Nowadays, we are spoilt by technology and there is a tendency to think in terms of a camera controlling the output of flash guns via its DTTL exposure system. Even better, it can do this without the use of cables via a WiFi set up. However, the arrival of digital cameras has made the use of older manual flash guns easy, even though you are denied the camera’s DTTL system.
Once upon a time, a flash gun was simply triggered by a camera hotshoe or, off-camera, via its flash synchronisation (synch) socket. Other ‘slave’ flash guns for fill-in or back lighting could be triggered via simple photoelectric triggers that fit the flash hotshoe and reacts to the main flash pulse with a very slight delay.
To get correct exposure demanded a flash meter – an exposure meter that can respond in a very short time (milliseconds). Readings were transferred from meter to camera and flash gun positions adjusted accordingly. Many professionals in studios used a polaroid film back to get a rapid assessment: with close-up work experiments had to be done with flash gun position noted and frames taken over a range of apertures to find the optimum. Nowadays you can use your camera’s LCD screen to make a visual assessment of exposure.
Positioning of flash guns:
Working on the small scale demands the same approach to lighting that you might encounter in a studio – in fact, in macro photography you can find yourself having to master a whole range of ‘skills’ from portraiture through to landscape:
In close-up and macro work there is often talk of the ‘effective f-stop’ eg at 1:1 you have 2-stops less light reaching the sensor since it has spread out (see the basic macro blog entries) as you move forward to get sharp focus. If you are handling things manually using guide numbers, as of old, then this had to be accounted for manually. However with a TTL metering system this is taken into account for light reaching the sensor is measured irrespective of extension.
One thing does work in your favour when using a purely manual set-up and that is that you can find run tests to determined a suitable flash position to give, for example, correct exposure at f/16 (marked on the lens) at a reproduction scale of 1 : o.5 ( 1/2 life-size magnification). The flash could be fixed via a bracket (or held against the camera) and the same settings used when you moved in to get 1:1 magnification (or focused with an internal focusing lens). The reason is that although you introduce an extension within the lens system and that effectively means light intensity on sensor or film is reduced, the flash itself moves nearer the subject. This compensates for the reduction in light reaching the sensor since both obey the Inverse-Square Law of light intensity (double the distance between source and sensor and you get ¼ of the light intensity, triple it and you get 1/9th and so on). Which is why you can keep the flash in the same position relative to the camera body.
As you work with higher magnifications you have to remember that marked aperture on the lens becomes an ‘effective aperture’ (eg at 1:1 scale of reproduction f/16 is equivalent to an effective aperture of f/32 and image softening because of diffraction at this smaller aperture become more pronounced even if depth of field becomes greater. There is alway this trade-off between depth of field and diffraction at small apertures and part of the skill of the photographer lies in getting this right.
In the past, before the ‘miracle of TTL flash in the Olympus system I used this manual exposure method for years with great success. I would set up the calibration with a neutral ‘grey” card (18% reflectance) then opening up the lens slightly (½ – 1 stop) with a dark subject (less reflective) and closing it by the same amount for a light, highly reflective subject.
Setting up manual flash:
In recent years many photographers have begun using a ‘manual’ system with the LCD screen taking the place of a polaroid film back to assess lighting balance…so much easier. Many studio guns can be slaved to a central controller but do not operate via a camera TTL system but employing manual flash guns is easy, even though you are denied the camera’s DTTL system. The LCD on your camera allows near instant visual appraisal and, especially using the histograms, you can fine-tune a manual system quickly.
In a studio set up (either indoors or outdoors as in the MYN project) you can, with a little practice, know where to place your flash guns and with a quick exposure to check you are set to go time after time if your set-up does not change. Many of the more powerful flash guns allow you to switch off all control via a camera’s DTTL metering system and control the power output in a series of ratios full: ½, ¼. ⅛. 1/16, 1/32 etc and between those for fine adjustment there is further ½ or even ⅓ stop fine-tuning possible.
With a power output control in a flashgun, the electronic system ‘siphons’ power to a quench tube and the flash output is very much reduced and also a great deal faster. This is something dealt with in blog posts on ‘in-flight’ photography. The table below shows the change in flash pulse duration that occurs with fractional power output. Such flash units become high speed flash units capable of stopping rapid action which I have used with in-flight images of hawkmoths.
Radio triggers, with a command unit on the camera and receivers on the guns, can work with both TTL and manual systems and obviate the need to use numerous flash cables that can be both inconvenient and a hazard.
Cameras that meter using a pre-flash – a workaround
With my Nikon Speedlight system, I have often used the R1C1 macroflash unit with the camera’s DTTL exposure system and, via the command control on the camera, set the lighting ration I want from these guns. A Nikon SB900 acted as the background flash set on ‘manual’ and controlled its output from the same command unit. The mix of manual and DTTL control has served me very well.
I thought, when I purchased a Sony NEX 7 and a suitable Sony flash, that I could trigger the Nikon gun as a manual unit to give backlight – in those white-panel acrylic shots. It did not work because Sony employ a pre-flash system that emits a pulse of light at low level before the main flash and their cameras meters this when that light is reflected back from subject to the camera sensor. Unfortunately, that pre-flash triggers the background flash when it is fitted with a small photo-cell operated flash trigger and so it fires before the shutter opens for the main exposure…result, no backlit white panel visible.
One work around is to use the DTTL system for the main flash (metered from the camera) but to use a background flash controlled manually with a trigger that delays its firing. I purchased a small, cheap and cheerful, Chinese-made unit (Seagull SYK-5) that has a control allowing you to set a delay by trial and error until the flash is not triggered by the pre-flash. It proved slightly temperamental so I resorted to another method: set the Sony Flash to manual mode (on the flash) and also set the camera to manual. This action suppresses the pre-flash and you can use both main and background flash in a manual set-up – it is relatively quick to get things right with the LCD (and the histograms) as a visual guide to the exposure you want.
Controlling Background Illumination
Photographers in the MYN project tend to use flash units that operate manually. Success depends on using a unit behind an acrylic/perspex panel and a diffused light source(s) in front,. The mix of backlighting and frontal-fill creates images with an edge translucency that is not obtained in any other way. The power of the flash gun behind the acrylic panel can be adjusted (via the ratio control) and/or its position relative to the panel – chosen to give the required brightness – usually a read-out of 255 in all Photoshop/Lightroom channels: a perfect white.
You can see this from the histograms on the LCD where all three colour peaks (red, green and blue) that are pushed as far to the right as possible before clipping occurs.
© Paul Harcourt Davies – neither images(s) nor text may be used in whole (or in part) without the express permission of the author.