ASTRO PHOTO
 
  INTRO   |  IRIDIUM FLARES  |   STAR TRAILS  |   ISS  |   SUN ANALEMMA  |   LINKS  |   GALLERY



INTRODUCTION

First of all, I would like to thanks "The Earthrounders" for giving me some space on their Internet Site to publish these pages.

Astro Photography can be a fascinating hobby.There is no need for special equipment: a camera, a steady tripod, a precise time piece, an intervalometer are all that is needed to get started, plus a lot of patience.




1. IRIDIUM FLARES

The Iridium Flares are made by the reflection of the Sun on the photocells and antennas of the Iridium satellites. They are only visible when the Sun is just below the horizon. To the naked eye their appear like a brillant flash that comes and go briefly but on the long exposure photographs one can see the trajectory of the satellites.

Iridium Flare
Iridium flare close to α and β Centauri
(Soutern hemisphere).
October 26, 2012

The best prediction of the flares is on this excellent Web Site:
www.heavens-above.com
The number of opportunities to watch and photograph the Iridium Flares is limited and is also influenced by the weather and the position of the moon.


2. INTERNATIONAL SPACE STATION

The passage of the International Space Station can seen and can be photographed. It will look like a line among the background of the stars. It is the brightest of the other man made satellites. Predictions are available on : www.heavens-above.com



The International Space Station passing overhead.
September 25, 2010




3. STAR TRAILS

Star Trails are probably the most beautiful night photos. They can be taken with both film and digital cameras.

3.1. Film cameras
3.2. Digital cameras


3.1. Start Trails with film cameras.
This is probably the simplest way: Just fix the camera on a steady tripod and open the shutter on "B". The film can be colour or black and white and tests will be needed to find the right aperture considering the ISO rating of the film.
Very long exposures will run the risk of shaking and of "reciprocity failure" with colour film. (Digital cameras do not have the problem of 'reciprocity failure' but have the problem of "noise" on very long exposures). A series of tests need to be done to find the right aperture and how much 'reciprocity failure' can be tolerated.


3.2. Star Trails with digital cameras.
Digital cameras can also be used for star trails. There are two ways of using them:
   3.2.1. with a long exposure.
   3.2.2. with multiple exposures and 'stacking' those multiple exposures.

3.2.1. Long exposure. The process is the same as with a film camera but now, instead of the 'reciprocity failure' of the colour films we are faced with 'noise' where pixels that should stay become visible. Some modern cameras have a function called " noise reduction". It has the great inconvenient of requiring extra time for the camera to 'remove' those visible pixels. It may be good to try first with the noise reducion switched to "OFF".

Example of exposures: ISO= 400, time = 15 minutes:
f: 5.6 f: 8 f:11

The same spot with 25 exposures of 5 minutes stacked as one picture.Here

3.2.2. Multiple exposures. Another way is to take multiple exposures (sometimes hundreds of them) and to 'stack' them in post-processing. This has another advantage is that we can remove some unwanted frames before the 'stacking' is done. Several programs can do that rather easily:
www.startrails.de
www.markus-enzweiler.de/software/software.html

Examples of Star Trail Stacking here.




4. SUN ANALEMMA

4.1. Sun Dial
4.2. Film camera
4.3. Digital camera
4.4. Software


The Analemma is the reprentation of the position of the Sun as seen through the year at the same time. It looks like a "8" figure. This is due to the difference between "Sun Time" and "Clock Time". That difference well known to astromoners and navigators is called the "Equation of Time", with a maximum of about 18 minutes in April and November, and is zero in April, June, September and January.
Analemma of the Sun (Southern Hemisphere)
Analemma of the Sun (Northern Hemisphere)


4.1. Sun Dial
The easiest way to materialise the Analemma is with a sun dial, {although it is not a truly photograpic method) marking the end of the shadow of a stall (gnonon) at the same time through the year. The markings do not have to be at regular intervals as long as they can be linked by a curve.
.

The Sun Dial showing the shadow on October 30th
(Southern hemisphere).

With the Sun dial oriented North-South, the Analemma sould be centered on the board. Depending of the longitude of the obervation place, one has to calculate the time where the observation must be made. Indeed, within a time zone, all clocks should show the same time, but the "Sun Time" or Local Mean Time will be different at each longitude.
To get the LMT of a place one must know its longitude. For every 1 one is West of the time "zone's standard longitude", add 4 minutes to LMT to get standard time. For each 1, East, subtract 4 minutes.
The "zone's standard longitude"is most of the times at the center of the time zone. It can be found on a map on this Site: http://www.worldtimezone.com/
Here is an example of LMT calculation. My longitude is E11640', the longitude of my time zone (Zone 'Hotel':UTC+8) is E120.
The difference between the 2 longitudes is:
120 - 11640' = 320'
3 x 4 = 12 minutes
20' x 4 = 80 seconds = 1 minute 20 seconds
Difference = 13 minutes 20 seconds
As my East longitude is West of the standard meridian, I must ADD the difference to the "Clock" time, therefore to take a picture of the sun at 12 noon (sun time, LMT) the clock should show 12:13:30



Plotting the Sun Analemma with dates around the year (Southern Hemisphere). The horizontal scale is much enlarged. Using this plotting, one can position separate photos along the year. The Equinoxes fall around March 20 and September 20 -22 and the Solstices around June 20-21 and December 21-22 depending of the years.
More details on "Wikipedia".


