Question on High Speed Sync (for Nikonians)

[rpcrowe]

It seems to me that my Canon DSLR cameras are more simple to use at speeds over the maximum sync speed (1/200 for some cameras and 1/250 for others like my 7D). Simply choose High Speed Sync and forget about it from then on.

When you have chosen a speed above the maximum sync speed, the camera shoots in HSS.

When your speed is at or slower than the maximum sync speed the Canon automatically reverts to standard sync.

You never have to revert to choosing standard sync.

[William W]

. . . There is only one sync speed. Just where does that mysterious second sync speed stands for?

One possibility is as previously mentioned:

Possibly the selection of two Auto FP Shutter Speeds in the more recently released cameras, has come about because of advances in Nikon Flash Technology; that’s why I suggested that this additional feature might be supported by only some, not all, Nikon Dedicated Flash Units.

For example the X-sync that is stated in the Specs of most (all?) SLR Cameras has a note indicating that is applicable to the dedicated units and often another note specifying that a slower x-sync speed might be applicable to other Flash Units.

This is especially applicable when using Studio Flash Heads.

WW

[William W]

. . . Look at the link dje gave earlier. http://neilvn.com/tangents/auto-fp-f...on-d300s-d700/

I did, earlier.

My understanding of that article adds validity to exactly what is written in the user manual that I quoted.

WW

[pnodrog]

I don't think so.
First curtain opens, when it reaches the other site the flash will be activated immediately. At sync time this will be the fastest time that the sensor is 100% exposed. With a faster shutter time the second curtain will be closing already before the first has stopped opening. Independent of the flash duration, the first part of the exposure will not be exposed by the flash if the shutter time exceeds the sync time.

So far it's clear to me that the longest sync time is the real sync time. In case of the D610 it's 1/200 and in case of D300 or D700 it's 1/250. Why is that first step faster as the sync time so important or different????

George

At any shutter speed when there is a period that the sensor is fully exposed you need to subtract the travel time for each curtain to calculate how long that state actually is. At 1/250 sec (4 millisec) the fully open state could be as short a 3 milliseconds which is shorter than the T.1 time at max power of some xenon tubes. Nikon have no way of knowing the exact specification of a flash unit that will be used with the camera or the temperature or any other factors that may effect T.1 time, so Nikon can only give a caution regarding power loss etc.

The benefit of allowing the use of the flash in this marginal sync zone is that for some model flash units that either have or are operating at a power that brings the flash full into sync will have more power and greater battery life than when they are forced to operate in the FP mode. For some photographers it may be a significant advantage.

[William W]

^ +1

For some photographers it may be a significant advantage.

indeed, some Photographers go to, what other folk might consider extreme lengths, to attain very fast sync speeds.

Using their existing DSLR for example, some modify older (usually medium format) Leaf Shutter Lenses.

Others buy another digital camera for the purpose of being able to use the full power of the flash at very fast shutter speeds.

I have done both.

WW

[PhotomanJohn]

L.Paul - You beat me to it. Folks were not taking into account the duration of the flash burst. At 1/320, part of the tail may get cut off but that is still brighter than HSS.

John

[george013]

I did, earlier.

My understanding of that article adds validity to exactly what is written in the user manual that I quoted.

WW

Maybe we don't understand each other. From your post:

One immediate take home win from this is, effectively if “1/250 Auto FP” is selected, then (in P and A modes) you have are using the same camera, but it is now capable of X-Flash Sync = 1/250s (and not 1/200s).

From, sorry, wiki. I hope you mean the same x.

X-sync is the simplest to explain and implement: the flash is fired at the instant the shutter is fully open. Electronic flash equipment produces a very short flash

If, in this example, the shortest time the sensor is exposed fully is 1/200, how can I get a fully exposed sensor with 1/250? Without the use of high speed flash. I don't think the curtain speed is changing.

George

[george013]

At any shutter speed when there is a period that the sensor is fully exposed you need to subtract the travel time for each curtain to calculate how long that state actually is. At 1/250 sec (4 millisec) the fully open state could be as short a 3 milliseconds which is shorter than the T.1 time at max power of some xenon tubes. Nikon have no way of knowing the exact specification of a flash unit that will be used with the camera or the temperature or any other factors that may effect T.1 time, so Nikon can only give a caution regarding power loss etc.

The benefit of allowing the use of the flash in this marginal sync zone is that for some model flash units that either have or are operating at a power that brings the flash full into sync will have more power and greater battery life than when they are forced to operate in the FP mode. For some photographers it may be a significant advantage.

