If you were shooting inside with a single light, you’d be concerned about where it was located and what direction it was pointing in, right? ¬†You wouldn’t just get someone to randomly position and focus it, then work around whatever it gave you. ¬†You want your lighting tools to do the best job they possibly can.

Unless you have a huge budget for serious HMI firepower, shooting day exteriors means you have one lighting unit only – the sun. ¬†And whilst you can’t control where and when it’s going to appear, you can calculate both of those and use that information to your advantage. ¬†A sun position calculator draws on a heady yet ultimately simple bunch of celestial mechanics to figure out the path of the sun through the sky at any given point on the Earth, for any given time.

Using that knowledge, you can perform all sorts of tricks, from the simple to the incredibly helpful:

• Work out sunrise and sunset times for anywhere on the planet on any date
• Work out exactly what compass bearing the sunrise will appear at, for those glorious long lens African savannah shots
• Work out how long the shadow of any given object will be at any time of day
• If your shooting location is surrounded by tall objects like buildings or trees, work out – months or years in advance of the shoot if necessary – the precise time when the sun will clear the top of a building that’s 55 degrees above the horizon from where your subject’s going to be standing

It’s a tool any DoP, gaffer or professional stills photographer needs to have in their arsenal. And thanks to the iPhone, we have a perfect mobile computing platform for the job, and thankfully the guys at Chemical Wedding have stepped up.

Helios Sun Position Calculator at ¬£17.99 joins pCam (the film calculations package, review coming soon) at ¬£23.99 in the category of “unsually expensive iPhone applications”, and that is going to be the first thing that hits any prospective customer seeing as Apple, in their wisdom, don’t allow demo versions of software in the App Store.

If you can get over the sticker shock – and I’m speaking here to an audience of film industry professionals – let’s not forget that we wouldn’t think twice paying the same amount ordering a few extra brackets or clamps or something in a lighting rental package if we thought they were going to help out on a shoot. ¬†And that would be per day – ¬£17.99 gets you Helios forever.

The market leader before Helios is probably sunPATH, at $99 (¬£61), a venerable desktop Mac or PC tool that does the calculation side of things, spitting out PDF charts, combined with a Suunto compass/inclinometer for actually being able to point at the spot where the sun’s going to appear.

With the exception of the compass (and more on that issue later), Helios loaded onto a iPhone replaces both these tools with ease.

The main screen of the application lets you select a date and location easily, and I liked that there’s a single button to press under each selection to preset the date or time to ‘today/now.’ ¬†For location, you can either get Helios to use your iPhone’s GPS to find your location, which works very quickly presumably because the location accuracy required is the level that the iPhone gets pretty much¬†instantaneously¬†off cell tower triangulation, rather than having to locate the GPS satellites. ¬†And if you don’t happen to be at wherever you’re calculating for, there’s a database of major cities around the world, or you can enter lat/long co-ordinates.

Once that’s done, the main screen, shown above, gives a compass display showing the sun’s bearing at the time, date and location you’ve chosen. ¬†The whole compass ring can be rotated with your finger (this is actually really cool, because if you set the time, date and location to where you’re at, and rotate the ring so the sun icon is pointing towards the sun in real life, you’ve just made yourself a little impromptu compass!), or you can drag the sun icon itself to different compass bearings and the time shown will update to show you what time it would be when the sun is at the bearing you’ve chosen.

Of course, bearing is only one part of the puzzle. ¬†On the far left of screen, Helios gives you the inclination of the sun in degrees above the horizon, and perpendicular to this is a black bar showing shadow length as a result (really just the other side of a right angle triangle, of course). ¬†The end of the shadow bar gives you the ‘shadow ratio’, so if it’s saying 1.2 you know an object 1 meter high would cast a shadow 1.2m long at the time you’ve set Helios to.

The second display mode of Helios is SkyView, showing the track of the sun across the sky with the centre of the diagram being directly above your head and the red circle around the outside being the horizon. ¬†In testing I found this a really useful way of gauging how ‘toppy’ or ‘sidey’ the sun was going to be during say the mid-morning, when looking at different shoot dates a month apart.

The final display, calling on the iPhone’s built in accelerometer, is the¬†inclinometer. ¬†After a short calibration procedure which I found slightly confusingly described, the display gives you a black¬†artificial¬†horizon. ¬†You can then ‘sight’ along the long edge of your iPhone at an object above the horizon and read off the angle to it from the screen. ¬†The developers haven’t missed a trick by pulling in the data from the other displays into this screen, so based on the location and date you’ve set, the inclinometer shows the two times and compass bearings during the day that the sun will be found at that angle. ¬†This is very useful for working out when the sun will clear tall obstructions around your location, whether so you can shoot in bright sunlight, or so you can avoid it. ¬†It’s probably not the world’ most accurate tool – you don’t want to go surveying with this thing – but the accuracy is well within the requirements of the job in hand.

Working with Helios just as I walked around town today, thinking about the sort of questions I’d have if on a location scout or shoot, I found myself reaching for my iPhone and finding an accurate answer when before I’d have just guesstimated the sun position for a certain time of day. ¬†The attractive design and well thought-out menu structure only make it less of a barrier to get the thing out of your pocket in the first place.

There’s a lot of rumours flying around that the next hardware update to the iPhone, likely to be announced in the next few weeks, will contain a magnetic compass to help improve the GPS and enable turn-by-turn directions, as well as being accessible by third party apps. ¬†I’m sure the second Chemical Wedding get their teeth into the compass APIs they will have that integrated into the app, which would take it up to a full five star rating for me. ¬†At the moment, you still need to carry around a trusty Silva compass. ¬†But with the compass integrated into the iPhone, you can easily imagine a mode where you just point the phone anywhere on its own and it reads out what time of day the sun would be closest to where you’re pointing… or even, if you wanted the sun at a very precise point for some reason, what date you should come back on to achieve that.

One suggestion I came up with that could improve it would be integrating a simple weather report for the location and date given and superimposing some sort of graphics onto the compass wheel on the main screen, so as you drag the sun around the compass you can see times of day where it might be behind cloud, rain etc.

Other than that – this app will more than pay for itself the first time you use it for a day’s exterior work. ¬†I look forward to more film software from Chemical Wedding.

[rating:4]