Question on High Speed Sync (for Nikonians)

[dje]

A recent informative thread on HSS here initiated by Bruce has renewed my interest in this subject. My question relates to Nikon cameras such as my D610 which have two HSS settings, "1/200 (Auto FP)" and "1/250 (Auto FP). I believe the D810 has similar settings but with speeds of 1/250 and 1/320 , which is presumably because the D810 has faster shutter curtains.

I assume that with each setting, HSS comes into play for speeds above the shutter speed shown. But why have two different settings (that are so close anyway) ?

Dave

PS: "Auto FP" is Nikon speak for HSS !

[William W]

A guess:

Is the 'normal' X-sync speed of the camera 1/250?

Then if yes -

Activating HSS (or Auto FP) you lose the equivalent of about 2 Stops of 'light power' - I reckon this in MFWD.

Using Flash without HS activated at or below the X-Sync Speed, there is no loss.

I guess that the Nikon engineers have found a way to crib 1/3 Stop more shutter speed without activating HSS and figure that in some shooting scenarios would it would be better to have the HSS kick in at one third of a stop faster than the "normal" X-Sync speed and thus more flash power and all Shutter Speeds slower.

Hope that makes sense? I didn't phrase it all that precisely.

WW

[dje]

A guess:

Is the 'normal' X-sync speed of the camera 1/250?

Then if yes -

Activating HSS (or Auto FP) you lose the equivalent of about 2 Stops of 'light power' - I reckon this in MFWD.

Using Flash without HS activated at or below the X-Sync Speed, there is no loss.

I guess that the Nikon engineers have found a way to crib 1/3 Stop more shutter speed without activating HSS and figure that in some shooting scenarios would it would be better to have the HSS kick in at one third of a stop faster than the "normal" X-Sync speed and thus more flash power and all Shutter Speeds slower.

Hope that makes sense? I didn't phrase it all that precisely.

WW

Bill the Nikon handbook is confusing (to me anyway !) but I think the maximum sync speed for the D610 is 1/200. (it is probably 1/250 for the D810). So if I chose 1/250 as the max sync speed before Auto FP kicks in, I would in fact be cribbing the use of 1/250 in normal flash sync mode. Not sure whether there is any marginal effect with this such as slightly un-even illumination across the sensor with this setting - or maybe it's just a loss of "safety margin" with timing.

One view I read somewhere is that you may as well use the higher setting all the time. If there is no dis-advantage with this, why have two settings in the first place ?

Dave

[george013]

Bill the Nikon handbook is confusing (to me anyway !) but I think the maximum sync speed for the D610 is 1/200. (it is probably 1/250 for the D810). So if I chose 1/250 as the max sync speed before Auto FP kicks in, I would in fact be cribbing the use of 1/250 in normal flash sync mode. Not sure whether there is any marginal effect with this such as slightly un-even illumination across the sensor with this setting - or maybe it's just a loss of "safety margin" with timing.

One view I read somewhere is that you may as well use the higher setting all the time. If there is no dis-advantage with this, why have two settings in the first place ?

Dave

I begin to believe that the differences between the 2 sync speeds is related to FF and DX mode. In DX-mode you can use a higher speed. A small part of the sensor is not used. I'm not sure but until now the only logical explanation.

George

[dje]

I begin to believe that the differences between the 2 sync speeds is related to FF and DX mode. In DX-mode you can use a higher speed. A small part of the sensor is not used. I'm not sure but until now the only logical explanation.

George

Interesting point George although it doesn't mention that in the user manual. I'm afraid I don't know how the change from FX to DX is implemented.

Dave

[Stagecoach]

I begin to believe that the differences between the 2 sync speeds is related to FF and DX mode. In DX-mode you can use a higher speed. A small part of the sensor is not used. I'm not sure but until now the only logical explanation.

George

For info, the D300 that also has the 1/250 and the 1/320 Auto FP (HSS) settings the same as the D810 is only a DX sensor.

I did read up on Auto FP/HSS use a while ago but my brain did not store the info but recall some testing with examples that had been done to show the difference between use of the two speeds in one article.

[dje]

For info, the D300 that also has the 1/250 and the 1/320 Auto FP (HSS) settings the same as the D810 is only a DX sensor.

Thanks Grahame, I guess we can eliminate the FX/DX theory.

Dave

[pnodrog]

From my D800 manual page 300 there is a drop in flash power depending on shutter speeds from 1/320 - 1/250s but not as great as the reduction above 1/320 in full FP mode.

[pnodrog]

Want to push the standard sync speed? Have a read of this.

I should imagine it varies slightly camera to camera as quality control probably only checks that it meet the basic sync specification.

[dje]

From my D800 manual page 300 there is a drop in flash power depending on shutter speeds from 1/320 - 1/250s but not as great as the reduction above 1/320 in full FP mode.

Thanks LPaul

This article seems to support that description.

Dave

[george013]

For info, the D300 that also has the 1/250 and the 1/320 Auto FP (HSS) settings the same as the D810 is only a DX sensor.

I did read up on Auto FP/HSS use a while ago but my brain did not store the info but recall some testing with examples that had been done to show the difference between use of the two speeds in one article.

Then we can forget that explanation.

@dje
Even in that article I can't find the difference between 1/250 and 1/320. Van Niekerk says that with 1/320 HSS will be used. But that counts for everyting faster as 1/250.

I wait for the defintive explanation.

George

[dje]

Then we can forget that explanation.

