Corporal Si Longworth is one of 38 trained British Army photographers. He left a career in aviation to pursue his passion for photography; capturing everything that military life has to offer. He is currently in Afghanistan as the Task Force Helmand Photographer on Op HERRICK 18.
I have been mulling this latest blog over in my mind now for some time. Do I hit you with a full-on technological geek-off, or do I make subtle references and entice those that want to, to throw a few words into google and discover for yourselves?
I have decided to meet in the middle somewhere. Hopefully you will find what I am going to talk about useful or interesting, and if you are not into photography, maybe you will just want to keep reading anyway as you have nothing better to do. I can hope..
Photography is all about light; natural or what we create ourselves to carve out texture, detail and depth to a two dimensional image. We generally need light in our images, and it can be helpful or it can be a curse.
I was happy with my photographic knowledge until recently when I had to turn to a friend and expert lighter, Paul Brownbridge to solve a problem. Paul was a senior instructor in the Army Photographic trade when I attended the course at the Defence School of Photography. He recently emigrated to Australia and works for Creative Force. To see more of his personal images, go here.
My problem: The sun was too bright for my flashes. His solution: Sunglasses… Well, sort of.
Smaller hole = less light
A little background information. Please bear with me on this one.
A camera’s shutter speed is made possible using a focal plane shutter that travels horizontally. It has a front curtain and a rear curtain which travel independently of each other. During any exposure, the front curtain begins to travel, opening up a hole to allow the light passing through the lens to hit the digital sensor (or film in old money). Depending on how fast or slow the selected speed is, depends on how soon after the rear curtain travels to close up that gap. On a Nikon D4 at 1/250th of a second and slower there is a point at which the entire sensor is in view of the light, as the front curtain has travelled it’s full distance before the rear curtain starts. Faster that 1/250th and the rear curtain begins its journey before the front curtain has completed it. This effectively enables really fast shutter speeds.
This speed, usually around 1/250th of a second is known as the flash sync speed, and here is why:
When a pulse of light is emitted from a small speed-light it lasts only a short period of time; anywhere between 1/1050th of a sec (at full power) to 1/41600th of a sec (at its lowest power). Generally then, it would beat the shutter to the chase in most instances. However, as I said, faster than 1/250th of a second the whole sensor is never fully revealed at once because of the rear curtain. So during the exposure the light emitted from a flash will only record on that part of the sensor that isn’t being obscured by the travelling curtains at that moment in time.
To recap; because the flash fires much faster than the shutter can operate, it doesn’t matter what speed the shutter is opening and closing slower than 1/250th of a second because the entire pulse of light will record on the entire sensor. It is for this reason that shutter speed does not affect flash output.
Without diving any deeper into the rabbit hole, let me just reassure you that what does affect flash output in our images, is (amongst a few other things) aperture. Just like reducing the aperture from f4 to f5.6 allows half the ambient light to reach the sensor, it also halves the amount of flash light recorded on the sensor too. Smaller hole = less light.
Sorry about the technical bit. If you want to know more, then “let me just Google that for you”.
So back to my little problem I had out here…
Neutral Density (ND) filter
Let’s say I have a portrait and I want to make the background blurry so I choose a large (wide open) aperture to give me a shallow depth of field. (The distance between the closest and furthest point in your image which is in acceptable focus) At high noon in open sunlight out here, you will need a very high shutter speed to match the wide open aperture; possibly 1/1500th of a second or faster. At these high speeds, my little hotshoe flashes just cannot cope. I want to use a flash to make my subject ‘pop’ out from a slightly underexposed background, but I cannot.
This dilemma was bugging me and I happened to be chatting to Paul about it via the wonder of facebook. Living in Australia gives him similar issues when trying to take pictures outside. He explained a solution that I thought I would give a try.
I was hoping he was going to send me over a whole team of assistants like the big-hitting photographers get, to hold huge sunshades over all their subjects. No such luck. I would have to put my hand in my own pocket on this one.
There is a gadget on the market called a variable Neutral Density (ND) filter. It screws to the front of your lens and acts like an adjustable set of sunglasses allowing the user to vary the degree of light getting in. They are not cheap. I initially bought a middle of the range one and was not happy with the results. It worked fine on the mid range 24-70mm lens, but was completely soft (out of focus) on the longer zooms. Not to be put off, I decided to invest one and ended up with one from Tiffen. I will be honest. It works a dream.
When I dial up the ‘sunglasses’ effect to the maximum, allowing a lot less light into my lens, I have to reduce my shutter speed to compensate. At full whack I can easily achieve 1/250th of a second with a wide open aperture of f2.8. I am talking about the middle of the day, bright burning Afghan sun. The kind of sun that burnt the front of my body when I exposed it for the first time on my tour the other day for a mere eight minutes.
Small flashes in bright sunlight
For those of you who haven’t fallen asleep yet, you will hopefully be thinking: “Oh, now he’s back down to the flash sync speed and he can use his flashes again”. You guys and girls get a gold star for staying with me. And here are some shots to prove it:
Hey, I know that to some of you who are still reading this, these will all be irrelevant numbers, so in simple terms buying this little gadget has given me the ability to use my flashes to creative effect whereas I once couldn’t. I no longer have to run for the shade.
Of course, it doesn’t stop people squinting in the harshness of the sun, but you can’t have everything can you.
Here are a couple of examples where I have been able to use a mixture of direct flash and soft diffused light from small flashes in bright sun. I hope you like the results after painfully reading the know-how.