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05/15/2005 02:36:52 AM · #1 |
Anyone else got the combo above?
I've got a (minor) niggle...
The 580ex is meant to zoom to the correct length to cover the size of the sensor, one of the new features over the 550ex and all...
If I zoom out to 17mm with the 17-40 the flash says it's zoomed to 24mm, with the symbol up to say it's figured the sensor size out.. But I get bad vignetting.
Changing to manual zoom on the flash and setting it to 24mm gives far less vignetting, although still a little...
Looking at the front of the flash, the 'auto zoom' position is definately different to the manual position.
Can someone else with this combo give it a go, and see if this is common..
It's not a show stopper as I usually use a lumiquest pocket bounce anyway, but it'd be nice to know if I'm going mad or not...
Cheers, Me.
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05/15/2005 09:38:37 AM · #2 |
I don't have the shoemounted flash, but i was told to use the light spreader plastic thingy when using a 17 widelens. On top of the flash, there's a little white plastic card you can pull, which in turn flaps out a light spreading thingy, that's what i mean... by a light spreading thingy...*cough*. Its what will give you enought light for a 17mm opening.
Sorry can't help ya more.
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05/15/2005 12:35:35 PM · #3 |
| That's correct, you need to pull out the build-in Wide Panel (not the catchlight panel which is white). This will extend the flash coverage to 14mm wide-angle lenses. Refer to your 580EX maual on page 20 for more info. |
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05/15/2005 06:27:43 PM · #4 |
Thanks for the replies,
The coverage without the panel is 24mm.. the 17-40 @ 17mm is effectively a 27.2mm lens.. In my mind it should cover it. With the panel the coverage is good, but I don't think I should need it with the 1.6x crop, which the 580ex is meant to understand...
Hence the reason I wanted someone who has the combo to try it.
Cheers, Me.
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05/17/2005 04:46:59 AM · #5 |
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05/17/2005 04:54:43 AM · #6 |
Originally posted by KiwiChris:
Thanks for the replies,
The coverage without the panel is 24mm.. the 17-40 @ 17mm is effectively a 27.2mm lens.. In my mind it should cover it. With the panel the coverage is good, but I don't think I should need it with the 1.6x crop, which the 580ex is meant to understand...
Hence the reason I wanted someone who has the combo to try it.
Cheers, Me. |
the lens is still 17mm, the cropping only happens on the sensor. Plz do not mistaken effective focal lenght with crop factor.
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05/17/2005 06:17:31 AM · #7 |
Originally posted by zerocusa:
the lens is still 17mm, the cropping only happens on the sensor. Plz do not mistaken effective focal lenght with crop factor. |
Sorry?
Yes, the lens is 17mm, and the cropping is an effect of the size of the sensor, but the crop factor still effects flash coverage from the flash zooming, hence the crop factor zoom feature on the 580ex flash.
The flash 'knows' the sensor size and zooms the flash to match the sensor size+focal length. On the 1.3x and 1.6crop SLR's this means that you 'waste' less energy lighting up the area outside the frame in theory.
The FOV on my 20D at 17mm is the same as a 27.2mm lens on a Full frame or film SLR.
The 580ex can zoom to 24mm equivalent on a FF sensor or film SLR.
Therefore, the flash that can zoom to 24mm on a full frame camera should be able to cover the full frame for that lens at 17mm on my 20D which is equivalent FOV of a 27.2mm lens.
This feature works well with the kit lens (18-55). But with the 17-40 It appears to incorrectly identify that wide end, and not zoom all the way out, giving excessive vignetting at 17mm.
Using the manual zoom feature of the flash and setting it to 24mm significantly reduces the vignetting, to a similar level I get with the kit lens. This makes me believe that either the lens, camera, or flash is not quite doing the job correctly, probably the lens as it is the variable.
Hence my originial question about someone else being able to test the problem with the same combo.
Cheers, Me.
Message edited by author 2005-05-17 06:18:32.
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