Settings for the Canon EF 100mm f/2.8L IS USM Macro Lens (both macro and portrait)?

Question

I have a crop body camera (Canon T3i) and I'm renting the Canon EF 100mm f/2.8L IS USM Macro Lens for the weekend. I hope to use it for both macro shots and portraits. Can you recommend an aperture and shutter speed for both handheld use (when I'm leaning in to photograph a bug) and for portrait use with a tripod? I plan to shoot outdoors in daylight, though I'll be in the shade some of the time. It's supposed to be sunny out tomorrow. I'm planning on keeping ISO at 100 in the sunlight and 200 in the shade. Please advise if I should change that.

For my macro shots, I'm hoping to get a bug in focus on either the left or right side of the frame and have the remaining 1/2-2/3 of the frame filled with bokeh. The portraits will be of two adults and a child, taken outdoors with a timer on a tripod.

I searched online and read that hand-held use requires a shutter speed one to five times the focal length, so I'm guessing I need a shutter speed between 1/100 and 1/500 for the macro shots? I'd love to get opinions on this, especially factoring in that the lens has IS.

Answer 1

Once you get into the Macro range, a lot of the bets are off for more conventional rules of thumb. Because your subject is so close, the depth of field (DoF) is razor thin at wider apertures. Even when stopped down to f/8 or so there will still be plenty of bokeh in the background for anything that is any distance at all behind your subject. With the narrower aperture, of course, comes the need for slower shutter speeds. Image Stabilization (IS) will help to a degree, but the closer you are to your subject, the more blur the same amount of movement on the subject's part will create (because when your subject is several feet away, moving 1/8 of an inch is barely detectable, but when your subject is several inches away, moving 1/8 of an inch will move the subject a quarter of the way across your viewfinder).

If you want to do true Macro, then the lens must be set at the Minimum Focus Distance (MFD). This is the only position at which you will get a true 1:1 reproduction ratio. To bring your subject into focus you set the lens at MFD and then move the camera towards or away from the subject until the point of focus is where you want it. Typically this involves a tripod with a mount that is capable of sliding forward and back, such as the popular Arca-swiss type quick release plate. It is very difficult to do hand held macro work without an external flash to help compensate for the narrow aperture you need for large enough DoF as well as the light you and your camera may be blocking from the subject because you are so close to it.

As far as the portraits go, most of the conventional rules apply. Use a DoF calculator to determine the best aperture to get just enough DoF to keep each person inside limits of the DoF. At 15 feet, for instance, you have just under 1.5 feet of DoF with a 100mm lens at f/5.6 on your T3i. At 10 feet and f/2.8, you've got just under four inches (3.84") DoF.

Answer 2

There isn't a right or even recommended setting for shutter speed or aperture in this situation. Aperture should be determined specifically based on the amount of background blur you want. If you don't care about the background blur, you would want to set it somewhere in the middle to reach ideal sharpness (I'm not sure the ideal on that lens, though the exact ideal may very well vary from one version to another, so experimentation is best.)

As far as shutter speed, faster is generally better for handheld shooting, but it's probably not going to be super critical. As fast as possible while maintaining a low ISO and not so slow that you start noticing motion blur from camera shake. Again, this is a matter of experimentation and depends on both the light available and your personal level of skill.

For portraits, it's fairly common to look for background blur so shooting at f/2.8 is probably ideal, though if you are shooting more than one subject you may have to close it down a little to get satisfactory focus on everyone. Based on two adults and a child, if the child is in front, you may need something more like f/4 or f/5.6 to get a wide enough depth of field, but it will depend on how far away you are. I'd recommend either doing it by trial and error or using an online depth of field calculator to figure out what you need.

The big thing is remember that there isn't a right or wrong answer. Understand what each parameter controls (aperture - blur, shutter - stopping motion, ISO - noise) about the image and balance them to shoot to taste.

As far as the impact of IS, there should be a number of stops of IS power associated with the lens. If it is 4 stops of IS for example (such as the 70-200 f/2.8L IS II) then you could drop the shutter 4 stops slower than the rule of thumb would normally indicate.

Update: I confirmed from the manual for the lens that it also does 4 stops of IS. Canon suggests using the 1/100 rule (with the IS moving it up from 1/500.)