We all need one good TTL hot shoe speedlight for walk-about bounce use (do use your Small pull-out white bounce card, repeat Small). And that result can be mighty good too, but then we often wonder what happens if we try a little harder? Off camera lights make a big difference. Umbrellas make a really big difference - when up close they give very a soft light, very flattering for portraits. And another light or two makes a really big difference too. The question then is which way to go? It is easy to put speedlights into umbrellas, and this works well. Or we could get actual studio lights. The following comparison speaks of more studied fixed setup multiple lights, like for umbrellas in the living room. The following about the difference is intended to be an introduction for those not yet familiar with these studio practices. There is a strong Nikon bias here, but much of this is not brand specific.
A quick summary first. People differ in what is important or acceptable to them. You might be able to setup your automatic speedlight Commander system and take your picture and finish, all in a few minutes. You will still be metering manual lights then, still making fine adjustments, but we do that because we enjoy making it be exactly right. There are pros and cons to both systems, they are simply different.
The automatic remote wireless speedlight Commander system is phenomenally easy and convenient. Here is a better look at it. However it is not without limitations, and the downsides are:
Studio lights overcome much of the above, and offer expandability and versatility too, but are NOT portable or automatic. Any manual flash system (speedlights or studio lights) allows total and precise control, but the downside is that it is very manual. Tedious even (but a flash meter makes it be fast and easy). However, this is also the strong plus which appeals to many people, because then you can do absolutely anything you are able to do, the limitation is only in your abilities to imagine and do it.
I have four Alienbees studio lights, two Nikon SB-800, and currently, four other speedlights. All are totally awesome. They all just flash light, but they do different things, in different ways.
A summary of capabilities from below:
|Automatic TTL operation||Many/Most||None|
|Portability||High (small, and batteries)||Low|
|Duty Cycle / Cooling - Repetitive flashing||Low||High within reason if fan cooled|
|Ability to reaim to Follow Fast Action||High on hot shoe with TTL automation||None|
|Speed to freeze extreme motion||Exceptional at lower power levels (called "Speedlights")||Moderately decent, but most are not exceptional|
|System Expandability||Low for TTL, High if Manual flash||High - almost all are Manual flash|
|System Versatility (adding Modifiers)||Low, difficult||High, made to mount modifiers|
|White Balance||More blue at low power||Most monolights are more red at low power|
Speedlights: Most, but not all, speedlights offer TTL. These offer TTL for one flash connected to the hot shoe, but in digital today, multiple flash units require a system like the Nikon Commander to do multiple TTL flash (with compatible flash units).
Studio lights: None offer TTL.
This is of course a major difference - automatic TTL vs. Manual flash operation. Manual flash is a fine system, especially popular and usually preferred in a multiple light studio situation. You set up your lights carefully, and you don't want TTL to be changing the exposure when the subject turns their head and affects the reflection and the metering. But if you do want TTL, you gotta have the proper speedlight system, and all other differences may not count if you want TTL. This choice must be decided first. (But see System Expandability below)
Studio lights: Low
Often next most important. Speedlights are battery operated, and are used without an AC power source or wires (downside is all those AA batteries to keep charged). Speedlights are small and light-weight to pack and carry. Quick automatic TTL setup and ability to follow fast action are also large factors of portability (next). Studio lights are larger and more bulky, and will need a source of AC power... not normally thought of as portable or automatic.
Speedlights: Very High with TTL automation
Studio lights: Very Low (re: umbrellas)
The setup section should make it obvious that the automatic metering can handle quickly changing situations instantly, no comparison with the manual system. The hot shoe speedlight obviously aims with the camera. Even fixed TTL lights remeter the scene as it changes. The commander system is automatic point&shoot TTL multiple flash. Fixed manual lights require a fixed subject.
Speedlights: Exceptional (called Speedlights)
Studio lights: Moderate
Most studio lights are voltage controlled, meaning they reduce voltage to reduce power level. This makes them perhaps twice slower at lowest power. Extremely adequate for the portrait studio, but not for fastest extreme motion. But speedlights get very much faster at lower power levels. Speedlights are always charged to full voltage, and to reduce power level, they suddenly cut the flash off in midstream. Speedlights are not fast at maximum power level, but they get fast at reduced power... much faster than any possible shutter speed. Not at maximum power level, maybe only about 1/300 second at maximum power. But 1/4 power might be 1/2700 second. 1/32 power might be 1/17800 second. The Nikon SB-800 speedlight references 1/41600 second at 1/128 power.