4.2. Film camera

The first photograph of the sun Analemma is attributed to Dennis di Cicco in 1978-1979. The picture was first published in the June 1979 of the magasine Sky & Telescope. Since, the legend says that more explorers have walked on the Moon than photogaphers have succeded in photographing a full sun Analemma. And also that no one has succeded in less than 3 years...I must say this is my third year...and probably my final year with a film camera, having finally discovered the advantages of using digital cameras.
It must also be said here that some pictures of sun analemmas are almost "too perfect", without any 'misses" and in a perfect shape. It is impossible to imagine that through a full year there will not be some days when the sky is so overcast that the sun is invisible... Also some analemmas are shown on some lanscape, showing that the pictures had been "photoshoped" or "doctored". As the images of the sun have to be taken with a very dark fliter, no sign of any lanscape should appear on the final photo unless it is "added". To which extend such "doctoring" should be considered?

A search on Google will show these Analemmas and more...

A rather "easy" way to photograph the Sun Analemma is to use a film camera. The choice goes to a 35 mm camera as it has to be able to use a wide angle lens (to cover the full analemma) and to be able to take multiple exposures on the same frame of film.
I have used a Nikon FE SLR camera. It also has the advantage of being capable of being fitted with a motor drive (MD12). This drive allows the camera to be remotely controled. As the batteries (8 x AA size batteries) would not last a full year, I did built a power adapter that fits the battery compartment and is powered by a 12 volt power pack.
In order not to have to be present 40 times at the very right time, I did write GBasic program that would trigger the camera on the chosen dates and at the right time. More on that program in the paragraph 4.4.
Forty frames are normally enought to show the Analemma. Two tables show when to take those 40 photos. It should be noted that to create 'almost' equal spacings between the photos, the gaps on the calendar are not equal: this is due to the variation of the speed of change of the equation of Time.
The tables are available here:
Table for Leap Year
Table for non-leap year



4.3. Digital camera

The next step is to use a digital camera. That does away from the processing of the film, of mixing chemicals, etc.
But as digital cameras do not do multiple exposures but a series of single exposures, these (40 of them) will have to be 'joined' together. One way is to use the layers of some graphic programs but this is not simple. Fortunately there are programs that do this job of "stacking' those multiple exposures into one only image. Several programs can do that rather easily:
www.startrails.de
www.markus-enzweiler.de/software/software.html
I use a Canon EOS 400D, digital SLR camera. My settings have been:
ISO = 200
f4
1/200 sec exposure

I take 40 exposures throughtout the year. See the yearly tables.
Table for Leap Year
Table for non-leap year

Another advantage of using a digital camera compared to a film camera is that each picture can be downloaded and viewed at any time. With a film camera one would have to wait for the year to end before being able to view any of the pictures. Also with a digital camera, one can create a 'progressive' stack of the 'progress so far'.
That is what I plan to do in 2013-2014 with my first 'digital Analemma', producing and publishing a 'progress so far' on a monthly basis starting in December 2013. Watch this space...

But one must remember that most digital cameras have a "reduced" size sensor and with the same lens will cover a narrower field then the would with a "film camera".
For more, consult Wlkipedia at: wikipedia.org/wiki/Digital_cameras#Sensor_size_and_angle_of_view





4.4. Software

In order not to have present every time a photo had to be taken, I wrote a short GWBasic program to trigger the camera at the right time and on the right days. I could only use a parallel port to interface the computer to the camera. The interfacing was done by using a Kemo M125 Module.
www.kemo-electronic.com
Other similar modules/interface cards could also be used. Here are a few examples of similar intrefaces:
www.sunrom.com/156
www.cnc4pc.com/Store/osc/product_info.php?products_id=47

The outut of the interface triggers a 12 volt relay that in its turn triggers the camera. The parallel port is much easier to program than the USB Port. I did use GWBasic which is also very simple to write.
The program reads the date and the time from the computer and when both date and time are right, a signal is sent to the port throught the proper address:
Decimal: 888
Hex: 378h
The line reads: Out 888,1 This triggers the camera and takes the photo. Then a delay of one second is introduced and all bits are reset to zero, simulating the finger on the camera button, pressing and then letting go by sending the signal: Out 888,0
Due to the orientation of my camera and in order to have the full analemma in the camera frame, I calculated that the photos had to be taken at 14:40 local time. As GWBasic counts the seconds from midnight in the '$time' string, 12:40 would be 45600 seconds after midnight. For the days the photos have to be taken, I used the list as per the tables given elsewhere. The intervals between the days for those 40 photos are not equal in order to have the intervals roughly equal on the photos. This is due to the variations around the ecliptic.
The program is listed here:
ana10.pdf
In a variation of the programe a picture of the sun is also taken on a daily basis on a second EOS camera, independently of the original 40 pictures.




5. LINKS

This is a recap of all the links previously mentionned:
www.heavens-above.com
The best Site for any prevision.
www.worldtimezone.com/
Time zones and their center meridians.
www.markus-enzweiler.de/software/software.html
Stacking software.
www.startrails.de
Stacking software.
www.kemo-electronic.com
Source of the M125 parallel port module.
www.sunrom.com/156
Another parallele port module.
www.cnc4pc.com/Store/osc/product_info.php?products_id=47
Another parallel port module.

And finally the ultimate e-book on the subject is:
http://philhart.com/shooting-stars




  INTRO   |  IRIDIUM FLARES  |   STAR TRAILS  |   ISS  |   SUN ANALEMMA  |   LINKS  |   GALLERY


 
Latest update: November 17, 2013
Copyright Claude Meunier, 2012 - 2017
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