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Subject: "Understanding Flash Sync Speed" Previous topic | Next topic
jshankin Registered since 19th Jan 2007Wed 14-Jan-09 03:47 AM
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"Understanding Flash Sync Speed"


Commerce Township, US
          

I appreciate any help with this question. I attended the Nikon School course on the SB800 and flash. Winston was a great teacher, but I left with a question unanswered or brushed over as he had to stay on topic. I'm not grasping the use of Flash Sync Speed. I understand Flash Shutter Speed. But could someone shed a little light on the former? I want to understand this feature completely with Auto FP as well. I'm looking for the concept and then examples for use. I read the manual already but it just tells me how to set it. Thank you.
Regards,

Jerry

  

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Reply message RE: Understanding Flash Sync Speed
Chan Tran
14th Jan 2009
1
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edmun
14th Jan 2009
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jshankin
14th Jan 2009
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Socrates Silver Member
14th Jan 2009
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14th Jan 2009
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14th Jan 2009
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Arkayem Moderator
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15th Jan 2009
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Chan Tran Registered since 04th Dec 2003Wed 14-Jan-09 04:11 AM
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#1. "RE: Understanding Flash Sync Speed"
In response to Reply # 0


Aurora, US
          

Flash sync speed is shutter speed settings that would sync with the flash correctly. I have not heard of the term flash shutter speed but wouldn't they be the same?
A camera with a focal plane shutter can only synchronize with the flash at certain shutter speed or slower. Most of today's cameras such shutter speeds are of 1/250 or slower.
Auto FP sync allows to sync at higher shutter speed by making the flash flashes several flashes rather than one but doing so would reduce the flash power significantly.

  

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edmun Registered since 16th Sep 2003Wed 14-Jan-09 06:15 AM
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#2. "RE: Understanding Flash Sync Speed"
In response to Reply # 1


eugene, US
          

the camera shutter is open all the way with shutter speeds up to synch speed so a flash can expose the whole frame.

At speeds shorter than synch speed the camera cheats on how it makes a fast exposure. It does it by using a narrow slit to achieve the faster fake shutter speed

because it uses a slit -- the flash only exposes part of the frame.

FP flash cheats by doing several pulses to cover the total frame. How it does this I am unclear but it works.

If you have a old photo book -- look up speed grafis and see how they did this -- the old books are really clear on this and how focal plain shutters distort moving action.

ledmun

  

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jshankin Registered since 19th Jan 2007Wed 14-Jan-09 01:50 PM
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#3. "RE: Understanding Flash Sync Speed"
In response to Reply # 2


Commerce Township, US
          

I understand the sync speed concept, but not the application....yet. Why the different choices in that menu option (I think it's e2)?

First: I notice in the menu settings that I can set it to 1/320 FP or 1/250 FP. Why are there two from which to choose? Why not just have one "FP Mode" to cover all speeds past the camera's fastest sync mode (1/250 I think for D300)? So why not just 1/250 FP to cover it from that level on up?

Next: Why does that menu setting have all the slower speeds listed as options if FP mode makes the most sense to leave it set on? I don't understand why the camera just doesn't have an Auto FP built in as a default and eliminate that menu. Given all this, when would I want to use 1/100 instead of, say, 1/120th FP?

Lastly, there is the other Flash Shutter Speed menu option (I think e3) that I do understand.

All in all, I'm trying to tie these two menus together so I can use them to the fullest and use correctly. This is my hot topic right now because I'm getting terrible results with my D300 and SB800 with indoor shots. Some shots are little kids moving around indoors, other shots are people just gathering. I need to get these settings down so I can expose correctly. Thank you for helping.
Regards,

Jerry

  

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Socrates Silver Member Nikonian since 01st Apr 2008Wed 14-Jan-09 04:49 PM
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#4. "RE: Understanding Flash Sync Speed"
In response to Reply # 3


US
          

First, regular shooting (not FP). There are two shutter curtains that move vertically. Initially, both are up and the shutter is blocked. One moves down to open the shutter and, a brief time later, the other moves down to close the shutter. A normal flash is so brief as to be virtually instantaneous. At slow shutter speeds, one curtain opens the shutter, the flash fires, and then the other curtain closes the shutter. At high shutter speeds, the miles per hour speed of the curtains require that the second curtain start its movement before the first curtain is finished. That's the reason for the "traveling slit" and if the flash fired under those circumstances, only the slit would be illuminated.