Now, lowest power is not much power, but guide number at 24 mm at ISO 100 and 1/32 power might be 5.3/17 (m/ft). This is GN 34 (feet) at ISO 400. So that is very suitable to stop water or milk drop splashes at f/16 at 2 feet... at 1/17800 second. Adequate to stop hummingbird wings at 1/25000 second (up close to the feeder at low power if in the shade). This is how high speed flash photography is done. You can gang two speedlights if more power is necessary. See the picture below about speed. See more about this speed..
Note that this is NOT about HSS flash units. Forget HSS for speed, HSS has Zero speed, same none as continuous sunlight or incandescent light, and are the slowest possible flash, and only have shutter speed to help them. HSS means High Speed Sync (sync at any speed), and it does NOT mean anything remotely like High Speed Flash. Speedlights are High Speed Flash.
Studio lights: High
A top end speedlight in an umbrella (24 mm flash zoom to fill it) will meter one stop less intensity than a 160 watt second Alienbees B400 placed in the same umbrella. One stop more is double power. And we can buy larger studio lights, a Alienbees B800 at 320 watt seconds is two stops brighter than the speedlight. We could combine multiple speedlights in one umbrella, two equal lights are one stop brighter than one, and each time we double the number of equal flashes, we double the light, which is one stop. But the cost of larger studio lights is looking real good then.
The speedlight power level is generally adequate, but sometimes marginal. For manual mode use at ISO 200 with umbrellas, f/11 is about maximum for close portraits (four feet to reflected fabric), and f/5.6 for groups (ten feet to reflected fabric). This power seems just adequate, but the real problem is that recycle time (waiting until next shot possible) will be rather slow at higher power levels.
How much power? You need to know that an ISO 200 camera with a 160 watt second light works identically to a ISO 100 camera with a 320 watt second light. These are fully equal combinations, no difference. ISO 100 requires double power of ISO 200, and 320 watt seconds provides double power of 160 watt seconds. So when someone advises you need 320 watt seconds, better ask what ISO they use, and compare to your own situation. Either combination is more than enough power for normal indoor use. Either combination will photograph groups of people at ten feet at f/8 with a white umbrella. That is full power, but how much more power do you need? Greater power is only needed for greater distances, like 20 feet needs 4x power of 10 feet, or perhaps for smaller apertures, like f/22 needs 4x power of f/11 (neither is very likely to occur). If you buy too much power, you must always operate at minimum power. We always want the umbrellas up close to create softest light for portraits, and close does not need so much power. Close portraits normally must be turned down about three stops anyway (like 1/8 power). The SB-900 (in an umbrella) is half power of a B400, and it is often enough power. I am saying that my opinion is (based on having and using all of this stuff) that 320 watt seconds is uncomfortably too much for ISO 200 cameras used indoors (needing to be turned down maybe four stops, to 1/16 power level). My opinion is too much power is worse than too little, because we always have f/5.6 and f/4 available if too little.
In fact, if you want to shoot portraits at wide apertures like f/2 or f/4, forget the higher power lights, only speedlights will go that low. In the general case, studio lights will likely be more about f/8 or f/11. But portraits at f/8 or f/11 have much merit too. But f/11 can be a very serious demand on speedlights in umbrellas.
What does a 320 watt second flash power rating mean? Actually, the term Watt Seconds is energy, the product of Power times Time duration, and it implies that a 320 watt second flash would produce light at about the equivalent energy of 320 watts of fluorescent light bulbs for a one full second exposure. And many more incandescent light bulbs, since their efficiency is so low (incandescent mostly produces heat, but fluorescent and flash have similar efficiencies.) A one second exposure won't stop motion in portraits, but flash can do it nearly instantaneously, which allows a 1/200 second shutter to see all of the energy. Inanimate subjects would not care about shutter speed, but flash is vastly more usable for human portraits.
