www.scantips.com

Basics of Flash Photography
Four Fundamentals we must know

4.     Flash pictures are double exposures

Any flash picture is a double exposure, once from the flash, and once from any ambient continuous light that might be present. These two effects work differently, with different rules. The ambient may be an insignificant level indoors, or it may be overwhelmingly significant when using fill flash in bright sunlight. We might be able to ignore the ambient indoors, but generally must match it in daylight. There are always these two effects to be considered in any flash picture. Note again, they have different rules.

OK, so knowing that instantaneous flash is not affected by shutter speed (see Part 2), and knowing any continuous ambient light is so affected, we can use that fact. Indoors, perhaps a studio lighting situation, using tungsten modeling lights with studio lights, we can use maximum shutter sync speed (without affecting the flash exposure at all) to reduce that ambient continuous so that it does not affect our picture. No orange tungsten light in our daylight color balance flash picture. Or in a normal room snapshot setting, we might intentionally use a slow shutter speed to show and maximize the contribution of that continuous room light, for a warmer "ambient" look. It is our choice. We can control the continuous ambient light with shutter speed, block it out or allow it in, independent of the flash exposure. We only need to know that any flash picture is a double exposure of the two situations. With flash, we always have two decisions to make - proper aperture so flash power level is possible, and indoors, if we want the ambient included or not (outdoors in daylight, we are probably going to have to account for the sunlight).

The flash exposure will not care about whatever shutter speed we use, but we have choices, and our choice ought to be intentional. When we use the camera's A or P exposure mode indoors, when we turn the flash on, we see the automatic shutter speed increase from "slow" (perhaps 1/8 second metered in the dim room?) back up to 1/60 second. Not for any reason other than this is the lower limit set by the camera when using flash - we do not need a slower shutter speed if we are using flash. Not all models do this, but many models have a menu for this: Flash Shutter Speed (and there are ways around it, camera Manual mode allows any permissible shutter speed, or Slow Sync option uses whatever the camera actually metered for ambient). This minimum lower shutter speed limit with flash (often a 1/60 second default for minimum shutter speed with flash) is simply because if there is some degree of ambient, we might be able to hand hold 1/60 second. But you may prefer to keep out the continuous ambient, because tungsten is orangish in color. Or if you are using the very fast flash for the purpose to stop motion, only 1/60 second shutter may allow dim ambient to blur what the fast flash stopped. If you noticed the metered light reading BEFORE you turned on the flash, it was surely slower than 1/60 (if dim indoors - but in sunlight, you get the actual that it meters). So indoors (with insignificant ambient), it seems much better to always use camera Manual M mode with flash, which allows us to set the shutter speed as we wish, either slow to allow the continuous ambient in, or fast at maximum sync speed to keep it out. It is our choice, but the automation will choose 1/60 second, possibly not for reasons useful to us. The Speedlight flash power used in TTL mode will depend only on the aperture and ISO values, and the TTL flash exposure is still fully automatic even in camera M mode.

To say the obvious: There is no camera intelligence that can treat one area of the picture different than any other area. It may choose one area to meter with preference, but the camera settings can only use ONE aperture setting and ONE shutter speed setting. The flash can only use ONE power level. These single settings affect everything in the picture (there is no magic). ISO, aperture and shutter speed affect the continuous ambient light exposure. ISO and aperture and flash power level affects the flash exposure. TTL automation tries to determine some of those settings, but the one big thing important to realize is that our manual Flash Compensation also affects the flash (power level and exposure), as we see fit. If TTL automation does not give the result you want, then you can moan, or you can simply fix it. :) Flash compensation is a main trick for getting great flash exposures. Flash compensation should be considered (if not used) for every TTL flash picture, and certainly in any new situation.

Understanding these few fundamentals will greatly simply and explain about everything you see happening with flash.

Camera exposure mode for flash

Sunlight - Camera P mode (Program) is good to use for fill flash outdoors in the daylight. We must meter the continuous ambient daylight there (it being extremely significant and cannot be ignored), and P mode does that well and automatically. And other modes can do it well too, but limitations of maximum shutter sync speed is often a problem with fill flash in sunshine.

