16 Nov 2010

Light Wrap & White Background Portraits

lighting technique, Speedlighting Blog No Comments

In response to a question  in relation to light wrap from a student this weekend I thought I would post a short run through of  a corporate shoot I did in Reading today. Light wrap is where the light from the background is reflected back and wraps around the subject. Depending on the look required this can be detrimental to corporate shots as the wrap represents and area of low contrast in the image. This  may be desirable in fashion images but needs watching in corporate images where an accurate and evenly lit representation of the client is all that is required.

The bulk of my commercial photography work takes place in back rooms and boardrooms of banks and other businesses – bread and butter white background portraits. I am never sure what space the client will give me until I get there but it all adds to the excitement when I discover it’s a 5.0m square store room and they want team shots  done as well. No matter where I am though the principles are always the same for this type of shot.

When I set out in the photography business I aimed to travel light inspired by David Hobby and his Strobist philosophy. Inevitably I have acquired more gear on the way and where I previously did this sort of work with speedlights and Pocket Wizards  I more often than not use the Quantum system with a Qflash Pilot mounted on the camera. The reason for this is that I like being able to make adjustments to the lighting from the camera position rather than pulling the speedlight down and making and adjustment to each light. That way I am continuously interacting with my client rather than with my gear. A rough shot of the set up today below:-

The approach I adopt with this type of photograph is to light the background separately from the foreground.  The starting point then is to light the white background to as close to pure white as I can get it and for today’s shoot I used two Quantum Qflash X5d-R’s although you could be using any flash head of course. The subject is then lit from the front with a single flash shot through an umbrella slightly higher than the subjects head and camera right. This shot shows only the background lights firing giving me a spread of f16 between the lights at the background – excuse the model – its a lonely world working on your own. Don’t worry about the framing as this is just set up to illustrate the point.

The background lights are placed left and right of the camera position about 1.5m back from the white background. I tend to aim the left hand light just left of center and the right hand light just right of center. The idea is to give an even spread of light across the background although in practice given the space constraints this may not be possible. I never use a light meter anymore but for the purposes of this walkthrough I took my trusty Sekonic meter along to meter the output of the flash heads. In this situation I managed to achieve f16 right across the background. Where the light tapers off from the center of the flash beam it overlaps with the tapered light from the flash on the other side making up the difference. If you think of light like paint from a spray can you might be able to visualize what I mean.

Remember that we are talking about an image lit by 100% flash so the ambient light has no part here – if you remember from previous posts the shutter speed controls the ambient and the aperture the flash. The shutter speed will need to be equal or less than the maximum sync speed of the camera – in my case a Canon 5DMkII  so 1/200th sec – so I tend to work at 1/125th sec. The camera sync speed is the only consideration here as there is next to no ambient light in the room I am in and what is available is tungsten and so a different colour temperature to my flash light. As an aside if I wanted to use the ambient in this dark room my shutter speed would have to be down at 1/30th sec (without any flash) before I would start to see it in the image.

Whilst we are on the theory part and remembering there are three sides to my exposure triangle I set my ISO at 100. I have all the flash fire power I need to get the finest detail I can so no need for high settings here. Sometimes if I am using my Speedlight/PW set up I might need to push the ISO higher just to give me a bit more headroom on the aperture but the Quantum heads have more than enough power for today’s job.

For the front light I am going to be using a Quantum flash head shot through an 80cm umbrella. Remember that the larger the apparent size of the light the softer the light so I am taking a 15cm diameter light & shooting it through an 80cm umbrella thereby nearly trebling the size of the light source. I am also going to want to get this light in as close as possible to my subject without intimidating them or interfering with my ability to shoot freely. Usually it ends up being about 1.5m between the subjects head and the umbrella. Remember this is not a set up studio shot –  this is shooting 20 or so people in three poses as quickly as possible with the least fuss to the client. This shot shows our model – OK me- lit only with the front light coming from just above head height camera right. A meter reading on my face showed this to be f8.

I usually like to have about f8 of light hitting the subject which gives me plenty of margin for minor tweaks. I tend not to make any changes to the power output on the flash head as I prefer to move the main light stand in or out to control the power output. The clients I am shooting today specify three poses for each member of staff one of which is  seated pose so it is easier to recompose the position of the light rather than make an adjustment to its output. Keeping the dialogue going and the flow of the shoot is paramount to getting happy corporate portraits. There is no room for technical interruptions to this process and your subject rarely cares to know anything of your craft. Here is the shot with both front and back lights firing.

If I have f8 on the subject then I usually am looking for a stop and a half to two stops more on the background – that way I get a nicely blown out white background. In this situation f8 on the front of the subject would mean F13/f16 on the rear. This is where we get to the wrap effect. In this particular situation I want to keep the wrap – the amount of light being reflected back around the subjects head/body from the background – to a low level. These are corporate portraits for identifying the employee not headshots for Match.com. In order to eliminate wrap the reading on the rear of my subject needs to be equal to or less than the reading on the front of the subject from the main light.

In this case a balanced lighting set up would be a reading f8 on the front of the subject and f8 on the back – the f8 being generated by reflection of the background lights off the white background. The background is in effect one huge soft box – in my case 3.0m x 3.0m. Once my reading on the rear of the subject creeps up over f8 the wrap effect get greater not only around the face but also around the body starting with the body parts closest to the background. The effect is such that in extreme a dark suit for example would start whiting out to a grayish hue and that area of the image would lose definition.

For the next image I increased the power of the rear lights to full power giving me a meter reading on the back of my head of f10 – nearly a stop over the reading from the front of f8 – notice the light starting to wrap round my face and the highlights on the shirt camera right starting to blow out.

The wrap can be controlled by two factors therefore – the power of the background light and secondly – and more importantly – the distance of the subject from the background. If they are too close then wrapping is almost inevitable – my background is lit to a higher level than the foreground and the closer my subject gets to it the more light will fall on him and the greater the differential between the metered reading on the back of the head than the front. In this next example I moved the model, camera and front light forward by 1.5m so that the model (well me) was standing 1.5m away from the background. The meter reading on the back of my head was f16 – twice the metered reading from the front.

Notice how we have now lost contrast in the image and while this might be a great look for a fashion shoot it will not cut the mustard with a corporate client – no matter how much you do to the image in Photoshop you cant pull back what is not there in the first place.

One other factor to take into account is ceiling height. If the ceiling is low and white then some of the background light will be reflected forward off the ceiling and this can completely throw you off if you are not aware of it. One of the things I mean to try in the future for these small space shots is erecting some kind of black canopy over the subject area – kind of a black gazebo – I’ll post the results here.­­­

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