It can be a plus to operate speedlights at lower power levels when possible (speed, recycle, battery life, etc). Studio lights at minimum power are more of a liability, since consistency of variations of color and intensity is a smaller percentage if more near full power. Speedlights become very fast (short flash duration) and become more blue in color at low power level. Studio lights (not all, but most of them) are the full opposite, and become slower and more red in color at low power... Very different designs. The speedlight probably shifts color more at low power, but both shift color with power. The second page of this article covers details of that.
Studio lights: Fast
This depends on power level of course. Recycle is the time you wait on the Ready light, until the next picture is possible. Speedlight recycle is slow at higher power levels, up to a few seconds, depending (flash model, power level, battery type and degree of charge). A few seconds can be a very long time when the subject hits their peak. Better studio lights are very much faster, and often recycle nearly instantly in most situations. The Alienbees B400 spec rating is 1/2 second recycle at full power, and I normally use mine near 1/8 power, which I would call instantaneous recycle. A shooting rate of one frame per second seems easy for my Alienbees (it surely overheats speedlights, but most studio lights are fan cooled). However, the cheapest studio lights may not recycle any faster than the speedlights. Recycle time is a pretty big deal in practice, it affects waiting on every picture.
Studio lights: High
Speedlights can easily be damaged by overheating due to too many flashes too fast, without sufficient cooling time.
Studio lights usually contain fans, and the flash tube is not enclosed, and any normal use seems no issue to them.
Speedlights: Low (speaking of TTL use - manual flash is no issue)
Studio lights: High
How many lights? Main and fill lights are real good of course. The background light makes a big difference too. And the hair light adds the sparkle that also makes a big difference.
It is often said we should start with one light and a reflector, as the way to begin learning about lighting. A white foam board from the craft store works great as a reflector. See Google. The one light method can certainly give great pictures, and the method is revealing about the shadows, and surely we should all do some of that as a learning step, but it reminds me of the grade school kids learning math by not being able to use the calculator yet. Not intended to be easy. The reflector is useful but limiting - it must go in the only place it will work, and it only does whatever it does. A second light can go wherever you want it, and its intensity can be turned up or down to do what you want. Simply much easier to use.
The Nikon Commander/System can control TWO remote groups from the camera commanders, or THREE remote groups from the SU-800, SB-800, or SB-900 commanders. You can put multiple flashes into any group, but they all work alike in one group. The group is the entity which can be individually controlled by the commander. All lights in one group receive the same commands. If you use two lights, put them into different groups so they can be controlled individually.
So, if you have more lights, like Main and Fill and Background and Hair lights, how to combine these four into two or three groups is a limiting problem for the speedlight Commander. Then Manual flash and a light meter will become your favorite method. But if you will never use more than two lights, the automatic speedlight system may have much appeal, for good results with rapid setup. Portable automatic remote wireless point&shoot TTL multiple flash. Awesome.
However, manual lights (including manual speedlights) are never an issue, you can add as many as you wish to setup. And studio lights accept a wide range of modifiers.
Studio lights: High
Speedlights work great in umbrellas, no issues, and umbrellas are fantastic, no issues, but adding softboxes or grids or snoots is considerable issue for speedlights. Because not only are there few choices available, but the speedlight already has its focusing reflector system to control the light beam, which is always going to be focused and relatively narrow, whereas the studio light is generally used bare bulb and ultra wide in these accessories, 180 degrees or more (except umbrellas need a confining reflector). But a speedlight zoomed to 24 mm is just about right to fill an umbrella. This is true of any size, 32, 45 or 60 inch umbrellas, because the larger umbrellas have longer shafts to equalize their size which the lights see.
Studio lights offer vast choices of lighting modifiers, and much is easily available and designed to fit, to the limit of whatever you want to pay for. These also have modeling lights, used both to judge results, or to aim the lights.
Flashes produce near Daylight color, a fairly close match. However, flashes also vary their color temperature with their power level.
Speedlights: Become more blue at low power. Changes perhaps 500K degrees Full to 1/32 power (approximate).
