paul womack wrote:
> Following some recent developments in my photography set up, I offer
> these (this?) photo:
...
>
> http://galootcentral.com/components/cpgalbums/userpics/10152/saw_t-
> eeth.jpg
Since several people expressed an interest, here's the low down on how I
got those photos.
Executive summary: it wasn't point 'n' shoot; it involved lots of light,
close focus, HDR.
The long version...
The problem with saw teeth is that they're small, and made from shiny
metal. The size problem is easy to get round if your camera will focus
VERY close. Mine will (many compact digital cameras will).
It's a Canon A630,
http://www.dpreview.com/reviews/specs/Canon/canon_a630.asp and will
focus down to 1 cm (under 1/2 inch, Paddy).
It also has manual focus (that's a pain to use, but it has it).
The problem then becomes one of how do you get a camera so very close to
the subject; I have a Benbo Trecker tripod, where the main column can be
adjusted to be horizontal, and the camera facing down. I have often used
this to get "looking down" shots on flat items (books, saws etc).
http://groups.google.com/group/rec.photo.equipment.35mm/browse_thread/t-
hread/0a097027cee21607/b06c28ed3cd2cfc9#b06c28ed3cd2cfc9
http://tinyurl.com/3d9phs
But in this mode the only way to adjust the height is by adjusting all 3
legs on the tripod, which is tedious.
I adjourned to my workshop and made a tripod-extension-widget: http://g-
alootcentral.com/components/cpgalbums/userpics/10152/camera_extend.jpg
This simply has a standard mount thread (1/4" UNC) at one end (from Lee
Valley, thanks to ALF)
http://www.leevalley.com/wood/page.aspx?c=3&p=40361&cat=1,43455,52800
and a camera fixing bolt (same spec...) at the other. In the middle it's
a simple sliding slot, held by a 1/4" bolt and wingnut. This allowed the
camera's height to be fine adjusted easily. This extension ain't exactly
rigid, but it's fine indoors, where there's no wind, and I use a shutter
delay of 5 second to allow any movement generated by camera handling
(pressing the shutter) to die down.
http://galootcentral.com/components/cpgalbums/userpics/10152/saw_how_to-
p_close.jpg
The light is supplied by 4 angle poise lamps; using multiple light
sources reduce shadows.
http://galootcentral.com/components/cpgalbums/userpics/10152/saw_how_to-
p_long.jpg
Of course, if you simply take a photgraph under these circumstances, you
will encounter major issues with over/under exposure, since saw teeth
(especially freshly filed ones) are rather shiny.
The answer is HDR, which has been described elsewhere better than I
can do it:
http://en.wikipedia.org/wiki/High_dynamic_range_imaging
The task at the point of taking the photographs is to shoot a "bracketed
set"; a range of otherwise identical photos which vary only in shutter
speed. Some cameras have built in support for this, but mine doesn't.
However, with the CHDK third party software, it can be added.
http://chdk.wikia.com/wiki/Main_Page
I set the shutter speed bracketing value to 1 2/3 EV, http://chdk.wikia-
.com/wiki/CHDK_firmware_usage/AllBest#Tv_bracketing_value and used
"custom" drive mode, with 5 second delay, taking 5 photographs.
This gives me a massive overall EV range, the defining property of HDR.
I then downloaded the photos to my Linux laptop (Fedora FC8)
I used the "enfuse" program to merge them; since I only wanted the saw
teeth, I cropped that part of the image from each photo to avoid
unwanted pixels influencing the HDR merge operation.
http://wiki.panotools.org/Enfuse
Since the sawteeth image is pretty much monochrome, and I was simply
trying to get a "good" exposure I used the following enfuse options:
enfuse -o output.jpg --wExposure=1.0 --wSaturation=0.1 --wContrast=0.1
--compression followed by a list of input files.
To get the side show of the teeth, I used another, more usual, tripod, a
Gitzo Tatalux Reporter,
http://groups.google.com/group/rec.photo.digital/browse_thread/thread/c-
d1f23bf89e8735a/c8f512fb34edad03 http://tinyurl.com/2ml8gq
and again used my home-brew extension for final position of the camera:
http://galootcentral.com/components/cpgalbums/userpics/10152/saw_how_lo-
w_close.jpg
All other aspects "as before".
I hope this has been of at least some interest to at least some member
of the Porch. Since many of the choices I made were driven by equipment
or facilities I happen to have, I would not expect anyone to follow what
I did in all details, but I hope it offers guidance or inspiration as to
what is possible.
BugBear
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