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The Zeiss Telementor (63mm OG, 840mm focal length refractor) of the 1970’s is like this. If you screw the eyepiece holder directly into the telescope tube you won’t be able to achieve focus, either an extension tube or a diagonal is required. Zeiss manufactured six different extension tubes (in the range 20mm to 80mm, and usable singly or in multiple) to cover all circumstances.
‘Classic’ Newtonian reflectors of a few years ago had the opposite problem because the eyepiece tube couldn’t be too long as it would cut into the light path inside the main tube. (i.e. use of a diagonal was impossible.)
The Tomline Refractor at Orwell Park also suffers from poor prime focus image position (too far up the tube) which similarly makes the use of a diagonal impossible.
On the other hand a by-product of a ‘focal reducer’ or a ‘Barlow lens’ is a shift in the position of the focal plane image. The image is moved away from the objective with a Barlow and toward it with a focal reducer. This allows you to get the image plane nearer where you want it, but you have to accept a reduction or increase in magnification for any given eyepiece.
James,
Would it be possible to replace the two bevel cogs with an ordinary cog and a worm gear?
The worm would be attached to the handle and provide such mechanical disadvantage that the slit would not have enough energy to spin the handle. The downside of this arrangement would be a very great increase in the time it took to open/close the slit.
Bill.
Now looking a lot more spectacular in SoHO LASCO C3.
Attachments:
The BAA Memoirs are available on SAO ADS.
https://ui.adsabs.harvard.edu/search/q=bibstem%3AMmBAA&sort=date%20asc%2C%20bibcode%20asc&p_=0
Unfortunately the person doing the scanning doesn’t seem to have worked out the pagination and sometimes the content doesn’t match the title!
Bill Barton,
Deputy Director, Historical Section.Larger than Mount Everest, apparently?
Surely the monkey is using lorgnettes (handheld spectacles)?
There was a printed index issued at our centenary in 1990. It covered volumes 51 to 100.
An index to volumes 1 to 50 was issued (in 1963!), but the print run was very short.
New refined prediction for reentry is 21 February 2024 16:31 UTC ± 5 hours.
The BAA Memoir can be found at the following web address
https://articles.adsabs.harvard.edu/full/1898MmBAA…6….1.
This image shows Sir Robert Ball Lecturing aboard the s.s. Norse King.
I’d guess the gentleman on the extreme left is E W Maunder, and then Mrs Maunder before Dr A A Common. I cannot identify anyone else as their faces are not so well known.
Attachments:
I’d be interested in the full explanation of this too, but in the meantime I’d like to make two points
1, In the past meeting attendance was limited to bona fide BAA members, but members of affiliated societies could also attend. This may no longer be the case with live streaming. This also applied to other BAA membership benefits (e.g. advice from Section Directors).
2, One of my local astronomical societies subscribes to several astronomy magazines and it is a very real benefit of membership to be able to read current magazines purely for the much cheaper price of membership. How local societies will still be able to obtain the JBAA & Handbook is, currently, not obvious.An extra day of rail strikes has just been announced for Friday, September 1.
Annoyingly September 2 has been announced as a strike day on the railways.
Full contact has been re-established!
John,
I’m afraid not. Our venue was not fitted for streaming (or recording) and only summaries will appear in the Section News and the Journal.
Bill Barton,
Deputy Director.Found in the Daily Star Newspaper of a few days ago.
And now this!
Mairan (co-longitude 44 degrees (sunrise)) is located in the Jura Mountains between Oceanus Procellarum to the west and Mare Imbrium to the east. Page 36 of our Handbook will tell you when it becomes visible (at sunrise) and invisible (at sunset). Mairan has a similar latitude to the prominent crater Plato, but is 34 degrees east of it. Mairan has a similar longitude to Aristarchus but is 18 degrees north of it.