Studio lights: Become more red at low power (speaking of most monolights, which are voltage controlled). Changes nearly 400K degrees, Full to 1/32 power (approximate).
The big deal about the Paul C Buff Einstein lights is that it has a mode to combine these two methods in a controlled way, offsetting each color shift, to be Constant Color with power level.
Speedlights: Relatively High for TTL, but there are inexpensive brands of manual lights.
Studio lights: could be lower or higher than branded TTL speedlights
The Nikon SB-910 is about $550, which is more than the cost of TWO $225 Alienbees B400, each of which is also twice as powerful as the SB-910.
The Nikon SB-700 is about $325, $100 more than one Alienbees B400. The SB-700 does TTL, and hot shoe walk around bounce flash well, which studio lights cannot, but studio lights are more versatile in their own world of lighting modifiers, and also recycle faster.
Some Yongnuo and Neewer flash models are very inexpensive, yet deliver good performance and are popular.
If using more than a couple of lights, add the cost of a good flash meter for a manual light system. Sekonic is very good, and the $309 Sekonic L-358 was overwhelmingly popular (but discontinued and superseded now). It has extra features I don't need. I skimped to get the $233 Sekonic L308S, which is fine and uncomplicated and easy to use, and it offers all I could need to meter flash - however it only does Shutter Preferred readings, which is required and perfect for flash, but which is less convenient for me outdoors for general camera use. See Do I need a handheld light meter?", which is about the Sekonic L308S. A histogram is NOT a light meter, but with only one light, we can use the camera LCD image result and the histogram instead of a flash meter. For two lights, see the White Towel method. For three or more lights, I think we must have a flash meter, which is also how we set each light's power relative to the others. You will certainly enjoy having a flash meter... it is the difference in knowing or not. It allows easy and repeatable setups, next day too.
The Alienbees are inexpensive lights, but very good ones, good enough to perform excellently for many years. They have wonderful support and service too, and the most bang for the buck, and are by far the most popular lights used in the USA (they operate on 120 volt AC). I have four, two B400 and two B800, and my opinion is these are great, and about as low cost as you want to go, since we never want to worry about our lights, regarding reliability and consistency.
Mounting: The studio lights only need a regular light stand and an umbrella. A softbox will need a heavy stable stand with wide footprint. The speedlights also need an umbrella bracket and a flash shoe. See here about some kits.
Speedlights are called speedlights for a reason. When up close at lowest power levels, speedlights are much faster than studio lights. At low power levels, they have a very short duration flash, 1/20,000 or 1/30,000 second, which is ideal for high speed photography, to stop very fast motion... water drop splashes, etc. This is why the name speedlight. The shutter speed cannot exceed the maximum flash sync speed (typically ballpark of about 1/200 second), but the flash is greatly faster than the shutter (illuminated for a shorter duration), and the shutter only affects ambient light, which does not matter in halfway dim situations at f/16 (this one was bright mid-day, but in shade under a patio roof). See more details.
Poking a water balloon - Speedlights can stop fast motion, sound triggered here by the audio "pop", before the water collapsed.
Speedlights: Fast Setup (assuming TTL automation)
Studio lights: Slow Setup (manual lights)
This is surely the largest factor for many people. Immediate automatic wireless remote point&shoot TTL multiple flash setup vs. tedious manual setup, but which offers absolute and full control.
Using the Nikon Commander/Remote system, you set one remote flash to be in group A, and one flash to be in group B (so the commander can individually control them). You throw the two lights out there somewhere (more care and planing is a good thing pictorially, but the system doesn't care what you do). Be sure to rotate the remote flash bodies so that the side sensor is aimed at the commander on camera. See More here.
Then the commander will individually preflash and meter each remote flash, and set their individual power levels so that they each meter the same intensity at the subject, regardless of their distances or bounce or modifiers. This includes the internal flash if it is set to contribute in TTL mode. This takes a small fraction of a second, combined into the shutter button, but before the shutter opens. This is immediate automatic wireless remote point&shoot TTL multiple flash setup. You can also set your lighting ratio in the commander menu, and the system will do that too. This is an Awesome capability. But it is also automated, and not extremely versatile. Certainly very convenient, but automation is never complete control, sometimes there are surprises.
