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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 08 Feb 2014 (Saturday) 18:11
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Canon 70-200 2.8 IS version 1 Question

 
Take1more
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Feb 08, 2014 18:11 |  #1

I just picked up a 70-200 2.8 IS today for $1200 but I can't figure out why my images are all coming out under exposed when I use a bounce flash. The only way I get a good exposure is direct glad but I hate that. If I switch bad to my 50mm 1.4 everything looks perfect with bounce or diffuser. What am I doing wrong? All my shots were at 1/100 ISO 100 and f2.8 100 with ETTL


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Gear: Canon 5D Mark III, Canon 70D, Canon T3i - 18-55mm, 55-250mm, 50mm f/1.4, 18-135mm, Canon 70-200L 2.8 IS 1, 2 Yongnuo YN-560 II Speedlite, Yongnuo YN-568EX II Speedlite

  
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sun5150
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Feb 08, 2014 18:16 |  #2

your flash might not be reaching the distance you zoomed at.




  
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Take1more
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Feb 08, 2014 18:18 |  #3

Interesting.. It that something the zoom on the flash can fix?


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Gear: Canon 5D Mark III, Canon 70D, Canon T3i - 18-55mm, 55-250mm, 50mm f/1.4, 18-135mm, Canon 70-200L 2.8 IS 1, 2 Yongnuo YN-560 II Speedlite, Yongnuo YN-568EX II Speedlite

  
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HuskyKMA
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Feb 08, 2014 20:08 |  #4

How far to your subject?


Canon 40D w/ BG-E2N Grip| 400mm f/5.6L | 70-200mm f/2.8L IS II | 28-135mm f/3.5-5.6 IS | 10-22mm f/3.5-4.5 | Gitzo GT3541LS w/ RRS BH-55

  
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EOS5DC
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Feb 08, 2014 21:52 |  #5
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This has nothing to do with the lens. My guess is that you are not using enough ISO. When I use bounce I set my ISO to: Aperture X 100.

Examples:
f/2.8 needs ISO 280, I set it to 320.
f/7.1 needs ISO 710, I set it to 800.
f/2 needs ISO 200, I set it to 200.
f/11 needs ISO 1100, I set it to 1250.

I also leave my FEC at +2/3 just about all the time.


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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raksphoto
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Feb 08, 2014 23:11 |  #6

The reach of the flash zoom head in most speedlites does not match the focal length range of the 70-200mm f/2.8L IS USM, esp. if your camera is not a full-frame camera. As a result, depending on your camera type, quite a lot of the 70-200mm lens focal range is necessarily under-lighted. In the ETTL system, the camera controls the quenching of the speedlite. If your zoom length is set outside what the flash head can deliver, the ETTL will encounter a signalling error, basically due to mismatched range in lens focal length vs. that of the flash. The speedlite under these conditions won't produce enough light for the scene.

A possible mitigation is to use the flash in manual mode, bypassing ETTL.


2x 7D Mark II | 70D | 5DSr
EF-S 10-18mm f/3.5-5.6 IS STM | EF-S 17-55mm f/2.8 IS USM |
EF-S 70-300mm f/4-5.6 IS II USM | EF 70-200mm f/4L |
EF 135mm f/2L | EF 100mm f/2 | EF 85mm f/1.8 | EF 50mm f/1.2L | EF 35mm f/1.4L EF 100mm f/2.8L IS USM MACRO

  
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EOS5DC
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Feb 08, 2014 23:25 |  #7
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raksphoto wrote in post #16675099 (external link)
The reach of the flash zoom head in most speedlites does not match the focal length range of the 70-200mm f/2.8L IS USM, esp. if your camera is not a full-frame camera. As a result, depending on your camera type, quite a lot of the 70-200mm lens focal range is necessarily under-lighted. In the ETTL system, the camera controls the quenching of the speedlite. If your zoom length is set outside what the flash head can deliver, the ETTL will encounter a signalling error, basically due to mismatched range in lens focal length vs. that of the flash. The speedlite under these conditions won't produce enough light for the scene.

A possible mitigation is to use the flash in manual mode, bypassing ETTL.

I agree with the conclusion of your first paragraph, if not the logic. It is not a 'signalling error'. It is the law of inverse squares at work. At longer distances you need either more light, or more sensitivity (ISO). A particular flash can only put out so much light. Your only other option is ISO. Use it. If it were a 'signalling error' my method outlined above would not work.

I can use my 100-400 at 400mm with a flash at 100 feet with high enough ISO, which pretty much kills your long-lens signalling error theory.

BTW, putting a flash in manual mode does not give it more power. Cranking up the ISO will give it more effective power.


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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Take1more
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Feb 08, 2014 23:39 |  #8

I really don't like to crank up the ISO because of the added noise but I guess I can use a shoot-through umbrella that's right next to the subject with a remote trigger on the camera. Thanks for all the input.


Take1more.com (external link)
Gear: Canon 5D Mark III, Canon 70D, Canon T3i - 18-55mm, 55-250mm, 50mm f/1.4, 18-135mm, Canon 70-200L 2.8 IS 1, 2 Yongnuo YN-560 II Speedlite, Yongnuo YN-568EX II Speedlite

  
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EOS5DC
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Feb 09, 2014 00:57 |  #9
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Take1more wrote in post #16675137 (external link)
I really don't like to crank up the ISO because of the added noise but I guess I can use a shoot-through umbrella that's right next to the subject with a remote trigger on the camera. Thanks for all the input.

