What ho

I've been trying to make some HDR light probes over the last few weeks. It's
tricky. :) The "stainless steel" balls I got from a garden centre were not up
to scratch... much deformation was apparent on the surfaces. They weren't even
stainless steel - plastic with a chrome coating probably, and even the
strongest permanent magnet I could lay hands on failed to grip the surface more
than fractionally.

So, I purchased a 60mm ball bearing from ebay instead, and this seems to work
very well. It has some slight scuff-marks which I can no doubt polish out in
time, but otherwise gives very sharp reflections.

My camera seems adequate to the task, although it would have been very difficult
without the CHDK upgrade to the Canon firmware (thanks to tgq for the link). I
have two tripods, which I have 'calibrated' for HDR-gathering (even drawing a
line round the neck of the larger one to mark the elevation!), and a great
little plastic tub-thingy which sits on the larger tripod and supports the ball
nicely.

However, I am having a few problems, particularly with image alignment. I'm
using HDRShop for the whole process, following the tutorial here:

http://gl.ict.usc.edu/HDRShop/tutorial/tutorial5.html

It works a treat, but often I find that the rotated image doesn't quite match
the other image after unwrapping. The points I select in the editor match
perfectly, naturally, but the images seem to diverge near the edges. I'm not
entirely sure why this is happening, but making sure the ball is centred in the
frame when taking the pictures seems to help considerably. Can any resident
HDR-makers shed any light on this?

In any case, here's my test scene so far, using the probe I made at the weekend.
I don't have a light-dome setup so I've cheated a little by using a single
light-source to account for the sun.

Bill

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