inward/outward
6th of March 2008 (Thu), 08:26
Picturecrazy put a very good experiment for us all to see here in the forum testing the 580EX II auto mode with that of an old Canon and the Nikon flash.
I have some questions about this test and possible reasons why the auto mode of teh 580 EX II resulted in underexposure...
Here is the link to the experiment I am referring to:
Canon auto mode experiment (http://photography-on-the.net/forum/showthread.php?t=431513&highlight=580EX+II+auto+off+camera)
In my opinion, the hot (bright) window is throwing off the auto mode sensor. I would need more info on your settings, ie. aperture and ISO and guide number read.
If I understand auto mode sensors on flashes, here is what I think is happening...
The Canon 580EX II has a larger guide number than the other two flashes (especially the older Canon flash, but is probably close to the Nikon's range) for a given zoom.
Perhaps this being the case results in the Canon having a longer effective range for its auto mode than the others for the same aperture and ISO settings. I fully understand for a given distance, if a flash is able to effectively light at that distance, the same ISO and aperture settings should result in the same exposure; however, my issue is with the effective range of the auto mode's sensor.
If this is the case, one would think that if the Canon auto sensor reaches further in evaluating the light level of the scene, then it is possibly reaching the window and compensating downward; where the other flashes are not reaching that far with their auto mode sensor. If they are not reaching that far, they will evaluate the scene as darker and expose for the subject better (at least in Picturecrazy's situation).
My suggestion is to understand first what the ISO and aperture inputs where and the distance between the flash and subject and the flash and the window.
If the Canon has a longer effective range for the auto mode than the other flashes and its sensor can reach further, then wouldn't it make sense we would have to move the Canon back further from the subject (in Picturecrazy's scenario) to keep Canon's effective auto mode range from reaching the window?
If you can tell me that the effective distance (guide no read from the back of the flash for the given ISO and aperture input for Picturecrazy's scenario) for the auto sensor indicated it was shorter than the distance to the window, but would reach the subject; AND it still under exposed, now that is a problem. BUT; however, if you the flash indicated its effective range would reach the window, then underexposure is perfectly understood and moving the flash back, or reducing the aperture input into the flash's auto mode settings would be required.
If this has already been vetted, please ignore, but I read through the post and wasn't satisfied this had been addressed exactly.
Picturecrazy, can you provide the information, please? The reason I am so interested is because I was thinking of auto mode being a viable off camera alternative to manual mode.
Thanks,
IO
I have some questions about this test and possible reasons why the auto mode of teh 580 EX II resulted in underexposure...
Here is the link to the experiment I am referring to:
Canon auto mode experiment (http://photography-on-the.net/forum/showthread.php?t=431513&highlight=580EX+II+auto+off+camera)
In my opinion, the hot (bright) window is throwing off the auto mode sensor. I would need more info on your settings, ie. aperture and ISO and guide number read.
If I understand auto mode sensors on flashes, here is what I think is happening...
The Canon 580EX II has a larger guide number than the other two flashes (especially the older Canon flash, but is probably close to the Nikon's range) for a given zoom.
Perhaps this being the case results in the Canon having a longer effective range for its auto mode than the others for the same aperture and ISO settings. I fully understand for a given distance, if a flash is able to effectively light at that distance, the same ISO and aperture settings should result in the same exposure; however, my issue is with the effective range of the auto mode's sensor.
If this is the case, one would think that if the Canon auto sensor reaches further in evaluating the light level of the scene, then it is possibly reaching the window and compensating downward; where the other flashes are not reaching that far with their auto mode sensor. If they are not reaching that far, they will evaluate the scene as darker and expose for the subject better (at least in Picturecrazy's situation).
My suggestion is to understand first what the ISO and aperture inputs where and the distance between the flash and subject and the flash and the window.
If the Canon has a longer effective range for the auto mode than the other flashes and its sensor can reach further, then wouldn't it make sense we would have to move the Canon back further from the subject (in Picturecrazy's scenario) to keep Canon's effective auto mode range from reaching the window?
If you can tell me that the effective distance (guide no read from the back of the flash for the given ISO and aperture input for Picturecrazy's scenario) for the auto sensor indicated it was shorter than the distance to the window, but would reach the subject; AND it still under exposed, now that is a problem. BUT; however, if you the flash indicated its effective range would reach the window, then underexposure is perfectly understood and moving the flash back, or reducing the aperture input into the flash's auto mode settings would be required.
If this has already been vetted, please ignore, but I read through the post and wasn't satisfied this had been addressed exactly.
Picturecrazy, can you provide the information, please? The reason I am so interested is because I was thinking of auto mode being a viable off camera alternative to manual mode.
Thanks,
IO