|
Author
|
Topic: M15 Sextants Glare on sun sight
|
navstar
|
posted June 12, 2013 12:36 PM
Hi:
I just purchased the Davis Mark 15 sextant and I went through the adjustments. I tried to take a sight on the sun and there is a very bright reflection when looking through the scope (I have all of the filters down on both the index and horizon). There is not sun image visible with all of the shades, but a very bright reflection around the perimeter of the scope tube. I don't want to damage my eye. What is the problem?
Thanks,
Bill
|
|
David Burch
|
posted June 12, 2013 02:36 PM
Sound like the mirrors might be out of alignment.
Have you checked and set the side error? there are several steps, as outlined in the Plastic sextants book, starting with a perpendicular check looking at both mirrors at the same time. in the book we use a couple dice for this.... to help you find the right page. but you do not need any aids to get it very close.
after side error, need to check the index error. this does not have to be precise.
sounds like something might be way off.
another thing to check to see how bad the alignment might be is to check the reveal along the edge of the mirrors in their housing.
This too is in the book, with illustrations.
Please let us know if that solved the problem.
From: Starpath, Seattle, WA
|
|
David Burch
|
posted June 13, 2013 07:33 PM
Just noticed that you say *all* of the shades are down. that is not right. remove all of the horizon shades, and just one or two of the index shades, then adjust the latter for the right brightness.
Horizon shades are only used for bright glare on the horizon.
Please refer to the sextant book mentioned above for more details.
sorry i missed this important piece of info from your question.
From: Starpath, Seattle, WA
|
|
navstar
|
posted June 13, 2013 08:54 PM
Thanks, I did the adjustments again and it took most of the glare out of the telescope tube. I do have the follow up questions.
1. When it says to use a “distant landmark” to align the horizon mirror, how far away or close should that object be to best make this adjustment?
2. Is the reason that the half mirror (vs. full mirror) is recommended to have that vertical split of the object being sighted (e.g., sun) to verify that the sextant is being held vertically and not at an angle?
3. Please clarify your point “check the reveal along the edge of the mirrors.” It is not clear what you are referring to in this suggestion.
I asked David in a phone call about printing some sections of the Plastic Sextant book. He told me I would have to buy (which I did) the pdf version to be able to print some pages. Please inform David that the pdf version that he recommended of the Plastic sextant book (he suggested buying it through Bilbary) does not allow it to be printed. According to Bilbary it is a restriction on the format provided to them from Starpath. It would be nice to be able to print key pages to take into the field with the sextant and not having to rely on the computer version.
|
|
BKachline
|
posted June 14, 2013 10:52 AM
I have a black Mk-15. I used a piece of sandpaper to rough the inside of the sight tube to cut down on the glare.
|
|
David Burch
|
posted June 14, 2013 05:31 PM
The three questions raised here are answered in detail in the book How to use plastic Sextants. Please refer to that book for the answers.
We provide a free PC ebook copy of the text with the purchase of a sextant from us.
I am sorry there was a misunderstanding about what i said. My statement was that *none* of our ebooks can be printed. This is done for two reasons. 1 there is no copy protection to a file that can be printed, and 2. we have print copies of all the ebooks we make.
I recommended the pdf ebook as an option for viewing our ebooks on a Mac. That was the context of the conversation, and the only meaning implied.
I understand that Bilbary has refunded your purchase of that ebook, which shows what a good company they are. We recommend them for all of our ADE ebooks.
It was also my understanding from our phone conversation that you had access to a PC computer. If that is the case, then please check the ebook on that source.
It was also stated in that conversation that this book is very important, not only to the use of plastic sextants but to all sextants. In short, one way or the other, you will be best served by obtaining and referring to that book for almost all questions about sextants.
From: Starpath, Seattle, WA
|
|
David Burch
|
posted June 14, 2013 05:32 PM
to follow up on the note from BKachline:
I believe there are references here to two different "tubes."
I assume the original question was referring to the view through the actual telescope, which is different from the empty sighting tube that Davis provides. The latter has some value for use with sextant piloting, but not often of use for celestial sights.
In any event, thanks for that hint on the sight tube. I have not done piloting in bright light, so we will keep this in mind if it comes up.
From: Starpath, Seattle, WA
|
|
David Burch
|
posted June 14, 2013 05:38 PM
PS. if there are key sections of any of our ebooks that you want a copy of, blow them up on the screen and hit the Print Screen button.
That copies the page to the clipboard, and then they can be pasted into any program you have that has a print function.
Also the Kindle versions of our books can actually be viewed on any smart phone, so they could be loaded there and read in the field.... just have to pan around and zoom some to see details.
From: Starpath, Seattle, WA
|
|
navstar
|
posted June 23, 2013 03:26 PM
Thanks
|
|
|
