Photography Tips

When I wrote about exposing for two light sources I explained how I had exposed the image for the sky and for the flash, but I didn't fully explain how I was using the ambient light or how easy it is to do. So I’m going to give you my Sunny 16 Rule for Macro, but first an explanation of what the Sunny 16 Rule is…

If you are shooting on a bright sunny day then you can set your Fstop to 16, and your shutter speed to the reciprocal of the ISO that you are using. So if you want to shoot at ISO 100 then your shutter speed is 1/100 of a second. Need to shoot at 1/200? Then set you ISO to 200. With those settings you’ll get pretty close to the ambient exposure on a bright sunny day –when shooting toward infinity…

You can easily shift the exposure around, you just have to make sure that you keep the ratio between Fstop, shutter speed, and ISO the same. Want to shoot at F11 instead of F16 and stay at ISO 200? No problem –you can increase your shutter speed by a stop to 1/400 of a second (it would have been 1/200 at F16) to eliminated the stop you gained by moving from F16 to F11. Or if you wanted to set your Fstop to 11 and your ISO to 100 then you could increase the shutter speed to 1/200 of a second. Piece of cake…

But what about shooting at life size –does the Sunny 16 Rule still work? It does, but you have to take into account the effective aperture you’re shooting at when the lens is focused at life size, which is two Fstops higher than what you have the camera set to. If you have your camera set to F16 then the effective aperture at life size is actually F32. You’ll have to make up that two stop loss and if you wanted to keep your shutter speed at 1/200 of a second you’ll have to set the ISO to 800…

But lately when shooting at life size I've been using F11 which is effectively F22. That’s only one Fstop higher than 16, and if I want to keep the shutter at 1/200 of a second then all I have to do is set the ISO to 400 and on the 40D that’s not a problem –and with good noise removal ISO 400 isn't an issue on most cameras (I use Noiseware Professional). So with the camera set to F11, 1/200 of a second, and ISO 400 I am pretty close to the ambient exposure for the background –but not the subject! Since the sun is the light source, and it’s so far away, the number of photons per square centimeter that are bouncing off of things in the scene and back into the camera is the same, no matter what the distance between them and the camera is. But distant objects will reflect more light into the camera than objects that are close simply because the surface area of distance objects is larger. Larger objects reflect more sunlight –a no brainer. So the farther away an object is the better the exposure for that object will be with the Sunny 16 Rule.

This is where the flash comes in. Since the ambient light is exposing the background it’s a simple matter of putting the flash into E-TTL mode and letting the camera determine the exposure for the foreground. The end result is a nice balance between the ambient sunlight and the flash. You have to diffuse the flash, and the better the diffusion is the smoother the transition between the flash light and the sunlight will be. It’s also best to under expose a little with the flash.

The image I've included with this post is an example of using the Sunny 16 Rule for Macro, and it’s the third time I've used it in a blog post. As soon as I have another example of this technique I’ll change the image ;)

A final note: At life size I could set the Fstop to 11 (effectively F22), the ISO to 200, and the shutter speed to 1/100 of a second to expose for the background. But when using the Sunny 16 Rule for Macro I’m shooting close the ambient exposure for the subject, how close depends on the angle of the sun –if it’s over my shoulder then there is a lot of sunlight hitting the subject and coming right back into the camera and I might not be able to freeze all motion with the flash. I still need to experiment with shifting the shutter speed instead of the ISO to see how much I can lower the shutter speed and still get a sharp subject. If you want to experiment on your own one way to do it, and to see the effectiveness of the ambient light, is to set up your camera and take a few shots without the flash turned on. If the subject is completely black in the frame then the flash will freeze the motion for you even if you’re using F11, ISO 100, and 1/50 of a second.

An example of using the Sunny 16 Rule for Macro. I was shooting this bee while the sun was behind some moderate cloud cover. The temperature was in the low teens Celsius (that’s low 50s Fahrenheit for those of you who are metrically impaired ;) and the bee’s metabolism dropped since it didn't have the sun to help keep it warm. Shooting at ISO 200 gave me this exposure:

Photo by: John Kimbler

Notice that there is some green in the background, but not much. It’s pretty much a flash only shot –not enough natural light to help expose anything in the scene. But then the sun came out, and I knew that I could change to ISO 400 and get the natural light to expose the background for me and that’s what I did for this next shot:

Photo by: John Kimbler

Identical scenes with the same camera settings for aperture (F11) and shutter (1/250) but with a higher ISO and more natural light in the second image –the background is completely illuminated by the sun and not the flash. I could have changed the Fstop to 8 and left the ISO at 200, but I didn't want to give up any depth of field.

Very easy to do and the final image doesn't look like a flash shot because the background is exposed…

John Kimbler is a network engineer who turned to photography as a hobby, his main interest is in the field of macro photography. Here's link to his website and blog.

The Sunny 16 Rule for Macro

Related Reading