FP is a whole new ball game and the nature of electronic flash makes true FP physically impossible. In the old days, we had FP bulbs which were, quite simply, long-burning bulbs with a flat response. Bulb fires and then the shutter opens. The bulb continues to fire until after the shutter closes. Electronic FP is a fake-out of the bulb FP and, with your camera, the two FP settings are an engineering compromise.

  

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jshankin Registered since 19th Jan 2007Wed 14-Jan-09 04:56 PM
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#5. "RE: Understanding Flash Sync Speed"
In response to Reply # 4


Commerce Township, US
          

Right. I understand what it's doing and how the shutter is working in FP mode. But do you have any info to help with my other questions? Thank you for your help.

Regards,

Jerry

  

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Socrates Silver Member Nikonian since 01st Apr 2008Wed 14-Jan-09 07:17 PM
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#6. "RE: Understanding Flash Sync Speed"
In response to Reply # 5


US
          

The concept is that, to the extent possible, FP is attempting to mimic continuous ambient lighting. It IS very inefficient and you want to use it in such a way that it's rarely invoked.

The only real application is a portrait in bright sunlight where you want some fill lighting from the flash but, at the same time, you want to minimize depth of field. That mandates a large aperture which, in turn, mandates a high shutter speed. Don't get an ulcer attempting to determine just how much illumination you'll get from the flash. Take whatever you can get and let experience be your guide for future shots.

By the way, your camera will not invoke FP until it has absolutely no choice. For example, in Program, the actual program curve will change! As the ambient lighting increases, the shutter speed will not go higher than the normal flash sync for your camera until the lens has reached minimum aperture. In both Aperture mode and Program mode, if you have Auto-ISO on, FP will not be invoked until after the ISO has maxed out.

  

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cwthompson Silver Member Nikonian since 30th Jun 2003Wed 14-Jan-09 07:31 PM
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#7. "RE: Understanding Flash Sync Speed"
In response to Reply # 5


Kelowna, CA
          

I'll try and clarify one use for different shutter speeds during the use of your flash. Suppose you are taking a picture of your family standing beside the Christmas tree. You are using on-camera flash pointing directly at the family (not the ideal light but trying to keep this example simple). Set the flash to TTL mode and the camera on manual, ISO 200, 1/250, f/8.0. Lets assume this gives a nice exposure of the family but the rest of the room, lamps etc are dark. Now try changing the shutter speed to 1/60. Notice the room is much brighter and the family is still correctly exposed.
The lesson here is that at the maximum flash sync speed (usually 1/250) and slower, shutter speed controls the ambient exposure and does not affect flash exposure. Aperature is what controls flash exposure. The reason for this is from max shutter sync speed (1/250) and slower the shutter is fully open for the duration of the flash burst. Therefore it doesn't matter whether you have the shutter set at 1/250 or 1/8, the sensor still gets the same amount of light from the flash. Changing the aperature is what changes the amount of flash reaching the sensor. On the other hand, changing the shutter speed does affect the amount of ambient light reaching the sensor. Simple rule to remember, shutter speed controls the amount of ambient reaching the sensor, aperature controls the amount of flash reaching the sensor. This is also aspplicable in outdoor photography with flash and is very useful in darking skies etc. while the subject is lite with flash.
Hope this makes some sense and helps answer your questions. There is an enormous amount of material on flash at www.strobist.blogspot.com. Start with his Flash 101 on the site and go from there. Good luck.

Craig W. Thompson
WYMAN GALLERY PHOTOGRAPHY
www.wymangallery.com

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberWed 14-Jan-09 07:44 PM
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#9. "RE: Understanding Flash Sync Speed"
In response to Reply # 5


Richmond Hill, GA (Savannah), US
          

Jerry,

I thought of one reason why you might want to limit the maximum shutter to a speed slower then the true Shutter Sync speed.