Using manual lights (studio lights, or manual speedlights), you manually meter and adjust each light yourself, to set its power level to meter what you want. This takes a few minutes, each light individually. Manual mode is very popular for fixed studio situations, because it offers total control vs. automation. But multiple lights will need a handheld flash meter to meter and set the power level of each individual multiple light. Manual lights means that YOU do it. Beginners seem to fear manual mode, but you are not on your own, you have the flash meter to measure everything. You know much more about what is happening than with any automated system. Some people pretend the camera histogram can be used as a light meter. But not with multiple lights, they certainly are on their own then, because we need to have a clue what each light is doing. The flash meter lets us control each light, each does precisely what we tell it to do. Manual lights will not automatically re-meter and change at every frame during the shoot, which is a strong plus in the studio, and a strong negative for moving action shots.
To do that manual setup: You meter at the subject, with handheld incident flash meter, with only one light turned on at a time. An incident meter sees and measures the light itself, and is pointed away from the subject, so it does not matter if the subject is wearing a white dress or a black dress - it measures the light instead, and it will come out right. The Sekonic L358 meter is incredibly popular and well liked. The Sekonic L308 is a bit less expensive and simpler to operate, but it is only shutter-preferred, which is perfect for flash but less suitable for outdoors general purpose use.
I would suggest you set your flash meter to read in tenth stops (1/10 stops). For greater precision of course, but mainly, if the main light meters f/10, and you want the fill light to be 1/2 stop less, or one stop less, then how much is that? It may not be obvious, but if in tenths, the meter reads f/8 + 7/10 stop, so 1/2 stop less is simply f/8 + 2/10, and one stop less is f/5.6 + 7/10. Trivial to do in our heads then, very precisely. However, do remember, f/8 + 7/10 stop is NOT f/8.7. It is f/8, plus about 2/3 stop towards f/11, which is about f/10. Simply just set this camera aperture to two clicks more than f/8, or one click less than f/11 (third stops). We never care about this actual numeric value, but the camera will tell us then anyway. Then you know your lights actually meter what you want, because you directly set each one accurately.
The easy way is to use a temporary PC sync cord between flash meter and the light (moved from light to light), so that the flash meter button can trigger the light to be metered (the flash meter has the same PC connector as is on the camera, to do this). From the subject, you point the meter at that light and meter it, and set the light's power level so that it does meter what you want it to be. Learn to be consistent in the way you hold the meter at the subject so the distances are representative.
Perhaps you want the main light to meter f/8 (at the subject), and the fill light to meter f/5.6, for a one stop lighting ratio. In the speedlight TTL Commander system above, you simply specify -1EV for the fill light in the commander menu, but in the manual system, we have to make it happen. Some writers call this one stop difference a 2:1 power ratio, and others technically call it a 3:1 lighting ratio (see Chuck Gardners page). So when you read about "2:1 ratio" some place, you have no clue which they meant unless they tell you which (many text sources do offer explanations). Men's ratios might be stronger, and women and children often use less ratio, more equal lights. A one stop difference is a good ballpark all-purpose ratio. Anyway, you set the lights to the ratio you want.
Then maybe the background light is to be f/8, same as main, or more or less, however you want it to look - the background level is a very powerful control (a white background ought to be about 1/2 stop brighter than the main light. A black background should avoid having any light on it). This level is speaking of an incident meter aimed at the light from the background (not at the subject this time). You meter the light at the object you are illuminating.
The hair light is metered at the hair (aimed at the light), and hair varies, so it may be one stop less power than the main for very light hair, or one stop more than the main for very dark hair. This hair part is trial and error until you get a feel for hair color.
Then last thing, you turn on main and fill together, hold the meter under the subjects chin, and point the meter at the camera, and meter both for the lens aperture setting. These two will meter slightly more than the strongest one, 1/3 to 2/3 stop more depending on the ratio, or one stop more for two equal lights both covering subject. If exact final value matters to you, you can start with setting the main to this 1/3 or 2/3 stop lower value next time. The background and hair lights will not affect subject exposure, but leave them off or shield the meter with your body if possible, while metering this.
