Pixiq

My last post was an assessment of the Sigma 105 mm f/ 2.8 macro lens as a serious objective for macro use. For approximately the same price as a new Nikon or Canon macro lens of the same focal length you could buy the Sigma macro lens together with Sigma's own make of macro light the EM -140 DG macro flash.

For a lens and light pairing from either Nikon or Canon you are going to have to part with much more cash. So, it seems appropriate to give you the low down on the Sigma EM -140 DG and reveal some of the results I have obtained with the one in my possession for the last four years.

The EM -140 DG  offers full DTTL functionality with compatible cameras and is sometimes wrongly advertised as a 'ring light'.  The flash unit in fact houses twin flash tubes - not a tube that encircles the lens and the output power of these can be varied from the control unit that sits on top of the camera body. With the tubes set to give you equal output then you get essentially shadowless lighting of the kind you would expect with Ring Flash. Then, if you want to create a degree of modelling by having the flashes at different powers this can easily be set from the control buttons and  the LCD display on the flash control unit.

• The Sigma EM -140 DG unit boasts a quality and specification comparable with that of dedicated offerings from the major camera manufacturers. It comes in a carrying case that also includes TWO adapters (55mm and 58mm) with 52mm, 62mm, 67mm, 72mm and 77mm available separately so that the unit can be fitted to a range of lenses.
• The flash head unit is separated by a coiled cable from the control unit that houses the batteries to power the unit, the capacitor that produces the flash discharge and electronics that controlling it and the communication with your camera's metering system.
• Flash output power is adjusted on the control unit and you can alter the power ratio of illumination from the tubes from 8:1 to 1: 8 - representing a difference of three stops between the tubes
• You can also adjust Flash compensation by up to ± 3 stops which is very useful because you might have the lighting balance on the subject you want but you need to lift or lower the level to get correct exposure.
• The exposure compensation buttons on the camera itself can be used to adjust background exposure without affecting the flash (taken care of by the controls on the flash) - you usually set a synch speed less than the maximum for this and need wind-free conditions other wise you might get ghosting. There is a main flash exposure plus an ambient light exposure - the subject has moved slightlybetween the two. You can check out some detail on this from one of my earlier posts on macro lighting.
• The unit works with the DTTL flash mode of the camera make for which it is intended (Sigma-STTL, EOS-ETTL, Nikon-iTTL). Before buying one of these check out the Sigma site to make sure that your camera is on the compatibility list.
• There is a modelling light activated by pressing the lamp button on the control: it stays illuminated for about 20sec.
• The unit works particularly well with macro lenses from 50mm - 105mm focal length - the flash tubes are both too near the lens axis and low powered to give good relief with 150mm -200mm focal length macro lenses. 
• A quick measurement on my work bench shows that, with a 105mm f/2.8 macro lens (Sigma) set at 1:1 reproduction ration (life-size) the flash tubes are just 10cm from the subject: the tube centres are 10cm apart... the flash comes from about 27° off -axis. Enough to give good relief with tubes set at 1:2 or 1:4, for example.

The Sigma  EM -140 DG also incorporates  a number of those 'advanced' features available in system flash guns:

• Modelling Flash - A short burst of flash pulses produces a strobe effect just long enough to assess the balance of the flash heads.
• Second Curtain Synchronization - The flash can be set to trigger just as the second shutter curtain begins to close rather than at the point where the first is wide open. It is effective with moving subjects where, during the movement, the shutter is open and the ambient light creates a ghost exposure. With normal first curtain flash synch this ghost is in front of the subject - with second curtain it lies behind as a sort of ghost trail that captures the sense of movement.
• Multiflash Operation - When set on the control unit, this option will allow a series of pulses with firing frequency adjustable between 1Hz (one pulse per sec) and 199Hz so that you could capture several stages in the passage of a moving object on a file. 
• Slave Flash control - This unit can be designated as a 'master flash' and used wirelessly to control other Sigma flash units.

Using the Flash in Manual Mode

Before I bought a Nikon macro flash unit I used the Sigma flash (Sigma mount) in its manual mode via a mount that converts the unit to manual use and does not transmit any data to and from the camera other than the pulse to trigger the flash.

It worked very well and I had done the same with a Nikon SB29s that did not permit DTTL flash with the Nikon D100 I was assessing for a review. In practice,  you do few tests (see the post of macro flash), then find a combination of aperture and shutter speed to suit by using the camera LCD to assess the scene visually. There is a peculiar statement in the Sigma instruction manual    "…The shooting in manual mode requires a very advanced technique".  It just ain't so.

FP Flash - this was something that appeared in the review of the Nikon R1C1 where the control unit did it all for you. Here you can lengthen the flash pulse so that it is firing for the whole of the time the shutter is open and thus you can use shutter speeds higher than the maximum synchronisation speed of the camera used.

SPECIFICATION

The Guide Number is 14 (in metres @ ISO 100)-  for both tubes when the flash is fired at full power.

• Power source                        4 x AA batteries (Alkaline, Ni-Mh, Ni-Cd)
• Angle of coverage                 80 degrees vertical  and horizontal
• Weight                                   430g without batteries
• Dimensions controller           76.7mm   x 136.2mm x 82.4mm
• Dimensions Flash                 126.6mm x 128.8mm x 30.5mm_
•  Compatible Cameras           EOS-ETTL,  Nikon-iTTL,  Sigma-STTL, Sony ADI,       Pentax PTTL
• RRP US $480.00            UK  £379.99

CARE - All flash tubes can heat up during a series of pulses and the manual advises waiting for at least 10 minutes after firing a number of times in sequence depending on the power output.

• Full to 1/2 power no more than 15 continuous shots
• 1/4 - 1/8 power 20 continuous shots;
• 1/16 - 1/32 power 40 continuous shots;
• Multi-flash - a cycle of 10 pulses.

Conclusion

In use with a Sigma camera SD14 body I find the unit gives consistently accurate exposures - as usual, with very dark or very light subjects some tweaking can be necessary. With practice you learn to judge the kind of things that demand a little tweaking (white flowers, black beetles) and make the adjustment beforehand.

It is an excellent unit for the money and a worthwhile buy for anyone who feels the outlay on Canon or Nikon macro flash units offputting.