flash technology

• see also:
  • remote flash for cameras
  • flash sync
  • flash modifiers
  • studio flash
  • using flash outdoors creatively
  • how to set Olympus FL36 and FL50 flash guns
  • photography and camping main index page
• on the net:
  • basics of using flash off the camera:
    • http://strobist.blogspot.com/2006/03/lighting-101.html and related webpages
  • Quantum wireless-enabled flashes for Nikon/Canon/Olympus/etc:
    • http://www.qtm.com/QFlash/
    • http://www.robgalbraith.com/bins/content_page.asp?cid=7-7899-8650 
  • Metz flash
  • flash photography with Canon EOS cameras:
    • PhotoNotes.org article
    • Bob Atkins' comparison of Canon Speedlites
  • flash photography with Olympus digital cameras:
    • TTL flash for Micro Four Thirds cameras
    • more details on flash options for Four Thirds and Micro Four Thirds cameras
    • English Bob's guide to using the FL-36 and FL-50 (pdf)
  • flash light meters:
    • manual for Minolta IV F see http://www.butkus.org/chinon/index.html 
  • safety of legacy flash units - the issue of high trigger voltages potentially damaging your camera:
    • Botzilla's guide
  • concert or event photography when flash is allowed:
    • http://photo.net/learn/concerts/mirarchi/concer_4.htm 
      • use of Slow Sync - 1st vs 2nd sync; 
      • manual exposure mode, relatively wide aperture for narrow DOF, raise ISO to 400-800, set shutter according to ambient light; use a light modifier if close enough to subject such as Stofen diffuser, or better still, a Rogue FlashBender or MagBounce
      • see https://photofocus.com/2016/07/01/how-to-use-on-camera-flash-for-events/
      • https://fstoppers.com/education/getting-great-light-any-event-203695
  • polariser film to put on your flash:
    • http://www.edmundoptics.com:80/onlinecatalog/displayproduct.cfm?productid=1912 

• the amount of light hitting a subject from a flash decreases by the square of the distance, THUS if you double the distance, you reduce the light hitting the subject to a 1/4 which is 2 f stops less light.
• if you bounce a flash off a white wall, you must use the total distance of flash to wall PLUS wall to subject as your flash to subject distance AND THEN allow for light loss of about 1 f stop (ie 50% light loss) from bouncing off the wall.
• similarly, shooting through a white translucent material such as a flash umbrella will lose perhaps 1 f stop of light depending on material used.
• a flash unit can output a variable amount of light up to its maximum output which is measured by its Guide Number (GN).
• BUT beware, with modern “zoom” flashes, their stated GN only applies to maximum zoom, thus if using a wide angle or normal lens, the broader coverage required will result in a lower GN.
• the Guide Number allows you to determine either:
  • the maximal range of the flash to subject for a given aperture and ASA/ISO
  • the appropriate aperture to use on full output for a given flash to subject distance and ASA/ISO.
• thus a GN of 45m at 100ISO means that at maximal output using ASA 100 film or ISO 100 setting on your digital camera:
  • at f/4.5, the correct exposure should occur when the flash to subject distance is 45/4.5 = 10m
• most built-in flashes on cameras have a GN of about 12m at 100ISO which is very limiting but still useful.

1. change the aperture (includes putting a filter on your lens such as a ND or polariser)
2. change the ISO
3. change the flash output (includes putting diffusers over the flash or bouncing flash off walls, etc)

• changing shutter speed mainly effects the ambient lighting mix, although at shorter speeds, it may impact on flash output if the duration is shorter than the flash duration (see below) and there may be some issues with flash sync.

• NOTE:
  • that changing shutter speed will have NO EFFECT unless you choose a shutter speed faster than the X-sync of the camera which is about 1/180th sec (ie. avoid using shutter speeds like 1/500th sec with flash as results will be less predictable) .
  • You can use this to your great advantage by adjusting the shutter speed you can determine how light or dark the scene is as lit by ambient light and not the flash light. If you want to see outdoors on a sunny day as you would normally expose it and you are using your flash, then just set shutter speed so that it will expose correctly for sunny day when using your set ISO and aperture values.
  • your effective maximum GN is drastically reduced if you forget that your polarising filter is on - this cuts exposure by 2-2.5 stops and can really confuse you!!!

• analog TTL - camera has a sensor which detects light bouncing off the film then tells flash to turn off when it is enough
• digital TTL - camera instructs flash to fire pre-flashes then determines the correct output for the main flash exposure
  • some systems may include AF setting to make this more accurate (eg. Canon's eTTL II), but these only work if flash is on the camera and not being bounced, and the lens provides distance information to the camera.
  • when in a hurry, this is usually the best way to go
  • great for fill-in flash outdoors to reduce shadows in portaits, etc as camera will meter for ambient light and automatically determine exposure settings and flash output.
• nb. TTL = Through-The-Lens metering and thus takes into account any filters used in case you forgot!

