"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> "Bill Pragnell" <bil### [at] hotmailcom> wrote:
> > As an aside, I have recently ordered some mirrored spheres from a garden centre
> > (of all places!) to do exactly what you described, or at least attempt it. I
> > suspect the actual photography will be the difficult part. My camera's not an
> > SLR, so I hope it's up to the task... oh well, good excuse to buy me a new toy
> > if it's not!
>
> Good luck and have fun!
> I have made a few in the past
> (http://barberofcivil.deviantart.com/gallery/#HDR-Light-Probes) using a regular
> digital camera (Canon S2, with 12X optical zoom though) and steel balls (those
> chinese stress balls ~2" diameter).  I used HDRSop and followed the tutorials
> to assemble them (http://gl.ict.usc.edu/HDRShop/tutorial/tutorial5.html).

Ahh! Shooting lightprobes - I've managed to spend some time on that too!

My setup is a chrome-plated pinball, a Canon IXUS 860 (aka the SD 870 in the
US), and a couple of super cheap table-top tripods (one for the camera, one for
the ball).

The pinball by itself was good, but even though it looked very well polished,
when you took close-ups of it, you could see all the almost microscopic
scratches on the surface. They were especially bad with bright lights (the sun,
light bulbs, etc). The first one started to rust after a while too.

Chrome-plating it got rid of the scratches, and finally gave it a true mirror
finish. It should also make it more or less rust-proof as well.

It's interesting to consider that while the perfectly reflective, perfectly
spherical ball is the stereotypical ray-traced object, getting one in real life
is much, much harder than you would think...

I also use CHDK firmware on my Canon, as it lets me automate taking 10 shots,
each one f-stop apart, as well as several other useful tricks, like locking the
focus to the minimum distance the camera will allow, and loading overlays on the
screen so I can exactly place the pinball at the correct distance from the
camera to match that focal distance. I only wish I had a camera that had a
better macro ratio at full zoom.

I use Photoshop to convert the 10 images into an HDR, then HDRShop to convert
that into a lat-long image. I shoot from two positions approx 90 degrees apart,
and combine the two lat-long HDRs into a single one in Photoshop again.

Lately I've started using LightMapGen to give me light dome data from the
images, and also shooting HDR backplates (normal shots of the environment) that
you can use to place in the background of a render. The light probes are almost
always to low res to look good behind objects in your scene, unless they are
very out of focus.

> A few pointers for you:
>
> - Make sure you use a good dynamic range.  Check your scene beforehand with your
> camera, decrease stops until the scene is mostly dark and light sources are as
> dim as possible, then increase until the scene is mostly saturated

I find that two stops over-exposed to seven stops under exposed (which is 10
exposures) captures most environments very well, even those with the sun in
them. I'd suggest at least three shots (2 fstops over, normal, two fstops
under), or four (+2, 0 -2, -4) as a minimum. The underexposed shots capture
lights more accurately, and make reflections look much more realistic.

> - make sure there is minimal movement of background objects (ie, cars driving,
> people walking, even fast moving clouds) as this can be quite evident and cause
> visual errors in assembling the HDR.

Clouds in particular move ore than you think they do...

> Most of all, have fun!  Try to pick scenes which will produce interesting
> reflection or lighting effects.  And by all means post them where I can get
> them, I'm always looking to expand my collection.

Also try to take images with different types of light in the same scene - a
otherwise boring office shot of mine turned out to be a favourite light probe
because it had florescent lighting from the office, and overcast daylight
coming through the windows.

> One further item of interest.  If you have a Canon camera, you may want to check
> out CHDK (http://chdk.wikia.com/wiki/Main_Page). I have it installed on my
> cameras and it installs easily and doesn't harm the camera at all.  It can give
> you a few advantages such as the scripting ability so you can setup your camera
> push a button once and wait, minimizing jitter (look in the user-made scripts
> section, I actually have a couple in there myself that are for HDR usage).
> Also it makes shutter speeds available beyond those avaiable in the standard
> camera (available shutter speeds from 64s to as fast as 1/32000 or possibly
> even faster, yes that is three zeros) it can make a point and shoot Canon
> camera far more powerful than any DSLR money can buy!

I agree - CHDK is an absolute marvel. Definitely check it out if you have a
Canon camera.

> -tgq

Cheers,
Edouard.

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