7 Working Distance

An important feature of any macro lens is the distance it allows between its front lens and the photographed subject at full magnification. This distance is known as the working distance. If it is too short, your lens may not only scare away your subject, but also cast a shadow on the scene.

The working distance of a lens d_work is determined by its minimum focus distance (MFD) between sensor and subject d_min, the flange focal distance of the camera between sensor and lens mount d_flange, and the length of the lens barrel between lens mount and front lens d_barrel as

dwork

=

dmin – dflange – dbarrel

(W1)

Note that if your lens extends for macro photography, you will have to use its maximum length here. If you are using a lens extension tube or a teleconverter, you will have to subtract its length as well.

For example, consider the AF macro lenses available in the Micro Four Thirds system (all figures rounded to full mm):

lens	MFD	flange focal distance	barrel length	working distance
	dmin	dflange	dbarrel	dwork
Olympus 30 mm f/3.5 Macro	95 mm	19 mm	60 mm	16 mm*
Olympus 30 mm f/3.5 Macro	100 mm	19 mm	60 mm	21 mm
Lumix 30 mm f/2.8 Macro	105 mm	19 mm	64 mm	22 mm
Leica 45 mm f/2.8 Macro	150 mm	19 mm	63 mm	68 mm
Olympus 60 mm f/2.8 Macro	190 mm	19 mm	82 mm	89 mm
OM System 90 mm f/3.5 Macro PRO	224 mm	19 mm	136 mm	69 mm**
OM System 90 mm f/3.5 Macro PRO	250 mm	19 mm	136 mm	95 mm

All at 1× magnification, except * at 1.25× magnification and ** at 2× magnification

 

7.1 Focal length and working distance

Obviously, a longer focal length allows for a (much) longer working distance. So does a longer focal length make a better macro lens?

If you are after dragonflies in the wild or want to take photos of coins with natural light, it is certainly a good idea to use a longer focal length. Note that a telephoto lens with a lens extension tube may also work well for non-moving subjects.

On the other hand, if you want to take photos of the underside of mushrooms in their natural habitat or other things in tight spaces, a shorter focal length may be the only chance to get the image. So as with other photographic subjects, it depends on what you want to do.

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