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Basics of Flash Photography

Beginners Guide to Select a Hot Shoe Flash

This article is about choosing a speedlight for the hot shoe. Not specifically which flash, but rather about the big questions, to help think about what you need.

The speedlight flash can be used on the camera hot shoe, either as direct flash or as bounce flash, either as the single main light, or as fill flash, possibly to lighten harsh dark shadows in bright sun. The flash can be used off-camera, maybe in umbrellas, maybe multiple flash units, maybe for studio portraits or for tabletop or macro work. Or the speedlight can be used to stop fast motion of water drop splashes or hummingbird wings.

The first big concern is "How will you use the flash?". What do you need it to do? For any time the light is dim or harsh, but there are several options, and so much that can be done. The question is: Will you? What features do you need?

• Will it be used only as an on-camera direct flash, always aimed straight ahead? Like using flash on a compact camera, to only to be a stronger flash than the camera's little internal flash? Sadly, this seems to be most novice users, those who never bother to learn anything more. In which case (if you only use full Auto modes of everything), you really don't need features, and the inexpensive TTL flash models should suffice well with point&shoot automation (until you are ready to participate more). If you are willing to participate in the process, there are really neat things to do to greatly improve your flash pictures, using the various flash features to help. But make no mistake, while flash is easy, and extremely rewarding, it is a little different, and you have to take the first step. Wade in and try something, a little experience is an extremely useful thing.
• Will it be used For bounce flash? Hopefully at every possible opportunity? Bounce adds natural smooth gradient shading tones which really improve the picture. The hot shoe flash head is aimed up at a white ceiling (or at a white wall). This bounce reflection becomes a large soft light, from a better direction (not flat frontal light), which is much better lighting, better flash pictures. Bounce is perfect for great indoor pictures of friends and family. Wedding photographers use bounce to ensure their pictures will sell. But bounce does require flash head tilt and swivel, and greater flash power. TTL mode will be a tremendous help for bounce flash. So is your goal to learn a thing or two about getting great flash pictures, or do you expect to only try to ignore flash? Really, that seems to be the choices. I hope to encourage you to seek better flash pictures. Flash is certainly the fun part.
• Do you need capability to use an off-camera remote flash? For better lighting angles? Maybe for macro work, or perhaps in umbrellas for soft portrait lighting? Soft light is Easy. You will need a way to trigger the remote flash.

  A flash can do so much for you, to make the situation's lighting be exactly as you want it to be.

Did we mention speed?   A speedlight capturing a punctured water balloon. 105 mm DX, ISO 400, f/16, 0.8 second shutter (actually, it was manual Bulb shutter... open shutter, poke the balloon, flash triggered by "pop" sound, close shutter, which the Exif says took 0.8 second). Punctured balloon collapsed, leaving the water still standing, before it collapsed. Flash up close (3 feet) at 1/64 power level so the Nikon SB-800 flash duration is 1/30,000 second. Which is the reason camera flashes are called speedlights (can freeze very fast motion). A few studio flashes are same as speedlight design, but many are of a different design, still fast, but not speedlight fast.

This balloon was in normal daylight patio shade ambient (not in bright sun, but far from dark). The big point here is that ISO 400, f/16, 0.8 second was insufficient exposure of the ambient light. That picture would be dark without the flash (so no motion blur is seen from the continuous dim ambient). But the flash was close, and bright, and very fast, and instantly froze the motion of the collapsing balloon and water.

Or the strawberry dropped into a spoon of water. f/22 0.5 second, but the speedlight flash stops the motion. The f/22 keeps out the continuous ambient light, which would have blurred the motion.

Or for pictures of the kids with routine bounce flash, that speedlight flash duration speed at half power would be maybe 1/1000 second. And the bounce flash would be better portrait lighting too.

The first main question will be about using Manual flash mode, or TTL flash mode? Many of us use both for different duties, and optimum would be a speedlight that can do both. But beginners with no flash experience absolutely need a flash that can do TTL for them.