You don't want to raise the ISO on a 70D above 100 because of noise? Please excuse my frankness, but that makes no sense at all. The 70D is quite capable of very good, low-noise photos at extreme ISO levels. I have only used a 70D at the sales counter, but it has to be better than the 60D. This is the 60D at: ISO=12,800, f/5.6, 1/15s. It isn't a photographic masterpiece, but it not inundated with noise, either.


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Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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raksphoto
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Feb 09, 2014 01:45 |  #10

EOS5DC wrote in post #16675122 (external link)
I agree with the conclusion of your first paragraph, if not the logic. It is not a 'signalling error'. It is the law of inverse squares at work. At longer distances you need either more light, or more sensitivity (ISO). A particular flash can only put out so much light. Your only other option is ISO. Use it. If it were a 'signalling error' my method outlined above would not work.

I can use my 100-400 at 400mm with a flash at 100 feet with high enough ISO, which pretty much kills your long-lens signalling error theory.

BTW, putting a flash in manual mode does not give it more power. Cranking up the ISO will give it more effective power.

Changing the ISO is a form of exposure compensation, and that can work. The reason it's needed is indeed inverse square-law, because the flash head cannot put out sufficient light. There is a signal error because with fully automatic ETTL, the pre-flash measurement cannot work when the lens focal length is longer than the flash head zoom -- they misalign. You can compensate with ISO, which as you suggested, effectively increases the usable EV, allowing exposure with the flash zoom at a hard limit. This is a form of gaming the ETTL system, and sure it can work.

The purpose of manual flash is to circumvent pre-quenching, given flash-head zoom vs. lens focal length mismatch. In other words, to defeat the ETTL system. This can work too, plus it can work more flexibly. You can manually choose the flash zoom angle to get the best far-end fill after (presumably) ceiling bounce, thus shaping the light. Then, you can manually choose the power level, to gain the EV needed. There are limits of course, and more ISO could still be needed, depending on the flash-to-subject distances. But taking ETTL offline enables the photographer to be in charge, to extend beyond the limits of automation.


2x 7D Mark II | 70D | 5DSr
EF-S 10-18mm f/3.5-5.6 IS STM | EF-S 17-55mm f/2.8 IS USM |
EF-S 70-300mm f/4-5.6 IS II USM | EF 70-200mm f/4L |
EF 135mm f/2L | EF 100mm f/2 | EF 85mm f/1.8 | EF 50mm f/1.2L | EF 35mm f/1.4L EF 100mm f/2.8L IS USM MACRO

  
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Take1more
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Feb 09, 2014 01:45 |  #11

EOS5DC wrote in post #16675211 (external link)
You don't want to raise the ISO on a 70D above 100 because of noise? Please excuse my frankness, but that makes no sense at all. The 70D is quite capable of very good, low-noise photos at extreme ISO levels. I have only used a 70D at the sales counter, but it has to be better than the 60D. This is the 60D at: ISO=12,800, f/5.6, 1/15s. It isn't a photographic masterpiece, but it not inundated with noise, either.

You're right it's just stubbornness on my part. I upgraded from a t3i whish wasn't as good but I never adjusted.


Take1more.com (external link)
Gear: Canon 5D Mark III, Canon 70D, Canon T3i - 18-55mm, 55-250mm, 50mm f/1.4, 18-135mm, Canon 70-200L 2.8 IS 1, 2 Yongnuo YN-560 II Speedlite, Yongnuo YN-568EX II Speedlite

  
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EOS5DC
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Feb 09, 2014 02:36 |  #12
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raksphoto wrote in post #16675280 (external link)
Changing the ISO is a form of exposure compensation, and that can work. The reason it's needed is indeed inverse square-law, because the flash head cannot put out sufficient light. There is a signal error because with fully automatic ETTL, the pre-flash measurement cannot work when the lens focal length is longer than the flash head zoom -- they misalign. You can compensate with ISO, which as you suggested, effectively increases the usable EV, allowing exposure with the flash zoom at a hard limit. This is a form of gaming the ETTL system, and sure it can work.

The purpose of manual flash is to circumvent pre-quenching, given flash-head zoom vs. lens focal length mismatch. In other words, to defeat the ETTL system. This can work too, plus it can work more flexibly. You can manually choose the flash zoom angle to get the best far-end fill after (presumably) ceiling bounce, thus shaping the light. Then, you can manually choose the power level, to gain the EV needed. There are limits of course, and more ISO could still be needed, depending on the flash-to-subject distances (and aperture). But taking ETTL offline enables the photographer to be in charge, to extend beyond the limits of automation.

You are effectively saying that ETTL artificially limits flash output, and that you can work around this by NOT using ETTL. Bunk. While it is true that manual flash affords the shooter more control over the situation, it in no way allows you to get more light on the scene than is possible with ETTL. Max output is max output, regardless of mode. Once the flash, in ETTL mode, is putting out a maximum burst, nothing you can do with the flash, or the camera can make it put out more. All you can do is make the camera more sensitive to light by raising the ISO. You state as much in the highlighted part of your quote, which I parenthetically fixed for you.


Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II

  
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Canon 70-200 2.8 IS version 1 Question
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