For example, using fill flash outdoors in the sunshine is important, but sometimes fairly difficult. The daylight exposure is Sunny 16, so for ISO 200, we expect 1/200 second at f/16 in direct sunshine. The fill flash must match that, more or less (you may want the fill to be a stop or so less). But f/16 at say 10 feet requires Guide Number of 160 at ISO 200 (but divided by 1.414 is equivalent to GN 113 in an ISO 100 chart), possibly close to our flashes capability, at least at wide zooms. And 1/200 second is very near our shutter's maximum sync speed, so we cannot go faster, to convert Sunny 16 to say 1/800 second at f/8 (to gain flash power).

Said again slowly: Fill flash in bright sun is difficult, because ISO 200 and Sunny 16 says sunlight exposure in bright sun is f/16 at 1/200 second. This f/16 requires much flash power, so we have limited distance range - and our depth of field choice is limited to f/16 too. The problem is that we are prevented from readjusting it to equivalent exposures of say f/8 at 1/800 second (which would be the same equivalent daylight exposure, and requires only 1/4 the necessary flash power), because the maximum shutter sync speed with flash is around 1/200 to 1/500 second on various camera models. We cannot sync 1/800 second shutter with flash. Simply a fact of life.

Shady conditions or overcast days are not so extreme, but Sunny 16 says bright sun is going to need more like f/16. We can of course use camera A mode, but we need to know about f/16 for flash sync. Because, if we try to set .6 in A mode in bright sun, the camera will just show the warning HI, since .6 cannot set the 1/1600 second shutter it requires to do this job - due to the maximum shutter sync speed it allows with flash. We have to know that, except camera P mode does it for us.

So then we might try Auto FP High Speed Sync mode for a faster shutter speed to do the 1/800 at f/8, or even 1/6400 at f/2.8, and that does work, but the FP flash power drops drastically. The FP flash itself is modified to generate a continuous series of smaller flash pulses to mimic continuous light, so the focal plane shutter can work. Auto FP shutter sync mode (on many camera models with focal plane shutters) will allow any shutter speed faster than maximum shutter sync speed with flash, but at much reduced power level from the flash, which greatly limits the distance range of the flash (see Part 2, Continuous vs Flash). The rear LCD on the SB-800 and SB-900 flashes will show that maximum distance range currently in effect.

Fill flash in bright sun is is a difficult problem, so we may need to seek some shade for our picture. A neutral density filter, or a slower ISO setting, can help with a wider aperture regarding depth of field. Both of these affect flash and sun equally. However, if extra flash power is available, we of course turn the flash power back up (TTL or manual flash), but we cannot turn the sun back up. So turning up the flash creates a ratio change of flash to sun (with ISO or ND filter). The easier solution for flash power is either a closer flash distance, or a more powerful flash. A large studio light used outdoors can overpower the sun at reasonable distances, but cannot overcome the maximum shutter sync speed issue.

The rules are the same for all continuous light, and planning goes much better when you realize what is happening. Nikon's TTL BL flash mode is for balancing the fill flash to the daylight. TTL BL mode tries to match flash to a bright ambient (outdoors), whereas the TTL mode ignores ambient and makes flash match aperture (for indoors). But note that the best fill flash fills subtly, adequately but without even looking like flash was used, so for this fill flash, we normally want to specify about -1 EV to -1.7 EV (stops) flash compensation, so the flash does not overwhelm. This reduced level also helps us provide the necessary flash power too, in the bright sunlight.

Indoors - Flash conditions indoors usually see an insignificant amount of continuous ambient room light. The light is dim (compared to daylight), which is why we need flash. Metering that low ambient room light is normally not possible with flash, because the camera normally enforces a minimum 1/60 second shutter speed when the flash is used (discussed above.) The room where we need flash is probably closer to 1/2 to 1/10 second ambient. If 1/60 worked, we may not need the flash. So... this 1/60 is NOT about the flash. The 1/60 second commonly seen is just a minimum shutter speed limit with flash, since we do not need a slower shutter with flash.

