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FORUMS General Gear Talk Flash and Studio Lighting
Thread started 19 Mar 2008 (Wednesday) 22:40
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Flash output consistency observations

 
Curtis ­ N
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Mar 19, 2008 22:40 |  #1

While testing the output consistency of various flash units for Robert to add to this thread, I decided to also test the consistency of several units using various automatic flash metering systems. I learned a few other things, too.

The first thing I realized was that none of the battery powered flash units were completely recycled when the ready light came on. In consecutive pops, waiting five seconds after the ready light resulted in as much as 4/10 of a stop more power in manual mode, with the greatest differences being at the higher power settings. This was true of every unit I tested, one each of four different brands. The moral of this story is that if you're picky about consistent flash output, you need to be patient and wait for it to recycle completely, especially if you're using full or half power.

My Alienbees B1600 did not exhibit this behavior. Firing it as soon as the ready light came on gave me just as much light as when I waited five more seconds.

The other conclusions I can draw are as follows:
1) Traditional auto mode is more consistent than E-TTL (or E-TTL II). This is not a general indictment of E-TTL, since there are many differences between these two metering systems and the difference in output consistency is not so great that it should preclude us from using E-TTL when conditions dictate.

2) The Canon 580EX II had more consistent output than the other two E-TTL compatible brands I tested. While the performance of the aftermarket brands was not so poor as to consider them junk, it is perhaps a reminder that we get what we pay for. As I conducted the tests, it was apparent that the pre-flash from the 580EX II was significantly more consistent than the others, and it stands to reason that an inconsistent pre-flash will yield inconsistent exposure with E-TTL.

I would caution everyone not to draw more conclusions from the data than I have already mentioned. While my knowledge of statistics is not sufficient to calculate a reasonable margin of error, the data was taken from relatively small samples (10 pops each unit), and measured with a meter that has an accuracy of +/- 0.1 EV and rounds each reading to 0.1 stops.

Testing protocol info:
The E-TTL readings were taken using a Canon 300D, and the E-TTL II readings were taken using a Canon 20D. My Promaster 7500DX is an older version, not compatible with E-TTL II. The camera was on a tripod, aimed at a grey streaked background about 6 feet away. The readings were taken with a Sekonic L-358 meter in cordless flash mode, taped to a stand just in front of the backdrop.

E-TTL and E-TTL II measurements were taken by using Flash Exposure Lock to separate the pre-flash from the exposure flash.

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Titus213
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Mar 20, 2008 00:18 |  #2

Thanks for this testing - very interesting. I assume by traditional auto you mean the 'auto-thyristor' mode? And I would have expected the difference between strobes and flash units in the way they dump to give the flash units an edge on quick recycle.


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oldfella
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Jun 14, 2009 06:31 as a reply to Titus213's post |  #3

Having made several gizmo`s, I can confirm that electronic control of flash is amazing. the first one I got from an electronics book that started me off on this line. It triggers a flash from sound and also light. Hope to post a shot of it shortly. the second one was to count the number of flash`s from the onboard flash then fire a main flash from the second flash.A Casio compact flash that I have fires three flash`s, so I had to redesign the original to fire the main flash on the third flash.




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Wilt
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Sep 11, 2009 00:26 |  #4

Curtis,
Robert and I did flash consistency measurement, where we looked at firing immediately after ready light, and also letting 5 sec. pass before firing. The Metz flashes which I tested were very consistent for both situations; Metz flash units were indeed fully recycled when the ready light came on.

http://photography-on-the.net ...php?p=5109312&postc​ount=1


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apersson850
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Sep 11, 2009 01:28 as a reply to Wilt's post |  #5

I think you are wrong in assuming that one flash is compatible with E-TTl but not E-TTL II. As far as the flash is concerned, there is no difference. The difference between E-TTL and E-TTL II is in the metering and evaluation of the light, and that's done entirely in the camera.

If that old flash doesn't work on newer cameras, it's most probably something else in the protocol it doesn't know about. That's always a risk with 3rd party accessories.

In real world use, when you not always use FEL, you also have to consider the fact that the evaluation of the pre-flash may differ from one occasion to another, in spite of the changes in the image being rather small.


Anders

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Wilt
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Sep 14, 2009 10:53 |  #6

Curtis N wrote in post #5151973external link
While testing the output consistency of various flash units for Robert to add to this thread, I decided to also test the consistency of several units using various automatic flash metering systems. I learned a few other things, too.

The first thing I realized was that none of the battery powered flash units were completely recycled when the ready light came on. In consecutive pops, waiting five seconds after the ready light resulted in as much as 4/10 of a stop more power in manual mode, with the greatest differences being at the higher power settings. This was true of every unit I tested, one each of four different brands. The moral of this story is that if you're picky about consistent flash output, you need to be patient and wait for it to recycle completely, especially if you're using full or half power.

From the Canon 580EX owner manual...

Check that the flash is ready.
~ The pilot lamp will first turn green (ready for
quick flash), then red (fully recycled or flash
ready).

~ To fire a test flash, press the pilot lamp.
About Quick Flash
Quick flash enables a flash to be fired before flash-ready, when the pilot lamp
is still green.
Although the Guide No. will be 1/6 to 1/2 that of the full output, quick flash is

effective for near subjects and when you want a shorter recycle time.
Set the drive mode to Single. Quick flash cannot be used in the continuous

shooting, FEB, manual flash, and stroboscopic flash modes.


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Curtis ­ N
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Sep 14, 2009 16:38 |  #7

Wilt wrote in post #8622993external link
Curtis,
Robert and I did flash consistency measurement, where we looked at firing immediately after ready light, and also letting 5 sec. pass before firing. The Metz flashes which I tested were very consistent for both situations; Metz flash units were indeed fully recycled when the ready light came on.

Thanks for that, Wilt.

For clarity, my testing of the 580EX II was done immediately after the ready light turned red, vs. 5 seconds after it turned red.


"If you're not having fun, your pictures will reflect that." - Joe McNally
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Flash Photography 101 | The EOS Flash Bible external link| Techniques for Better On-Camera Flashexternal link | How to Use Flash Outdoors| Excel-based DOF Calculatorexternal link

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kylefornia
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Dec 02, 2009 18:42 |  #8

I'd be interested to see how nikon flashes compare. oh wait is that a forbidden word around here. hope my account doesn't get deleted.


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Curtis ­ N
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Dec 02, 2009 19:13 |  #9

Get off your butt, do your own testing and post the results.

POTN members discuss other brands often. This won't jeapardize your account. Some have been banned for terminal stupidity, however.


"If you're not having fun, your pictures will reflect that." - Joe McNally
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AntonLargiader
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Dec 27, 2011 08:39 |  #10

Here's a page nicely showing the change in flash output depending on the state of charge, for the 430EZ:

http://www.chem.helsin​ki.fi ...sh-discharge/redwait.htmlexternal link


T2i . 18-55 IS . 70-300 IS USM . 70-200 2.8L IS . 28mm 1.8 . 100 Macro . 430EX II . TT1/TT5 . Bogen/Manfrotto 3021 w/3265 ball-mount

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