Why the Highest Sync Speed?

I'm reading throught the strobist.com website and he always says he sets his camera to the highest sync speed for the most flexability. Why is this exactly? I think it may be because if you are shooting at a lower ISO (say 100) with a shutter speed of say 1/125 your flashe can only give you half the ammount of light that it could give at ISO 200 and 1/250. But do you always need to get the maximum ammount of light out of your flash? Does his style of shooting just push his flash to it's limits?

Does it give you the most flexability with the lighting ration?

A high synch speed results in almost all of the exposure being made via the very brief electronic flash burst, with little contribution from ambient light. If you are shooting high speed motion, that results in a sharp motion free image.

Why NOT the fastest synch speed: But that is NOT ALWAYS what we want!!! For example, if you use a slow shutter speed it can capture the scene via the ambient light, so a room behind the subjects in a photo appear as a lighted room, not a dark cave! Or rapid motion is frozen by the flash, yet ambient light also allows the moving subject to register in the photo as a blurred trail behind the frozen subject...a sense of motion is conveyed.

Wilt wrote in post #5824829
A high synch speed results in almost all of the exposure being made via the very brief electronic flash burst, with little contribution from ambient light. If you are shooting high speed motion, that results in a sharp motion free image.

Why NOT the fastest synch speed: But that is NOT ALWAYS what we want!!! For example, if you use a slow shutter speed it can capture the scene via the ambient light, so a room behind the subjects in a photo appear as a lighted room, not a dark cave! Or rapid motion is frozen by the flash, yet ambient light also allows the moving subject to register in the photo as a blurred trail behind the frozen subject...a sense of motion is conveyed.

So the highest sync speed is where he starts to give him the most flexability in regards to the lighting ratio?

doidinho wrote in post #5824748
do you always need to get the maximum ammount of light out of your flash? Does his style of shooting just push his flash to it's limits?

As you have already determined, using X-sync speed allows the lowest ISO and/or largest aperture for proper ambient exposure, thereby reducing the flash power required.

Reducing flash power results in faster recycle times and longer battery life. At full power, you'll need to wait 5 or 6 seconds between shots. At 1/4 power, you can fire at least 4 shots in burst mode. Sometimes this is the difference between getting the shot, or not.

Using a faster shutter speed also reduces motion blur problems which leads to a better keeper ratio.

As Wilt explained, using a slower shutter speed is often advisable in order to get some ambient exposure in low light environments.

Curtis N wrote in post #5824950
As you have already determined, using X-sync speed allows the lowest ISO and/or largest aperture for proper ambient exposure, thereby reducing the flash power required.

Reducing flash power results in faster recycle times and longer battery life. At full power, you'll need to wait 5 or 6 seconds between shots. At 1/4 power, you can fire at least 4 shots in burst mode. Sometimes this is the difference between getting the shot, or not.

Using a faster shutter speed also reduces motion blur problems which leads to a better keeper ratio.

As Wilt explained, using a slower shutter speed is often advisable in order to get some ambient exposure in low light environments.

Great info, thanks. I never would have thought about reduced recycle times and increased battery life; an important part of the eqation.

The strobist techniques center on using mainly portable flash as MAIN light. In that situation it is always correct to start with the highest x-sync as this will minimize motion blur especially in moving subject. When balancing ambient with flash a different set of rules apply.

Just for experiment try shooting with flash in manual mode with highest sync-speed and then adjust it down. You will find that shutter speed has no effect on flash exposure but the higher the x-sync the less ambient light enters the lens and effects those parts filled by ambient light. Hence at x-sync you can clearly see MOSTLY effect of flash exposure at given f-stop. That is mostly the case of shooting everywhere else but in BRIGHT sunlight. In bright sunlight the higher the x-sync you camera has the opposite applies as sun overpowers anything else that flash throws at the subject.

I don't quite understand what Curtis means by:

I usually find that at least indoors your ambient will be generally way lower then x-sync unless you are shooting with extremely bright settings. From above it suggest that using higher shutter allows for lower ISO and largest aperture. That it not the case from my experience. Your ambient exposure would generally be much lower. If you have enough light to shoot the subject at x-sync (1/200th with low ISO and largest aperture) then you may as well not bother with flash unless it is a fill-flash. In that case just set your flash to 1 or 2 stop below ambient and you will have a sweet spot which will create a pleasant results 90% of the time. Less flash power means faster recycling of course.

