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photostation.md

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Photostation

Physical setup

Full-sized herbarium sheets

  • Camera stand high, its top aligned with bottom of ‘Herb sheet’ sticker
  • Horizontal boom at maximum extension
  • Place color strip in line with ruler
  • Position specimen snug against frame at the back, and snug with ruler on the right.

Cryptogam envelopes

  • Camera stand at lowest possible height (on bottom ‘stop’)
  • Horizontal boom at minimum extension (also on ‘stop’)
  • Place color strip on wooden frame, in middle
  • Position specimen:
    • Unfold envelope
    • Carefully remove specimen on card
    • Lay opened envelope against wooden frame, with label text on right side; adjust position so the barcode is in the exact middle
    • Place specimen on top of envelope, on left side; adjust so that it is close to middle but not obscuring barcode.

Lights

Switch on large LED lamps. Note that they seem to take a full minute to get to maximum brightness and whiteness.

Camera (Canon EOS 5D Mk IV)

Settings

  • Mode on main dial: M (for Manual exposure and aperture)
  • In Settings menu, set Autorotate to OFF
  • The following camera parameters are set by the script on the computer each time a photo is requested (using gphoto2): ISO (to 200), White Balance (AWB), Aperture (f8), Shutter speed (~1/10), Focus mode (Manual).

Set lens focus manually

  • Make sure the camera lens is set to MF (Manual focus), and the USB connection is unplugged
  • Stand on a chair or on the table (!) and look into the viewfinder
  • Manually adjust the focus ring to set clear focus on the specimen parts nearest the center of the viewfinder. Do not worry if the label is slightly out of focus.
  • Once the images are being taken in production you may need to adjust the focus with tiny nudges, using trial and error, to get the best possible focus.
  • If you encounter a very thick specimen, you may need to stand on the table again and readjust the gross focus.

Running the script

  • On the digitization Mac, find the ‘digitization’ folder on the Desktop and double-click ‘digitize’. It is a (Bash) shell-script program and will open a Terminal window and run in that.
  • Follow the instructions!

Tweaking the shutter speed

The only parameter in the script which may need tweaking is the camera’s shutter speed. In general we want the minimum possible aperture, to give maximum depth-of-field, so to adjust exposure we might tweak the shutter speed. Because the specimen and camera are unmoving and quite stable, we can use long shutter speeds (down to 1/2 second). If you need to try a longer shutter speed to get more brightness, edit the SHUTTER=... value on line ~16. Allowable values are in camera_options.txt file, near the bottom. Some possible values: 24 = 1/8, 26 = 1/13, 28 = 1/20, 32 = 1/50, 35 = 1/100.

Troubleshooting

You may find sometimes that the script returns some garbled message about not finding an image. The camera can get ‘locked’ by the script in certain situations and be unable to take an exposure. The surest way to get out of this ‘lock’ is to switch off the camera, unplug the camera USB, quit the script (Control-C), close the Terminal window, and start the process again.