NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2012 Jul 23, 07:33 -0700
Hi Stan
First, work on the focus. The magnifier sits on an arm that seems to deflect at the slightest touch. So getting the focus set is most important.
Instead of worrying about the entire vernier, just look at the nonius. The nonius is the "zero" of the vernier and you always need to see that. So get that in focus and make sure you retain focus over the entire range of angles. Do this in a brightly lit room, eliminating the darkness issue.
Once you have that, turn out the lights. Place your LED behind the diffuser. Look for the nonius again. When I do this, I get scintillations off of the graduations (of which the nonius is one). Take your time, you know its in focus, its just a matter of illumination. Placing the LED in front of the diffuser will be too bright and there will be too much glare.
Consider this, if you can see the graduations by mark one eyeballs, you should be able to see them magnified. Its just glass and metal, are you going to let that beat you? :-)
As Alex points out, its not as easy as the drum. There is an advantage to the vernier though. There is absolutely no wear to a drum mechanical you don't have, eliminating that uncertainty. Once you have mastered the vernier, an entire world of older instruments become available to your use.
Best Regards
Brad
Brad,
I've tried red and white LEDs behind and in front of the diffuser. Any of them is better than nothing, and, of course, red would be better for preserving night vision, but none of them are really satisfactory. Maybe it is just a personal problem.
Stan
-----Original Message-----
From: Brad Morris <bradley.r.morris@gmail.com>
To: NavList <NavList@fer3.com>
Sent: Sun, Jul 22, 2012 9:00 pm
Subject: [NavList] Re: Heath vernier sextant
I use a red LED behind my diffuser.On Jul 22, 2012 8:23 PM, <slk1000@aol.com> wrote:I was just given a 1940 Heath and Company vernier sextant, as a gift from a 96-year-old friend (yes, 96!) who stopped using it when he got an Astra IIIB. He bought it used right after World War II. It appears to be complete and in excellent condition, including three telescopes, a sight tube, two eyepiece filters, a "pick" tool, and the original box and key. Even the mirrors are in great shape.
I have a couple of question about it, though:
1) What are the eyepiece filters for? From my amateur astronomy days, I would have to call them a sun filter (very dark) and a moon filter (green). My best guess is that they allow you to view the sun and moon using the telescopes alone, without the sextant.
2) I'm having a heck of a time trying to read the vernier scale. The magnifier works (not as well as the trunnion-mounted one on "Heath and Company's best vernier sextant" (on Bill Morris' site), I'm sure) , but it seems that when I have it in a position to read the scale it blocks the light, making it difficult to read the scale. There is a diffuser screen that I imagine is supposed to help, but how? With an external light source? (I'm pretty sure Bill will be able to answer this.) Even if I could read it, figuring out which of 50 vernier lines aligns with one on the arc seems daunting
3) The sextant does not seem to have any adjustments with holes where the "pick" tool would be used. It seems a slotted screwdriver would be more appropriate. The serial number on the certificate matches the sextant. What else could that tool be for? Is it possible that this is not the original box, and the certificate was moved from the original box?
Stan