In summary:

With flash being the MAIN light always start with highest x-sync and meter your flash to determine f-stop at a given ISO. You can do that with a flash light meter or by eyeball Mark101 through histogram. E.g. Set your flash to light the object in whatever fashion you like (bounce, diffused, snoot etc). Set the flash power at what you think is "right" like 1/2 then meter by taking a shot or using flash light meter. Once you got your f-stop then just shoot at these setting for 100% reproducible results unless your subject changes distance to flash. You can work it in reverse by setting you camera to whatever f-stop/x-sync combo you like then dial the flash power up/down untill you get "right exposure". Remember STTR and shoot in RAW. If you later decide to give your photos some ambient light start dropping your shutter speed (keep f-stop the same) and watch more ambient come in into the frame.

With flash acting as a FILL light, determine exposure for ambient using f-stop you like to use. Once you got your tv/av combo set your flash power 1 or 2 stops lower as to whatever you like. Remember there is more ways to reduce flash power then by actually reducing flash power on the flash unit. This is done by increasing flash-to subject distance (eg. bouncing off ceiling or walls or moving flash unit) and using diffusers(umbrellas, soft-boxes, screens and etc) among other things. As long as you don't exceed the x-sync then you photos will be fine. If your speed goes above x-sync then you will have to drop your av down to at least x-sync or you will end up with black band on the edge of the frame.

Of course you can also have a combination of two where the subject is lit by FLASH and the background it lit by ambient. Here it will be really up to you as to what settings to use to produce pleasing results. The principles remain the same however.

If you don't abuse your flash even at full power it should give your thousands of shots in general. I doubt using the strobist techniques will really "push his flash to it's limits". Your flash is designed to work reliable at full power for many repeated firings.

Hope it makes sense in some way,

Flagpole
Sydney, Australia

David is generally trying to balance or even over ride the ambient light with the flash. Remember to he is shooting Manual, not ETTL (or whatever Nikon calls it) so this is not the same as putting a Canon flash in High Speed Sync. It is shooting at a fast shutter speed, many times the fastest your camera will sync with the flash. You must also figure in fastest speed your radio trigger or cable connection will allow (a G9 with wired connection is 1/2500). By shooting with a high shutter speed you get more choices as to lens openings, distance to subject and flash power settings. Again this is all about shooting Manual, ETTL will not do the things he does. The best you can do is read and reread the Lighting 101 and 102 on the Strobist blog - David explains things way better than I can.

Jack

Flagpole wrote in post #5826400
I don't quite understand what Curtis means by:

As you have already determined, using X-sync speed allows the lowest ISO and/or largest aperture for proper ambient exposure, thereby reducing the flash power required.

The lower your ISO, and the larger your aperture, the less flash power is required to illuminate a subject at a given distance.

So for example, given "sunny 16" lighting conditions, you could choose 1/100 shutter speed and f/16 to properly expose the ambient. A flash unit with a GN of 160 feet would give proper exposure at 10 feet at full power (160 / 16 = 10).

By shifting to 1/200 shutter speed and f/11 (identical ambient exposure), that same flash unit would give proper exposure at 14.5 feet at full power (160 / 11 = 14.5), or 10 feet at half power.

This simple shift in exposure settings results in the flash power requirement being cut in half.

Curtis N wrote in post #5824950
As you have already determined, using X-sync speed allows the lowest ISO and/or largest aperture for proper ambient exposure, thereby reducing the flash power required.

Reducing flash power results in faster recycle times and longer battery life. At full power, you'll need to wait 5 or 6 seconds between shots. At 1/4 power, you can fire at least 4 shots in burst mode. Sometimes this is the difference between getting the shot, or not.

Using a faster shutter speed also reduces motion blur problems which leads to a better keeper ratio.

As Wilt explained, using a slower shutter speed is often advisable in order to get some ambient exposure in low light environments.

So is this the reason why people use higher ISO?
Sometimes, I just really don't get why people use higher ISO with small aperture. Such as f16.
Why don't they use lower aperture and lower ISO?

Curtis N wrote in post #5824950
As you have already determined, using X-sync speed allows the lowest ISO and/or largest aperture for proper ambient exposure, thereby reducing the flash power required.

Reducing flash power results in faster recycle times and longer battery life. At full power, you'll need to wait 5 or 6 seconds between shots. At 1/4 power, you can fire at least 4 shots in burst mode. Sometimes this is the difference between getting the shot, or not.

Using a faster shutter speed also reduces motion blur problems which leads to a better keeper ratio.

As Wilt explained, using a slower shutter speed is often advisable in order to get some ambient exposure in low light environments.

