Buy a sextant

[albyreto]

Hi

I have a Mark 15 plastic sextant and I want to buy a better one.. 
I've heard about Astra IIIb and Astra Professional... differences? what is the best?

Other tips are welcome!!!

Thank you
Alberto

[c_davidson]

Albyreto,

Firstly, I have a III-B and really like it and have had no problems with it.  The red LED light for night sights is somewhat hard to read on the minutes knob.   I use the whole horizon mirror and find it easier to use than the split horizon mirror.

The practice bubble horizon is better than nothing but no better than that.

As with any sextant- make sure you do not drop it!

Clendon

This is from Celestaire;

Just as the Astra IIIB has become world famous as the premier low cost metal sextant, the Astra III Professional Model with its low cost, high accuracy, and excellent handling qualities is destined to be the standard for professional seamen.

Its construction is similar to the Tamaya sextants in that it has a bronze arc fused to an aluminum frame. The bronze arc can be manufactured to a higher tolerance than aluminum, which gives the sextant higher accuracy. At the same time the aluminum frame keeps the over-all weight low enough that fatigue is not a problem as with a solid bronze or brass sextant. Nevertheless, the additional weight of the bronze arc adds about 8 oz. and gives the instrument an excellent balance and 'heft'.

The handle is a new more comfortable design, and has an electrical outlet suitable for powering accessories. Except for the weight difference, accuracy, and handle improvement, it is exactly the same sextant as the basic Astra IIIB, and has all the attributes of it. These include thoroughly tested mirrors, maintainability, and the ability to quickly and economically change the horizon mirror type.

The sextant comes with a 3.5x40 telescope and wooden case as standard equipment. Optional items include a 7x35 telescope, zero magnification sight tube (see page 11), a practice bubble horizon (see page 13) which facilitates effective back-yard practice without the need for a sea horizon, and a more expensive Professional Artificial Bubble Horizon. This provides a 2X power artificial horizon for use on land, or at sea if extremely calm conditions exist and the natural horizon is not visible. It connects to batteries in the handle for night lighting, and incorporates a dimming rheostat for use with faint stars. Shipping weight includes all accessories which are ordered from this page. SW 20 lbs.

[LouisC]

Hi

I have a Mark 15 plastic sextant and I want to buy a better one.. 
I've heard about Astra IIIb and Astra Professional... differences? what is the best?

Other tips are welcome!!!

Thank you
Alberto

Alberto,

I'm no expert but from what I've read one of the best sextants is the Tamaya Jupiter.  Cost is around $2,000.

I would really love to get a Freigberger yacht sextant. 

Lou

[Douglas Denny]

Hi

I have a Mark 15 plastic sextant and I want to buy a better one.. 
I've heard about Astra IIIb and Astra Professional... differences? what is the best?

Other tips are welcome!!!

Thank you
Alberto

Any relatively modern sextant with a metal frame and in obviously good condition should give good service and quite adequate accuracy for practical navigation. 

A micrometer drum for measuring minutes is now standard, and is easier to use than a vernier sextant, but a good quality vernier sextant is still accurate and more than adequate for practical use for celestial navigation.
The British sailor Sir Alec Rose sailed single-handed around the globe (which is why he was knighted as was Sir Francis Chichester)  using his metal frame vernier sextant - now on display in Portsmouth museum.

The most expensive is not necessarily the "best".   More money usually only means more bells and whistles and better finish, therefore better 'looking': but not necessarily better accuracy of what its function is - measurement of arc - accurately.

I have various sextants but the 'best' of all was amazingly cheap costing about £200  ($240  exchange rate Jan 2016), bought about four or five years ago;  it is a Russian SNO-T and was new, unused in the original box.  These were ex-Russian Navy released presumably as surplus to requirements.

The box it came in was very basic,  but the sextant itself is superb quality and accuracy - better I think than my Zeiss Freiberger Precision surveyor's Trommel (drum) sextant.

Check the 'feel' of the Index arm movement along the scale, and for any movement in the index arm bearing (at the top of the sextant.  If it is smooth and free (but not too free, i.e. not sloppy) with no obvious dents or marks showing distress or dropped, then it should be a fair bet for being Ok.