Then set that metered aperture value on the camera. Camera is Manual mode of course, with shutter speed at the camera's maximum shutter sync speed (ballpark of 1/200 or 1/250 second on most cameras), to keep out any distracting continuous ambient light (for example, the modeling lights). You may want the modeling lights left on to keep subjects pupils smaller. Turn on all lights and move the sync cord from the flash meter to the camera, and have at it. You probably say WOW then (but check your first shots, esp the hair light, You can still make corrections). The first time you do this, you can first take one shot without the sync cord in camera, to be sure you have a black picture from modeling lights only at final f/10 1/200 second exposure (or whatever). This setup does take a few minutes, but you have absolute total complete control of every detail, and manual lights are very popular in fixed studio situations for that reason. Note that you can trivially duplicate this same setup next time, simply by metering the lights the same way.
PC sync cord connectors:
Camera: PC Male connector on cable.
Sekonic flash meter: also PC Male connector on cable
Many speedlights (Nikon and Canon): PC Male connector on cable (so a PC Male to PC Male cable to connect to either camera or flash meter). Some are also threaded, fits both Nikon or Canon, and you can use either threaded cables or regular PC cables.
To use PC sync cables on speedlights without the connector, there are foot mounted adapters to add a PC sync connector. Also hot shoe adapters for cameras without PC sync. These are different adapters, one fits the flash foot, and one fits the camera shoe.
Other speedlights: A mixed bag, there are a few different connector possibilities, not all are PC... pay attention.
Studio lights: Usually either a 1/8 inch (3.5 mm) mini phone plug, or a 1/4 inch (6.3 mm) phone plug.
Extension cord: A PC Male to PC Female cable is an extension cord for any PC Male cable end. Most PC cables are these, but will also require at least a short length of PC Male to PC Male to connect to camera.
This is the biggie, most complicated, most restrictive, and least understood. Speedlights or studio lights can use any triggering method.
For manual operation, we can use a sync cord, or optical slave triggers, or radio triggers. Studio lights always include optical slave triggers, so we might use a sync cord or a radio trigger from camera to one light, and it will trigger the others optically. A sync cord is no issue when the camera is on a tripod, but if walking around with the camera, the trailing wire is not good. You can add an inexpensive hot shoe adapter to provide a PC sync connector on cameras without one (the Nikon AS-15 is an excellent one, which can be clamped down so it won't shift position). Optical triggers work perfectly indoors in studio situation (already included in many flashes, and is all that you need indoors), but work less well outdoors in sun, or in room with other photographers firing their flashes, triggering yours.
PC sync cords and optical slave triggers and non-optical radio trigger models require manual flash operation. Radio triggers will allow greater distances than optical, and can work well around or through obstacles, and offers more reliable operation in bright sunlight situations. But which is generally an unnecessary expense in the studio (opinion). Radio triggers require manual flash operation (new exceptions are the new Radio Poppers brand, and the newest Pocket Wizard models).
The same triggering methods work for speedlights, but very few of them have the optical trigger built in, and some do not have a PC sync port for the sync cable. The Nikon SB-800 and SB-900 have both. Either accessory can be added to the others (some of these mount on the flash foot, some connect to PC connector).
The Nikon Commander remote wireless operation is a very convenient triggering choice, but it uses low power line of sight light for communication between commander and remote (it flashes commands before the shutter opens). Obstacles are generally a problem for light, but room reflections at close distances can sometimes help go around it (indoors). A major downside is all the flashing by the commander signaling, and also the remote preflashes, which adds shutter lag time, and causes pictures of the subject blinking. The Nikon SU-800 commander uses invisible infrared signaling, which minimizes this blinking, but the remotes still preflash. The camera FV Lock option is the full work-around to prevent that, and also to prevent the automation from re-metering every frame individually. FV Lock separates the flashing and metering and blinking into a separate operation, before the shutter. Then the shutter button simply uses that remembered Flash Value. Pay particular attention the little L lock symbol in the viewfinder (mentioned in the camera manual), indicating when the camera has this remembered Flash Value (we lose it when the display times out).