• TTL flash mode: This mode is the Point&shoot automatic flash, easy to do, rather like flash on compact cameras, however camera metering is not always precise. It normally is pretty close though, and TTL is really handy, for walk-around flash, especially for following motion (kids running around, etc). But again, we have to watch it and sometimes correct it as we see necessary. The way we control DSLR TTL flash is by using Flash Compensation on the camera (see what it does, then simply fix it). In this sense, DSLR TTL capability is way ahead of compact camera automatic flash. The Nikon Commander even allows a couple of remote TTL units to be controlled.
• Manual flash mode: Manual flash is nothing like point&shoot automatic flash. Absolutely no detail of manual flash is automatic. Manual flash mode means it is YOU who has to manually set flash power level precisely for correct exposure of every picture — nothing else but the human operator (you) is going to do it. Nothing is automatic. This does NOT mean difficult, it just means you must add the step to determine and adjust manual flash power, for each picture situation. If your capability can easily change a light bulb, then you can learn how to pay attention to the flash exposure. One way is that if the flash result is too bright, then you turn it down until it does better. This is easy for photo enthusiasts, but seems to be harder for those that cannot be bothered with it. But this is definitely a step that manual flash requires of you, and automatic TTL flash can make that be more automatic.

  And then, manual flash mode can offer maximum control in fixed studio use, etc, in that you can do exactly what you want without automation getting in the way. A handheld flash meter is often used individually for multiple lights in the studio, but for walking-around hot shoe flash, one manual flash is easy to adjust by trail and error — by watching results on the camera rear LCD and the histogram, and then correcting to how you see it needs to be. This will be about like the last time in a similar situation (experience), but without a meter, it can involve a few tries, and frankly, you have to be willing to bother with it. Not everyone is, but manual flash can offer more exact control... if you have the time and patience.

  And again, if you are trying to follow motion, like kids running around, or aiming at different kids at the party, you won't have much time to mess with adjusting manual flash for each picture. But once we verify TTL compensation once (in this situation), it easily and automatically adjusts for different variations in the same situation, for example like in same room. TTL becomes point&shoot flash, really handy.

  We do have to sometimes tweak automatic TTL flash a bit too, but the difference is really just a matter of degree, and the initial starting point is already pretty close for TTL. Both Manual and TTL modes have advantages and disadvantages in their situations (fixed control vs. automatic point&shoot), so there are strong uses for both. Think a little, about what can actually help you. I mostly use manual flash in fixed studio situations, and TTL flash for most else (like fill flash in bright sun, or hot shoe TTL bounce flash indoors).

TTL Control:

• It is the camera that meters TTL flash and sets the flash power level (including third party TTL flash units). However, the camera meter that we see is only about the ambient light, and the settings it controls are about ambient. The camera has another invisible meter system for TTL flash, to set the flash power level for the settings that flash discovers is already in effect. Then the hot shoe communication tells the TTL flash what power level to use. The flash only has to flash as told. Flashes do need reliability and consistency to comply and perform well, accurate and repeatedly, always the same as was set, manual flash mode too. But it is the camera that controls TTL flash.
• Then optimally, the human brain watches the results, and knows and does what more is necessary (see How Light Meters Work). The way we control what automatic TTL flash does is with Flash Compensation. This is a plus/minus flash adjustment to what the automation is doing — which is already pretty close, but then you simply do what you see is necessary, to get exactly the result you want. It means a little thinking about what we are doing. Which is Not hard, and it becomes easier with experience. Similar past scenes means we often already recognize what this scene will need, when we first walk up. But if not, simply just do what you see you need to do.

Terms: Note the term TTL has a few different meanings. We do say TTL generally (just meaning any automatic Through The Lens metering), but there are different designs, and for today's Nikon DSLR (those since 2003), we always specifically mean iTTL flash units (which we likely call TTL). The term TTL also specifically means older film TTL, no longer compatible. So "TTL" depends on the usage context, any general automatic Through The Lens metering, or specifically the old TTL version used with film cameras — or it may actually assume iTTL. The context generally defines it, and we get used to the confusion. 😊

Broad generalities about some feature groups of camera speedlight flash models:

• Brand Compatibility:

  Flashes which can do TTL must be compatible with the camera system brand, specifically must specify iTTL for Nikon, or ETTL for Canon, etc (this compatibility is called brand dedication, dedicated to work with one camera system brand). TTL specifications must mention being dedicated to your camera brand (says "for Nikon", etc). Among other things, the hot shoe pins are different among brands.

