Fisheye Photography for Fulldome Production
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From Digital Photo to Dome Master (top of page)
The specific numbers will vary depending on the pixel resolution of your camera and the coverage provided by the fisheye lens you are using, but invariably you will need to crop the image and then enlarge it to the resolution of the domemaster image format. See: http://webspace.ringling.edu/~lfjones/fulldome/domemaster/domemaster.html
Using the 10.1 Mpixel Canon XTi and Sigma 4.5mm Circular Fisheye as an example:
- The frame size is 3888 by 2592 pixels.
- The usable circular fisheye image area is approximately 2200 pixels diameter.
- So we crop the image to a 2200 by 2200 square, around the circular image, and then scale it up to about 185% of its original size to 4096 by 4096 - a standard domemaster dimension.
- Remember that the final projection at Bishop Planetarium is approximately 50 feet in diameter.
Focus (top of page)
- Because off the need to scale the image up, and the large viewing size, focus is critical.
- It is almost impossible to reliably visually focus a fisheye image in the viewfinder - everything is simply too reduced. We recommend using a notebook computer to examine test shots in the field, making tiny adjustments until you achieve the best focus.*
- Use as long an exposure as you can get away with (this depends of course on what you are shooting and the shooting conditions) and stop the aperture down as far as possible in order to increase the depth-of-field to as deep as possible. This may be particularly useful if you are shooting time-lapse because of the built-in delay between exposures.
*The Sigma fisheye has three marks on the focus ring: 0.135 meters, 0.2 meters and Infinity! Keep in mind also that Infinite focus and Infinity as marked on the lens barrel rarely coincide and can vary depending on the shooting conditions.
Exposure (top of page)
- Because of the 180 degree field-of-view, exposure with a fisheye is tricky. Shooting open-sky outdoors you get the brightest part of the sky (not to mention the sun) and the darkest foliage and shadows.
- We often shoot with a 2 or 3-stop neutral density gel (or polyester) filter inserted in the filter clip behind the lens. This works okay but I suspect that there is some degradation of the image and bright lights (including the sun) tend to streak in a straight line along the grain of the filter.
- Shooting in RAW format for the brightest area and pulling up the shadows after-wards is probably the best method.
- Keep in mind also that what looks like a perfect exposure on your computer screen will tend to be somewhat dim and lower in contrast and saturation when projected in the planetarium. It is almost always necessary to brighten, enhance contrast, and increase the saturation in post-production for the dome.
Tethered Camera Control Software (top of page)
- This is the idea of using a computer, tethered to the camera via a USB cable, to control the camera, and automatically download the images to the computer's hard-drive.
- If you are shooting with a Nikon DSLR, there is a page on ThePhotoGeek (article dated May 15, 2009) about Choosing Tethered Shooting Software for Nikon DSLR Cameras that you might find useful.
- If you are shooting with a Canon DSLR, a suite of camera control software is bundled with the camera at no additional cost.
- When we shot the opening and closing time-lapse sequences for our piece "Appalachian Trails" we used an Apple notebook running Canon's RemoteCapture software to take the expose at regular intervals (30 seconds) and the frames were automatically downloaded to the notebook, and displayed, as we shot.
Camera Orientation (top of page)
Finally, consider the orientation of the dome:
- The dome is above you and it is tilted at a 15 degree angle so that the front is lower than the rear.
- This will affect (or not) the way you shoot depending on what you are shooting and the effect you are trying to achieve.
Imagine that you are time-lapsing a landscape:
- If you wanted to get a horizon-to-horizon landscape and if there was no tilt to the dome you would point the camera straight up on a low tripod.
- To compensate for the tilt of the dome you could tilt the camera 15 degrees forward from straight up.
In the circular fisheye images this will cause the horizon to be visible only in the lower half of the image area and it will appear curved with the low point in the center of the visible part of the horizon (see the image at the top of this page.) When this is projected in the dome the horizon will flatten and be visible in front of the audience.