Take a look at that link again and watch the series "using non-CLS capable wireless flash". There you can see exactly that the sync speed for those camera's ia 1/250. The D300 and the D700. Don't mix up with the D610. You see the expected black strip. What makes the use of a Nikon-flash different? Without high speed tricks.


At sync speed the time that a fully open state exist, is 0. As soon the first curtain has arrived at the other site of the sensor, at that same time the second curtains starts his journey. At sync speed.

The T time of a flash is telling something of the flash time after the flash stated, after the peek. The sync time is discussing the start of that flash.

George

[george013]

I did find an article on nikon rumours dealing the flash of the D800. http://nikonrumors.com/2014/10/25/pu...nc-speed.aspx/
Out of that article

Nikon technical specs for the D800 flash sync speed are: up to 1/250 sec, synchronizes with shutter at 1/320s or slower (flash range drops at speeds between 1/250 and 1/320s).

What does this mean?

George

[PhotomanJohn]

At sync speed the time that a fully open state exist, is 0. As soon the first curtain has arrived at the other site of the sensor, at that same time the second curtains starts his journey. At sync speed.

I don't believe this statement is correct. The rated flash duration of most speed lights is about 1/1000 second at full power. This would mean that in order to evenly expose the entire sensor making full use of the output of the flash, the second curtain has to delay at least 1/1000 second after the first curtain is fully open. I makes sense that this is how the flash sync shutter speed is determined. Why would they recommend a shutter speed that doesn't take full advantage of the rated output of the flash?

John

[dje]

Following on from comments from LPaul and John, I've tried to put in some numbers for the D810.

My assumptions are :

• The first shutter curtain takes about 2.5 ms to traverse the sensor (based on some figures measured by Jim Kasson).
• The effective shutter speed (or time) for a rolling shutter is determined by the time the first curtain takes to traverse the sensor plus the time the sensor is fully exposed before the second curtain starts to close. (providing the shutter speed is slower than the curtain speed, 1/400s or 2.5 ms in this case)

Based on these assumptions, a shutter speed of 1/320s (3.1 ms) will have the sensor fully exposed for about 0.6 ms (ie 3.1 -2.5). A shutter speed of 1/250s (4ms) will have the sensor fully exposed for 1.5 ms (4-2.5). As the flash is fired at the start of the sensor fully exposed time, this means that for 1/320 SS, there is 0.6ms for the flash to fire and decay whereas for 1/250 SS, there is 1.5ms for the flash to fire and decay.

The figure of 1.5ms should be adequate for full illumination by the flash but with a figure of 0.6 ms, you will probably miss some of the significant output from the flash as it decays - hence a small drop in exposure. This could also involve some dark banding at one edge as shown in the reference I linked to.

Make sense ?

Dave

[William W]

Make sense ?
Dave

Yes.

Thank you.

WW

[William W]

George, I think the crux of you not understanding my explanation is that you have not accepted the premise that:

For any one particular camera the “x-sync speed” will be different depending upon the FLASH UNIT that is being used.

***

Maybe we don't understand each other. From your post

One immediate take home win from this is, effectively if “1/250 Auto FP” is selected, then (in P and A modes) you have are using the same camera, but it is now capable of X-Flash Sync = 1/250s (and not 1/200s).

From, sorry, wiki. I hope you mean the same x.

X-sync is the simplest to explain and implement: the flash is fired at the instant the shutter is fully open. Electronic flash equipment produces a very short flash

If, in this example, the shortest time the sensor is exposed fully is 1/200, how can I get a fully exposed sensor with 1/250? Without the use of high speed flash. I don't think the curtain speed is changing.

I agree the curtain speed is NOT changing.

As I have mentioned several times before in this conversation, I think that it is simply the ability of the newer FLASH UNITS to rise and execute their Full Flash OUTPUT in a shorter time than previous FLASH UNITS could.

I think that Nikon, is just exploiting that technological advancement.

***

At sync speed the time that a fully open state exist, is 0. As soon the first curtain has arrived at the other site of the sensor, at that same time the second curtains starts his journey. At sync speed.

I think this statement is ever so terribly incorrect.

Also if you are basing your thinking on this statement as being a fact, then it is probable that is why what I am writing will not make sense to you.

“Sync Speed” is all about indicating the shortest shutter speed that will allow any particular FLASH UNIT to:

1. be triggered
2. rise to power
3. execute full power

For any DLSR (or SLR) Camera there are actually several “sync-speeds”.

The most common "sync speed" that is stated in specifications and discussed is the “x-sync”.

