TPE is a useful tool

I purchased a very useful iPad app called ‘The Photographer’s Ephemeris’ (TPE). It’s also available as a free downloadable program for a PC – the functionality seems to be the same, so the desktop version is a good way of seeing whether you think it is worth purchasing.

An ephemeris is a navigation tool used in celestial navigation. It shows the various positions of planets etc at different times of the year. The TPE app is an adaptation for use by photographers who want to plan a particular shot such as a sunset or a crescent moon at a particular location or want to make sure they have side or back-lighting for the scene.

The system works by placing a marker at the location on the app’s map where you want to take the shot from. The app then shows the direction of the sunrise and sunset/moonrise and moonset as viewed from that point using four lines. It also shows the current position of the sun or moon at a particular time. The photographer can move a slider through the day to see the sun or moon’s position changing as the day or night progresses. It also show times, angles of elevation of the sun and moon, phases of the moon and other useful data.

A second marker can be placed on the map to help you determine when the sun or moon will become visible from your camera position based on the difference in altitude between your camera (red pin) and the subject (grey pin). For example, the view from my house in Spain is across a valley towards ‘La Maroma’ (a mountain that is just over 2000 metres in height, my house is at 500 metres altitude). In the morning it is some time after sunrise before the sun is high enough to clear the mountains and be visible from the house. The time taken varies through the year. Knowing the time of sunrise tells me the time the sun starts to rise but I could be waiting an hour for example before the sun emerges from behind the mountains – not a problem when I can keep nipping in to fill my coffee cup – but a nuisance when out in the field, particularly if you want a particular intensity of glow in the sky before the sun crests the mountain. With the app, the planning of a shoot becomes simpler – more predictable.

This example explains it more practically. Near to my house there is a plateau which also looks across to Maroma and has a large iron cross on it (about 5 metres high). Planning a shot, looking across from the plateau to the mountains, with the cross in the foreground and with the sun emerging from behind the mountains is an easy task with ‘The Photographer’s Ephemeris’. First I drag the red pin to the position on the map where I would probably set up my camera. Next I place the grey pin on top of the mountain range I can see from the camera location. The app tells me that the camera is at an altitude of 820 metres looking across to a position (grey pin) that is at an altitude of 1,430 metres. The clever part of the app though is that it calculates when I will be able to see the sun above the part of the mountain range I can see from the camera’s position (red pin). So on 1 January 2014 (I could go through the year and beyond, day by day if necessary to check the best day and time to take the particular shot I want) the app tells me that the sun rose at 08:29 (I was still in bed!) but I wouldn’t be able to see it in the frame from the proposed camera position until 08:50. So if I wanted the effect of the sun on the sky without the sun being physically in the shot I needed to be in position and ready from around 08:30 to 08:45. The app also tells me that on the 1 January 2014 at the proposed camera location, twilight was at 08:00 therefore I know I would have had some daylight to help me get in position and sett the camera up in time. A useful piece of information because the terrain in that location is difficult to walk on and there are snakes in the area so it’s better if you can see where you are going!

This sequence of images taken about six weeks ago (November 2013) shows the results from using TPE to help me get my camera set up at home in time to capture a set of images when the colour of the sky would be changing rapidly as the sun rises. TPE calculated that twilight on that day (19 November 2013) would be at 07:30, sunrise at 07:59 and by 08:54 the sun would be fully visible in the frame (important to know because the colours in the sky would therefore be ‘whiter’ and because of the low angle of the sun when it emerged from behind the mountains there would be a risk of lens flare). In the image showing the sun starting to emerge from behind the mountain side I have had to stop down the exposure to cope with the increased contrast which made the mountain side and sky darker compared to the previous exposures. The framing of the shots was governed by an exercise I was undertaking for a photography course, otherwise the emphasis of the framing would have been on the sky rather than the mountain side. The sixth image (07:59) shows the framing I would have preferred without the constraint of the course’s brief for the exercise.


  1 comment for “TPE is a useful tool

  1. January 2, 2014 at 12:32 am

    Very nice series and interesting to see the time information. I use TPE on my iphone and carry it with me whenever I am on an outdoor shoot. Congratulations on your new blog … it looks like you are off to a great start.

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