• flash sensor must point at subject and user sets an aperture and ASA/ISO on the flash to match the camera's settings
• works well but being a reflective light meter, can be fooled by bright/reflective surfaces, dark backgrounds or nearby objects
• don't forget to allow for any filters on the lens.
• great when you do not have TTL functionality or flash is incompatible for TTL.
• many modern flashes do not have this functionality 
  • the Canon 580EX II has it but most other Canon flashes do not including the 580EX

• user sets a manual flash output level (eg. full, 1/2, 1/4, etc), each setting will have their own GN value.
• user determines camera aperture & ISO by either:
  • trial & error
  • calculations using GN, or,
  • preferably an incident flash meter placed at the subject and pointing at the flash
    • favorites include the Minolta IV F or VF light meters, or even a 1degree spot meter if you can't put yourself in the subject's position and you have to use reflective metering with meter aimed at subject.
    • flash meters can be set to 3 main modes:
      • ambient - just measures ambient light levels
      • corded flash - connect a PC sync cord from flash to light meter and press button on meter to trigger flash.
      • uncorded flash - flash will automatically detect flash firing and display exposure BUT may be tricked by digital flash pre-flashes when using TTL modes.
• for set situations, manual flash can in the end be the least confusing as it removes flash output variability as a source of error when things just don't seem to be going right, then you can check for other causes of error:
  • filter on the lens you forgot to account for
  • camera shutter speed to fast for sync and thus not getting all the flash output

• the built-in flash in most cameras has a maximum output measured by Guide Number (GN) of 11-13 metres at ISO 100 and can be used for:
  • main flash (although results usually won't be too flattering for portraits)
  • fill-in flash
  • as an optical trigger for other flash units (helps if you can power the built-in flash down)
  • to provide catchlights in eyes when the main light won't do this (also helps if you can power the built-in flash down)
• what this means is that if you are using ISO 100 and f/5.6 then 11/5.6 = about 2m and so only subjects at 2m will be able to be exposed adequately when it is on full power. Subjects beyond this distance will be progressively darker, while subjects closer than this will be lighter.

• My favourite is to go fully manual and check the histogram afterwards - if I need more light then I manually adjust them (use M exposure mode on the dial and manual flash mode on the menu). One of the great features with the Oly's which is not often found elsewhere is that you can manually reduce the built-in flash output on the menu system. NB. the flash +/- setting is not functional here as this is only for auto flash.
• if you really want to calculate these yourself rather than use trial and error:
  • the correct aperture to use will be (approx) = GN of manual flash setting x ISO sensitivity / subject distance in metres.
  • here ISO sensitivity is your selected ISO related to ISO 100 so ISO 200 = 1.4, ISO 400 = 2, ISO 800 = 2.8, ISO 1600 = 4
    and on the Olympus E330 (think it is same for E500), the GN in metres at ISO 100 for various manual settings are:
    • full = 13, 1/4 = 6, 1/16 = 3, 1/64 = 1.5.
• Next, you can just use the camera's auto exposure modes eg. A or P but avoid S.
  Here you will be responsible for setting the ISO and in A mode also the aperture, the camera will try to control the flash output for you. You can use exposure compensation to tell camera to adjust the exposure.
  • NB. if the Olympus menu function flash+/- and +/- is set to ON, then any flash +/- compensation you select in the menu will be ADDED to the +/- main exposure compensation that you have selected.
• BUT if the subject is too far away for maximum flash output to work at the settings you have used, then the subject will turn out dark no matter what exposure compensation you tell the camera to use.
• Now, although the built-in flash is really handy, for best photos, you should get a 2nd flash that you can use off the camera to give different lighting effects such as more flattering bounce lighting, etc, but this is quite a bit more difficult for most to get their heads around. But if you need more flash output then you may need to resort to this.
• the Olympus E330 and E500 cameras have a menu setting which allows flash compensation (flash +/-) to be ADDED to the general exposure compensation value (+/-):
  • If you have the flash +/- and +/- setting set to ON, then the camera will ADD the exposure compensations in BOTH the flash +/- setting AND the main exposure +/- setting.
    • eg. if for example, each was set to minus 1 EV then the exposure will be minus 2 EV as they are added.
  • If you have the flash +/- and +/- setting set to OFF, then the camera will ONLY use the exposure compensations in the flash +/- setting AND IGNORE the main exposure +/- setting when it determines the auto flash exposure.
  • The auto flash works even when dial is set to M (manual exposure) as long as the flash mode is set to a non-manual flash mode (eg. AUTO, redeye or Slow), but when dial is set to M mode, the main +/- exposure compensation is not available and thus whatever setting you have the flash +/- and +/- setting set to, it behaves as if this is set to OFF.
  • One advantage of having the flash +/- and +/- setting set to ON is that you can rapidly change your flash exposure using the +/- button when using an exposure mode that is not M on the dial.
  • Thus say you take you pic in Aperture priority mode (A on the dial) and flash set to AUTO and the picture turns out too dark, you can check the histogram and see where the right edge is, then go back to picture tqking mode and adjust the +/- button (by rotating dial while holding it down) to a + value (eg. +1 EV) and re-take the photo.
  • If the histogram on the second photo has not moved more to the Right, then you can assume the flash is not powerful enough for your aperture, ISO settings and subject distance, THUS you need to change these (or remove that damn polarising filter).
    