Importantly, please also note that "x-sync" is really only an ‘indicative’.

When "x-sync is quoted as a camera's specification, it is stated implied or assumed that the Photographer will be using a Dedicated Flash Unit for that particular camera.

The “x” in “x-sync” designates a reference for "xenon" flash units – which most (all?) modern Flash Units are.

*

Maybe a practical example will assist: one of my Canon DSLR’s has, according to the specifications, an x- sync speed = 1/200s - and those specs state that x-sync is for the specified Dedicated Canon Flash Units.

But there is also a very important note in my camera's specifications that, for any other than Dedicated and Specified Canon Flash Units “be sure to test any non Canon Flash Unit to be sure it synchronizes correctly with the camera.”

And to go further the specifications 'suggest' another x-sync here: “with Studio Flash the x-sync speed 1/125s is suggested”

But yet, I know from my own testing that with some of my Studio Flash Heads, I must use 1/100s as the "x-sync" for that particular camera.

In each case the curtain speed on my camera is not changing. But the different 'x-sync' that I must use are simply because the DIFFERENT Flash Units that I use take a different amount of time to: trigger; rise; execute at full power; and fall.

***

Back to the Nikon D610 and the Nikon Flash Units that Camera lists as ‘dedicated’.

My guess is that the more modern Nikon Flash Units have developed either a slightly quicker trigger time and/or rise time to peak power - and that little technological gain is being exploited.

WW

Post script -

BTW picking nits, because it is important in this particular case – I think that the wiki quote as posted is not as precise as it could be:

X-sync is the simplest to explain and implement: the flash is fired at the instant the shutter is fully open. Electronic flash equipment produces a very short flash

More precise would be:

"X-sync is the simplest to explain and implement: the flash unit is triggered when the shutter is fully open. Electronic flash equipment produces a very short flash"

The wiki quote tends to imply that the “FLASH” (i.e. all the light from it) happens “instantaneously” and at “the instant” the shutter is fully opened – and that does not happen at all.

What does happen, are the Functions listed below.

It is important to note that each of these functions below takes a period of time to happen, albeit that some Functions take an incredibly short time.

When the shutter is fully opened, then (and that is maybe after a very small period of time):

1. the flash unit is triggered

2. the flash rises from zero power to full power

3. the flash is at full power

4. the flash decays from full power to zero power

[george013]

@Richard,
That's exactly how it normaly works. But the question was why nikon uses 2 different sync speeds.

@John,

I don't believe this statement is correct. The rated flash duration of most speed lights is about 1/1000 second at full power. This would mean that in order to evenly expose the entire sensor making full use of the output of the flash, the second curtain has to delay at least 1/1000 second after the first curtain is fully open. I makes sense that this is how the flash sync shutter speed is determined. Why would they recommend a shutter speed that doesn't take full advantage of the rated output of the flash?

I think thats correct. But it's not the duration that's important, but the startingtime of the flash. The duration is worked out in the T-factors, what was called here the tail of the flash. But it could be important if Nikon moved to the second curtain wihout telling.

@ Dave,
The curtains have a fixed speed. The speed of that curtain happens to be the sync-speed. Curtain 1 has opened completely and then curtain 2 starts to close. That's how you get an exposure of 1/250, a sync-speed by example.
From the same link you gave http://neilvn.com/tangents/auto-fp-f...on-d300s-d700/



@William,
I don't know anything of a varaiable x-sync and I can't find anything on the net.

For any one particular camera the “x-sync speed” will be different depending upon the FLASH UNIT that is being used.

You may want a longer time due to all kind of reasons, by example the delay with wireless, but you cant get a shorter time without some tricks. And one of them is FP or highspeed flash. From your former post

For example the X-sync that is stated in the Specs of most (all?) SLR Cameras has a note indicating that is applicable to the dedicated units and often another note specifying that a slower x-sync speed might be applicable to other Flash Units.

Going slower as the sync-speed is no problem. But going faster without FP, that's where this thread is about.


I don't have a flash anymore, stolen. But if somebody could make a picture with a D700/D300, 1/320 auto fp and with a shuttertime of 1/320 and look in the exif for the rear curtain? Or with the appropriate settings with another camera.

George

[William W]

. . . @William,
I don't know anything of a varaiable x-sync and I can't find anything on the net. Going slower as the sync-speed is no problem. But going faster without FP, that's where this thread is about.

George,

There was never a mention of a 'variable' x-sync speed.

There was mention of there being A DIFFERENT x-sync speed, depending upon what Flash Unit is being used.

