Arrangement for design and manufacture of specialized equipment for bird flight photography. Results of the use of equipment and various types of film. Letters and requests from hobbyists about bird photography. Correspondence with C.H. Percy, president of Bell & Howell Co., about results using B&H cameras; Dr. William Guild about operations at Science Center in St. Petersburg, Florida, including the use of Greenewalt's photos. Also correspondence with E.W. Farber to obtain special strobe lights; W.D. Libby, Eastman Kodak, about special film development and evaluation of new films. Congratulations about newly published Hummingbirds and many requests for information and assistance; Eliot Porter, wildlife photographer in Santa Fe, New Mexico; Correspondence with various photographers regarding equipment choices, film preferences, etc. and suggestions for resolution of problems. Invitations to submit work for various photographic exhibitions; development of improved equipment. Shared experience with other experts and friends.

Greenewalt met Edgerton through meetings of the MIT Corporation, and they began an extended correspondence drawing from Edgerton’s work on high-speed photography to provide assistance and equipment that aided Greenewalt’s work on bird flight. Edgerton built specialized strobe lights for Greenewalt and assisted in analysis of problems.