The weather held, and I got a second chance to capture an image of the fireflies flashing in my backyard. This time I set up two cameras, reduced the aperture (so a greater distance would be in focus), increased the ISO to increase the brightness (dealt with the increased noise in post processing), and set the focus distance to ~70 feet (locking the focus ring with gaffer tape). This time the composite images were better. I will try again tomorrow.
Fireflies in my backyard. Composite of 110 images taken with a Nikon D3s camera and 600 mm f/4 VR lens. I liked this image, and used the camera parameters to help my efforts to get better images tonight.