Lead'Air Inc. has announced innovative new aerial survey multi-focal lenses at the 2019 INTERGEO in Stuttgart, Germany.

October 09, 2019 -- The GSD, Ground Sample Distance (or resolution), is the key specification of any digital aerial photo mapping project. For a given camera and focal length, the GSD determines the altitude above ground AGL at which the aircraft must fly. Flying higher or lower changes the GSD and inherently produces images that do not meet the project's specifications. This limitation is now obsolete on all Lead'Air aerial cameras. Lead'Air is developing multi-focal lenses, which allows the planner to choose the mission altitude while preserving the required GSD. When circumstances (weather, ATC, etc.) require an altitude change, the survey aircraft crew can select a new altitude on the fly while maintaining the required GSD.

This system is based on commercially available variable focal lenses.  The lenses are entirely re-engineered in Lead'Air's optical lab and converted to photogrammetric lenses, which are configured with different predetermined focal lengths. A Lead'Air multi-focal lens can have up to 20 preset focal lengths; each setting corresponds to a given altitude and GSD and is calibrated to true photogrammetric standards. The lenses are motorized and precisely controlled by the FMS system. On his screen, the operator chooses at which altitude he intends to fly, and the software automatically amends the flight plan. The lens adjusts itself accurately to the correct focal length, and the focus is fine-tuned to ensure maximum sharpness. Manual input is not necessary.

Example. Your crew is attempting to fly a major city with an extensive air traffic control zone around its main airport. It is not unusual for a hard-working air traffic controller to transmit "unable to comply at 5,000 feet" and to decline the entry into his airspace. A survey aircraft equipped with Lead'Air multi-focal lenses can request another altitude which the delighted controller will be glad to authorize. Alternatively, the aircraft can climb above the controlled airspace and finish the mission instead of landing and waiting for another good weather day. Anyone who has flown aerial surveys in congested controlled airspace will appreciate the operational improvements such lenses will bring to the profession.

Lead'Air is currently manufacturing multi-focal lenses for the 50-megapixel small format digital cameras (Nikon, Canon, etc.) which are re-engineered by Lead'Air and used on the MIDAS oblique cameras. As well, we are assessing Multi-focal lenses for medium format cameras (Hasselblad, etc.). Upgrading older Lead'Air aerial camera systems with multi-focal lenses is possible.

Example; D850 Nikon with Lead'Air multi-focal lens 80mm to 400mm configured to capture 2-inch (5 cm) GSD with a vertical camera and oblique cameras at 45 degrees. The table shows the focal lengths corresponding to each altitude.

 

Alt. AGL feet

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

GSD

2-inch (5cm)

Vertical mm

80

104

130

156

182

208

234

260

282

Oblique mm

113

147

184

220

257

294

331

368

400

We are discovering other advantages of multi-focal lenses by the day, and there is no doubt that aerial surveyors will find many more beneficial applications.

For example, the above Nikon multi-focal lens would allow the operator to collect resolutions between 2 inch and ½ inch (5 cm – 1 cm) using the 400 mm focal length between 11,000 feet and 2,000 feet. The focusing will automatically adjust for the selected altitude, and the lens will have a calibration report for each possible altitude.

 

GSD

5 cm

4 cm

3 cm

2 cm

1 cm

Alt. AGL feet

10,680

8,548

6,410

4,270

2,140


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