Point is, this ambient room light is normally insignificant indoors, and we cannot reasonably attempt to balance it with fill flash, not like using fill flash in sunlight. The flash is the major light indoors, pretty nearly the only light indoors. So that makes the TTL flash mode be the correct flash mode indoors, NOT TTL BL indoors. Normally nothing to balance it with indoors. Flash TTL mode is for when the flash is the major significant light source, and TTL BL flash mode for when the flash is to be balanced with significant ambient light (which is normally sunlight).

Second point is that any automatically metered camera exposure settings are only about the room ambient light, which is normally insignificant indoors. Instead of trying to meter the insignficant ambient room light, we can instead choose an aperture more appropriate for our flash goals (like available flash power). The flash does not care what shutter speed is, but we can select a shutter speed to control (boost or reduce in our picture) the small amount of ambient room light (our choice).

Camera exposure modes for flash INDOORS

No matter what P, S, A, or M camera mode you select, TTL flash is always still automatic flash exposure. TTL flash automatically chooses the appropriate flash power level for whatever aperture you set, regardless of how you selected it.

Camera P mode (Program) is NOT a versatile choice for flash indoors. It might be great for fill flash outdoors in daylight, but indoors with a hot shoe flash, it will use 1/60 second at f/5, every time (Slow Sync or Rear Curtain Sync can bypass the 1/60 second lower limit). I am saying f/5. It may be f/4 to f/5, depending on which camera model. And the small internal flash may allow a maximum aperture of f/2.8 to f/3.5 in P mode with flash - since the small internal flash has little power. In minimal lighting (indoors), this depends only on ISO, not on the flash range needed. Higher ISO setting will worsen and reduce this maximum aperture slightly. This f/5 is a guess for average flash situations, conservative and probably always works, which is good. But every flash picture you ever took, or ever will take, be it direct flash at three feet, or bounce flash at 15 feet (VERY different situations), every one will be 1/60 f/5 if you use P mode indoors with flash. If you bought the expensive f/1.4 lens, P mode will never use that wide aperture for flash indoors (it will use f/5). If you specify ISO 800 for conditions needing more light, camera P mode probably will only use f/7 then, maybe when you most need the wider aperture (P mode seems counterproductive for indoor flash). We really do not have to accept f/5 1/60 second for every flash picture we take indoors (see A or M mode). But P mode works very well with fill flash outside in daylight however.

Camera S mode (Shutter) -- ??? Wrong choice indoors. It will work, the TTL flash is automatic for any aperture, but what is the aperture? (rhetoric, it surely is always wide open in S mode when indoors where we need flash). Instantaneous flash could not care less about shutter speed, so why are we giving preference to that? Perhaps for action outdoors in daylight, but aperture is critical for flash power. Mode S has no advantage for flash indoors. Flash power level is about aperture. Indoors with no significant ambient to interfere, the flash duration is what stops action. The flash duration is faster than any possible shutter speed. Instead think camera modes A or M for indoor flash.

Camera A mode (Aperture) will use 1/60 second at the aperture you set for most cases of flash indoors. (For flash in sunshine outdoors, since the shutter speed cannot exceed maximum shutter sync speed, we probably see many warnings of HI exposure in A mode (unless we know to set f/16), for apertures needing faster shutter speeds, but which cannot do them due to max sync speed limiation - use P mode with flash outdoors to prevent that). Back to indoors: You can choose a wide aperture to minimze flash power (like for bounce which needs a lot of power), and reduce recycle time. Or you can choose a narrow aperture for closeup subjects, for depth of field, or to not overpower the subject. Again, f/5 is good average and reasonable choice in many cases. For bounce from high ceilings, you may want to use ISO 400 too, and/or f/4 (faster recycle). But we normally always get 1/60 second shutter indoors with flash. There are menus and options to allow other shutter speeds than 1/60 second (Flash Shutter Speed menu, Slow Sync, Rear Curtain Sync, even S mode), but if you want other shutter speeds, then you should be using camera M mode, because it is so much simpler to do anything you wish there.

Camera M mode (Manual) - The TTL flash mode is still automatic. It is only the camera settings that are manual. Any automatic camera meter reading was determined from the ambient light, which is not about the flash. That automatic metering (like A or P mode) is helpful to match ambient outdoors in daylight, but the light is insignificant indoors now, which is why we need flash. So indoors, camera Manual mode lets us set things up for the flash picture double exposure, any way we want it.

