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Forums Lobby MASTER YOUR TOOLS - Hardware & Software Nikon Speedlights & Lighting topic #40113
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Subject: "Why double flash?" Previous topic | Next topic
alexanderbaxter Registered since 18th Aug 2008Sat 07-Mar-09 03:24 PM
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"Why double flash?"


Mesa, US
          

Hi!
I'm somewhat new to flash photography but am trying to learn how everything works. I have a D80 and a SB800 mounted on the camera. The other evening I was out in my back yard about 6:00 P.M. (75 degrees, sorry) taking flash pictures and using ambient light. My camera flash mode was slow/rear. My ISO was 400. I was in Aperture Priority with f3.5 setting on my 18-135 lens. My SB800 was set at TTL BL FP. This worked great. My pictures were just what I wanted. My question is why did the flash fire twice? It was my understanding that in slow/rear the front curtain will raise, the sensor will gather ambient light, the flash will fire and then the rear curtain will close. It seems that the flash is firing after the front curtain opens and again before the rear curtain closed. Any help in understanding how this works would be greatly appreciated.
Alex

  

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Replies to this topic
Subject Author Message Date ID
Reply message RE: Why double flash?
ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography
07th Mar 2009
1
Reply message RE: Why double flash?
gkaiseril Gold Member
07th Mar 2009
2
Reply message RE: Why double flash?
PAStime Silver Member
09th Mar 2009
6
     Reply message RE: Why double flash?
Arkayem Moderator Awarded for his high level skills in flash photography
09th Mar 2009
7
          Reply message RE: Why double flash?
gkaiseril Gold Member
09th Mar 2009
8
               Reply message RE: Why double flash?
PAStime Silver Member
10th Mar 2009
9
Reply message RE: Why double flash?
alexanderbaxter
07th Mar 2009
3
Reply message RE: Why double flash?
ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography
07th Mar 2009
4
Reply message RE: Why double flash?
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
07th Mar 2009
5

ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography Charter MemberSat 07-Mar-09 03:38 PM
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#1. "RE: Why double flash?"
In response to Reply # 0


Powder Springs, US
          

The first flash was the pre-flash that is metered by the camera in order to accurately set the final flash to the appropriate level.

Scott Chapin
Powder Springs, GA, USA
Nikonians Team Member

  

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gkaiseril Gold Member Nikonian since 28th Oct 2005Sat 07-Mar-09 03:43 PM
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#2. "RE: Why double flash?"
In response to Reply # 0


Chicago, US
          

With the rear shutter synch, the camera determines the correct flash exposure at the half press with CLS pre-flashes, and then at the full shutter release the shutter opens and just before the shutter closes the Speedlight flashes. This is causing a longer delay between the Speedlights preflash and the exposure flash than you are accustomed to and long enough for you to see the pre-flashes and the exposure flash as 2 very distinct flashes.

George
My Nikonian Galleries

  

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PAStime Silver Member Nikonian since 10th Feb 2009Mon 09-Mar-09 03:08 AM
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#6. "RE: Why double flash?"
In response to Reply # 2
Mon 09-Mar-09 03:12 AM by PAStime

Kingston, CA
          

>With the rear shutter synch, the camera determines the
>correct flash exposure at the half press with CLS pre-flashes,
>and then at the full shutter release the shutter opens and
>just before the shutter closes the Speedlight flashes.

Hi. If I'm understanding you, you are saying there are preflashes on half-press of the shutter release button. I certainly don't see any on my D90 and SB-600. The pre-flash occurs on *full* press of the shutter release button. At that moment, the camera:

1. sends a pre-flash
2. meters the scene using the sensor in the viewfinder
3. flashes some more to send power/exposure information to remote slave flashes, if any
3. opens the shutter
4. then fires the flash(es) for purposes of capturing the scene (either front or read curtain)

Cheers,
Peter

My gallery (a work in progress): http://peterstokes.net/Exhibit

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberMon 09-Mar-09 07:34 PM
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#7. "RE: Why double flash?"
In response to Reply # 6


Richmond Hill, GA (Savannah), US
          

>Hi. If I'm understanding you, you are saying there are
>preflashes on half-press of the shutter release button.

There are no preflashes on the half-press.

When you are using rear or slow sync, the preflashes occur immediately when the shutter is fully depressed, but before the shutter opens. Then, the shutter opens, and the main flash occurs right before the shutter closes.

So, if you are using a long shutter, you will see the preflash followed by the main flash.

Russ
Russell MacDonald Photography
Nikon CLS Practical Guide

  

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gkaiseril Gold Member Nikonian since 28th Oct 2005Mon 09-Mar-09 08:25 PM
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#8. "RE: Why double flash?"
In response to Reply # 7


Chicago, US
          

My mistake.

When one use the FV lock option, the Flash exposure Value is determined by the series of pre-flashses and then only the tigger flash occurs at the full shutter release.

Thanks.

George
My Nikonian Galleries

  

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PAStime Silver Member Nikonian since 10th Feb 2009Tue 10-Mar-09 02:21 AM
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#9. "RE: Why double flash?"
In response to Reply # 8


Kingston, CA
          

>My mistake.
>When one use the FV lock option, the Flash exposure Value is
>determined by the series of pre-flashses and then only the
>tigger flash occurs at the full shutter release.

Hi George. Your message reminded me of the FV lock option. I haven't experimented with that. Thanks for the idea Peter

My gallery (a work in progress): http://peterstokes.net/Exhibit

  

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alexanderbaxter Registered since 18th Aug 2008Sat 07-Mar-09 04:10 PM
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#3. "RE: Why double flash?"
In response to Reply # 0


Mesa, US
          

Thanks Guys,
That makes sense. I knew that you would know the answer.
Alex

  

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ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography Charter MemberSat 07-Mar-09 04:26 PM
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#4. "RE: Why double flash?"
In response to Reply # 3


Powder Springs, US
          

In fact, you can use rear curtain sync to meter your flash. With a slow shutter speed, you can wait until after the pre-flash to push the button on your meter prior to the final flash. That way your true flash level will be metered by not reading the pre-flash.

Scott Chapin
Powder Springs, GA, USA
Nikonians Team Member

  

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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources. Charter MemberSat 07-Mar-09 10:51 PM
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#5. "RE: Why double flash?"
In response to Reply # 0
Mon 09-Mar-09 06:13 AM by jrp

Phoenix, US
          

Alex:

Welcome to Nikonians.

Go here for an explanation and discussion of the Nikon CLS preflash and image capture sequence.

Regards,

HBB in Phoenix, Arizona
Nikonian Team Member

Go here for a list of membership upgrade benefits.

Photography is a journey with no conceivable destination.

  

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Forums Lobby MASTER YOUR TOOLS - Hardware & Software Nikon Speedlights & Lighting topic #40113 Previous topic | Next topic