  Manual-mode-only flashes do not require brand dedication. These only use the center one pin shoe contact (same as PC sync cords and radio triggers are one pin), which provides only manual flash mode, and brand compatibility is not important then, so long as it fits into the hot shoe (Minolta and Sony use a different hot shoe, otherwise, hot shoes are standard for manual flash — or rather, standard enough for manual flash). However, if the manual flash zooms to follow the camera, it will specify some degree of brand compatibility, and communicates with camera in some degree.

• Speaking of the least expensive third party brand models ($50 to $100 class):

  Some inexpensive models only have Manual flash mode (no TTL).

  Or some inexpensive models only have TTL flash mode — No Manual mode, automated flash only. Saves hardware cost of menu displays and buttons. This seems a reasonable option for those who don't want features for automatic direct flash, just to be more power than the internal flash. But more features can really help when you get into it (zoom, and tilt and swivel and power for bounce, off-camera use, etc). Interpreting the specifications about what a flash does is not always easy, but do make sure a TTL flash is said compatible with your camera brand (Nikon or Canon, etc). Otherwise, TTL will be no go.

  But today, we have several inexpensive Chinese flashes that offer full features for the same low price range. See the Review Links here at page bottom.

• Next group up in price have a menu to select flash modes, Manual, TTL, and other modes, and generally, offer more extra features too. Extra price normally buys bounce and more power level (Guide Numbers). And probably buys faster recycle time too (and using rechargeable NiMH batteries also improves recycle time).
• Top group in price may also have options to work remotely with the Nikon Commanders (not so many third party do, but some do). Some may mention wireless remote flash control, but may refer to their own system and flashes, which might not include Nikon's Commander system (which is called AWL). Read the ad words carefully. In particular, read user reviews carefully. Nikon Commander compatibility will mention Channels 1-4 and Groups A,B,C.
• Resources and Buying Research: Read any user comments posted with it (at B&H and Amazon, even if not buying there). See if the flash manufacturer has a web site with the user manual (for description and specifications, but also, the user manual probably has a full Guide Number chart in it). Also for a specific model, search Google for brand, model, and the word REVIEW. Other users with the flash can tell you much there.

  Speedlight+flash+at+Amazon -   Can sort by flash brand or by lowest price, etc. Prices are good, model selection is good, but the descriptions are skimpy. Amazon does have Yongnuo and Neewer flashes, which have become rather popular, because they are inexpensive. Read online reviews. (I have Nikon speedlights, and recently bought a Yongnuo flash, and have learned to spell and appreciate it).

Old flash models

Used flashes can be a good buy, but old TTL flash models for film cameras cannot do TTL on digital cameras. TTL flash is simply quite different between film and digital cameras. Film TTL metered the lens reflection from the sensor (the film), but that doesn't work for digital. Digital TTL first fires a weak preflash which is metered reflected from the subject. Nikon also had a different early digital D-TTL flash system, no longer compatible. The current Nikon DSLR do their iTTL. Canon DSLR do their ETTL. If the flash is older than 2003, there is no possibility that it can do Nikon iTTL.

The only Nikon iTTL flashes (for digital) are SB-300, SB-400, SB-500, SB-600, SB-700, SB-800, SB-900, SB-910, and SB-R200 (the three digit models). Older Nikon flashes with only two digits, like SB-24, SB-26, or SB-80 cannot do today's iTTL. However, those old ones can still do Manual flash mode very well with digital cameras. And several may also have a non-TTL Auto mode that can meter itself, and can do automatic flash exposure that way. The old ones can't do the current CLS hot shoe communication however, so you inconveniently have to manually enter the f/stop and ISO into the flash unit menu, so Auto mode will know the camera's target goal (Manual mode does not need that, you only set power level).

Nikon offers this Compatibility Guide for combinations of older and current flash and camera models, showing the features that will be available. Nikon manuals are online here.