• using electronic flash in your photography involves consideration of the following main issues:
  • amount of light or exposure:
    • there are a number of ways to get the desired amount of light from a flash unit:
      • manual calculation:
        • this is handy if the subject is very light or dark or dominated by background that would fool light sensors, but requires a bit of thinking.
        • you need to set the aperture on the camera according to the flash guide number for your ISO setting divided by the distance from the flash to subject.
        • if you are bouncing the flash then you must use the total distance of the light path and then adjust your aperture to open it from the calculated amount by 1-2 stops depending on the loss of light from the surface used to bounce the light.
        • it helps if there is a range of manual output levels you can select, for instance, older flashes like the Metz CT-1 has only one manual setting, the Metz 45CL-4 has M, M/2, M/4 & M/40, while newer flash guns may have up to 25 output levels.
      • distance priority manual flash:
        • you set aperture and distance on camera which relays this info to flash which sets output, great for weddings, products where metering may be fooled by white or black subjects
        • Nikon SB-800
      • flash auto sensor:
        • you set the camera aperture according to the flash auto setting & the flash will attempt to deliver the correct amount of light as it detects in its sensor. 
        • if subject is too far away, flash will fire its maximum output but image will be dark and hopefully flash will tell you there was a problem. In this case you need to either increase your ISO or open your aperture setting or both.
      • TTL flash:
        • camera controls light output of flash.
        • see below
    • too much light:
      • check the flash unit's minimum GN because this may be too high for fill-in flash for subjects closer than 2m with wide apertures that are desirable for portrait work.
        • for example, using a 85mm f/1.4 lens at ISO 400 for ambient light with subject at 2m and using flash to fill-in under-exposing by 1EV requires an effective GN at 100 ISO of about 0.5-1 in metres.  
  • duration of flash:
    • this is mainly important when trying to stop subject movement or camera shake (see below)
    • full output flash is about 1/200th sec on most units, and as you halve the output, you generally shorten the flash exposure by half.
  • relative amounts of light between various flash units used and existing light
    • assuming each flash is simultaneously triggered, either by cord, slave trigger device or manually if long exposure allows this, this can be achieved in a number of ways:
      • NB. existing light contribution to exposure may need consideration and is usually altered by changing shutter speed as this does not effect flash contribution unless it becomes faster than the X-sync of the camera in which case the flash will not light the whole frame or will not work.
      • it is helpful if the flash unit has a modeling light to visually check likely result, but if this is not available then either review of a digital image or use Polaroid film is handy to confirm the result is what you desire.
      • manual calculation:
        • knowing the GN for each flash, set its distance from subject to get desired effect, the accuracy of doing this can be aided by use of an accurate flash light meter, which requires each flash to be fired separately and its light on the subject measured either by incident (with meter aimed at flash unit) or reflected (meter aimed at subject), and then adjusting flash distance or manual output setting accordingly. 
        • Obviously this is cumbersome but may be suitable for static situations such as studio work.
      • flash auto sensor:
        • set each flash unit to its auto setting and use the f-stop setting on the flash to create relative differences in outputs.
        • flash sensor must be pointed at subject
      • wireless-TTL flash: see below
  • quality of light:
    • the small area of the flash results in hard, sharply-defined shadows which may not be suitable for many subjects.
    • the quality of light can be modified by diffusers, filters and by bouncing the light off surfaces to give a larger effective area and thus less sharply defined shadows and less specular highlights.
    • see flash modifiers.
  • shape of the light:
    • most flash guns are designed to output a rectangular shape over a reasonably wide coverage area to allow lens as wide as 28mm to have adequate light coverage
    • older flash units may allow addition of wide angle or telephoto lens to control the spread of light
    • some newer flash guns have a motorised auto “zoom” function which sets the coverage according to the camera's lens focal length, which enables output to be conserved and faster recycling times and higher maximum GN at telephoto.
      • eg.  Metz MZ series; Olympus FL36/50; Nikon SB-800/600;
    • macrophotography and beauty photographers often prefer circular ring flash:
      • Olympus OM ring flash system but unfortunately does not work in TTL mode on digital cameras.
      • Olympus Digital ring flash system
      • Alien Bees ABR800 ring flash - an AC-powered studio flash
    • in studio settings, it is nice to be able to shape the light further:
      • restrict light to certain parts of frame by use of snoots, barn-doors, etc, although these are generally not available to electronic flashguns, but are widely used with the larger monobloc strobes
      • to create a desirable catchlight shape for the eyes by use of umbrellas or soft-boxes, etc.
• additional features & issues:
  • red-eye reduction:
    • if a light source is close to the camera lens axis, then it will light up a subject's retina resulting in red pupil in the photo.
    • this can be minimised by:
      • turning the subject away from the camera
      • placing the flash as far from the lens axis as possible whilst still retaining the desired modeling effect
      • constricting the subject's pupil to minimise amount of light being reflected from the retina, this can be achieved by shooting in bright light with light behind you (but this may make subject squint) or most camera flashes and some external flashes can be set to pre-fire a flash to constrict the pupil. 
        • The pre-flash may incorrectly trigger any slave triggered flash guns.
    • this can be repaired by either:
      • in-camera red-eye removal (some cameras from late 2004 such as Olympus C7070)
      • in computer red-eye removal - many programs available to help you edit out the red eyes.
  • AF assist illuminator light:
    • some flash gun-camera combinations utilise the flash to provide extra light (usually via an infrared beam) to allow faster auto focus in dim light situations
      • need to ensure compatibility, eg. wide AF illuminator needed for Nikon D2H's 11 AF sensors.
      • most modern Metz flashes are capable
      • for use off the camera, some flash manufacturers have an on-camera TTL AF module to provide the illuminator beam whilst connecting to the flash for TTL flash, eg. Nikon's SC-29 Off-Camera TTL cord.
    • some cameras have the AF assist light built-in to the camera eg. Olympus C8080, Nikon D70
  • slow sync / rear curtain sync modes:
    • usually a flash is set off at the start of the exposure, but this means for longer exposures of moving subjects, the subject is frozen at the start position and then there is motion blurred for subsequent movement
    • rear curtain sync (2nd curtain) fires the flash at the end of the exposure and thus allows subject to appear sharp from the flash at the end of the blurred motion trail which is more natural.
    • slow sync allows one to set long exposure times (otherwise many cameras will default to 1/60-1/180thsec shutter speed when using flash)  and can usually be combined with either front curtain or rear curtain sync.
  • high FP sync modes:
    • while most digital cameras have a X-sync of 1/180th (Nikon D70 has 1/500th!), some cameras have a high FP sync mode (pioneered by Olympus) that allows flash sync at very fast shutter speeds which may be useful for fill-in flash in sunlight:
      • Olympus E-1 camera with Olympus FP50 flash: 1/4000th sec (n/a on Metz adapter yet)
      • Nikon D2H, D2X & ?D70 with Nikon SB-800/SB-600/Metz MZ series flash: 
      • Canon e-TTL capable combos eg. Metz MZ series:  1/2000th/1/4000th sec
    • The primary drawback is that pulsing the light causes a reduction in overall light output and thus range. When you have FP mode engaged you typically get about a third less range than you would if you were shooting with normal flash.
  • rapid sequence capability:
    • this determines the shortest interval between successive photos and is dependent upon:
      • flash gun recycling capabilities for given power supply & state of batteries
        • many flash guns have a recycling time of 5 sec after a full discharge on fully charged batteries which deteriorates as the battery charge falls.
        • some flash guns have faster recycle times
      • rapid sequence flash gun mode availability:
        • eg. Metz CL-4 has a “winder” mode that is a manual mode at 1/40th output and allows 2fps shooting
      • how much residual charge is left after each flash, the more the shorter the recycle time
  • stroboscopic flash:
    • this is rapid sequence flash outputs in the one exposure to allow stroboscopic action photos
    • only some flash gun-camera combinations have this capability:
      • Metz 54MZ-4, 70MZ-5; Olympus FL-50 (with E-1 camera);
      • Sigma EF 500 DG Super SA-N: The multi pulse flash features enable reduced power setting from 1/4 to 1/128 in 6 steps and the pulse frequency of the flash can be set from 1Hz to 199Hz.
      • Speedlite 420EZ: 1-5 Hz.
        Speedlite 430EZ: 1-10 Hz.
        Speedlite 540EZ: 1-100 Hz.
        Speedlite 550EX: 1-199 Hz.
  • modeling light:
    • some flashes (eg. high end Metz) allow you to fire the flash for a few seconds so you can see the effect of the light on the subject, but this consumes considerable battery power.