Aperture contols the flash power needed (camera M mode or any other mode), and therefore the flash recycle time. We set aperture for the flash power level (judged by recycle time). Trying to be very clear: Aperture and ISO certainly affect the flash exposure, so we do see the exposure of manual flash mode at a fixed power level change with aperture or ISO. We have to manually set that manual flash power level to be correct for the aperture or ISO. But automatic TTL flash mode will simply automatically react to aperture or ISO with same automatic "correct" TTL exposure, by using a different flash power level (automatically). So we may not see it change, may not realize it changed, but flash power level does change big time with aperture or ISO. But flash power is relatively limited, not infinite, so we must pay attention. Watch your Ready LED.

In camera M mode, we can set any shutter speed up to the cameras maximum shutter sync speed, or we can set it as slow as we want it to capture more of the dim room ambient light. The flash exposure does not care what shutter speed is, and will not change. The flash duration is fast, faster than maximum shutter sync speed, so therefore, actual shutter speed controls only the ambient room light, fast shutter to keep it out, or slow shutter to allow it in - our choice. Studio portraits always want maximum shutter sync speed to keep the ambient out (for example, the modeling lights). Family snapshots may want shutter slower, for the "warming" look of the tungsten room lights. Again, it is our choice. We do not have to accept 1/60 second. We can think about it instead. But as first beginning step in using camera M mode for indoor flash, we can always use 1/60 second and f/5 as a starting point, a home base. This is the same values P mode would have used, and it will do the same thing in camera Manual mode, and it usually should give a decent picture (remember, the TTL flash is always automatic flash exposure). But with camera Manual mode, there are other choices too. We can more optimally change aperture or shutter speed, for the specific purposes mentioned. A little experimentation will be very helpful.

The automatic flash in TTL mode gives automatic flash exposure in EVERY camera mode (including camera Manual mode.) This is true for direct flash, bounce flash, flash in umbrellas, etc. Not to say it is always perfect, it's not. We often have to add a bit of flash compensation to "expose to the right" on the histogram, and then it is perfect (How lightmeters work may be of interest). In automatic TTL flash mode ("Through The Lens" metering for flash exposure), the first thing that happens after the shutter button is a preflash. Some of that preflash reflects back into the camera lens, where is it metered (measured), and the flash power level is set to give the correct exposure for the lens aperture in effect at the moment. What varies in automatic TTL flash operation is the flash power level (the camera exposure settings remain constant, whatever we set, or whatever the ambient light meters). We can choose the lens aperture ourselves to determine the ballpark flash power level that will be required, but we always get correct TTL flash exposure, regardless of which aperture we choose (within the range of what the flash power can reasonably deliver). This means however, that A (Aperture) and M (Manual) modes are very important and useful for flash indoors, since the aperture setting controls the flash power (and recycle time).

Note: Flash compensation changes TTL flash power level, and it only applies to TTL flash, either on hot shoe or TTL remotes. Manual PC cord flash is affected by the flashes power level setting, but the camera cannot affect that. The camera has an Exposure Compensation which affects both the metered ambient and the TTL flash, and it has Flash Compensation with only affects the TTL flash. These two compensations add together for the TTL flash.

Rear Curtain Sync can be useful when a slow shutter speed and significant continuous ambient light (room light or sunlight) can be expected to blur the motion, and you want to see that blur. The very fast flash duration will stop the motion, however a slow shutter speed can blur it anyway (if there is significant continuous ambient light to do it).

Front curtain sync is the normal flash mode, with the flash being triggered at the start of the shutter duration. The flash finishes quick, and then the shutter remains open longer, so the ambient blur appears later (out where it isn't yet), appearing to lead the motion. Rear curtain sync waits to fire the flash until almost the end of the shutter duration, so that the shutter blur occurs first, which appears to follow the subject (back where it used to be), which looks more natural.

