Sometimes at my frog and reptile workshop we have a glass frog species. They are fascinating because you can see inside their body through their very thin skin. To show the translucency of this guy, I put it on a sheet of glass and held the flash beneath. I allow the environment to completely blow out, and I overexpose the frog to prevent it from becoming a silhouette. How much overexposure is determined by trial and error. All flash units have an exposure compensation feature that allows you to tweak the light output, and that's how you can vary the exposure. If you shoot on manual exposure mode, which I do for the whole workshop, you can also vary the lens aperture as well as the distance of the flash to the subject to adjust the exposure. My settings for this were 1/200, f/32 for complete depth of field on the tiny frog, 200 ISO, and I used a ring flash along with a 50mm macro lens.
4 Comments
Jan 9, 2017, 7:17:56 AM
Jim - Hi Bob, Sometimes you need a longer macro, like when shooting butterflies who don't allow a close approach. But with macro flash, the shorter lens -- 50m or 60mm -- is ideal. Natural light can be used as long as the subject is motionless so you can use a tripod and a small aperture for depth of field.
Jan 8, 2017, 7:58:52 AM
Bob Vestal - Thank you, JIm. Very helpful. I had not thought about the impact of focal length in relation to light source. Clearly, there are physical situations where you cannot get as close to the subject as you would want to when using the 50mm. However, I guess in those situations, unless there is sufficient natural light, it might be better to use a couple of small soft boxes. Then, a longer focal length like 100mm becomes a good choice.
Jan 6, 2017, 8:58:04 AM
Jim - Hi Bob, I prefer a 50mm macro because that forces the 'working distance' -- i.e. the distance between the camera and subject -- to be less. That means that the light from a ring flash envelopes the subject more, illuminating both the dorsal and ventral sides of the tiny frogs. As the working distance increases, and as the ring flash is further from the subjects, the light becomes more harsh because the ring flash approaches a point source of light.
As to what ring flash I recommend, the Canon MR 14EXII is the best, although there are several other options that are less expensive. You want a ring flash that provides enough light so you can use f/32 for each picture. At great magnification, you need as much DOF as you can get.
Jan 5, 2017, 11:06:27 PM
Bob Vestal - The creatures that you photograph in your workshop are so interesting. Cannot attend this year, but sometime I hope. A couple of questions: (1) My macro lens is a Canon 100 mm (also an EF-S 60 mm, which cannot be used with full frame camera). Would either or both of those lenses work for the this type of macro work? Your lens here is 50 mm. Is that your preferred focal length for macro? (2) What is your recommendation for a ring flash unit?