Older cameras had much slower sync speeds than current cameras.

If two photographers were working together at the same event, and wanted to mix and match their shots, and one was using an older camera with a slower sync speed, you might want to set the newer camera to the same sync speed so the pictures from both cameras would have the same amount of ghosting.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberWed 14-Jan-09 07:33 PM
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#8. "RE: Understanding Flash Sync Speed"
In response to Reply # 3


Richmond Hill, GA (Savannah), US
          

>I understand the sync speed concept, but not the
>application....yet. Why the different choices in that menu
>option (I think it's e2)?
>
>First: I notice in the menu settings that I can set it to
>1/320 FP or 1/250 FP. Why are there two from which to choose?
>Why not just have one "FP Mode" to cover all speeds
>past the camera's fastest sync mode (1/250 I think for D300)?
>So why not just 1/250 FP to cover it from that level on up?
>
>Next: Why does that menu setting have all the slower speeds
>listed as options if FP mode makes the most sense to leave it
>set on? I don't understand why the camera just doesn't have an
>Auto FP built in as a default and eliminate that menu. Given
>all this, when would I want to use 1/100 instead of, say,
>1/120th FP?
>
>Lastly, there is the other Flash Shutter Speed menu option (I
>think e3) that I do understand.
>
>All in all, I'm trying to tie these two menus together so I
>can use them to the fullest and use correctly. This is my hot
>topic right now because I'm getting terrible results with my
>D300 and SB800 with indoor shots. Some shots are little kids
>moving around indoors, other shots are people just gathering.
>I need to get these settings down so I can expose correctly.
>Thank you for helping.
>Regards,
>
>Jerry

Jerry,

Flash Sync speed is Menu item e1, and is the highest shutter speed that can be set on the camera when the flash is being used in normal sync mode. I agree with you. I see very little use for the any flash sync speed less than the maximum. I always want my shutter to go to the highest speed possible that will still allow the full duration of the flash to occur between shutter-open and shutter-close. On the D300 that is 1/250th.

The 1/320th sync speed is somewhat of an anomally. Read the note on page 289 that say, "flash range drops as shutter speed increases". This wouldn't happen if 1/320th was truly a flash sync speed. This tells me that there is something wrong with the timing of the shutter versus the flash that causes part of the flash duration to fall outside the shutter-open period.

If the flash is used in Auto FP Sync Mode, then the shutter can be set to speeds higher than the Flash Sync Speed. FP stands for 'Focal Plane' which is the type of shutter we have in our cameras. If you increase the shutter past 1/250th, the flash output changes so that it puts out a long burst that covers the entire time the focal plane shutter is moving (ie, 1/250th sec). This long FP burst will no longer stop action like the normal sync, and it is weaker power.

Flash Shutter Speed is set in Menu item e2. This is the LOWEST speed the shutter can go to when the camera is automatically choosing the shutter speed. The default setting is 1/60th, which is the lowest shutter speed that most people can handhold a camera at without getting excessive camera motion blur. This keeps your backgrounds sharp when shooting indoors.

You can set the shutter below the Flash Shutter speed manually in camera Manual mode, and the camera can automatically pick speeds lower than menu e2 if you select Slow or Rear Sync.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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jshankin Registered since 19th Jan 2007Wed 14-Jan-09 08:17 PM
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#10. "RE: Understanding Flash Sync Speed"
In response to Reply # 8
Thu 15-Jan-09 01:04 PM by Arkayem

Commerce Township, US
          

>1/250th sec). This long FP burst will no longer stop action
>like the normal sync, and it is weaker power.
>
>Russ, I'm following your answer, but why won't it stop action at >higher shutter speeds? If I increase the speed to 1/500th and I'm >in FP mode, the flash will fire continuously while the shutter >opening scans the sensor, but why won't it freeze the action? I'm >thinking indoor sports (high school basketball).

What I mean is that the flash in normal sync fires at faster than 1/1000th sec. When you go into FP mode the flash becomes 1/250th sec to cover the full travel time of the FP shutter.

