Judging by the number of questions I get from photographers concerning the working distances of macro lenses I think it is a good subject to talk about.
The working distance of a macro lens, not to be confused with minimum focus distance, is the distance between the front of your lens and the subject. This is different from the minimum focus distance which instead means the distance to the subject as measured from the focal plane mark on the camera body, not from the front of the lens. Working distance is a more important figure since it tells how much space you have between the front of your lens and your subject. Working distance generally increases with longer focal length lenses, shorter lenses usually have shorter working distances.
Working distance can give you an idea of what kind of subjects you can work with without disturbing them. I prefer the 150-180mm range macro lenses when working with small creatures. While a short working distance is perfectly suitable for coins, stamps or other stationary objects, it can impossible to work with small live creatures. Lighting can be a challenge on a lens with a large diameter and short working distance due to lens barrel blockage. Longer lenses with more working distance can offer more room for lighting.
Working distance figures don’t always tell you all the information that you need to know since they usually do not include a lens hood in the measurement. The real working distance, that is from the front of the lens hood on to the subject, is just about impossible to find online.
So what does this actually mean for the photographer working in the field? The following images show actual working distances for three of my favorite and most often used Sigma lenses.
The Sigma 105mm F2.8, 150mm F2.8 and 180mm macro lenses were all set at Life-Size magnification and minimum focus distance. In each of the images the subject was positioned so that is was sharp at the center, but note there may be some slight subject movement in the images due to a slight breeze.
At the top the Sigma 105mm F2.8 EX DG OS HSM APO Macro working distance was 82mm or 3.23 in from the center of flower to the front of the lens hood.
In the center the Sigma 150mm F2.8 EX DG OS HSM APO Macro measured a working distance was 112mm or 4.41 in from the center of the flower to the front of the lens hood.
At the bottom the Sigma 180mm F2.8 EX DG OS HSM APO Macro measured in at a working distance was 127mm or 5 in from the center of the flower to the front of the lens hood.
These images should be useful to people in the market for a macro lens or for those thinking about upgrading to a new lens. It is interesting to see that the two longer lenses have a huge sensor to subject distance but a lot of that space is filled by a longer lens barrel and larger lens hood.
Working Without a Hood for More Working Distance
If you normally work with a lens hood but you would like to gain some extra working distance you can remove the hood to gain lots of extra working distance. Sigma macro lens hoods are very deep, the Sigma 150 mm lens hood is a full 3 inches deep. How much more distance do you actually gain in the field?
The Sigma 150mm F2.8 EX DG OS HSM APO Macro at 1:1 with the supplied hood in place gives you 112mm or 4.41 in from subject to the edge of the hood. With the hood removed the working distance jumps to 178mm or 7 in, a 37% gain!
Photographing without a hood on a Sigma 105mm F2.8 EX DG OS HSM Macro figures will give you a gain of 50mm or 1.9 inches or a 38% gain in working distance. The Sigma 180 gain would be 90mm or 3.54 in, a full 42%.
When comparing macro lenses, dont forget to consider the physical length and hood depth of a lens to get a real idea of the working distance that you would see in the field. Remember that removing a hood can is an easy way to get a big increase in working distance.
Working Distance and Sensor Format
One of the biggest sources of confusion and misinformation out there has to be on the subject of working distance and how it relates to sensor size.
For macro photography you should only be concerned with apparent magnification because filling the frame is much more important than a specific magnification ratio. For non-scientific imaging a smaller DX sensor will produce more apparent magnification than a full frame sensor since the object fills more of the frame at a given magnification. In other words an object that fills the frame on a full frame sensor body at 1:1 magnification, will have much more working distance and Depth of Field when filling the frame with the same subject on a DX sensor body since you won’t need as much magnification and will be photographing from a farther distance.
What kind of increase in working distance can you expect from changing the sensor format then repositioning the camera to reframe the subject at a similar size in the viewfinder?
Here I shot with the Sigma 180mm F2.8 at 1:1 in full frame format then switched to a DX sensor format and repositioned the camera results in a 46% gain in working distance. At 1:1 and full frame sensor mode the working distance was 128mm or 5 inches, then going to DX sensor mode measures out at 200mm or 7.87 inches with the same framing.
How Sensor Format Effects Image Depth of Field
Working distance is not the only gain you will see switching sensor formats trust me. There was a big gain in depth of field when switching formats and matching apparent magnification in the viewfinder, but I will have to share that information at another time. That will be the subject of my next Sigma Blog post: how sensor format effects image depth of field.
Note: The examples in the post are unscientific examples so I recommend not going out and buying a new lens based on these results alone, go to your nearest dealer for a test drive before buying any new product.
Robert O’Toole is a Sigma Pro and has been a professional photographer for more than 10 years. As an accomplished instructor, Robert leads wildlife, nature and macro photography workshop tours across the US and internationally. For more info visit Robert’s web site at robertotoolephotography.com