Douglas Denny.  Bosham.  England.

[c_davidson]

Collecting sextants can be an expensive but very satisfying hobby!

I would really love to get an Observator Mark 4.

Here it is- (notice no filters!  Some sort of film/filter is inside the telescope).

Found it here- Observator Mark 4






How do you like it?  Freibergers are beautiful too!  Love the Soviet Sno-T.

Clen

[Douglas Denny]

   

Collecting sextants can be an expensive but very satisfying hobby!

I would really love to get an Observator Mark 4.

Here it is- (notice no filters!  Some sort of film/filter is inside the telescope).

Found it here- Observator Mark 4






How do you like it?  Freibergers are beautiful too!  Love the Soviet Sno-T.

Clen

It is indeed a very fine sextant.
The filters are inside the telescope unit which is an advantage as they shouldn't suffer spray or dust contamination.
It is similar to the so-called lifeboat sextants made by Henry Hughes and Son.

I will try to send a photo (I have not tried it yet), . .of myself using my Frieberger whilst sailing around Ireland about three years ago.  The position line obtained was within a mile of GPS position.  It should have been better than that as the sextant was more than capable of better accuracy - I probably wasn't trying hard enough !

I agree, collecting sextants is a satisfying though costly pastime.  One can get immense enjoyment from having any sextant though - and if it becomes a passion, well you can always find another later perhaps, and another .. etc  :-)

Douglas Denny.

[c_davidson]

Douglas,

Now that's a handsome photo! Is that a magnifying glass near the index clamp? What is the index vernier scale graduated down to? .2 .4 ,6 .8? Or are there individual lines for each of the tenths?

Clen

[Douglas Denny]

Douglas,

Now that's a handsome photo!  Is that a magnifying glass near the index clamp?  What is the index vernier scale graduated down to?  .2   .4   ,6   .8?  Or are there individual lines for each of the tenths?

Clen

Silly Me !  That's not my Freiberger in the photo;  that's the SNO-T. . . I had forgotten I took the SNO-T to try out whilst on the sailing trip around Ireland.

The Freiberger and SNO-T look almost the same - frame shape and colour, micrometer drum etc, but you are correct, that is indeed a magnifying lens you see on the photo with the SNO-T.  The Carl Zeiss Frieberger has a scale lighting attachment on the index arm near the micrometer drum.

Both have the same micrometer drum markings:  sixty,  one minute of arc divisions on the micrometer drum.

The one minute divisions are very near 2mm apart so it is easily possible to estimate to within 0.2 minute of arc and when practiced it is possible to be reasonably sure of 0.1 minute of arc estimated.

I modified the SNO-T when using it for Lunar distance measurements by sticking a very small piece of clear sheet plastic onto the datum marking next to the drum with vernier markings which I had printed onto the clear plastic.
This gives reliable vernier measurement of 0.1 moa from the micrometer drum.  (See pic).

The Freiberger sextant telescope proved to have considerable prismatic errors inherent in the field of view from one side to the other which gave me confusing results for Lunars.  Hence it is important using all sextants to keep measurements viewed as near as possible in the centre of the field of view.

The SNO-T proved to have less prismatic error and more reliable results in use.  Both however, are very good sextants.

I include a picture of my Box sextant which is a beautifully made precision instrument, which though only about 75mm in diameter is capable of reliable measurements within one minute of arc.

The three pics are: 1)   SNO-T micrometer drum with stuck-on vernier scale I attached
                             2)   Carl Zeiss Jena Freiberger survey sextant (which allows measurements over 200 degrees)
                             3)   Troughten and Simms  Box sextant.

Douglas Denny.

[P.Rutherford]

Douglas,

I've never seen a SNO-T up that close. It looks like a remarkably well made instrument.

Does the box sextant lend itself to marine navigation?

Do you have a Plath sextant by chance?

Paul

[Douglas Denny]

               

Douglas,

I've never seen a SNO-T up that close.  It looks like a remarkably well made instrument.