• ensure ambient lighting does not significantly contribute:
  • ensure your exposure is at least 3 stops under-exposed for ambient light levels - adjust this by changing shutter speed up to the shortest for flash sync for your camera (usually 1/180th sec for digital SLRs)
• check the flash duration:
  • full output from many flash units results in flash duration of about 1/150th to 1/200th sec - probably not short enough to stop action
  • the Metz 50MZ-5 flash durations are:
    • 1/200th at full GN50m; 1/500th at half; 1/1000th at 1/4; 1/2000th at 1/8th; down to 1/20,000th sec at 1/256 at GN 3m
  • thus, you may need to increase ISO, shorten flash-subject distance &/or open the aperture to achieve really short exposures
  • let's imagine we wish to use f/5.6 at 400ISO at 3m from subject with the Metz 50MZ-5 using a 50mm lens setting, the effective GN at 400ISO is 100m on full, but GN needed at 400ISO is 5.6x3m = 16.8m, and thus the flash would need to fire at 16.8/100 = 0.168 = 1/6th power which would give a flash duration of 1/1500th sec.
  • moral is: buy the most powerful flash you can so you can get to really short flash exposures.

• this requires dedicated connections between flash & the camera, unless the flash is in-built into the camera
• 1st developed by Olympus on its OM-2 camera of 1976, with film SLR cameras, light passed through the lens and reflected by the film is continually measured by the flash sensor during exposure until the correct exposure has been achieved.
• TTL for digital cameras works a little differently as you cannot use light reflected of the “film” or sensor anymore so alternative metering is used via a pre-flash measurement of a lower power flash burst prior to the main flash.
• current best, least complex TTL system appears to be Nikon's i-TTL.
• accurate TTL fill-in flash for daylight photos is best on Nikon's i-TTL or Canon's ETTL II. Olympus does not seem to support it yet.
• standard TTL flash:
  • user sets ISO, aperture or shutter speed with option to set exposure compensation for ambient light levels separate to flash exposure compensation, and camera sets TTL flash output to give even illumination but not fill-in.
  • camera detects when sufficient light has reached camera after shutter has opened & then turns off the flash output.
  • to achieve fill in, user may be able to set flash exposure to minus 1 stop for example so that ambient light is exposed properly while flash is under-exposed 1 stop but enough to fill in the shadows.
  • Olympus OM TTL-auto:
    • no pre-flash; analog system for OM film cameras;
    • Olympus T20, T32 flash
    • Metz SCA 300 with SCA 321 adapter
  • Canon A-TTL:
    • Canon's 1st attempt (with T90 film & EOS cameras) but very poor and no longer used as it really only determined if subject was out of range, the pre-flash didn't actually meter the exposure.
    • fires pre-flash when half press shutter release, unfortunately if flash is tilted or swiveled, the main flash fires as the pre-flash which is very distracting
  • auto-aperture TTL:
    • camera determines best aperture as well as TTL flash metering
    • eg. Nikon D70 + Nikon SB-800/600 + CPU lens
• balanced TTL fill-in flash:
  • camera attempts to set flash output to fill in the shadows but not overpowering the ambient light, most use pre-flashes to determine exposures needed but these have problems:
    • may cause subject to blink & be caught in mid-blink
    • may falsely trigger normal optical flash slave trigger units
    • can confuse handheld flash light meters
  • Nikon matrix-balanced TTL fill-flash:
    • camera adjusts ambient light exposure via its matrix sensor and adjusts TTL flash so that flash is not over-powering for the ambient light and provides fill in of the shadow areas.
    • Nikon allows either spot or CW metering.
  • Nikon 3D Multi-Sensor Balanced Fill-Flash (D-TTL):
    • DX camera analyses likely subject distance from its AF sensors and using its 3D matrix metering system via 18 preflash pulses, determines the correct flash output to create a natural balance between main subject and ambient background lighting.
    • DX master flash must be on camera for D-TTL to work, in this case camera should be set for spot metered TTL as camera will not know where flash is in relation to camera-subject.
    • with type G or D CPU lens: full 3D functionality
    • other CPU lenses: distance information not included thus not 3D
    • non-CPU lenses or in spot-metering: standard TTL only 
    • Nikon D70 / D100/ D1 series with SB-50DX, SB-80DX, SB-600, SB-800, Sigma EF 500 DG Super SA-N
    • Nikon i-TTL (see below)
      • an evolution of D-TTL that incorporates more accurate systems for pre-flash. The pre-flash fired is much stronger and of much shorter duration than D-TTL to achieve greater accuracy using the flash sensor. Forms part of Nikon's Creative Lighting System (CLS).
  • Canon evaluative TTL (e-TTL):
    • introduced 1995 with Canon Elan II/50 camera
