jrsforums
11th of March 2007 (Sun), 19:57
In "How does ETTL-II work?" ( http://photography-on-the.net/forum/showthread.php?t=46311&highlight=ettlii ) the white paper makes a statement about ETTL-II evaluative flash metering, "...The metering areas having a small difference are selected as the flash exposure metering areas. (Areas with very big differences between ambient and pre-flash readings are excluded or down weighted because they are assumed to contain a highly reflective object or that the subject is not in that part of the frame. The algorithm avoids chronic underexposure problems in such situations.)..."
I find this to be true. However, it appears to only be true if the flash head is positioned in the "direct" (normal, straight ahead) position. I find that if I am using a diffuser, such as a Stofen, with the head angled up for bounce, any specular reflections will quench the flash and result in a severely underexposed image. If the head is moved back to the direct position, even with the stofen still in place, the quenching stops.
I do not see similar with ageraging flash metering. There is no quenching in any head position.
Do others see the same? Any thoghts why this happens?
My best thoughts were that it might have something to do with the lens focal distance info, which I believe is not used by the flash algorithm unless the head is pointed directly ahead. However, this is not consistent with the quote above.
Thanks....JOHN
I find this to be true. However, it appears to only be true if the flash head is positioned in the "direct" (normal, straight ahead) position. I find that if I am using a diffuser, such as a Stofen, with the head angled up for bounce, any specular reflections will quench the flash and result in a severely underexposed image. If the head is moved back to the direct position, even with the stofen still in place, the quenching stops.
I do not see similar with ageraging flash metering. There is no quenching in any head position.
Do others see the same? Any thoghts why this happens?
My best thoughts were that it might have something to do with the lens focal distance info, which I believe is not used by the flash algorithm unless the head is pointed directly ahead. However, this is not consistent with the quote above.
Thanks....JOHN