(Too much detail, sorry) Connecting some older flashes to the camera can have special concerns. All flashes do put a voltage on the trigger contact on the flash foot or the PC connector, called sync voltage. The camera shutter shorts that voltage to trigger the flash. The ISO spec allows 24 volts, but today, this is normally around 5 or 6 volts. But some old flashes might put a couple hundred volts there, dangerous to some digital circuits. All Nikon DSLR cameras are rated to withstand 250 volts (see manuals: at Optional Speedlights, or search PDF for "250 V"). The later Canon DSLR are rated 250 volts now (earlier EOS said only 6 volts). And some other cameras are low rated, so the concern about digital sync voltage damage comes up. The only way to know what you have is to measure it yourself, with flash turned on but not connected, and simply measure the DC voltage on the foot center pin to the metal foot frame (Other articles). Touching that pin to measure it can slip and cause it to flash, which is fine, that's how it works, but do expect this possibility, and aim it away from your eyes, and do not lay it face down on a surface that the flash tube heat will scorch (definitely can happen). If there is excessive sync voltage on a nice studio flash unit worth keeping, get a $50 Wein Safe-Sync to protect the camera. If is an old cheap speedlight, the $50 is much better spent towards a newer unit. All of the old Nikon speedlight flashes are a safe voltage, but old Vivatar and others, possibly not. Measure the voltage before connecting them to the camera.

Just saying though, we spend hundreds on a fancy modern DSLR, which can do impressive TTL flash things, and it seems a shame to hang on to an obsolete old flash that cannot do any of it. But manual flash can still work, and does have its own virtues, especially in the studio.

How To Start with Flash, First Time

Just a quick rough idea for beginners who have never used a camera with settings before. Wade in, a little experience will be very helpful. Speaking here of a DSLR and a hot shoe flash (which maximum power capabilities do vary).

Note that the DSLR camera menu which sets TTL or Manual mode is only about the camera's internal flash, which is totally out of play when its door is shut. A hot shoe flash has its own menu about its mode, and totally ignores that camera menu (SB-300 and SB-400 are exceptions, they don't have their own LCD menu, so must use the camera menu, in camera models designed to recognize them).

For fill flash outdoors in bright sun, camera P mode is the place to start. That will meter the ambient sun and will set aperture and shutter speed for it, and the Nikon TTL BL system can do balanced fill flash automatically. Using fill flash can make a huge difference for dark shadows on pictures of people in bright sun.

For an indoor subject, any ambient is usually quite weak, nothing there to be metered (is why we need flash), so we usually just ignore the ambient. Set camera A or M mode (Aperture Priority or Manual camera mode — and a TTL flash mode is still automatic flash in camera Manual mode, at any aperture).

In A mode, set the manual aperture you want to use, which "depends", but often perhaps f/8 for direct flash or f/4 for bounce flash.

In M mode, maybe set same apertures (f/8 or f/4) and set shutter speed 1/60 to 1/200 second (any speed not exceeding cameras flash sync speed). The ambient is normally so weak this won't matter to it, but choose shutter settings depending on how much ambient light you want to let in, or want to keep out. The TTL flash is still automatic flash in camera M mode, and shutter speed doesn't matter to the flash, it only affects the ambient light (but see the Part 4 page). Just try it, you'll like it. M mode has advantages with indoor flash. If choosing A or P mode, the shutter speed will normally always be 1/60 second indoors with flash. Which will work, but in M mode, you can choose the best choice for the situation.

Auto mode is auto everything, not allowing any control, and it will want to open the popup flash door, and it will use Auto ISO and Auto White Balance (You set those in A or P or M mode if you want them on, and in A or P or M, you open the internal flash door if you want to use it). Except note that Auto ISO cannot be used with Manual flash (flash cannot respond to it), and it's a great idea to turn it off for TTL too. Auto ISO indoors will just increase the ambient to make the orange incandescent lights be objectionably orange.

In addition, more detail:

Indoor Direct Flash - Assuming a subject at about eight feet. ISO 100 and maybe f/8 aperture. Maybe f/5.6 for a lower powered flash, maybe f/4 for the cameras internal flash. Low ISO.

• TTL flash - Set flash to TTL mode. Aim camera and push shutter button. TTL meters a preflash and handles the power, regardless of (any reasonable) subject distance.
• Manual flash - Set flash to M mode. Power should be about like last time in similar situation, but maybe 1/4 power (for starters. Depends on distance and f/stop and ISO, also depends on zoom). Aim camera and push shutter button. You have to adjust the exposure (power, aperture, or ISO) for different distances. The little internal flash will struggle (if eight feet, try full power at f/5).

