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Ottway Monocentric eyepieces

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I just bought a pair of Ottway monocentric eyepieces of f.l. 7.5mm and 12.5 mm from ebay. As many of you will be aware, the monocentric is a specialist eyepiece with a small field of view and a low number of external surfaces, most suited for planets etc in  a telescope with powered tracking. They were cheap, so seemed worth a punt. Ottway are a well reputed UK maker, but no longer active.

When they arrived, I was disconcerted to find the barrels were a fraction over the standard 1.25" size and won't fit in a standard diagonal. Fortunately the barrel and active part unscrew to reveal what looks like a R.A.S. thread, and this will drop snugly into a 1.25" diagonal.  In short, these look old. Can anyone shed further light?

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I owned a TMB Supermonocentric 5mm for a while which was probably the finest eyepiece that I've ever used in terms of pure optical quality. The tiny eyelens, short eye relief and ~30 degree field of view made it quite challenging to use in my scopes which are on undriven alt-az mounts so we parted company eventually.

Other than that, my monocentric experience is zero I'm afraid. I'll be interested to hear what you make of yours :smiley:

Edited by John
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Finally got a chance to try out the two Ottway Monocentric eyepieces last night.  Telescope: 127mm Celestron Mak on Nexstar GoTo mount, (1500mm focal length), solar system aligned on Jupiter. Circle T prism diagonal.

I looked at Jupiter, Spica, epsilon1 Lyrae, epsilon2 Lyrae. Conditions: intermittent cloud, rising near-full moon. I compared the Ottways with my 10mm Baader Classic Ortho.

I'm not a particularly skilled observer, but I could not see much difference between the performance of the Ortho and the Ottways. The Ottways have a smaller field of view, but the performance did not appear to vary much between centre and edge. The 12.5 mm delivered a crisp image of Jupiter and its cloud belts and 3 visible moons . With the 7.5mm trained on Jupiter, the x200 magnification seemed a bit much and a large faint ghost reflection was coming from somewhere. Trained on stars, the 7.5mm gave an adequate image with diffraction rings and no spurious scatter.

Given these results, I expect I will try to use these eyepieces rather than consigning them to the 'vintage brass telescope' collection. 

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