I need to add comment about CurtisN's first paragraph above...
First, if you choose a large aperture, that does NOT always mean the need for high shutter speed...sometimes it does, sometimes it does not.

For example, if I shoot in a bright setting (let's assume 1/200 at f/4 is the ambient light reading) if I shoot a flash shot at that combo, the ambient exposure and flash exposure are equal and the flash probably did not need to output full power (let's assume 1/2 power output). So if I wanted the b/g to be a bit more subdued compared to the flash portion of the exposure, I would choose f/5.6 and leave shutter speed at 1/200, then the flash outputs a greater intensity of power, but the b/g gets -1EV of exposure in comparison.

For a different example, if I shoot in a dim setting (let's assume 1/30 at f/2.8 is the ambient light reading) if I shoot a flash shot at that combo, the ambient exposure and flash exposure are again equal and the flash again output half of its power. And if I wanted the b/g to be a bit more subdued compared to the flash portion of the exposure, I would choose f/5.6 and leave shutter speed at 1/30, then the flash outputs a greater intensity of power, but the b/g gets -1EV of exposure in comparison.

In both situations, I captured ambient light at -1EV compared to the flash portion of the exposure, but in one case my shutter was at the synch speed but in the other case it was 1/30. That comes back to my opening point, that does NOT always mean the need for high shutter speed...sometimes it does, sometimes it does not.

Sorry about the confusion but the original quote refers to 'ambient exposure' not flash exposure. Or am I getting something mixed up?

In the example above the shutter speed has no effect on the flash as it is only ISO and aperture which affect the flash exposure. So you could have left your sync speed the same and adjusted your f-stop by 1 stop and lowered your flash output by 1/2 to produce same flash exposure. The shutter speed should not matter unless your are shooting against the light source which overpowers the flash. At least all the information I read tells me that.

Flagpole

Flagpole wrote in post #5827015
Sorry about the confusion but the original quote refers to 'ambient exposure' not flash exposure. Or am I getting something mixed up?

In the example above the shutter speed has no effect on the flash as it is only ISO and aperture which affect the flash exposure. So you could have left your sync speed the same and adjusted your f-stop by 1 stop and lowered your flash output by 1/2 to produce same flash exposure. The shutter speed should not matter unless your are shooting against the light source which overpowers the flash. At least all the information I read tells me that.

Flagpole

Au contraire! (to the bolded statement). Technically you are correct, about the flash-only part of the exposure, but not about the ambient portion of the exposure.

In my example, the ambient light did indeed contribute to the overall exposure for the portions of the scene which are too far away to get much exposure from the flash! If my subject was 8' away, for example, anything farther than 16' away is -2EV in the flash output intensity (nearly black) in comparison, so the ambient MUST contribute in that part of the scene if it is to appear in the photo. (And for those reading this message, this (the 1/30 f/5.6 example) is the technique known as 'dragging the shutter' rather than shooting at the max synch speed.)

A way to play with this is to set up a small still life on a table, shoot this so that the background is say another room that is has an average daylight lighting - maybe the still life on a dining room table and the living room in the background. Now setup a flash on manual about 4-6 feet away at 1/2 power, this works best using a shoot through umbrella, set your camera to ISO 400 to give yourself some exposure room to play with. Set your shutter speed on 1/15th and chimp in some shots to get a nice exposure of your subject. Now leaving you ISO and F/stop alone shot the subject at different shutter speeds and watch the background. At 1/15th maybe you will get the subject and some background, but up at 1/250 your background will be black. This is a little bit of an example of shutter speed, F/stop, ambient and flash working together to get what you want.

Jack

Azzure_7 wrote in post #5826784
So is this the reason why people use higher ISO?
Sometimes, I just really don't get why people use higher ISO with small aperture. Such as f16. Why don't they use lower aperture and lower ISO?

I don't know why people do that. It might come from misunderstanding.

Aperture and ISO both affect exposure of both ambient and flash. So if you're at f/8 ISO 100, shifting to f/16 ISO 400 won't change either the ambient exposure or the amount of flash power required.

Regarding Wilt's comments - It requires somewhat of a different mindset when you're shooting in the bright outdoors vs. the dim indoors. But in both cases, it's easier to think about the ambient exposure first and figure that out before you start worrying about the flash.

Picking the best combination of shutter speed, aperture and ISO for the desired ambient exposure is usually a compromise, and the best compromise usually is a matter of preference. But typically in outdoor situations, setting your shutter speed at X-sync is a good place to start (that doesn't mean you need to stay there). Indoors, it's a different story.