As you go above the 1/250th point your shutter becomes a 'traveling slit' across the image. The smaller the slit the higher the effective speed.

So, as you increase the shutter above 1/250th, the 'traveling slit' is what stops the action, but you have to go above 1/1000th before it will stop action as well as the flash in regular sync mode. Then, the power of the flash becomes so weak at those high shutter speeds, that it becomes pretty useless in a basketball game. It won't light anything more than about 10 feet away at 1/1000th, even using f/2.8.

The main purpose of FP mode is for shooting fill flash on a bright day, so you can open the aperture wide open to blur the background.

Russ

  

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Socrates Silver Member Nikonian since 01st Apr 2008Thu 15-Jan-09 12:21 AM
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#12. "RE: Understanding Flash Sync Speed"
In response to Reply # 10


US
          

It will stop action exactly the same as a 1/500 shutter speed in sunlight with no flash. (Read my FP explanation in post #4.)

On the other hand, a "normal" (non-FP) flash burst with an SB600 will last 1/900 second at most and could possibly be as brief as 1/25,000 second. It doesn't matter that I'm keeping the shutter open for 1/250 or 1/200 or 1/60. The bulk of the illumination comes from the flash rather than from ambient lighting. The longer shutter openings don't do diddly for the main subject. Its primary benefit is in making the background a little less black.

  

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Ferguson Silver Member Nikonian since 19th Aug 2004Wed 14-Jan-09 11:38 PM
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#11. "RE: Understanding Flash Sync Speed"
In response to Reply # 0


Cape Coral, US
          

>The 1/320th sync speed is somewhat of an anomally.
>Read the note on page 289 that say, "flash range drops
>as shutter speed increases". This wouldn't happen if
>1/320th was truly a flash sync speed. This tells me
>that there is something wrong with the timing of the
>shutter versus the flash that causes part of the
>flash duration to fall outside the shutter-open period.

This has been something I've puzzled over, I posted on the D300 forum without response. It made no sense to me to have auto-FP on 1/250th if you also have it on 1/320th.

And it's definitely, for sure, operating in FP mode if you set the 1/250th setting and then shoot at 1/320th - dramatically less light. I've tried shooting at 1/250th vs. 1/320th both in non-FP mode and there may be less light but I had trouble seeing it.

But let's say that even at 1/320th normal (non-FP) it is slightly reduced flash -- it is still dramatically more than it would be in FP mode.

So why is there an auto-FP at 1/250th?

  

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Socrates Silver Member Nikonian since 01st Apr 2008Thu 15-Jan-09 12:27 AM
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#13. "RE: Understanding Flash Sync Speed"
In response to Reply # 11


US
          

"It made no sense to me to have auto-FP on 1/250th if you also have it on 1/320th."
As I explained earlier, that's an engineering design trade-off because a true long-burning electronic flash head is a physical impossibility.

"So why is there an auto-FP at 1/250th?"
My WAG (Wild-Assed Guess) is that it's a power management issue.

Don't over-analyze the camera. Spend your time taking pictures!

  

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jshankin Registered since 19th Jan 2007Thu 15-Jan-09 03:02 AM
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#14. "RE: Understanding Flash Sync Speed"
In response to Reply # 13


Commerce Township, US
          

Thank you fellow Nikonians for all your responses. Very helpful info.


Regards,

Jerry

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberThu 15-Jan-09 01:40 PM
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#16. "RE: Understanding Flash Sync Speed"
In response to Reply # 13


Richmond Hill, GA (Savannah), US
          

>"It made no sense to me to have auto-FP on 1/250th if
>you also have it on 1/320th."
>As I explained earlier, that's an engineering design trade-off
>because a true long-burning electronic flash head is a
>physical impossibility.

I don't think this is right.