    • fires a low-power preflash of known brightness from the main bulb to determine correct flash exposure. It measures the reflectance of the scene with the preflash just before the shutter opens using usual light metering, then calculates proper flash output to achieve a midtoned subject, based on that data.
    • “E-TTL is also generally superior to TTL and A-TTL when it comes to fill flash. The E-TTL algorithms are usually better at applying subtle and natural fill flash light to daylight photographs. E-TTL exposure is also linked to the current AF focus point, which in theory results in finer-grained exposure biasing than most multiple-zone TTL flash sensor systems.
    • More abstractly, E-TTL is a very automated system and isn’t well documented for the user. For instance, Canon have never published details on the E-TTL auto fill reduction algorithm. It takes a bit of experimenting to figure out how the system is likely to respond. And there’s relatively little user selection or choice in operation modes. Most flash units don’t, for instance, let you manually choose TTL, A-TTL or E-TTL flash metering at will.
    • All current Canon digital cameras with hotshoes - both the interchangeable-lens SLR cameras and the point and shoot digital cameras - support E-TTL (or both E-TTL and E-TTL II) and do not support either TTL or A-TTL. Even Canon digital cameras with internal popup flashes are E-TTL only. This means that only Canon EX flash units or third-party flash units with E-TTL support can be used with Canon’s current lineup of digital cameras. Older E and EZ flash units will not work correctly - no automatic through the lens metering is possible. You can get manual-capable EZ flash units like the 540EZ to fire in manual flash mode but this requires external flash metering.
    • Unfortunately, E-TTL has been a particular problem for digital EOS users. Many users report serious problems with wildly varying exposure when using an E-TTL flash unit with their Canon DSLRs. The main problem appears to stem from the way in which E-TTL on these bodies biases flash exposure heavily to the focus point. For this reason some digital EOS users have given up on E-TTL and gone back to the old-style autoflash units. Others routinely set their lens to manual focus once focus has been achieved, since the camera uses a centre-weighted average metering pattern for flash metering when in manual focus. The EOS 10D has revised E-TTL algorithms which rely on centre-weighted average metering for E-TTL flash, even if the lens is set to autofocus mode.”
    • “There are times when TTL metering may be more desirable than E-TTL. A common example is a studio setting where analogue optical slave units can be fooled by the E-TTL preflash. The 550EX, MR-14EX and MT-24EX let you disable E-TTL via a custom function, but they’re the only Canon Speedlites with this ability. All other EX flash units (220EX, 380EX, 420EX) will always operate in E-TTL mode when mounted to an E-TTL-capable camera, even if the camera is also capable of supporting TTL and even though they’ll work in TTL mode just fine on a type B camera.”
    • see flash photography with Canon EOS 
    • complex to use with multiple flashes
    • cameras: all type A EOS cameras;
    • flash guns: 
      • all EX series Canon speedlights; Sigma EF 500 DG Super SA-N;
      • Metz:
        • offers features that Canon do not - such as flash units with memory settings, built-in secondary reflectors, clip-on coloured filters and audio warning signals.
        • later Metz models (54MZ 3/4/4i or 45CL4dig or 76MZ5 or later) + require SCA 3103 M3 
        • BUT e-TTL will not work with a Metz gun if either:
          • filters attached to flash head of Metz 54MZ
          • 2nd reflector used (unless you have the 45CL4 digital, 76MZ-5 or later)
          • wireless remote TTL
    • with e-TTL, Canon also incorporated technology pioneered by Olympus to provide synch at fast shutter speeds:
      • focal plane (FP) or high-speed sync mode which allows fast shutter speeds by having the flash pulse at 50Hz to simulate continuous light sources, but the compromise is much reduced GN (more than a 1/3rd loss).
  • Canon e-TTL II (2004 see below)
    • introduced with the EOS 1D Mark II then 20D/350D to remedy the problems of the e-TTL system.
    • E-TTL II does not require any changes to either the flash units or lenses used with an E-TTL II camera - the changes are all basically internal to the camera body, hence an e-TTL compatible flash should be compatible with e-TTL II.
    • the biggest benefit of E-TTL II is that flash exposure is no longer linked to the active focus point.
    • it analyzes all metering zones before and after the preflash for improved flash metering:
      • determines the presence of highly reflective objects and excludes them from exposure calculations.
      • the 1D Mark II has two main modes:
        • C.Fn 14-0 on a Mark II allows E-TTL II flash metering to be subject-based, so it can use anywhere from 1 to 17 metering segments depending on the camera's analysis of the pre-flash information. This is not a spot meter reading, unless the camera determines that the subject is so small that it occupies only one of the 17 metering segments. Most subjects will cover a larger area than that. ⇒ evaluative metering
