celestial navigation software

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Yet another DIY sextant: the CamSextant

Build your own sextant

This is the 4th do-it-yourself sextant design published in this space. X-tant and CD-sextant are conventional marine sextants, using unconventional materials.

Recently I added the iphone Sextant. That device combines a telescope viewfinder with the phone and uses the phone gyroscope to read the altitudes.

The device described here, named CamSextant, is also an iphone sextant and is even easier to build. Instead of a separate eyepiece, I used the phone camera as s pointer device for observations.

An special app - also called CamSextant - was developed to work with it, combining the camera view to phone's gyroscope readings.

It is available on the Apple App Store.

 


iphone camSextant with lens and Sun filter

Warnings before you start

  1. While the phone gyro is a nice piece of equipment, it is not nearly as precise as a marine sextant. In a rocking boat, the gyro response is even worse. So - if you want to practice celestial navigation - get yourself a marine sextant. See Celestaire link in the end of the page.
  2. You don't need the eyepiece described below to use CamSextant app. The app works even without it.
  3. You do need the proper filter to observe the Sun. Failing to use the proper filter may result in damage to your eye and to your phone camera. Take care. Read more below.

CamSextant apps

Actually, I made two apps to work in concert with CamSextant.

Navigator - Complete celestial navigation app, with altitude capture, perpetual almanac, celestial calculator and star finder. Allows capturing readings and calculating your position using celestial navigation, in one go.

US$ 20
Navigator for iPhone/iPad
App Store
CamSextant - Simple sextant altitude capture using the phone camera. For those that want to do the calculations using traditional methods - pencil, paper and a Nautical Almanac.

Free
CamSextant for iPhone/iPad
App Store

 


Both apps allow calibration and capturing of altitude readings. CamSextant associates a camera view with cross hair.

Differently from marine sextants, which compensate instrument shaking naturally by design, the phone version must be hold pointing sharp to the object and steady while capturing the altitude. Difficult sometimes. Hold your breath. Tap gently.

It is also hard to see faint stars ( a camera limitation I guess ).

CamSextant app

CamSextant app is as simple as can be. By default, the camera view is zoomed in, to allow precise pointing. The angle of view is smaller than the regular camera app.

Calibration is done by pointing the phone to the sea horizon and carefully tapping the [Calibrate] button. This is the "zero" of your device. Instrumental altitude reading is automatically corrected after calibration. Use the X button to clear the calibration, setting it back to 0.

Once calibrated, to read the altitude Hs, point the device to the celestial object (a star, planet, Sun or Moon) and tap [--Mark--] ( or tap anywhere on the camera view ).

You'll hear a click. The app did not take a picture of the star. Instead it saves the local time and instrumental altitude Hs, as shown. The camera image is frozen for a couple seconds, so you can inspect the quality of the altitude capture. Tap again to release.

CamSextant can be used in landscape and portrait orientations.

note: Magnetic azimuth indicator does not work on some older phones.

tele-objective

You don't need any adaptation to the phone to use CamSextant app. A plain phone will do. But I wanted to try something different. The original iphone camera has wide field angle. This is not so good for a sextant viewfinder. Marine sextant eyepieces are more like tele objectives. The small field angle is important for precise pointing. To remedy that I bought one of those little phone lenses. It is a 8X magnification objective ( I'm not associated with the lens manufacturer in any way). There are a many options in the market. This is what I did:


Sun lower limb altitude, with 8x lens and Sun shade

 


moon sight


Moon sights without and with the eyepiece

Materials:

  • phone case. Use a rigid aluminum case (epoxy will not hold to a rubber case)
  • 8x magnification lens set for mobile (tele)
  • welder helmet dark glass (shade #14) - Cut the rectangular glass in two square parts. Go to a glass shop for that.
  • epoxy glue ( two components fast cure - 10 minutes )
  • brown packaging tape
  • iphone 5 or newer
This particular objective is supplied with a clip adapter, to attach the lens set to the phone (see below). This was not practical for my sextant design. I wanted the phone and objective to form a rigid unit. I cut off the clip part and kept the objective adapter. It was bond to the phone case using epoxy glue ( two components fast 10 min cure ).
  • Clean and sand the contact surfaces.
  • Make sure the camera and the objective axis are well aligned.
  • Mark the adapter position on the case, with a fine point marker pen.
  • Remove the phone from the case before bonding the objective adapter ( while liquid, a epoxy glue drop may ruin the phone camera ).
  • Glue the adapter to the case with epoxy glue. Watch position and alignment while the glue is curing.
  • Avoid skin contact with epoxy. Wash your hands well in the end.


8x objective and the original clip.
The clip part was cut off..




disassembled

 


..and the adapter was glued to the phone case

 


camSextant assembled with iPhone 6

 

This lens set has a manual focus adjustment, which I set to infinity.

I found the gyro sensor error can be as much as one degree, not a very good sextant. It may improve in the future. A decent sextant has an error of a couple minutes. Still, it is pretty amazing.

More construction details and tips can be found in Instructables site here

 

So you still need a classic sextant for celestial navigation.

 

. Warning: Don't use any optical instrument to observe the Sun directly, without the proper Sun filter installed. The UV rays can burn the eye, causing permanent loss of vision and other problems. Lenses in the instrument amplify the light power. Don't even look to the Sun without a strong filter.

In the case of CamSextant, pointing the device to the Sun without a proper filter may damage the phone camera permanently.

Best materials for Sun filter are:

  • Aluminized Mylar film - this is a material specifically developed for solar observation. Can be found in science supply stores. Best material available.
  • Welder's glass - strong filter used in welder helmets (used in this project ). Can be found in construction supply stores. Ask for shade number #14
  • other options:

    Photography film. Use a dark negative, with metallic silver coating. This means black-and-white film. Color film does not contain silver and will not filter the UV rays. Photography film is a vanishing species.
  • Dark floppy disk media. Vanishing too.

 

 

The filter to the left uses welder glass #14. Most welder lenses are rectangular. I had mine cut square in a glass shop and made the eyepiece adapter with paper and brown packaging tape.

The shade must be removable, to take off when observing stars, planets and Moon.

 

 

 

This text was also published as an Instructable.

 

 

 

Related links

Celestial navigation fundamentals

X-tant - DIY Octant project

CD-sextant - Minimalist DIY sextant

Navigator for iPhone/iPad App Store

CamSextant for iPhone/iPad App Store

Navigator home

Instructables

Facebook page

Buy a marine sextant from Celestaire.


 

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ęCopr 2016 Omar F. Reis

v 1.0 jan/2016