NavList:

Oh - and another point worth mentioning which I should have included in the previous posting about the results of the lunar distance measurements I made, was the prismatic effect of the telescope used on my Freiberger sextant which was noticable and significant.

The telescope is an 8 x 30 prismatic of unknown source - probably Russian or by Zeiss Jena. It is not the very best, but of quite good quality.

It is noticable that any off-centre light rays are refracted slightly by prismatic effect, being displaced slightly. The star aligned on the limb of the Moon is no longer on the limb if the image in the telescope is allowed to drift to the side of the field of view: move back to the centre again and it is back in alignment. The effect is small, but about one or two minute of arc which is serious with lunar distances.

It is important therefore to ensure the measurements are made centrally in the field of view of the telescope every time.

I found my arm tiring holding the sextant up in position and found I was drifting in the field of view to the side and had to correct myself constantly - until I used the tripod which took the main weight of the sextant and made life much easier taking sights.

Douglas Denny.
Chichester. England.
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