        • C.Fn 14-1 on a Mark II applies the E-TTL II flash metering algorithm equally to all 17 metering segments within the Area AF ellipse ⇒ averaged metering
        • NB. the Mark II never falls back to e-TTL I metering.
    • in addition it may use distance information if available
      • distance data is not used by E-TTL II if either:
        • lens does not report distance to camera (see http://www.bobatkins.com/photography/eosfaq/ettl2.html)
        • bounce flash (ie. if you tilt the flash head)
        • macro flash
        • wireless E-TTL flash
      • the distance information adds only marginal change to the exposure so will not be missed by most people.
    • flash guns: all Canon EX series - see above under e-TTL.
    • cameras which support E-TTL II:
      • EOS 1D mark II, EOS 30V/33V/7S/Elan 7N/Elan 7EN, EOS 20D/20Da, EOS 350D/Rebel X Digital/Kiss N Digital, EOS 400D/Rebel XTi Digital/Kiss X Digital, 1D mark IIN, 1Ds mark II, 1D/1Ds mark III, 5D.
    •  
  • Olympus digital TTL-auto:
    • not compatible with film-based OM TTL auto
    • uses pre-flash in either spot-metered, CW or iESP exposure modes
    • does not appear to use AF-measured mode
    • Metz flashes require SCA 3202 adapter (M3 for the E-1, and M4 version for E-300) AND a digital-enabled Metz flash such as Metz 54MZ4i, 45CL4 digital, 76MZ5.
  • Minolta P-TTL - Sigma EF 500 DG Super SA-N flash
  • Sigma S-TTL - Sigma EF 500 DG Super SA-N flash
  • Minolta ADI:
    • used in their 7D DSLR
    • calculates distance to subject in the flash calculation but flash must be on camera facing at subject
• wireless TTL flash:
  • i-TTL balanced fill-in flash:
    • arguably the best, and simplest TTL system available, is an advanced form of D-TTL
    • introduced Jan 2004 with the Nikon SB-800 flash and Nikon D2H camera, can b used on D70, D2X, and some functionality on Coolpix 8800 & 8400.
    • allows a master i-TTL flash to wirelessly control flash output of up to 3 other i-TTL flash groups (each group may have more than one flash), by setting exposure compensation for each group. A pre-flash is used to set the light outputs of each group & this can be locked (“FV lock”) so that one can zoom out and still get same exposure on the subject. 
    • 4 wireless frequency channels to minimise conflict with other photographers.
    • modeling lights can be remotely turned on/off
    • i-TTL compatible flash units:
      • Nikon SB-800; SB-600; Sigma EF 500 DG Super SA-N;
      • Metz 54MZ-4i with SCA 3402 M3 adapter
      • Quantum QTTL flash
  • Nikon D-TTL:
    • precursor to i-TTL but problematic in wireless usage
    • The main D-TTL pre-flash contains 18 discrete pulses arranged in a time pattern
    • The wireless flash tries to match what the camera is doing with the main flash. It starts firing with the first pulse and stops with the last. Then starts up again when the main flash occurs, as long as its recycle time can cope
    • flash guns: SB-28DX / SB-50DX / SB-80DX / SB-800 / SB-600; Sigma EF 500 DG Super SA-N
    • cameras: Nikon D1 series; Kodak DCS Pro 14n;
  • Nikon's older wireless TTL:
    •  
  • e-TTL II:
    • Canon 20D, 350D cameras with EX flash guns (esp. 550/580EX; 420EX only as slave; MR14/MT24 only as master).
    • allows slave control of up to 3 groups, supporting flash output ratio control, flash exposure bracketing (FEB), & modeling flash with flash output ratio.
    • e-TTL II compatible flash units:
      • Canon Speedlite 580EX II
        • see 1D MarkIII
      • Metz 54MZ-4i with SCA 3102 adapter
      • Quantum QTTL flash
    • e-TTL II wireless Speedlite transmitter ST-E2:
      • IR line of sight transmitter
  • Olympus wireless TTL:
    • Olympus finally stepped up to the plate and introduced wireless TTL in 2007 but you will need the latest cameras (eg. Olympus E3/ E420/E520) and the R versions of the Olympus FL flashes.
    • 3rd party flashes do not yet support Olympus remote TTL but hopefully will d so late in 2008.
  • Sony wireless TTL:
    • http://www.dpreview.com/news/0806/08062001sonyhvlf58am.asp 
  • Metz:
    • Metz sell a digital slave trigger SCA-3083 which allows light-triggered wireless TTL control of other compatible Metz units such as the 54MZ-3, 70MZ-5, 70MZ-4. This is not compatible with Canon's wireless system.
  • Quantum QTTL flash
    • modular system supports Nikon's i-TTL, Canon's e-TTL II
    • separate radio transmitters & receivers to control wireless TTL
  • Radio Poppers:
    • wireless (not IR) transmitters and receivers for flash units which retain TTL functionality for i-TTL (ie. Nikon) and e-TTL (ie. Canon).
    • each unit attaches via velcro to your flash and your IR wireless transmitter and converts IR signals to radio signals and vice versa, thus you still will need a IR transmitter from your camera as well (eg. Canon ST-E2 or Nikon SU-800).
    • not weatherproof though.
    • no longer stuck with IR line of sight restrictions as with Canon/Nikon systems.