The three pictures below are a tape dispenser swinging on a string (the motion is to your right in all cases). The ambient room light is morning window light, but not direct sun. D300 settings were ISO 200, 50mm, 1/20 second f/4.5, with a hot shoe manual flash at four feet. Frankly, 1/20 second seems abysmal to stop motion, but this is indoors, and I am tring to show blur here, blur caused by the ambient light. The SB-800 flash is at 1/32 power, which has a flash duration of 1/17800 second (spec chart in rear of flash manual). The flash certainly stops the motion of the swinging tape dispenser fine (note its shadow), but the 1/20 second shutter still allows the continuous ambient room window light to blur it severely anyway. There are clearly two separate exposures in a flash picture. The flash is very fast, but the much slower shutter continues the continuous ambient exposure much longer after the flash has finished.

Some people imagine that the delayed result of rear curtain sync causes a sharp stopped image superimposed on top of the blurred image (so is sharper), which may appear true of the leading edge, but the opposite is true of the trailing edge. So while there definitely are two separate exposures, and the flash does freeze the action when it triggers (and the continuous light continues blurring it), my imagination assumes the effect is not "on top" of anything. Each pixel can only contain the one total accumulated pixel exposure value, regardless of when. The only difference is when the flash occurs. Rear sync certainly does not hurt anything, however it only makes a difference with slow shutter speeds (and it is helpful with slow shutter speeds). Rear Sync will also ignore the 1/60 second minimum shutter speed menu limit with flash in A or P modes (rear sync is for slow shutter speeds).

Be that as it may, note that the point of this page is that if we had wanted to eliminate the blurring, we would eliminate the continuous ambient light by using maximum shutter sync speed (around 1/200 second) instead of a very slow 1/20 second. That fast shutter keeps out the continuous light, which is generally more true indoors, but it is more difficult outdoors in sunlight. Sure the shutter is set to be 1/10 the duration, which is faster, but also the continuous ambient light is now weakened to be over three stops more dim. The blur is simply too dark to be seen. The shutter speed does not affect the flash (which is the subject of this page). The flash is faster than the shutter speed. The tape dispenser is 3.2 inches long. Since the blur trail above seems about that same length too, then the 10x faster shutter should make a blur trail that is only 0.3 inches long, which would still be a blurred picture. But light that is too dim to be visible makes no visible blur trails, and the three stops can do that indoors. The third picture is all the same, the same flash, same room, same motion, just less the continous ambient light due to the faster 1/200 second shutter speed shutting it out.

Auto ISO works with hot shoe TTL flash too (but not with Remote flash - not in Commander mode and not in Manual flash mode), but auto ISO in every case does not trigger until whatever automatic adjustable settings reach their final limit. For example, camera mode S has hit the limit at the lens widest aperture before Auto ISO triggers. Camera mode A has to limit at the shutter speed in the Auto ISO settings (this intermediate menu limit prevents it having to first reach the actual 30 second lower shutter limit. The shutter speed will still go lower if necessary, after maximum ISO is reached. In camera mode M with no flash, Auto ISO triggers immediately, at any change when the selected aperture and shutter speed are not sufficient to give correct exposure, but with the TTL flash enabled, the TTL flash must limit out at max power before Auto ISO changes. In any mode when TTL flash is used, the flash has to reach its maximum power limit before Auto ISO triggers. Auto ISO always only operates at the extreme of whatever available limit exists.

All this is not 100% true, as the Nikon Auto ISO does seem to trigger early in many cases with flash. And another confusing quirk for Nikon flash is that the Auto ISO shown in the viewfinder never shows this ISO increase for flash. With flash, the viewfinder always shows the Base ISO, probably always ISO 200 or 100, with no hint Auto ISO will trigger. Probably because this ISO value is not known until after the TTL preflash. However, the final Exif data shown in the rear LCD image result statistics will show the higher ISO value (in red text) when it has triggered. I suppose my own straight-laced notion is that if we depend on Auto ISO, we are not in control, and we must be willing to accept surprises if not paying attention. :)

General flash tip: Always Watch the Ready LED, especially at any new setup. This Ready LED shows two things, when its recycle is Ready for next shot, and also shows a warning when sufficient power was NOT available for the previous shot. Recycle speed gives an indication of if you are near maximum power level or not. A slow recycle (a couple of seconds if NiMH cells) implies we are near maximum flash power. A quick recycle implies our flash power is set low (more is possible). Read and understand SB-600 page 29, SB-800 page 33, or SB-900 page D-4, about the insufficient power warning. The camera's Ready LED is accurate for a hot shoe flash, but it is only a crude approximation for a Remote flash. The remote flash can be made to beep this Ready signal.