Those are two entirely different statements.

And the thread is not about going faster or slower with than the x-sync speed, because the x-sync speed depends upon what flash is being used.

As already stated: the x-sync speed is dependent upon what FLASH UNIT which is being used.

I don't know how one can write that sentence any simpler.

However it seems you continue to not accept that and are making an argument predicted on the number which is written down in a camera's specifications as being a definitive.

That x-sync number in the camera's specifications is not definitive. It is only a guide.

WW

[William W]

. . . The curtains have a fixed speed. The speed of that curtain happens to be the sync-speed. Curtain 1 has opened completely and then curtain 2 starts to close. That's how you get an exposure of 1/250, a sync-speed by example.

That's the same incorrect premise, again.

If those pictures were taken with my Elinchrom Studio Flash Heads the results would be different, 1/200 would be darker at one side. And so would 1/180 and 1/160.

I encourage you to let go of the idea that the shutter curtain speed is the sole defining factor the x-sync speed

WW

[george013]

William,
It's going to be playing with words in stead of talking about flash and camera.
To me this is the same as variable.

There was mention of there being A DIFFERENT x-sync speed, depending upon what Flash Unit is being used.

There is something you refuse to understand.
Under normal conditions flash is fired at the moment the first curtain has opened completely. Exposuretime is determined by the moment the second curtain is starting it's closing movement. The flash sync time is the shortest time the sensor is ecposed completely. With the D700 that is 1/250. And what you are trying to tell me is that you can also take picture with 1/60, 1/30 or whatever slower. No surprise, Nikon can go as far as 30s, not counting bulb. The delay of your equipment and/or setup has nothing to do with the camera.

Going faster as the sync time will cause a partial unexposed sensor, showing a black part, the shadow of the second curtain. The faster your shutterspeed, the bigger that part.

If you want to use a flash with a faster shutterspeed as the sync-speed, then Nikon has to introduce some tricks, high speed flash. The original question, and still not answered is why there are 2 speeds at which you can activate high speed flash. The sync-time of the D700 is 1/250, just look at the shown photo's of Van Niekerk. What happens with 1/320 if high speed sync hasn't been activated?

I encourage you to let go of the idea that the shutter curtain speed is the sole defining factor the x-sync speed

That's not mine idea, but from Nikon, Canon, Fuije, Hasselblad etc etc.
What you're referring to is the correction you've to make based upon the equipment and/or setup you use.
George

[dje]

George the 1/320 images you showed above (post 34) are taken using an old Pocketwizard trigger without any compatibility with the Nikon Creative Lighting system. The 1/320 image taken with 1/320 Auto FP with CLS compatible equipment (also shown in that reference) indicates a much better exposure (but not perfect). So it would seem that Nikon have some tricks up their sleeve with their CLS compatible equipment.

As far as max sync speed is concerned, I can't agree that it is simply the curtain speed. There needs to be a finite period of time after the first curtain has opened and before the second curtain starts to close during which the flash exposure occurs. I believe this needs to be factored into the max sync speed calculation.

Dave

[William W]

It's going to be playing with words in stead of talking about flash and camera.
To me this is the same as variable.

No George.

Not playing with words.

Being very precise with words so that you might understand the concept.

***

There is something you refuse to understand. . . .

“The flash sync time is the shortest time the sensor is [exposed] completely.”

No, George, I am not “refusing to understand”.

I am unequivocally stating the statement is not accurate and as such it is: incorrect.

WW

[george013]

George the 1/320 images you showed above (post 34) are taken using an old Pocketwizard trigger without any compatibility with the Nikon Creative Lighting system. The 1/320 image taken with 1/320 Auto FP with CLS compatible equipment (also shown in that reference) indicates a much better exposure (but not perfect). So it would seem that Nikon have some tricks up their sleeve with their CLS compatible equipment.

As far as max sync speed is concerned, I can't agree that it is simply the curtain speed. There needs to be a finite period of time after the first curtain has opened and before the second curtain starts to close during which the flash exposure occurs. I believe this needs to be factored into the max sync speed calculation.

Dave

I choose for these photo's for here is exactly to see the relation between the flashmoment, not the duration, and the second curtain. If that curtain is not visible with the CLS-pictures and setting 1/320 auto fp, than I can only conclude that the flashmoment has changed. The more I think about it the more I believe it has moved to the second curtain. That peace of area covered by the first curtain is exposed by the tail of the flash. Look at the different T definitions. The difference between 1/250 and 1/320 is 0.875ms.

The definitive answer must come from Nikon.

George