When using 1/320th shutter in Auto FP Mode, the camera is still in the Regular Sync Mode. It doesn't go into the FP mode until ABOVE 1/320th. (At least it is not supposed to)

And if the flash is in Regular Sync Mode at 1/320th, the only reason that it would have less range is if part of the normal flash pulse was being truncated somehow. That could only be a timing issue.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberThu 15-Jan-09 01:30 PM
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#15. "RE: Understanding Flash Sync Speed"
In response to Reply # 11


Richmond Hill, GA (Savannah), US
          

>>The 1/320th sync speed is somewhat of an anomally.
>>Read the note on page 289 that say, "flash range
>drops
>>as shutter speed increases". This wouldn't happen if
>
>>1/320th was truly a flash sync speed. This tells me
>>that there is something wrong with the timing of the
>>shutter versus the flash that causes part of the
>>flash duration to fall outside the shutter-open period.
>
>This has been something I've puzzled over, I posted on the
>D300 forum without response. It made no sense to me to have
>auto-FP on 1/250th if you also have it on 1/320th.
>
>And it's definitely, for sure, operating in FP mode if you set
>the 1/250th setting and then shoot at 1/320th - dramatically
>less light. I've tried shooting at 1/250th vs. 1/320th both
>in non-FP mode and there may be less light but I had trouble
>seeing it.

At 1/320th shutter the power of the flash is essentially identical whether in FP or Normal sync. The difference is the length of time the flash is on.

In Regular Sync Mode, at 1/320th shutter speed, the shutter is open for about 3 milliseconds, and the flash is on at full power for about 1/1000th sec (1 millisecond), but part of it is being cut off for some unknown reason. There is obviously a timing problem of some sort.

At 1/320th shutter in FP mode, the shutter is open for about 3 ms, and the flash is on at about 1/4 power for 1/250th sec (4 milliseconds).

The result is that both modes provide about the same lighting.

I think they added the 1/320th FP Sync Mode mostly for bragging rights. I can't see that the slight increase in shutter speed from 1/250th to 1/320th is all that significant. I think they were forced to retain the 1/250th FP Sync Mode, because the new 1/320th FP Mode didn't work quite right.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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Ferguson Silver Member Nikonian since 19th Aug 2004Thu 15-Jan-09 03:02 PM
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#17. "RE: Understanding Flash Sync Speed"
In response to Reply # 15


Cape Coral, US
          

>At 1/320th shutter the power of the flash is essentially
>identical whether in FP or Normal sync. The difference is the
>length of time the flash is on.

I'm not near my camera now (shame!) but when I get some time I will post tests. I know I experimented and found that not to be true. Let me make sure we are saying the same thing:

Exposure 1: Set to 1/250th Auto-FP mode, and set shutter to 1/320th

Exposure 2: Set to 1/320th Auto-FP mode, and set shutter to 1/320th

I recall doing that several times, exposuing a seen with close and far objects so I could tell "reach", and finding far less distance lit in the first than the second.

Now I did it in auto-mode I think, maybe I'll try it also in M 1/1 mode on the SB and make sure this is not a metering artifact. Or a senior moment.

More later.

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberThu 15-Jan-09 03:34 PM
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#18. "RE: Understanding Flash Sync Speed"
In response to Reply # 17


Richmond Hill, GA (Savannah), US
          

>>At 1/320th shutter the power of the flash is essentially
>>identical whether in FP or Normal sync. The difference is
>the
>>length of time the flash is on.
>
>I'm not near my camera now (shame!) but when I get some time I
>will post tests. I know I experimented and found that not to
>be true. Let me make sure we are saying the same thing:
>
>Exposure 1: Set to 1/250th Auto-FP mode, and set shutter to
>1/320th
>
>Exposure 2: Set to 1/320th Auto-FP mode, and set shutter to
>1/320th
>
>I recall doing that several times, exposuing a seen with close
>and far objects so I could tell "reach", and finding
>far less distance lit in the first than the second.

Excellent experiment! However, you have to make sure this is done in very low ambient light, so the flash is the only contributor to the exposure.

Exposure 1 will fire the flash in FP mode which stretches the pulse across the shutter-open period, and Exposure 2 will fire the flash in regular sync mode which will fire a very short full power flash while the shutter is open.

Theoretically, there should be slightly less 'reach' in Exposure 1, because in FP mode the flash is not as efficient due to being stretched, and part of the stretched pulse falls outside the shutter-open period.