A homework assignment, to be sure you "get it"

I could show you some test pictures about how your flash pictures can control the continuous ambient light with shutter speed, but you really really need to do it and see it and believe it, to make this info be actually available to you. Please?

Indoors at night (or at least in room with no bright window sunshine to confuse things at first), turn on a regular table lamp, hopefully placed within a couple of feet from a wall, to illuminate that wall. You are simply going to take a picture of that wall and that lamp, from say 8 to 10 feet away. Use any lens and zoom that shows a few feet of wall width, including the lighted table lamp in the picture.

Set your cameras exposure mode to Manual M mode for this test. Your TTL flash will still give automatic flash exposure in this camera Manual mode.   Repeat: Your TTL flash will still give automatic flash exposure in this camera Manual mode. Try this once so you will believe it too. No reason to be scared of Manual camera mode with flash indoors, because it simply allows you to specify the aperture the automatic flash power must match, and to also specify the shutter speed which controls the ambient in the room.

Manual mode: Think of it this way, since flash is not affected by shutter speed, then for flash, M mode is exactly the same as A mode, in that we set aperture for the flash power either way. Camera M mode is good stuff for flash indoors (but matching sunlight usually requires a correct ambient exposure). Indoors in A mode, you will simply always get 1/60 second shutter speed, which is from your cameras menu for Flash Shutter Speed. 1/60 second there only means the ambient was not stronger than that, so the camera enforced a lower limit. We might as well set shutter for continuous ambient to be the way we want it, and M mode allows doing that.

For this test, set the ISO to 200, and set the aperture to f/5.6 or f/8. Open the internal flash door, or use hot shoe flash, in TTL flash mode.

Take a picture at say 1/30 second (M mode permits that). Include the table lamp in a picture of the wall.

Take another picture (the same picture), everything the same except at 1/200 or 1/250 second shutter (or 1/500 second on D40/D50/D70 models), or whatever fast shutter speed your camera allows as maximum shutter sync speed. Do stay OUT of FP HSS mode, we are speaking of regular flash here (if able to select 1/1000 second shutter with flash, then you are in FP HSS mode - get out of that for this, that is NOT "flash").

OK, you should notice that in the slow 1/30 second picture, the table lamp (a continuous light) appears as being lighted, and it is even illuminating a little of the wall and table it sits on. It's power does not reach very far (inverse square law). We have no reason to believe our f/8 at 1/30 second was a correct exposure for the area of the ambient continuous lamp, but it should be ballpark enough to make the point of this concept. Only the flash is illuminating the farther regions of the wall. The flash exposure was correct, because the camera TTL option metered the flash and adjusted its power level automatically to be correct for the f/8 aperture which we specified. The wall illumination is NOT from the lamp or from any ceiling light. Turn the flash off and repeat the picture (will be pretty dark then) to make this point to yourself.

in the faster picture, 1/200 second or whatever, the continuous light is diminished by these 3 stops of increased shutter speed (1/30, 1/60, 1/125, 1/250 is a 3 stop change). If your results match mine, the lamp does not even appear to be turned on. The shutter speed was too fast for the degree of continuous ambient we have - the shutter speed we selected simply kept it out. But the flash illumination of the walls is unchanged from the first slow picture.

See? Shutter speed does NOT affect flash exposure, but does affect continuous light. And in such flash pictures, shutter speed is our choice, slow to allow the ambient into the picture, or fast to keep it out. This is such a biggie to know and use. A fundamental of using flash.

In a picture such as this, you may have wanted some of the ambient light to register, warm and cozy so to speak. But if a picture of a person, you don't want the tungsten light making them orange, so you probably want to keep it out. It is our easy choice, whatever you want to do. In a studio flash situation, we never want the ambient, so we use the shutter's maximum sync speed. I might mention this surely requires using the camera's Manual mode.