Indoor Bounce Flash - Assuming standing under a ten foot white ceiling. ISO 400 and maybe f/5 aperture (which includes a small safety factor, and faster recycle, but small flashes may need ISO 800 for bounce). Don't stand too close for bounce, a normal 6 or 8 feet, but zoom in all you want. Aim flash head up at white ceiling, and pull out built-in bounce card, if present.

• TTL flash - Set flash to TTL mode. Aim camera and push shutter button. TTL meters preflash and handles the power.
• Manual flash - Set flash to M mode, probably near full power level. 8 foot ceilings need a little less ISO or power, 12 foot ceilings more ISO or power.

In all cases above, correct the results as necessary (as seen on camera rear LCD and/or histogram), adjusting Flash Compensation (TTL) or adjusting Power Level (Manual), and shoot again. If the Nikon Ready LED flashes three times immediately after the shot, that is the warning that the flash had insufficient flash power for the situation, and you should set wider aperture, and/or higher ISO, and/or move to a closer subject distance, or get a larger flash. If picture is too bright, turn the flash power down, or vice versa. Make it be perfect. First time will seem difficult, but a little experience makes it real easy real soon (often is about the same as last time in same situation). Simply adjusting poor results as seen needed is the easy way to get perfect results.

Flash Features

• Flash modes Manual and/or TTL, and other modes.
• Speed (short flash duration to stop motion). Camera flashes (internal flash or hot shoe flash, operating from batteries) are called speedlights, because they include special circuits to interrupt the flash tube current (to turn it off). They implement lower power levels by truncating the flash duration this way, to be much shorter duration at lower power. Therefore, operating at lower power levels makes them be very fast, suitable for capturing water drop splashes or hummingbird wings (like flash durations of 1/1000 to 1/30000 second, at various power levels). If flash duration is very fast (short), and if the ambient light is dim, then all that lights the picture is the short duration flash, which can be significantly faster than any shutter speed. Most studio flash units are not speedlights, but camera flashes universally are.
• Flash head tilts up for ceiling bounce flash. And a pull out bounce card to add catch lights in eyes? (easy to add a card with a rubber band, just don't make it too large to obliterate the bounce. The pull out card is about the right size). Bounce is a big deal, really important for the best hot shoe pictures.
• Flash head swivels sideways? Which allows ceiling bounce when the camera is turned up on its end in portrait orientation as shown (this was a bounce flash picture). See the highlights, and the shadows? The many gradient tonal values which differentiate surfaces, and show shape? This is NOT flat frontal light, considered boring. The pullout bounce card won't aim forward if swiveled, but a rubber band can attach a regular business card to the side of the head, which works fine.
• Sufficient power capability to be useful for bounce or umbrellas, which do need more power. We never have too much power for bounce.

  Eight foot ceilings are relatively easy for bounce power.

  Ten foot ceilings need more power or ISO. These next are vague numbers with ifs and buts which depend on distance and zoom, but I'd say standing under a normal 10 foot white ceiling, Maximum level that works well at (about) f/5.6 is: Nikon SB-800 ISO 200, SB-700 ISO 400, or SB-400 ISO 800. The problem with ISO too high is that it hurts white balance by increasing the orange incandescent or green fluorescent room lights too. But skating on the edge at maximum power is an iffy risk for TTL automation, and instead, a little more ISO should usually be comfortable there, allowing safety factor when moving around, and faster recycle. The numbers assume you and subject are standing. If sitting on the floor with the kids, the ceilings are a lot higher.

  Twelve foot commercial ceilings need all the power you can get (SB-800, ISO 400, f/4). (And a f/2.8 lens likely performs better at f/4 than a f/4 lens).

  Bounce is not difficult with decent flash power, but you will need decent power for bounce. We can never have too much bounce power. High ISO helps, but when in excess, also increases seeing the orange incandescent ambient lighting too.

  A metered power example in an umbrella: A SB-800 at full power (Guide Number 98, feet, 24 mm, ISO 100),
  mounted in one white reflected 45 inch umbrella (at 24 mm FX zoom at full shaft length to fill it):

  A subject four feet from fabric apex (portraits), meters f/11 plus 4/10 stop (f/13) ISO 200
  A subject ten feet from fabric apex (groups),    meters f/5.6 plus 2/10 stop (f/6.1) ISO 200

  Doubling ISO adds one stop of exposure capability. Each manual half power step is one stop (for example, from 1/8 to 1/4 power is one stop more light). This power rating is not in the speedlight specifications, except the Guide Number info can be useful for shopping. Charts there to compare power of Nikon brand flashes, and a method to compare any two speedlights (those sophisticated enough to have accurate specifications). Full power use causes a slow and inconvenient recycle speed however. Even half power makes a big difference (faster recycle, but aperture is one stop more open).

