"Edouard" <pov### [at] edouardinfo> wrote:
> Your ball bearing is about 2.3 times bigger than mine, so it should be able to
> give much better images. How much did you pay for it? I'm don't know where to
> look for bigger ball bearings where I live...

I paid GBP17 + postage, about GBP21 in total. It was from a uk seller, which
helped (cos that's where I am!). The guy was also selling balls up to 100mm,
but those were 45 quid (not counting postage!).

> My one inch ball bearing occupies about 850 pixels square with my 8 megapixel
> camera (Canon IXUS 860). You should be getting 2000 square pixels or so?

That's about right, my camera's 7.2Mp and I can juuuust get it focused at full
zoom from about half a meter away, although I can't get it to focus full-frame.
I'm getting 1700 pixels square after cropping. Perhaps I'll try the focus
override - forgot about that.

> (the sun or point-like interior lights) brings out even the smallest
> imperfections in the polishing. I got my ball chrome plated, and that made a
> huge difference.

Yup, I'm seeing quite a bit of flare from the scuffs on mine - you can see it in
the attached image!

> One last point - my ball bearings (I got three) started rusting after a couple
> of months of use. I'm not sure exactly what your one is made of, but don't
> touch it with your fingers, and clean it with a lint free cloth whenever you
> use it or store it.

I think it's stainless steel, so I shouldn't have any problems. I've never had
stainless steel rust before except through wet contact over months. Where on
earth can I get it chrome-plated, and how much would that cost?! :)

> CHDK is an absolute marvel :-) I used the custom grid function to draw a circle
> and crosshairs that precisely matches the position of the ball on screen to aid
> in getting it at exactly the right distance. I also used the "override focus"
> setting to force the camera to focus on the minimum distance at maximum zoom.
> Getting the ball in perfect focus had been a real problem up until that.

Aye, I mean to use the grid eventually too. I have a 'manual' focus on my
Powershot, but it's a bit primitive. The override should help!

> I use HDR shop to convert the images from spherical mirror projection (i.e. the
> HDR photograph) into Latitude/Longitude format, then do the stitching in
> Photoshop. I think there is an HDR version of GIMP - Cinepaint? Everything is
> much simpler to do in square lat/long format, and POV can use the resulting
> images just fine.

Actually the blending is very straightforward in HDRShop, I can knock up a mask
in the GIMP in about 5 minutes. I don't have Photoshop, so I am limited in my
retouching facilities. I should see if Cinepaint works under wine...

> Having the two images taken at max zoom will help, as will making sure that they
> are taken from exactly the same elevation and that the camera is absolutely
> level.

I have been, but I get the impression that elevation is not a problem when I'm
using HDRShop's 3D rotation during unwrapping. Keeping a constant distance
would seem to be vital, however - I'd guess the difference in perspective will
affect the squashed reflections at the edges quite strongly.

> Looks pretty great already - I'm really jealous of the extra resolution you are
> able to get!

Thanks, I'll put up a page of probes somewhere when I've got a few more!

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