OK, the room with bright sunshine was mentioned at the start of the homework assignment. That sunlight is continuous too, and works the same as the table lamp, but it is likely much brighter than artificial light, with enough strength to give the flash power a real run for the money. Therefore it is much harder to simply overpower and ignore like we can the table lamp.

But you can change aperture too. If you stop down aperture, the TTL flash will have to use more power to give the same exposure, and it will (up to its power limits). But stopping down reduces the ambient too (at same shutter speed), and the abmient is unable to compensate and increase (like the flash can). So stopping down is the second level of tool to reduce the ambient light. Setting shutter to maximum sync speed is obviously the first step.

I will relent and show this, as you need to know, but you really do need to repeat it yourself. Do it! So that you can and will believe it, to enable using it. Any quick flash picture of a lighted table lamp, from not too close. This one is an ordinary incadescent 40 watt lamp, with bright sunshine outside this window. These are ISO 200.

Internal flash - f/5.6 1/30 second

Internal flash - f/5.6 1/200 second

No flash - f/5.6 1/200 second
The camera meter was reading this as 1/3 second.

Note this is a picture OF THE LAMP, which is brighter and harder to handle than the light FROM THE LAMP. Sunshine is mighty bright too. So maybe not perfect, but still an awesome tool, which we need. We have at least a couple of stops of range to use for control. We could go to f/11 here to minimize the ambient even more (at maximum shutter sync speed), but aperture also affects flash power too, so another stop would need twice the flash power. But it is often a very workable choice.

This simple test (to try it and see) is just to prove that flash is NOT affected by shutter speed, but that we can use shutter speed to control the continuous ambient. If there is any question at all, then experiment a bit again, use a little different values but with the same concept in mind. Several values maybe, see how things work. For example, if you used ISO 200 f/5.6 then the fast 1/200 second picture probably can still just barely detect the lamp was on, where f/8 probably shows it dark (however I have not seen YOUR table lamp). If you used ISO 100 f/8, the 1/30 second picture may not be very impressively illuminated by the lamp. However I am not trying to discuss any specific table lamp or ISO, but only the general concept. Explore the situation though, and you should see the obvious control that you have. It is very useful.

Here is another try (daylight is continuous too). Approaching sunset, looking east. Bright area in window upper left is a neighbors roof in direct sun, behind a winter bare bush. These are ISO 400.

The flash illumination is the same, unaffected by shutter speed. In flash pictures, shutter speed is merely a choice to keep the continuous ambient light out, or to allow it in, but without affecting the flash exposure. We can use that. This is a N:Vision CFL lamp (camera left, green), and a GE Reveal ("daylight") tungsten lamp (camera right, red). Neither are ordinary incandescent lamps, but of course, both are continuous.

Note the subtle second level of control - compared to the first example, this higher ISO made both the incadescent and daylight brighter, relative to the flash power which became less.

Sometimes we may prefer the "look" of the slower shutter to capture more continous ambient. Me too, sometimes. But there are cases (especially in studio photography, or high speed flash photography) when all ambient is unwanted, and we need to know that maximum shutter sync speed is the major tool to keep it out. We have the choice, and this one is easy, because it does not affect the flash (and narrow aperture and/or low ISO increase that difference, because that does strengthen the flash).

One last point and you've got it. If the ambient is dark (a black picture if flash is not used) then it simply does not matter to anyone what shutter speed is (no ambient to register). See this link for a sample of high speed photography, where the shutter speed was BULB, manually opened and closed, typically at least 1.5 seconds. The room was dark at f/16, even if there was a table lamp turned on for humans to see. F/16 was to keep out ambient, and for closeup depth of field. Bulb and 1.5 second shutter is quite slow, but the speed of the flash duration is what stopped the action, not the shutter speed (assuming insignificant continuous ambient. The ambient COULD blur what the fast flash stopped, if allowed). Speedlights are named speedlights because they are incredibly fast at lower power levels. Shutters are simply never that fast, unsuitable for high speed photography.