11 Feb 2015

Balancing ambient light with flash light for stunning images

Speedlighting Blog No Comments

I am updating this post following comments from a student who came for a flash photography course in London last week. The post was originally triggered by an email I received from someone  in the US saying that he thought my Lens on Squidoo on balancing ambient with daylight was pretty  neat.

Balancing ambient light with flash light for stunning images

Ok so you have seen all those hyped up web sites about lighting with flash photography using remote flash (off camera flash) by photographers cum personalities. Have you noticed how they shroud the whole thing in mystery and jargon – does it make you feel as if there is some magic circle thing going on here? Well the truth is there is because they created their own little circle and they don’t want you in it – the reason?

Well if you knew how ridiculously simple it was to create stunning images with remote flash they wouldn’t be a “name” any more – sorry Chase/Syle/Joe. If you don’t know what this style of photograph looks like have a look at the Strobist pool on Flickr.

Ok here’s the deal. A crafted flash image has two elements to it:-

  1. Ambient light
  2. Flash light

I am going to assume its a reasonably sunny day just after sunset. I never use light meters for this type of work because I have great one in my camera. To gauge where the light is at take  a test shot in Program mode  – check the exposure reading – lets say its f8 @ 1/60th of a second.

Ok now you need to know that as a general rule the shutter speed controls the ambient light – its not actually true but it helps to think this way. If we want to make the sky or background moody and dark  the trick is to drop the ambient by one or two stops from the metered value to taste  ie we increase the shutter speed so that less light hits the sensor. The idea is that we under-expose the background and light the foreground or our subject back up to the metered ambient. This has the effect of separating the subject from the background and reducing the dominance of the background in the image.

So using the example above put the camera in manual and dial in 1/60 @ f8 as a starting point. Now increase the shutter speed to say 1/200 (my maximum sync speed)  shoot a frame and have a look at the result. If the background is too dark then reduce the shutter speed  to say a minimum of 1/50th first, if you need more light then up the ISO to your cameras comfortable maximum – on the 5DMKII this would be say 1200.  Only after you have done these two steps should you then start opening up the aperture from our f8. If  its still too light at 1/200 hit the ISO button and dial down the ISO and again if this doesn’t control the ambient enought look at shutting down the aperture from f8 to say f11.

The limiting factor on the ambient side is the flash sync speed of your camera – you may only get to 1/200th second before you start getting black banding in the image which is the shutter starting to show on the image. On my 5DMkII I can just about get to 1/250 with a slight hint of darkness from the shutter on the bottom of the image in landscape. The relatively low sync speed of the camera with the flash unit means that bright days will be difficult to manage as ideally I would like to sync up to say 1/1000th sec.

This is where it is important to understand the exposure triangle of ISO/Tv/Av  – for more on that get yourself a copy of Bryan Petersons fantastic book Understanding Exposure – its not the newest around but then the physics of the camera hasn’t changed. If we run out of shutter control – ie I am at my max sync speed of 1/200 my next port of call will be the ISO so that in bright conditions I reduce it to darken the ambient.

Generally this type of image taken in low light  does not present any technical problems. In low light – say just before sunset and well into early evening – we are able to use very slow shutter speeds to soak up the remaining ambient light. The slow shutter speed may mean that the background might get blurred but usually not enough to distract from the subject. What is important is that the subject is lit by flash which is a very quick pulse of light  released in milliseconds and freezes the subject in the frame giving us a very sharp foreground.

Now we have the ambient portion of the picture exposed to taste  – lets say we are at 1/200th sec at ISO 50 – and the background is darker than the test shot. Now we need to think about lighting our subject with flash.

As a starter position mount your flash off camera on a stand at 1/4 power about 1.5m from your subject just above head height slightly to the left or right shooting bare bulb or through a white umbrella. The trick here  is to light the subject back up to at least the ambient light. Have a look in the back of the camera and adjust the light to suit. If the subject is too dark we can either increase the flash power, pull the flash in closer or reduce the f stop, (ie increase the aperture of the lens) depending on the look we are going for.

  • Increasing the flash power has implications for the recycle time of your flash – it is good to keep your speedlight on ¼  or ½ power – that way we get a faster recycle time enabling you to work smoothly and to interact with the subject without waiting for the flash to recharge
  • Pulling the flash in closer will increase the amount of light hitting the subject – it will also make the apparent size of the light (relative to the subject) larger and therefore the light softer. Moving the light away from the subject will decrease the amount of light hitting the subject, reduce the apparent size of the light and therefore darken up the shadows.
  • Reducing the f stop (ie increasing the size of the aperture in the lens) will reduce the depth of field and will reduce the amount of ambient light  as well as the flash..

Its important to have an eye to the power of your flash as generally the more power your flash has the easier it will be to get the right balance between ambient and flash light. Therefore for me I would rather be shooting with a Canon 580EXII than a 270EX. Even better I would rather shoot with a Quantum head and battery pack for location shoots – the Quantum generally gives me enough power to compete with the sun on the brightest of days. Failing that its studio heads, maybe Bowens Gemini with battery packs.

A good tip on a sunny day is to place your subject in the shade – that way you don’t need a bank of heavyweight  flash heads to blast out the sun – the idea of this type of photography is to try and keep it as minimal, lightweight and as portable as possible.

And that’s it basically – no bull – no jargon – just get out there and try it and if you need a hand get in touch and come do a flash photography course.

Balancing ambient light with flash light for stunning portraits

The post was originally triggered by an email I received from someone  in the US saying that he thought my Lens on Squidoo on balancing ambient with daylight was pretty  neat. If you want to see it on Squidoo click here

Share the word
  • Digg
  • Twitter
  • Google Bookmarks
  • Facebook
  • LinkedIn
Comments are closed.