Does the box sextant lend itself to marine navigation?

Do you have a Plath sextant by chance?

Paul

The SNO-T is a very well made instrument.  My friend Bill Morris who wrote 'The Nautical Sextant' (a must for anyone interested in sextants) considers it probably one of the most accurate sextants ever made. 
As with all Russian equipment for the military ( like the T-34 tank) - solid, rugged, excellent for its purpose, better than most of its kind, no frills and probably no expense spared for it  providing it will do the job required,  but no more . .

Here is another picture of it with the higher magnification inverting telescope attached.
-----


The Box sextant is a beautiful instrument with an amazingly finely engraved silver index scale read directly with vernier reading on the index arm to one minute of arc.

I believe they were designed for desert navigation in WW1.  As such they are good for taking sights when on a stable platform (i.e. terra firma),  but as with all sextants,  not quite so easy at sea on a small boat with a moving horizon.

I have used it successfully on a boat but it has one main problem: the telescope is very small and the field of view is narrow;  this makes finding a star very difficult unless the sextant is already preset to the expected altitude.  It is not so much of a problem with the Sun and easy when altitude is pre-set.
------

No I do not have a Plath marine sextant and will probably never own one as they are just too much money for something that my SNO-T can equal. They are a wonderfully made instrument however, for those who can afford to lash out and not worry about the expense.

I do have two Plath aircraft sextants of WW2; one is a gyro horizon sextant.

Douglas.

[Rdutton]

Can you tell us what SNO-T stands for? It probably has provided some laughs for a name in English speaking countries.

Thanks for the excellent photos of your pocket sextant. They have always been a curiosity not knowing how or where they were used. Can you tell us the dimensions?

Roland

[Douglas Denny]

Can you tell us what SNO-T stands for?  It probably has provided some laughs for a name in English speaking countries.

Thanks for the excellent photos of your pocket sextant.  They have always been a curiosity not knowing how or where they were used.  Can you tell us the dimensions?

Roland

The definitive expert on sextants of all types (probably in the world) is Bill Morris, a retired medical doctor who lives in New Zealand.  A most pleasant and kindly man who is incredibly knowledgeable on anything to do with sextants and suchlike optical  instruments.
To quote from his book  "The Nautical Sextant" :- 

COPY:-

SNO-T:-  Sextan Navigacionnyi Osvetitelem T  (Tropicalised).
 
Made in Leningrad with inputs from Freiberger Prazisionsmechanik, and is a derivation of the latter's sextants though rather more heavily built and with a slightly smaller radius.
------

Although C. Plath was based in Hamburg,  on account of heavy bombing in WW2 they also had factories in East Prussia and Poland.   At least some of C. Plath's factory and machinery appears to have been taken over by the USSR at the end of the war, and sextants indistinguishable except in very minor detail from wartime alloy sextants continued to be produced into the 1960s as the SNO-M:   "Sextant for Navigation with Illumination - Maritime".
This series was followed by the USSR's  SNO-T.

ENDS.


You can read his "blog" here, it is very interesting indeed :-

https://sextantbook.com/blog/
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The Troughton and Simms Box sextant is  75mm diameter (about 3")  by 40mm (about 1 and1/2") deep.
In its leather case the size is :-   85mm x 55mm

The small telescope is 75mm long about x4 magnification and 12mm aperture.

If wanted the box sextant has a sliding brass sleeve with a pinhole in the sighting hole, which can be used instead of the telescope for direct viewing,  which makes finding an unknown object easier than the telescope with its narrow field of view.

Douglas.

[Guest]

The Mark 15 is pretty good but not great. It's tough to keep constantly having to adjust it.

[LouisC]

Time has past but I got a Mark 15 off of Craigslist and the Davis AH (junk) to go with it for $75.

The Mark 15 is small and easy to handle but not too accurate. It does get the job done and doesn't take up much space which is nice for carrying around....in the car.

Forgot to mention that it had case too.

[Fred_B]

Somebody mentioned it doesn't rust. Now that is good!

Have you guys tried using it without the "telescope".