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Forums Lobby MASTER YOUR TOOLS - Hardware & Software Nikon Speedlights & Lighting topic #38452
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Subject: "RE: New CLS Preflash Sequence Images" Previous topic | Next topic
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources. Charter MemberWed 18-Feb-09 04:29 PM
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#17. "RE: New CLS Preflash Sequence Images"
In response to In response to 16
Wed 18-Feb-09 09:07 PM by HBB

Phoenix, US
          

Colleagues:

As much as we would like to think that CLS does compensate for multiple, possibly overlapping remote groups, I am convinced it does not occur.

Consider: On-camera master contributing to the image capture illumination plus three remote groups, A, B and C.

1) CLS does not know how many speedlights are included in each remote group. The on-camera master is obviously just one.

2) CLS cannot know if all speedlights are illuminating the same subject or different subjects.

3) The system knows how many remote groups have been selected prior to shutter opening. That information is sitting there in the on-camera SB900/800 or SU800.

4) It is not clear if CLS know the type of remotes responding to preflash pulses. They could be SB900, SB800, SB600, SB-R200 units. I suspect the answer is no.

5) The exact content of the apparent multiple pulses by the master and each remote group remains a mystery. From the all-TTL image (top) I captured, it appears that the on-camera master emits three brief pulses and the remotes emit two. We know that the on-camera pulses must contain channel number, group code and exposure compensation value at a minimum.

6) With reflected light metering, CLS has no idea of the reflective nature of the one or possibly multiple subjects. Hence, it tries to make everything a neutral gray, group by group, based on what is reflected.

7) Trying to guess at overlapping illumination and subject reflectivity would likely lead to chaos. Given the above, I suspect that metering each remote group independently and leaving exposure compensation adjustments up to the photographer is a wise decision. After all, it is quite simple to do this.

8) Until I get my hands on a four-channel recording oscilloscope (not soon, given ongoing NAS priorities) this is as far as I can go.

9) I suspect the reason for delivering the exposure compensation settings prior to shutter opening is to avoid adding unacceptable delay during shutter open intervals, particularly at the max sync speeds (e.g., 1/250, 1/500). Assuming my rotational velocity is relatively constant and scaling the above images, the preflash sequence occupies approximately twice as much time as the shutter open interval of 1/30 sec, making it 1/15 second. Assuming that it takes one-half of this time to transmit the exposure compensation data to the remotes, this would be about 1/30 sec (0.033 sec = 33 milliseconds). When shooting at 1/250 sec (0.004 sec = 4 milliseconds) with on-camera master and three remote groups firing, there clearly is not enough time (4 milliseconds) to deliver 33 milliseconds of data.

10) While circuit times are very fast, they are not instantaneous. While the remote speedlights appear to be firing at relatively low power during the preflash sequence, they may need a bit of time to recycle in case they will be firing at full power during the shutter open, image capture interval.

11) I presented the above two images at 16 by 20 inches on easels at Winston Hall's Nikonian speedlight workshop here in the Phoenix area last weekend and we had a great time discussing them.

Thanks to all for your comments and discussion.

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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Pinned topicNew CLS Preflash Sequence Images [View all] , HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources. , Thu 15-Jan-09 08:25 PM
 
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dgillilan Silver Member
29th Jan 2009
1
Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
29th Jan 2009
2
     Reply message RE: New CLS Preflash Sequence Images
dgillilan Silver Member
30th Jan 2009
3
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bclaff Silver Member Awarded for multiple contributions for the Resources
03rd Feb 2009
4
Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
03rd Feb 2009
5
     Reply message RE: New CLS Preflash Sequence Images
bclaff Silver Member Awarded for multiple contributions for the Resources
04th Feb 2009
6
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nrothschild Neil is an expert in several areas, including camera support
04th Feb 2009
7
Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
04th Feb 2009
8
     Reply message RE: New CLS Preflash Sequence Images
jtzim
06th Feb 2009
9
          Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
06th Feb 2009
10
Reply message RE: New CLS Preflash Sequence Images
Arkayem Moderator Awarded for his high level skills in flash photography
15th Feb 2009
11
Reply message RE: New CLS Preflash Sequence Images
bclaff Silver Member Awarded for multiple contributions for the Resources
15th Feb 2009
12
     Reply message RE: New CLS Preflash Sequence Images
Arkayem Moderator Awarded for his high level skills in flash photography
15th Feb 2009
13
          Reply message RE: New CLS Preflash Sequence Images
bclaff Silver Member Awarded for multiple contributions for the Resources
15th Feb 2009
14
               Reply message RE: New CLS Preflash Sequence Images
Arkayem Moderator Awarded for his high level skills in flash photography
15th Feb 2009
15
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caprae
17th Feb 2009
16
Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
18th Feb 2009
17
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nightcat
18th Feb 2009
18
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Arkayem Moderator Awarded for his high level skills in flash photography
18th Feb 2009
19
     Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
18th Feb 2009
20
     Reply message RE: New CLS Preflash Sequence Images
bclaff Silver Member Awarded for multiple contributions for the Resources
18th Feb 2009
21
     Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
18th Feb 2009
22
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Lakeesh
10th Aug 2009
46
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
11th Aug 2009
47
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john barlow
24th Feb 2009
23
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bclaff Silver Member Awarded for multiple contributions for the Resources
24th Feb 2009
24
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john barlow
24th Feb 2009
25
Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
24th Feb 2009
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jrp Administrator JRP is one of the co-founders, has in-depth knowledge in various areas. Awarded for his contributions for the Resources
25th Feb 2009
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     Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
25th Feb 2009
29
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john barlow
25th Feb 2009
28
          Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
25th Feb 2009
30
               Reply message RE: New CLS Preflash Sequence Images
john barlow
25th Feb 2009
31
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
25th Feb 2009
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nl
26th Feb 2009
33
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
27th Feb 2009
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PAStime Silver Member
06th Mar 2009
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
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ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography
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Arkayem Moderator Awarded for his high level skills in flash photography
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ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography
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Arkayem Moderator Awarded for his high level skills in flash photography
09th Mar 2009
40
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ScottChapin Moderator Awarded for his high level skills in various areas, including Aviation and Birds Photography
09th Mar 2009
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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography
25th Mar 2009
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                         Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
25th Mar 2009
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                              Reply message RE: New CLS Preflash Sequence Images
km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography
25th Mar 2009
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                                   Reply message RE: New CLS Preflash Sequence Images
HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
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picmax
04th Nov 2009
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picmax
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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography
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picmax
11th Nov 2009
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
11th Nov 2009
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picmax
11th Nov 2009
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
11th Nov 2009
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Arkayem Moderator Awarded for his high level skills in flash photography
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picmax
15th Nov 2009
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Arkayem Moderator Awarded for his high level skills in flash photography
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picmax
16th Nov 2009
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16th Nov 2009
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16th Nov 2009
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
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16th Nov 2009
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
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Arkayem Moderator Awarded for his high level skills in flash photography
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HBB Moderator Hal is an expert in several areas, including CLS Awarded for his excellent article contributions to the Resources.
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17th Nov 2009
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28th Dec 2009
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15th Mar 2010
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16th Mar 2010
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01st May 2010
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