Strange Sextant error.

[Graham_Wright]

I have a fairly basic brass sextant by Ross of London.
I have just started to understand it but it has an error which I believe has happened since I acquired it.

The horizon glass mirror I am sure, gave me an a full view of the index glass. Now it is showing a view of the index mirror brass surround occupying almost half of the total view.
There is a slight degree of rotational adjustment in the horizon glass mounting but it is insufficient to restore the view of the index mirror.

A sextant is fundamentally a very rigid instrument and the error I have is, to me, inexplicable.

The index mirror is secure in its mount and is flush to the reference.

Am I missing something obvious?

 

[Bilgediver]

The eye piece has slipped sideways. It is on an adjustable sideways slide.

 

[jwilson]

I suspect your 'Ross London' brass sextant is a primarily ornamental reproduction, not a navigational instrument. But as Bilgediver says, the eyepiece/telescope could have moved. Or something could have bent.

 

[penberth3]

I suspect your 'Ross London' brass sextant is a primarily ornamental reproduction, not a navigational instrument. But as Bilgediver says, the eyepiece/telescope could have moved. Or something could have bent.

An interesting point. I know Ross made lenses, but I didn't know they made complete instruments, perhaps they didn't! I have seen Repro's using old names, or something very close.

 

[neil_s]

Yes - Ross did make sextants - or at least they sold them. Look very similar to a Heath with a three ring frame. I think Bilgediver has the answer to your problem. Enjoy your sextant - I find them very addictive!

 

[LadyInBed]

Does this help?


From: Celestial-Nav on my website

 

[MJWB]

Got two. One mine from years ago. One my dad's from even more years ago. Wonderful things.
If you are going to use it for navigation take it into an instrument maker, get it checked and the error documented.

 

[Graham_Wright]

The eye piece has slipped sideways. It is on an adjustable sideways slide.

I examined that. It is pivoted, not on a slide and rotating it does not correct the problem (as would be expected).
The horizon mirror likewise is capable of only slight (and insufficient) adjustment.

I suspect your 'Ross London' brass sextant is a primarily ornamental reproduction, not a navigational instrument. But as Bilgediver says, the eyepiece/telescope could have moved. Or something could have bent.

I bought it at a boat jumble many years ago and did assume it was merely an ornament. However, I have had it examined by an expert who describes it as "crude but usable". The mirrors are good and it was possible to remove the errors.
It is hard to find anything that has been "bent". Sextant frames are very rigid and this one is no exception.

 

[Bilgediver]

I bought it at a boat jumble many years ago and did assume it was merely an ornament. However, I have had it examined by an expert who describes it as "crude but usable". The mirrors are good and it was possible to remove the errors.
It is hard to find anything that has been "bent". Sextant frames are very rigid and this one is no exception.

Sorry to hear that Graham. I had exactly that problem a few months ago when I checked my sextant. Puzzled and never experienced this before. i then noticed the eye piece was off to one side. Not only that, I had inadvertently moved the light wire and that stopped it moving to the correct location. A few tweeks and back to normal.

 

[Graham_Wright]

Sorry to hear that Graham. I had exactly that problem a few months ago when I checked my sextant. Puzzled and never experienced this before. i then noticed the eye piece was off to one side. Not only that, I had inadvertently moved the light wire and that stopped it moving to the correct location. A few tweeks and back to normal.

I will have another look. Perhaps the telescope is on an eccentric pivot?