However, you will find that the flash 'reach' will not be a lot different, because (as noted in the D300 manual) flash power decreases as the speed is increased from 1/250th to 1/320th when using Auto FP 1/320th mode.

>Now I did it in auto-mode I think, maybe I'll try it also in M
>1/1 mode on the SB and make sure this is not a metering
>artifact. Or a senior moment.

Yes, it would be better to do this test in Flash Manual mode to keep the flash power constant.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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Ferguson Silver Member Nikonian since 19th Aug 2004Fri 16-Jan-09 12:48 AM
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#19. "RE: Understanding Flash Sync Speed"
In response to Reply # 18


Cape Coral, US
          

OK, I tried the experiment, but I also read the manual. Read the first part of this without cheating and reading the manual.

Both exposures are a D300 on a tripod, ISO200 at F11 with an 18-200 at 18mm, tripod mounted in "M" mode, and the shutter set to 1/320th second. Camera has fireware 1.10.

I set an SB-800 on top with fresh batteries. I put the diffuser on it because I wanted to do this inside (cool outside). I set it to "M" and 1/1, with head/diffuser pointed straight ahead.

I arrived at the F11 by some experimentation to get a decent exposure at non-FP mode and 1/320th. I picked a direction with a bit of depth.

I then did two exposures:

#1 had the camera e1 setting at "1/320th auto-FP". This means that the camera was NOT using the flash in FP mode.

#2 had the camera e1 setting at "1/250th Auto-FP", meaning of course that with the shutter at 1/320th it was operating in FP mode.

As you can see, there is a huge difference in available light for the exposure.

I then reduced the F-stop with all else the same until I got about the same exposure (by eye, not measure). That's the third exposure, it ended up being at f5, which was just a tad bright, f5.6 was just a bit dark. Histograms confirmed later. So if I remember the math that's about 2 and a third stop difference.

Now here is where I get really confused. The manual says this:

>Use auto FP high-speed sync with SB-800, SB-600, and
>SB-R200 flash units. If other flash units are used,
>shutter speed is set to 1/320 s. When the camera
>shows a shutter speed of 1/320 s in exposure mode P
>or A, auto FP high-speed sync will be activated if the
>actual shutter speed is faster than 1/320 s.

All that makes sense except I never noticed it says "P" or "A" only. Does this mean in "M" or "S" mode, which is where I've done all the testing to ensure I had an adequate shutter, that it won't work?

I don't seem to have enough light to get the shutter up to 320th in "P" or "A" and can't persuade it in "P" by rotating the command dials, it sticks at 60th. Going to think about this a bit.

Maybe that means I wasn't really operating in FP mode at the second and third exposure? Except I did compare to no-flash, and a no-flash is almost black in that condition (dim light at f11 and 320th). And the flash looks even.

Signed, even more confused.









Attachment #1, (jpg file)
Attachment #2, (jpg file)
Attachment #3, (jpg file)

  

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Ferguson Silver Member Nikonian since 19th Aug 2004Fri 16-Jan-09 01:00 AM
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#20. "RE: Understanding Flash Sync Speed"
In response to Reply # 19
Fri 16-Jan-09 01:04 AM by Ferguson

Cape Coral, US
          

OK, trying to honor the manual. I pointed the camera at a light in "A" mode and ISO 3200, and changed the F-stop until I could get a 1/320th shutter speed. So conforming to the manual. it's also about 6' from the camera, so M and 1/1 on the flash is too much power even with the diffuser but I left it on.

Exposure #1 is with "1/320th Auto-FP"

Exposure #2 is with "1/250th Auto-FP".

Now I conform to the manual, and with the shutter at 1/320th in both these I should have been with a normal front curtain synch for the first, and FP mode for the second.

And that's consistent with a LOT less power being delivered.

All makes sense except...

What the heck good is a 1/250th auto-FP mode?

Unless of course your flash only works in manual mode and you needed to get less power somehow.




