The more macro I shoot, the more aware I am of the importance of aperture choices for depth-of-field effects when shooting on a tripod. The differences between shooting wide-open and at f/18 – f/22 for a subject can be remarkable. It is also very important to understand depth-of-field when you are making decisions about focus-stacking. For this reason when I am shooting I always carry a notebook with me with a dedicated D3S/200f4 depth-of field table for the focal distances marked on the lens, from 0.5 – 4 metres and from f/4 to f/22.
Here’s what I do when I’m shooting and am concerned to maximize, concentrate, or minimize depth of field, or choose an aperture for stacking. First of all, I decide upon my composition and set up the tripod and lens appropriately. Then I consider my subject, and make a calculation about how much depth of field I want – using the focusing rack helps here, because you can run though from your desired near to far focus wide-open and take a reading off the mm scale on the rack. I then read off the focal distance from the scale on the lens.
Then I check my depth of field table, and select an aperture which will either give me what I want in a single shot or in a stack of shots. The latter is useful if you have a lot of detail you want to convey and/or you have a near background that wouldn’t be blurred out enough at a smaller aperture.
If I’m making a stack, I’ll then just make a little note in the notebook about it: e.g. ‘Ophrys herae 13mm dof, stack of 4 f/11, 3.2mm-1.9mm rack scale’. Useful in case you, or the wind, cock it up and you have to try again, and for when it comes to processing the shot. Since I always shoot manual focus I don’t have to move the focusing ring once I’ve focused in, so at least that’s one less thing to worry about.
Below is a copy of the table I keep in my book. There are smartphone apps for this too which can come in handy. From the table you can see that depth of field is often very shallow indeed with this camera/lens combination, so it’s as much a decision about the background as it is the subject. I get full aperture control as well as exposure preview in Liveview with the D3S so this comes in very handy in making decisions.