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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 20 Apr 2011 (Wednesday) 18:07
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Same settings, but requires different strobe output? (2 cameras)

 
funk1196
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Apr 20, 2011 18:07 |  #1

I'm thoroughly confused.

A friend and I were photographing water droplets the other day, and came across this baffling discovery.

My camera:
5D ii (full frame), 24-70mm @ 70mm.
f/8, 1/200, iso 200

Her camera:
Nikon D40 (1.5 crop sensor), 50mm @ 50mm.
f/8, 1/200, iso 200

Here's the odd thing.. we both used the same tripod, and used a strobe off-camera with pocket wizards, but when she shot (nikon), it required 1/4 output from my 580exii. To get the same exposure from my 5d, the 580 had to be set at 1/1 output.

What gives? Aren't all these light measurements supposed to be equal?
I also tried using a different lens (100mm macro f/2.8) on my 5dii and had the same issue.

I've also found that in the studio when i'm using power-packed strobes, i have to almost always work at the max power.


5D II, 16-35mm f/2.8L, 24-70mm f/2.8L, 70-200mm f/2.8L IS, 100mm f/2.8 macro.
T1i, 10-22mm, 17-55mm.
580EX II, 430EX II, ST-E2, EF 2X II

  
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thenextguy
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Apr 20, 2011 18:12 |  #2

I would think there's always going to be some error involved, but there shouldn't be that much error involved, I wouldn't think.

Try metering the exact same thing and see what readings you get with the two cameras.


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bohdank
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Apr 20, 2011 18:17 |  #3

Were you using extension tubes ?


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seattle1
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Apr 20, 2011 18:18 |  #4

Have you tried a slower shutter speed since 1/200 is the max on 5D II and the D40 can do 1/500.




  
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funk1196
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Apr 20, 2011 18:30 |  #5

@bohdank no extension tube. the 24-70 probably has 5 times as many elements, and is probably 3 times as long as her junky 50mm... could that be related?

@seattle how could shutter speed effect a strobe flash that fires so much faster than either of those shutter speeds?


5D II, 16-35mm f/2.8L, 24-70mm f/2.8L, 70-200mm f/2.8L IS, 100mm f/2.8 macro.
T1i, 10-22mm, 17-55mm.
580EX II, 430EX II, ST-E2, EF 2X II

  
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bohdank
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Apr 20, 2011 18:40 |  #6

Baffling.


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kenwood33
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Apr 20, 2011 18:44 |  #7

maybe your lcd screen brightness is at the lowest while her is the highest?


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mike_d
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Apr 20, 2011 18:47 |  #8

funk1196 wrote in post #12262405 (external link)
@bohdank no extension tube. the 24-70 probably has 5 times as many elements, and is probably 3 times as long as her junky 50mm... could that be related?

The difference between my 24-105 and 50/1.4 is maybe 1/3 stop. The 50 is definitely brighter for the same settings, but not that much. According to Canon's web site, the 24-70 has 16 elements, the 24-105 has 18, and the 50/1.4 has 7.




  
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seattle1
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Apr 20, 2011 20:08 |  #9

funk1196 wrote in post #12262405 (external link)
@seattle how could shutter speed effect a strobe flash that fires so much faster than either of those shutter speeds?

If your shutter closes during the flash you would get some dark areas or even a black band in the pictures when you get too close or over max sync speed. Having to use power pack strobes near full power seems strange as well.




  
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JeffreyG
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Apr 20, 2011 21:13 |  #10

funk1196 wrote in post #12262405 (external link)
the 24-70 probably has 5 times as many elements, and is probably 3 times as long as her junky 50mm... could that be related?

The difference noted is a full two stops. This is quite baffling and is certainly not attributable to light loss in lenses. I'm sorry to say but I cannot believe anything at this point aside from some kind of error in the reported outcome.

I once tested several lenses for actual light vs. reported aperture and I found a total span across a broad group of EF lenses of only 1/3 stop (this being +/- 1/6 stop from the average lens). So the issue reported is almost certainly not light loss within lenses.


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KenjiS
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Apr 20, 2011 21:28 as a reply to  @ JeffreyG's post |  #11

I could be wrong at this but if i remember correctly the "reported" sensativity on some cameras is lower than the "actual" sensitivity....this would affect exposure


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xarqi
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Apr 20, 2011 21:35 |  #12

I'd like to see the results of a series of experiments where both cameras, set at the same ISO, with lenses of the same speed, focussed on the same grey card from the same distance and angle, make exposures simultaneously in an otherwise dark room by manually firing the flash at different power levels while the shutters are held open using 'B' or a long exposure time.




  
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TheBurningCrown
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Apr 20, 2011 21:45 |  #13

Note that using the 100mm macro at full magnification WILL cause you to lose roughly two stops of light. But on the 24-70, I have no explanation for you.


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KenjiS
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Apr 20, 2011 21:52 |  #14

TheBurningCrown wrote in post #12263383 (external link)
Note that using the 100mm macro at full magnification WILL cause you to lose roughly two stops of light. But on the 24-70, I have no explanation for you.

I'd wager MOST lenses will lose a bit of light towards their MFD...


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xarqi
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Apr 21, 2011 00:00 |  #15

TheBurningCrown wrote in post #12263383 (external link)
Note that using the 100mm macro at full magnification WILL cause you to lose roughly two stops of light.

I find this claim incredible, it it means what I think it means.

Are you saying that if the 100/2.8 really is 100/2.8 when focussed at infinity, it becomes xxx/5.6 when refocussed to MFD?

My world view just doesn't encompass the notion of a viewfinder darkening by 75% just because I turned the focus ring of a lens from one extreme to the other.

Can someone enlighten me with some references please?




  
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Same settings, but requires different strobe output? (2 cameras)
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