Auto-bracketing and aperture fixation (for HDR and/or HDR panos)
There was just a flurry or info about HDRI and the importance of NOT using auto-backeting because of the need to maintain exact DOF with a constant aperture in order to merge photos in doing the HDR exposure-varying sequence. That raised the question, what does the camera actually do? The point was raised that when in A Priority the aperture would remain fixed (supposedly). That is fine for a single dimension landscape when one CAN leave the camera in A mode. But in doing a 360 degree pano one is supposed to be in M Mode to maintain the same exposure through the 360 degree rotation to facilitate stitching and blending issues. What does the camera actually do in M mode??
And then it occured to me that there is also the issue, perhaps problem solving issue, of how the camera reacts to a NON-camera aperture controlled lens such as the Peleng which is Manual Aperture controlled.
So I tried both my cameras, a Kodak DCS SLR, and a Nikon D2X in auto-bracket mode. I was able to establish that in A mode both cameras indeed kept the aperture fixed and varied shutter speed only, at least within a range that did not abutt on a shutter speed limit.
Then I tried both cameras in M mode and found the same thing. At least in the sequence in which I did it, going from A mode to M mode, both cameras continued to vary shutter speed only. That held true for the +2, 0, -2 maximum 3 shot limit on the Kodak and the 5 shot maximum variation on the D2X.
So it would appear that, for these two cameras at least, auto-bracketing is a completely compatible system in M mode for HDR only or a 360 HDR panorama and one should NOT assume that auto-bracketing will change aperture and cause DOF problems.
I did not put the Peleng lens on either camera to test that issue. If the cameras auto-bracket at all with a manual aperture lens, it could ONLY be with shutter speed.
Anyone have a different take on this?
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|Jan 13, 2007|