Comments welcomed on pictures: Http://linwoodferguson.smugmug.com




Attachment #1, (jpg file)
Attachment #2, (jpg file)

  

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Ferguson Silver Member Nikonian since 19th Aug 2004Fri 16-Jan-09 01:32 AM
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#21. "RE: Understanding Flash Sync Speed"
In response to Reply # 20
Fri 16-Jan-09 01:37 AM by Ferguson

Cape Coral, US
          

One final test. I read somewhere that at 1/320th the flash operates in normal mode but at a reduced power. I didn't really understand that since the duration is 1ms at full power on a SB800, and it doesn't appear to be true.

Simialr test to before, I set up on a tripod, D300, 18-200 @ 18, ISO200.

This time I set "e1" to 1/320th Auto FP for both cases.

Exposure's #1 and #3 were at 1/250th and F9.

Exposures #2 and #4 were at 1/320th and F8.

Supposedly the same exposure net, but flash output being the potential difference. Still the SB-800, "M" mode and 1/1.

I won't post all 4 pictures, they are visually almost identical (to me shots 2 and 3 were slightly brighter (which means one at 250 and one at 320).

I've put all four histograms onto one image below.

To me the conclusion is I have the same flash power at 250th and 320th with the SB800 and D300.






Attachment #1, (jpg file)

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberFri 16-Jan-09 04:24 PM
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#24. "RE: Understanding Flash Sync Speed"
In response to Reply # 21


Richmond Hill, GA (Savannah), US
          

I think you may be misinterpretting your results here.

When in regular flash sync, there should not be any difference in subject brightness when you change shutter speeds (assuming of course that the ambient is not contributing - you have to do these tests in very low ambient conditions).

You are actually proving that there is a a reduction in brightness when going from 1/250th to 1/320th when using regular sync, because you had to open up from f/8 to f/9 to make them the same brightness. You are proving that something is not timed right in the regular flash sync mode when using Auto FP 1/320th between the speeds of 1/250th and 1/320th.

If you repeat your test at lower shutter speeds, you will see that changing the shutter speed does not affect the brightness. It should never affect the brightness because the flash pulse is entirely contained within the shutter open period. There is definitely something wrong with the power or synchronizing of the flash at 1/320th.

It would be interesting to check if the flash is firing at normal power and duration between 1/250th and 1/320th. Maybe it's in some sort of pseudo-Auto FP mode? Maybe the duration is longer and the power is lower than the normal 1/1000th sec between these speeds? It really can't be a synchronizing issue, or you would get a bright top or bottom to your images.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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Ferguson Silver Member Nikonian since 19th Aug 2004Fri 16-Jan-09 04:31 PM
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#25. "RE: Understanding Flash Sync Speed"
In response to Reply # 24


Cape Coral, US
          

>I think you may be misinterpretting your results here.
>
>When in regular flash sync, there should not be any difference
>in subject brightness when you change shutter speeds (assuming
>of course that the ambient is not contributing - you have to
>do these tests in very low ambient conditions).

You are absolutely correct, I was not thinking this through correctly. all this appears to prove is that resulting image didn't vary significantly with 1/3rd stop.

What I was TRYING to show is

>It would be interesting to check if the flash is
>firing at normal power and duration between 1/250th and 1/320th.
>Maybe it's in some sort of pseudo-Auto FP mode?

and I would have had that test if I left it at f8. But even so, the lack of variation even given the f8 vs. f9 would seem to indicate that IF there is a difference in power utilization between 1/250th and 1/320th it is tiny, at or under 1/3rd stop.

Comments welcomed on pictures: Http://linwoodferguson.smugmug.com

  

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jshankin Registered since 19th Jan 2007Sat 17-Jan-09 03:34 AM
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#26. "RE: Understanding Flash Sync Speed"
In response to Reply # 24


Commerce Township, US
          

Hi Russ,

I just checked out your blog page. You explain the TTL/Flash concepts so well, that I will need to bookmark and check in daily for new postings or to reread your writing. You are very clear and it makes so much sense. You should teach flash classes for Nikon! I like how you write a lot on any particular aspect because it's thorough. You never write too much. Thank you!

