oh I understand now. Your way to proceed is to bracket a couple of stops below and above the "correct" exposure. In my opinion bracketing underexposed as a rule is not necesarry. Any underexposed shot (and -3 is VERY underexposed) doesn't provide additional clean information to the 0 and +3 shots.
My concept here is slightly different: take one shot making sure that you capture all highlights, but not underexposing at all, just make sure you don't blow information (a RGB splitted camera histogram is good enough to check this). This is the most important shot of all and after it you can forget about any additional underexposed shot.
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I've spent several hours over the past few days comparing Jonathan's 'split top layer blending method' with 2, 3 and 4 RAW images of the same scene loaded into HDR
The 'split top layer' method using just 2 images does not need an underexposed image. The bottom layer should just be an image correctly exposed for the highlights, which usually means when converting in ACR, approximately a minus 1 stop EC adjustment should be applied to 'recover' highlights.
My initial impression was that I was still getting a hint of the halo effect, but I now believe this was due to traces of silicon sealant around the edges of the window panes and/or inappropriate adjustments with Photoshop's Shadow/Highlight tool.
What I have noticed is that HDR in PSCS2 is not able to recover highlights well. If the lowest exposure is a full exposure to the right, the highlights will be slightly blown. In order to avoid this, I think it's necessary to include an underexposed image when using HDR.
Loading 16 bit TIF conversions into HDR seems to produce some pretty awful results.