Manual mode is very popular for fixed studio situations. It allows unlimited expandability and total manual control. Studio lights all include an optical slave trigger, so typically, we only trigger one of them, and let the light from its flash trigger all of the others. We can use a sync cord from the camera, or a radio trigger, to trigger that one light. The sync cord is no issue if camera is on a tripod, but for walk-around use, the radio trigger is better than a trailing wire. My own opinion is that otherwise, in the living room studio, the radio trigger is just more connections, more batteries, more cost, and is a totally unnecessary complication. I have the radio trigger, but I use the sync cord, for convenience with the flash meter mostly. Or a low power flash on the camera could trigger all of the slaves, but it must be in Manual flash mode (any TTL mode will fail).
The Nikon SB-800 and SB-900 flashes are extremely versatile in manual mode, and contain their own optical slave trigger mode called SU-4 mode, when they become just another optically triggered studio light. These two models will work great with manual studio lights, in any way, for example for a background light, etc. These are light-weight on a boom for a hair light, but are hard to aim without a modeling light. Older Nikon SB-80DX and SB-26 flashes also have the optical slave feature, but others do not. You can add a third party optical slave trigger (PC connector or hot shoe attached) to any manual flash. The actual Nikon SU-4 is such an addon slave trigger, and there are many others less expensive now (Ebay, and here is the list at B&H. These slave triggers have no batteries, and are powered by the sync voltage from the flash. This sync voltage is lower on the SB-600, and there are reports of unreliable slave operation, and some successes too. Radio triggers should work OK.
There are "digital" slave triggers, designed to ignore the first TTL preflash, and sync on the next flash. Some actually count preflashes, some just delay a short time, and trigger on the next flash. These can work with one hot shoe TTL flash, but cannot work with the Nikon Commander. This digital variety has additional timing circuits, which do use an internal battery.
The SB-600 provides no PC sync connector and has no SU-4 mode optical slave, and is not the best choice for remote manual mode in that sense, because it provides no means to remotely trigger it in manual mode. However, of course the foot mounted accessories can add a PC sync connector to it. Slaves and radio triggers typically use this PC connector, but there are flash foot accessories too. Make no mistake however, the SB-600 is still a fine choice for commander/remote wireless operation, or for hot shoe walk-around bounce operation. It is only the remote Manual mode that is more awkward, due to no PC sync connector, and the need for another accessory.
The Nikon Commander/Remote system is incompatible with handheld flash meters (it provides its own camera TTL metering means). The Commander is incompatible with Manual optical slaves. More words about this incompatibility.
Specifically, the Nikon commander emits many command signals which are seen by the flash meters or the optical slaves (Sekonic meters seem to filter out the infrared from the SU-800, but optical slaves do not). Also the TTL remotes all do their preflashes, which also triggers slaves. This happens before the shutter opens, so these triggered slaves are expended, and cannot contribute to the picture. Pick either the commander system or the manual system, and then go with it.
Digital flash is very different than the film flash we grew up with. All automated digital TTL flash does preflashes before the shutter opens. Did I mention that this makes the two systems incompatible with each other? Commander is incompatible with manual gear, such as optical slave triggers and handheld flash meters.
The Commander provides ability to set manual power levels, which is NOT at all the same as Manual mode, because it is still Commander mode, and is still incompatible with handheld flash meters, and with manual optical slave triggers. There is no remote TTL preflashing in that Commander manual mode, but there is still commander flashing to tell the remote it is to set a manual power level.
Strength wise, the commander signals are at a very weak level, whereas optical slaves are triggered by full power working flashes. This offers more room reflection and more distance and more reliability.
Hot shoe extension cords (Nikon SC-17, SC-28, SC-29) can do digital TTL (but for only one flash), but the cord lengths are pretty short (they tend to tip over the light stand if stretched farther than about four feet). You can chain two or three of these cords. The old SC-17 cord works fine and is plentiful on Ebay. You can also heat the old SC-17 cord in hot water and lay it out straight to achieve nearly 8 feet from it. The old SC-17 cord is the same as the new SC-28 cord, except it does not have the locking pin hole for the newer flash models. It sill works fine every respect, just drop the pin, hole or not, and the flash will stay there. The hole is easy to drill but is really not needed.
More words about Triggering options.