• Power rating is inconsistently advertised for speedlights, but the rating is by Guide Number. More definition on comparing, but Guide Number is the product of (flash distance x f/stop), for the case which specifies correct exposure. It accounts for the Inverse Square Law light falloff with distance. When we vary the distance and f/stop, keeping the same GN product will give the same exposure. ISO 100 is the standard for advertising these ratings. Speedlights with zoom have several values of Guide Number (for each zoom value). An old standard was to advertise guide numbers at 35 mm zoom. Later on, many started advertising maximum GN (at maximum zoom, the largest GN number). If it zooms, we really need the Guide Number chart in the user manual to see the complete situation. We can only compare Guide Numbers numerically if at the same zoom coverage.

  Guide Number may be specified in feet or meters. There are 3.28 feet in a one meter, so we simply multiply the GN value in meters by 3.28 to get the value in feet. Either way works, so long as we are consistent (but the Guide Numbers are 3.28x different). Expect units of meters for other than North America. When units are not stated, small values of GN around 20 to 30+ are probably rated for distance in meters, where larger values like 70 to 100+ are rated for distances in feet (it ought to say which, but sometimes doesn't. The user manual will be more specific.) We would like to think the GN ratings are accurate, and the major manufacturers do strive for accuracy (also meaning, little variation from unit to unit). Differences we see really might be about our own measuring procedure, or about our judgment of correct exposure. There is a large section on next page about comparing power of two speedlights by Guide Number.

• A flash head motor zooming to follow the lens zoom is common on better flash models. Zooming in concentrates the flash power into a smaller area (to match what the longer lens sees). The concentrated beam is brighter (within that smaller area). This does not waste flash power illuminating outside the area that the lens can see. Whether it zooms or not, it is important to know the widest lens the flash will cover, like 24 mm FX or 18 mm DX, etc. And if it zooms, it's good to know how far it will zoom, like for a 85 mm or 105 mm lens (These are normally FX zoom numbers). It still works if it zooms or not, it just does not get brighter into a smaller coverage angle.
• Recycle time (waiting while recharging to Ready after a flash shot) is important, but is hard to judge in the specifications, because the maximum time depends on the type of battery used (alkaline, NiMH rechargeable, etc). Recycle time is specified for maximum flash power using fresh batteries, probably NiMH because they are fastest, but sometimes the longest maximum is specified (alkaline). Sometimes inexpensive units use less robust power converters (to convert AA battery voltage to maybe 300 volts to recharge the flash capacitor for next shot). Low power levels should be very much faster, nearly immediate, but full power takes significantly longer, and discharged batteries take even longer, and alkaline batteries are slower than NiMH rechargeables.
• Auto FP flash or HSS flash mode is same thing, is a special flash mode which allows faster shutter speeds with flash (faster than the Maximum Shutter Sync Speed limitation), which is a capability to use wide aperture with fill flash in bright sun, like at f/2.8 and 1/3200 second (at only about 20% power level however, range is limited). It is called High Speed Sync (HSS) but which is definitely NOT high speed flash. The full opposite of fast, this mode is no longer a speedlight. Can be TTL or Manual flash mode, but both camera and flash must have this FP mode. The Nikon camera models with Commander, and the associated external SB flash models, do provide this Auto FP mode (the camera internal flash and the SB-400 cannot do this FP mode).
• Capability to work off-camera (not in the hot shoe), for example, mounting on a light stand with an umbrella. You'd think this was a given, and it is not always obvious, but a few flashes are too simple to do it. For example, the Nikon SB-300 and SB-400 have no menu capability, and instead these special models use the cameras menu for TTL or Manual flash, but which means they cannot work at all if not connected to the camera hot shoe (these do work on a SC-28 or SC-17 hot shoe extension cord). Then the following remote trigger methods are used.
• Off-camera remote triggering methods: A quick summary of the possible ways to trigger a flash. Note that many trigger methods support Manual flash only, many don't do TTL.

