Macro Photography, Depth Of Field and Sensor Size

One of the guiding dynamics in macro photography as always is depth of field.  There are many factors influencing DoF, several of which have been discussed on this site in other articles.  The size of the sensor in your camera will also play a roll in depth of field, in an indirect way.

Cameras with a smaller sensor size have the effect of providing greater DoF.  The sensor itself does not have any greater depth of field, but the way it interacts with a lens and optical principles does provide the ability to increase it.  By smaller sensor size I am referring to cameras with an image sensor less than full frame.  Full frame is defined as a sensor with the same dimensions as 35mm film, 24x36mm.

Taken with a Canon 7D and 100mm Macro IS

Taken with a Canon 7D and 100mm Macro IS

With a full frame sensor you must either be closer to the subject at the same focal length to fill the frame to the same extent or use a longer focal length lens.  This interaction of lens and camera opens up some choices about gear selection to create or exaggerate the effects of DoF.  We can try to make it great, as is usually the case, or we can limit it even further as a creative tool.

When you get closer to a subject with a full frame sensor you limit the depth of field.  This is because as you get closer to the subject the DoF becomes more and more limited as an optical property.  When using a longer lens to get the same subject size you also narrow the depth of field because longer focal lengths reduce depth of field as one of their optical characteristics.

Taken with a Canon 7D and 100mm Macro IS

Taken with a Canon 7D and 100mm Macro IS

This characteristic of camera to lens behavior provides some choices when choosing what gear you are going to use to create an image as mentioned above.  With the Canon APS-C cameras you get a focal length magnification of 60 percent.  This means if you use a 7D with a 100mm lens you are getting 160mm effective focal length.  To get a similar focal length with the full frame 5D MKII you would have to use the 180mm macro lens.  The 180mm lens will have less depth of field than the 100mm.  Which setup better helps you create the image you are looking for?

Both full frame and cropped sensors have their place in the camera bag. I have used both extensively for macro shooting.  In macro getting more DoF is always a battle and we can use every little bit of help we can get.  To recap though the sensor itself does not provide you any great depth of field.  The cropped sensor does allow you get greater DoF because you can stay farther away from the subject and you can use a shorter focal length to get the same framing of a subject.

Taken with a Canon 7D and 100mm Macro IS

Taken with a Canon 7D and 100mm Macro IS

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