On my Mak180 this gives me:

  • Bino + eyepieces:                1.20 x mono (normal) eyepiece magnification
  • With 1.6x barlow on bino:   1.75 x mono eyepiece magnification
  • With 2.0x barlow on bino:   2.12 x mono eyepiece magnification

- although of course on any telescope I would assume that non-parfocal eyepieces would get some slight variance in magnification when using a regular, i.e. non-telecentric, barlow, so I'd always use measurement to get the answer.

I wonder what level of magnification the William Optics Bino Barlows provide if screwed directly on the base of an eyepiece, rather than on the binoviewer nosepiece.

Anyone know?


Edited by great_bear
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