  Wired trigger:

  There are many various types of flash cables for Wired trigger, and the cable has to fit the connector. This Chinese cable and adapter stuff is inexpensive on Ebay, but Flash Zebra is one very reliable source (both reliable service and parts quality), and in particular, they provide excellent full descriptions of the parts, to know for sure which you may need. To show the connectors that I mention, I added Flash Zebra links below to typical cords showing the connector type. They have wide choices you won't find elsewhere, so buy from them, and hopefully they should forgive my links.

  • Speedlight directly in a camera hot shoe. If a dedicated flash (compatible with the camera brand), it can do any flash mode (iTTL, Manual flash) that all the gear can do.
  • Hot shoe extension cord. For example, Nikon SC-28 or SC-29 or SC-17 (see differences). Other than these hot shoe cables, all cables are for manual flash, there being no cables for the modern iTTL system which is optically triggered. These dedicated cables have all four hot shoe pins, and can support any flash mode that the gear can do. On these hot shoe cords, TTL mode is limited to ONE flash unit in digital systems. The coiled cords can be stretched to maybe eight feet, however the tension of the coiled cord limits useful distance to only 3 or 4 feet (else coil tension tug tends to tip over the light stand). Flash Zebra has some longer ones, also a shorter one for flash brackets.
  • PC sync cord. PC is still the extremely common flash cord connector today, on Nikon, Canon, Yongnuo, Neewer flashes, essentially all speedlights today. It is named PC for Prontor-Compur, from two German shutter companies in the 1950s, now defunct. PC has one central pin and a surrounding barrel, the one pin capable only of triggering Manual flash mode only. Not all cameras or flashes have a flash sync port, and if not, inexpensive adapters can be added to either the camera hot shoe, or another type to the speedlight foot. A PC flash cord (from camera to flash) has male connectors on both ends. An extension cord is male to female. A trailing flash cord can be an issue if walking around with the camera, but is absolutely no bother if the camera is on a tripod in a fixed studio situation. A description of a "2.5 mm" sync port is the common PC port. PC cables tend to slip loose easily. Some PC cables are "PC screw-lock", which screws into threads provided on the socket to hold them securely. All seem compatible, screw-lock cable into a non-screw-lock connector, or vice versa. All PC fits all PC.
  • A very rare speedlight might use a "3.5 mm" sync port, which is the same connector as a mini stereo audio cable phone plug, also called a 1/8 inch connector. it is used frequently on some wireless triggers like PocketWizard, and on some studio flash. These hold better in the socket. The camera end will still have PC connector. picture.
  • Studio flash commonly used a regular 1/4 inch (6.5 mm) phono plug at the flash end. Some like Alienbees use the 1/8 inch 3.5 mm plug just above. Again, the camera end will surely have PC connector. picture.
  • Nikon has a few three pin cables called TTL cables (SC-26 and SC-27, and older SC-18 and SC-19 are the same thing). These are ONLY for film TTL and will NOT handle digital iTTL. Some older film flash gear (and the transition SB-800) had Both PC and these three pin connectors. I mention them only to keep digital users away from them. They are not what you seek today for digital. Digital iTTL or eTTL has no cable concept at all (except for the hot shoe extension cables). I do use one of these to connect two SB-800 together, and then trigger one of them with a PC cord, for Manual flash with the pair. Optical slaves trigger multiple flash too.
  • Obsolete today, but the common North American two prong AC electrical plug connector has been used for flash sync, a few very old speedlights, and several old battery pack studio lights. Sometimes called HH sync (HouseHold). NEVER plug them into electrical power, they can only plug into appropriate flash sync on the flash. picture.
  • And there are other old types too, but not likely of much interest today.

