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Lens Focal Length
The 18mm to 200 mm lens furnished with the Nikon D90 Kit covers a wide range of
photographic requirements, from wide angle to long-telephoto. Focal length settings less
than 50 mm are not useful when the camera is used in a Cessna 182 or Cessna 172
equipped with a photo window. Taking photos at focal length
settings from 18mm to approximately 40mm results in the picture
including parts of the aircraft (landing gear, wing). Customers do
not want parts of the aircraft in the photo. In addition, when parts
of the aircraft are in the photo field, the camera's automatic focus
and exposure devices may not work correctly; the landing gear
may be in focus but the scene below may not!
Focal length is set by rotating the focal length ring.
Focal length setting
Choosing the best camera Pointing Angle and lens Focal Length
Consult the following table to select shooting parameters. Data is given for an aircraft
altitude of 1200 feet AGL. The data can be scaled for other altitudes as the scaling is
linear. Example, to fly at 1800 feet AGL, multiply the number in the rows "Horizontal
Image dimension in direction of flight" and below by 1800/1200 = 1.5.
Base upon the customer's requirement for image size at ground level, go down the table
and find the closest fit. For example, if the customer wants each photo to be about 800
feet by 600 feet, choose the first data column; 812 feet horizontal and 847 feet
perpendicular to the direction of flight is a close fit. From that column, find the required
lens focal length (50 mm) and camera pointing angle (45 degrees). The bottom data entry
in the column indicates that the aircraft will need to be directed to a point 1200 feet from
the target. Resolution at the center of the photo will be 2.3 inches!
Important – the data in the table applies to the Nikon D90 camera. Most of the data also applies
to the Nikon D200 although resolution values will be reduced slightly. For other cameras, the
data may be way off as other cameras may have different image sensor dimensions.
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