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Eyepiece 1.25" size??

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Sounds silly eh?

What size are your 1 1/4" eyepieces and what clearance have you in the visual back?

My reason for asking is this. I just this morning received a lovely WO erecting prism from FLO. Good service btw.

It won't fit into the visual back of my Astro Tech.

As a Toolmaker, I thought I'd measure it. Body size on the barrel is 1.247", and has a lip at the leading edge of 1.250".

I measured the visual back on the AT, and it is 1.249". Ergo, interferance fit. :D

All my other EPs fit, and for reference my visual back on my C8 is positively sloppy in comparison at 1.260". Yes, 10 thou clearance!

Typically my EP collection average 1.245", ie 5 thou clearance on the nonimal 1.250" size. All fit the AT nicely.

Who would you ring? Astrotech, or FLO?

I honestly don't know which one has the issue.

Currently my C8 visual back is on the AT and I can use it but this is so frustrating given that this is a stock size and has been for decades.

I rang FLO for advice but got the message machine.

Can anyone advise?:p

Thanks SGL.

Edited by Mr Bond
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I had a green A-T 66ED and a A-T erecting prism.

If I remember correctly, it was a tight fit in the back of the scope. But it did fit.

My eyepieces and accessories have very similar readings(varies 'tween 1.243"-1.245") to yours.

Sounds to me like the W.O. is a few thou bigger than norm. Bummer.


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Decision made. :D

I took the visual back down the garage and bored out a couple of thou. :p

No tearful phone calls, everything fits everything else AND, as a bonus I turned out the eccentricity in the eyepiece holder too.

What a lovely thing that WO erecting prism is. Just tried it properly in daylight on my AT66 APO/Swarovski eyepiece. Pin sharp, no (discernable) CA to my eye.

I love new toys!! ;)

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