mark@xxxxxxxxxxxxxxxxxxxx:
Came up with an idea. Toyed with the idea of trying some pinhole
photography but something always seems to get in the way. Came up with
an idea to turn a regular film/digital camera into a pinhole using a
body cap. Should work on any 35mm digital ect that would accept that
kind of cap, and an extra cap in the bag weighs next to nothing and no
bulk or extra stuff to lug around.
Now I suspect the smaller the hole the better as far as sharpness, but
is there a group of sizes that I should try? How much of a difference
in hole size should I allow. Granted a body cap isn't going to alter
the GDP, but its not like getting another piece of cardboard either. Id
be interested to hear thoughts and ideas of those with pinhole
experience.
here's a chart I popped together
http://members.iinet.net.au/~shahjen/PINHOLE.gif
remembering light of differing wavelengths focusses at different points, I
have the wavelengths included.
and different sized holes make different relative appertures depending on
the 'focal length' - so the scale on the (left) vertical axis is distance
in mm between the pinhole and the sensor/film .. the 'focal length'
- the radiating lines from 0,0 indicate different hole sizes you might make
- so if you follow the focal length line out from the vertical axis to where
it intersects the hole size line then go down to the horizontal axis, you'll
fine the relative apperfure expressed as an F stop value (for the purposes
of setting exposure)
- and looking to see whether it's anywhere near the sweeping wavelength
lines will let you see whether your planned setup is anywhere near the
optimum sharpness .. the further you deviate, the less sharp the results
will be
Apparently some say green is the best wavelength to base pinholes about.
So for example if you were trying to use a 35mm film camera or 35mm style
digi, you'd be looking at a bodycap to sensor distance of around 25mm-ish,
looking at the chart you'd see you'd really need a small hole (mine only
goes to 0.1mm so I'll use that) and where that intersects you'll see the
aperture is around f250 - you'll also see the wavelength curve crosses
around there for IR - so at least you're in the ballpark for optimum
wavelengths ..
If you'd been using a 1mm hole you'd see the f nmber is around f25 - but
you're so far from the optimum, everythign will be horrendously fuzzy :/
Let's say though you'd decided on a long focal length and set up a 0.25mm
hole at the end of a tube and had an effective focal length of 200mm, you'd
see you have a relative aperture of f800, but you'd be bang on the green
wavelength curve - that would be the optimum and you'd see the sharpest
result =)
