NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant Comparisons
From: Fred Hebard
Date: 2004 Mar 20, 12:15 -0500
From: Fred Hebard
Date: 2004 Mar 20, 12:15 -0500
Doug, No, I don't collect older equipment. I have been trying to acquire a sextant suitable for lunar observations, so I look for sextants with defects on Ebay that might still be serviceable. I have one British Husun that only has the "star scope." It's a 2.5x power scope. It's my understanding that a more powerful one would give more precise readings. I checked this by buying an old Simex-type sextant, which subsequently was sold. I have been looking for another Husun with the inverting telescope or another instrument. The Cassens & Plath was the first that came up which was suitable. In comparing the Cassens and Plath to the Husun, I would say, overall, that I prefer the Husun at this time. It's prettier, with the silver-inlayed arc; this increases my fondness for the instrument. The black crinkle finish is nicer than the Cassens and Plath's. All the screws are varnished or painted brass; there's no aluminum to corrode with steel screws or react with the brass or bronze (There's no corrosion on my Cassens and Plath; it doesn't appear ever to have been used for extended periods). The 2.5x scope on the Husun has a very wide field of view, wider than the 4x "star scope" on the Cassens and Plath. I have seen no optical aberrations in the Husun, while the Cassens and Plath star scope has chromatic aberration, which rather surprised me (reddish fringe on the bottom of the image and bluish fringe on the top). The aberration makes it more difficult to check index error by measuring the sun's semidiameter. The handle on the Husun is straight up and down. This makes some lunars easier, whereas the tilted handle on both brands of Plaths, while it makes looking at the horizon easier on the wrist, makes lunars more difficult. When holding the instrument between shots or while waiting, the Husun is less fatiguing to hold The star scope on the Husun is in close to the horizon mirror. This centers weight in the instrument, making it less fatiguing to hold. Being close in to the horizon mirror, the smaller mirror does not restrict the field of view of the instrument as much as one might suppose. I suppose the larger mirrors would be "faster" optically, however. The perceived weight of the two instruments is similar. I have not actually weighed them. The lamp on the Husun can be swung around to illuminate my wrist band when recording data. The lamp on the Cassens and Plath is guided to illuminate the scales only, making recording data more difficult. The box on the Husun is significantly smaller than the box on the other instruments. These are my impressions after two days. Fred ------------------------------------------------------------------------ Frederick V. Hebard, PhD Email: mailto:Fred@acf.org Staff Pathologist, Meadowview Research Farms Web: http://www.acf.org American Chestnut Foundation Phone: (276) 944-4631 14005 Glenbrook Ave. Fax: (276) 944-0934 Meadowview, VA 24361 On Mar 19, 2004, at 5:44 PM, Royer, Doug wrote: > By the way,do you collect older sextants?Don't you also have some older > British equipment you wrote about in the past?Just curious.