@dje
Even in that article I can't find the difference between 1/250 and 1/320. Van Niekerk says that with 1/320 HSS will be used. But that counts for everyting faster as 1/250.

I wait for the defintive explanation.

George

George in that article, compare the first row of 4 images (taken with 1/250 auto fp) and the third row of 4 images (taken with 1/320 auto fp). In the first row, the shot taken with a shutter speed of 1/320 is quite a bit darker indicating auto fp has set in. In the third row, the shot taken with a shutter speed of 1/400 is the first one that is darker indicating auto fp has set in. In each case, the last of the lighter shots is a little darker than the other light shots with a darkish band on one side. This to me indicates marginal timing on the flash sync.

Dave

[William W]

A recent informative thread on HSS here initiated by Bruce has renewed my interest in this subject.
My question relates to Nikon cameras such as my D610 which have two HSS settings, "1/200 (Auto FP)" and "1/250 (Auto FP) . . .
I assume that with each setting, HSS comes into play for speeds above the shutter speed shown. But why have two different settings (that are so close anyway) ?
PS: "Auto FP" is Nikon speak for HSS !

Please ignore the Shutter Speeds that I wrote in Post #2. I confused the other camera with the D610.

But I believe that my guess is now a good guess and I hope this explains it better:

I am discussing the Nikon D610.

Please see p327 of the D610 User Manual, it indicates the D610 has Flash X-sync = 1/200s

Now please see p237 of the Manual and read the functionality of the two different Auto FP settings.

1. Note: if 1/200 Auto FP is selected then in P and A modes the camera will ACTIVATE Auto FP if the shutter speed (selected by the TTL Meter) is FASTER than 1/200s

2. Note: if 1/250 Auto FP is selected then in P and A modes the camera will ACTIVATE Auto FP if the shutter speed (selected by the TTL Meter) is FASTER than 1/250s

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).

The relative "drop" in Flash Power is about two stops when Auto FP is activated, so you are simply gaining 'better camera specs' that allow an higher X-Sync. That might be useful in some circumstances.

(BTW - The above is what I was attempting to explain in post #2.)

Maybe the faster Auto FP works with only some (not all) dedicated Flash Units?

WW

[dje]

Thank you Bill, that is perfectly clear. I think what we have here is a choice between 1/200 with "guaranteed" flash sync performance and 1/250 whose flash sync performance is probably quite ok for many uses. The latter gives the advantage that you mention of course.

Dave

[pnodrog]

A bit of a guess but I assume it is related to the flash length of a xenon tube at maximum power.

A typical T.5 time at max pwr is 1 millisecond (T.5 is the time it is emitting above 50% power). The leading edge is very steep but the trailing edge has a far longer decay and the T.1 (10%) time can be as long as 4 millisecond (1/250th - sounds familiar) So some flash units may still be providing detectable illumination while the shutter is closing causing both a slight unevenness across the image and clipping the flash's full power.

At less than maximum power the flash duration will be shorter and more likely to fall completely within the shutter open time so may work totally satisfactorily.

This is a total guess from my understanding of xenon tube (very limited) and the tests I have seen. I have tried to find some verification of this speculation but have not found any.

[george013]

A bit of a guess but I assume it is related to the flash length of a xenon tube at maximum power.

A typical T.5 time at max pwr is 1 millisecond (T.5 is the time it is emitting above 50% power). The leading edge is very steep but the trailing edge has a far longer decay and the T.1 (10%) time can be as long as 4 millisecond (1/250th - sounds familiar) So some flash units may still be providing detectable illumination while the shutter is closing causing both a slight unevenness across the image and clipping the flash's full power.

At less than maximum power the flash duration will be shorter and more likely to fall completely within the shutter open time so may work totally satisfactorily.

This is a total guess from my understanding of xenon tube (very limited) and the tests I have seen. I have tried to find some verification of this speculation but have not found any.

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

[William W]

. . . 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 . . .

That might be your opinion.

It occurs to me that your opinion does not concur with the text of the Nikon D610 User Manual:

“e1 Flash Sync Speed

This option controls the flash sync speed

Option “1/250s (Auto FP) – . . . when the camera shows a shutter speed of 1/250 s in mode P or A, auto FP hgh speed sync will be activated if the actual shutter speed is faster than 1/250 s.”

(op cit p237)

WW

[William W]

I’d be interested to read a Nikon Paper on it.

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.

Are there any CiC members who are members of NPS?

Is there a Nikon equivalent f Mr Chuck Westfall?

WW

[george013]

That might be your opinion.

It occurs to me that your opinion does not concur with the text of the Nikon D610 User Manual:

“e1 Flash Sync Speed

This option controls the flash sync speed

Option “1/250s (Auto FP) – . . . when the camera shows a shutter speed of 1/250 s in mode P or A, auto FP hgh speed sync will be activated if the actual shutter speed is faster than 1/250 s.”

(op cit p237)

WW

[george013]

That might be your opinion.

It occurs to me that your opinion does not concur with the text of the Nikon D610 User Manual:

“e1 Flash Sync Speed

This option controls the flash sync speed

Option “1/250s (Auto FP) – . . . when the camera shows a shutter speed of 1/250 s in mode P or A, auto FP hgh speed sync will be activated if the actual shutter speed is faster than 1/250 s.”

(op cit p237)

WW

I don't have the D610 manual but in the D300 and D700 you will find exactly the same for the lower and the higher shutterspeed. There is only one sync speed. Just where does that mysterious second sync speed stands for? Look at the link dje gave earlier. http://neilvn.com/tangents/auto-fp-f...on-d300s-d700/

George