  Wireless trigger:

  • Optical slave trigger. Manual flash mode only. This is just a photo-detector (sensor of light), which triggers a Manual light in sync from the normal flash of any other Manual flash. Slaves are built-in on a few speedlights (Nikon SU-4 mode is an optical slave), and slaves are on all studio flashes (otherwise it is an inexpensive accessory to add). Simple, works really great indoors, no battery concerns, and the trigger signal is normally the full working power of the triggering flash, which is just from one of the other lights (that one must be triggered some other way). Inexpensive foot mounted slaves can be added to speedlights without them.
  • Radio trigger. Almost all are Manual flash only, but now there are a few that can support TTL. Some are relatively inexpensive. This is a transmitter attachment on hot shoe and a receiver on the flash, which triggers the flash via radio. Good outdoors in sun, or over greater distances, or through opaque obstructions. But indoors, frankly more hookup connections, and more power switches to remember, and more battery concerns makes me strongly favor optical slaves (indoors).
  • Proprietary camera systems that only work with system flashes (for example, Nikon Commander), a "smart" optical system that relays encoded data to the flash (like request for TTL preflash, or to send power level to the remote). This is the multiple flash TTL system for digital cameras (there are no TTL cables for flash on digital cameras). This complex system has more downsides than the others (obstacles to direct line of sight, distance, and sunlight), but multiple TTL flash is big advantage (but individual control is typically limited to two, or in some cases three flash units).

    A TTL flash requires communication with the camera metering system, so TTL has to be on the hot shoe, or a single TTL flash can connect with a hot shoe extension cable. Otherwise a Commander capability is the only way to trigger multiple or remote iTTL flashes for digital cameras (which becomes a unique feature). Nikon models SB-600, SB-700, SB-800, SB-900, SB-910 and SB-R200 can work remotely with the Commander (like in two umbrellas for example). A few third party flashes (for example Yongnuo YN565EX) can work with the Commander, but this feature is relatively rare. Lower end camera models (currently D3100, D5200) do not include a commander.

• External battery power packs: Some pros want a flash model with a high voltage connector port to attach a larger external power pack, which charges the flash capacitor directly and quickly. This second AA battery pack also has a converter that outputs around 325 volts to charge the capacitor directly. It does NOT make the flash more powerful, it's still the same capacitor and same voltage. But its extra batteries can provide many more shots for their big events, for users who need it. The additional batteries just last longer, and it also recycles faster (two power converters charging the capacitor faster, which can create more overheating concern).

If your camera model does not provide the Commander or Auto FP flash modes, then those flash features won't help (maybe on your next camera). That feature omission could make less expensive flash options be more attractive and justifiable. Nikon camera models which include the Commander also include Auto FP and FV Lock. Camera models without the Commander do not.

Opinion: In fixed situations (umbrellas, etc), I mostly use manual flash (and a handheld flash meter if multiple flash units). However, it seems obvious that indoors, everyone needs a good hot shoe TTL bounce flash (for example, to keep up with quick kids, or to do the walk-around pictures at the birthday party). And sadly, many of us need a kick in the rear to start thinking about getting better flash pictures (which bounce is). It is easy enough for anyone. For a Nikon camera, I don't necessarily imply Nikon brand flash, and today, there are good inexpensive Chinese flashes available with many features (like Yongnuo brand). But my thinking is that the SB-700 is an easy choice today — especially true if you have a camera model described as "higher than low end", which can use the Wireless Commander/Remote and Auto FP HSS features the SB-700 provides. Higher price cameras like D90, D300, D7000 and up have these features too, but lower price cameras like D60 and D3100 and D5200 do not (no Commander, no Auto FP mode). The SB-700 is pricey, and its features may be overkill if you only use hot shoe direct flash aimed straight ahead (however it does also offer GN Mode, really useful for direct flash). But TTL flash mode is something essential, features you can really use, all the time. It can do walk-around TTL bounce, like at parties or to follow kids playing. It can also do manual flash mode, and has a great SU-4 slave mode that works wirelessly off-camera, like in umbrellas. The SB-700 also works as a wireless remote with the Commander (and if you have a Commander, you do want to see this feature). It should do anything you need a flash to do. I use a couple of similar but discontinued SB-800, about ten years old now, and they have been absolutely wonderful. But if you will never bother to investigate and use these better features, then a lot less flash might suit you too. But flash really is pretty easy, and never learning flash would be a real shame.

See Reviews:

Neewer VK750 II    Yongnuo YN-565EX

Aperlite YH-700N    Neewer NW985N.

Part 2: A large chart of specs of a couple dozen speedlight models (the next page)

Comparing flash power level with Guide Number Ratings

Menu of the other Photo and Flash pages here