Regards,

Jerry

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberSat 17-Jan-09 01:38 PM
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#27. "RE: Understanding Flash Sync Speed"
In response to Reply # 26


Richmond Hill, GA (Savannah), US
          

>Hi Russ,
>
>I just checked out your blog page. You explain the TTL/Flash
>concepts so well, that I will need to bookmark and check in
>daily for new postings or to reread your writing. You are very
>clear and it makes so much sense. You should teach flash
>classes for Nikon! I like how you write a lot on any
>particular aspect because it's thorough. You never write too
>much. Thank you!

Jerry,

Thanks for the kind feedback!!

I haven't published a new article for a whiles, but I do have two new ones that I am working on. I hope to publish them in a couple of weeks.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberFri 16-Jan-09 04:05 PM
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#22. "RE: Understanding Flash Sync Speed"
In response to Reply # 19


Richmond Hill, GA (Savannah), US
          

Fergusen wrote:
"I then did two exposures:

#1 had the camera e1 setting at "1/320th auto-FP". This means that the camera was NOT using the flash in FP mode.

#2 had the camera e1 setting at "1/250th Auto-FP", meaning of course that with the shutter at 1/320th it was operating in FP mode.

As you can see, there is a huge difference in available light for the exposure.

I then reduced the F-stop with all else the same until I got about the same exposure (by eye, not measure). That's the third exposure, it ended up being at f5, which was just a tad bright, f5.6 was just a bit dark. Histograms confirmed later. So if I remember the math that's about 2 and a third stop difference."

Yes, this indicates that at 1/320 shutter on the D300, the power of the flash is over two stops less in FP mode than in regular sync. This is considerably more difference than I see in actual practice with my D200 going from regular sync to FP sync at 1/250th (The D200 does not have the 1/320th Auto FP Sync option).

The confusing quote from the manual:
>Use auto FP high-speed sync with SB-800, SB-600, and
>SB-R200 flash units. If other flash units are used,
>shutter speed is set to 1/320 s. When the camera
>shows a shutter speed of 1/320 s in exposure mode P
>or A, auto FP high-speed sync will be activated if the
>actual shutter speed is faster than 1/320 s.

Very confusing, I agree. I think this is referring to the indication you will see on the LCD and in the viewfinder when you use a flash other than the SB-600, 800, or R200 (ie, non-CLS), and you select Auto FP mode, and the camera chooses a shutter speed above 1/320th. Of course for the camera to choose a shutter speed, you have to be in P or A mode. For instance, if the camera selects 1/500th sec, you will see 1/320th in the display. This sounds really odd and wrong, but that is what I think this not is saying.

I know from personal experience that when you are using Auto FP mode, there is no difference in flash operation when in different camera modes. P, A, S, and M all work exactly the same with regards to FP flash mode.

You wrote:
"I don't seem to have enough light to get the shutter up to 320th in "P" or "A" and can't persuade it in "P" by rotating the command dials, it sticks at 60th. Going to think about this a bit.".

Yes, in low ambient conditions, and in A or P modes, the camera will always choose the 'Flash Shutter Speed' that you have selected in Menu item e3. You can defeat this by going into slow or rear sync. Then the shutter drops way down to expose the ambient normally. The only way to INCREASE the shutter in low ambient conditions is in camera M or S modes. Then, the camera does not have control of the shutter - you do.

Russ
http://russmacdonaldphotos.com/
http://NikonCLSPracticalGuide.blogspot.com/

  

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Ferguson Silver Member Nikonian since 19th Aug 2004Fri 16-Jan-09 04:12 PM
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#23. "RE: Understanding Flash Sync Speed"
In response to Reply # 22


Cape Coral, US
          

>Yes, in low ambient conditions, and in A or P modes, the
>camera will always choose the 'Flash Shutter Speed' that you
>have selected in Menu item e3. You can defeat this by going
>into slow or rear sync. Then the shutter drops way down to
>expose the ambient normally. The only way to INCREASE the
>shutter in low ambient conditions is in camera M or S modes.
>Then, the camera does not have control of the shutter - you
>do.

I understand but I was trying to conform to the (confusing) manual of using A/P.

  

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