Standard lenses, even those with a macro setting, require a minimum of 12” or more distance from the subject. True macro lenses are specifically designed to focus on very close subjects (even just a couple of inches away), but the trade off is a super shallow Depth of Field (DOF).
Even shooting at higher apertures, the actual DOF remains shallow relative to the background when shooting macro. Why is that?
Here’s something that might help illustrate how depth of field changes in relation to the distance of your subject. You’ll need a pen and one of those regular everyday flat rubber bands – the size that fits around your wrist.
Snip the rubber band with scissors so that it’s just one length of rubber rather than a loop. For demonstration purposes, lets just say the rubber band is now 8 inches long. Using a pen, make two marks on the rubber band. One at about 5 inches down the band, and the other at 7 inches (somewhere in that neighborhood anyway). Precision doesn’t matter here. (I got Bailey to help me out with this).
Imagine that the starting end of the rubber band represents the position of the front of your camera’s lens, and that the distance between the two points represents the focal plane for your lens. This is the “Depth of Field”. Increasing your aperture (to a higher number) increases the distance between the dots (conceptually speaking), increasing your depth of field. A setting of 22 pushes the dots apart, while 5.6 would move them closer together. [Depending on the lens, there are certainly limits as to how much you can increase or decrease your aperture.]
When your subject is close, the focal plane is pretty shallow with relation to the camera. Holding the rubber band at each end, stretch it (don’t snap yourself though!) and notice how the distance between the two marks increases proportionally to the distance from the starting end.
This simulates how the focal plane deepens when the distance between the lens and the subject is increased. So, both your aperture setting and the distance to your subject influence your lens’ depth of field.
When you’re on your belly in the yard shooting a ladybug on a blade of grass, the “rubber band” is only being stretched a tiny bit and the flower 2 feet in the background will be out of focus – never mind a distant treeline or mountain ridge, etc. When you’re much further back from your subject – perhaps and focused on VW Bug on the parkway – the “rubber band” is stretched out further, giving room for more things like the background to fall within your focal plane.
Not a fancy scientific explanation, but I hope it helps!