Powering your flash:

• see also:
  • http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM - tests AA rechargeables.
• most flashes are powered by 4-6 1.5V AA batteries which usually give a 5sec recycle time
• these can usually be replaced with cheap, rechargeable NiMH batteries but these have problems:
  • unpredictable, shorter life than NiCd, a single cell failing will stop the whole pack
  • ideally, should remain as sets and not mixed with different brands, age of battery, etc.
• some manufacturers (eg. Metz) have their own AA rechargeable battery packs
• alternatively, you can purchase separate generic lead acid power packs which reduce recycle time to 50%, and provide more shots:
  • Al Jacob's Black Box:
    • Al doesn't like AA batteries, NiMH or Li ion batteries.
    • He has made a lead acid black box for wedding photographers, etc using Canon/Nikon/Vivitar flashes;
    • recycle 3sec, 800-1000 shots; 90 days at 90% charge off a charger;
    • designed to be on a charger all the time when not in use.
    • two outputs; 6.4V peak; 2.7lbs; 
    • eg. power a Canon 580EXII via a Quantum MB-2 cable which leaves the battery door open for the cable.
  • Quantum 2:
    • for 9V flashes (eg. Metz 45 series);
    • lead acid battery with fuel gauge; 2 output jacks for separate flashes; 
    • holds it charge for months
    • 300 full shots per charge, recycle time 3-5sec
    • standard recharge 12hrs; fast charger 2hrs;
    • 940g
    • with the advent of AA NiMH batteries, these heavy packs are losing favour but are safer for your flash.
• high voltage packs via AC port (usually need AA's in to power LCD, etc still):
  • most manufacturers also have their own high voltage power packs to give faster recycle times:
    • Olympus FS-SHV-1  - recycle time less than 1.3sec and 250 full power shots
    • Canon CP-E4 - 8 AA batteries; 220g; recycle time < 1sec?
  • 3rd party accelerated packs via AC port:
    • if you want fastest performance and prepared to live dangerously in terms of strobe life, try an accelerated pack which supplies power via the strobe's AC port:
    • risk of damage to strobe as strobe electronics are being pushed beyond their design and may void warranty - see Al Jacobs 
    • Quantum Turbo SC Slim battery pack:
      • http://www.bhphotovideo.com/c/product/467222-REG/Quantum_Instruments_TSC_Turbo_SC_Battery_Pack.html 
      • use AC port of most recent Canon, Nikon, Metz (incl. 45 series) flashes, Olympus FL-50
        • see http://www.qtm.com/CompatibilityChart/?contenykey=CompatibilityChartres_set=yes&res=1280&resh=1024
      • high voltage NiMH pack; 1.5Hr charge; 400 shoe mount flashes per charge; fuel gauge; recycle time to less than 2secs;
      • 422g;
      • warnings when using with Canon 580EXII:
        • Be careful how you plug the cord into the flash - if it isn't lined up correctly you can push the flash socket in and it's off to Canon for repair.
        • plus see special note here
• low voltage NiMH power packs via strobe's battery terminal:
  • http://www.bvspulsar.com/
    • with 16 NiMH AAs in the QUICK-RECYCLE Module, the BVS PULSAR is about 1.6X as fast (1/3 to 1/2 LESS recycle time) as the Canon CP-E4 with 12 NiMH AAs (8 + 4 in the flash helping to drive external power).
    • “The QUICK-RECYCLE module in the BVS PULSAR uses two proprietary techniques to accelerate current flow beyond what is possible with a large high resistance HV battery. Plus it does this through the flash battery port, so the flash internals are removed as a limiting factor. This is not the case using HV port which is slowed by normal AA power flow to the flash.”
    • “it compensates for the lower voltage of NiMH batteries, pushing the pack voltage slightly higher than a lithium AA battery.