Why are macro lenses in many focal lengths?

My students ask me two questions when it comes to macro lenses. Why are there so many focal lengths to pick from? And, which lens do I buy?

Let’s start with the first, and the easiest question, remembering characteristics of a lens. Lenses affect angle of view, image size, perspective and in some applications, depth of field. You will remember, as the focal length gets longer, the image size increases and the angle of view decreases at any given distance. So, if you keep image size constant, you may do so from a greater distance with a longer focal length. So what does that give us?

Increased working distance!

Increased working distance is important for a variety of reasons. One, we can avoid making a shadow on our subject. We have more room for light, especially from flash. We may stay outside of the threat distance of our subject. And finally,  we can actually avoid getting bit or stung by dangerous or poisonous subjects.

The image below illustrates three Micro Nikkors: the 60 mm,  105 mm and the 200 mm. There are others from Nikon, Canon and many other manufacturers. But let’s just compare the specifications of these lenses just to get some perspective of capability.

Bracted gay feather, Liatris bracteata, Micro Nikkor 200 mm F 4.0 macro lens.

All three of these full frame (FX) lenses have the capability to focus from infinity down to 1:1 or life size on the sensor. So when reproducing a life-sized image, the 60 mm lens can do so at 8.6 inches (21.8 cm), the 105 mm lens at 12.0 inches (30.5 cm) and the 200 mm lens at 19.0 inches (48.3 cm). So in practice, an image at any given size may be made from a little over twice the distance away with each of the respective longer focal lengths.

With the longer focal lengths our angle of view is proportionately reduced as well, providing an opportunity to dissect the scene to produce a more narrow slice of life. And as a bonus, the longer focal lengths tend to be able to provide a more shallow depth of field, thus softer and more pleasing backgrounds.

So, which lens do you buy? That could depend upon price. The current price listed online from Nikon is $520 for the 60 mm; $985 for the 105 mm;  and $1795 for the 200 mm Micro Nikkor full frame (FX) macro lens. So, the rest of the answer depends upon whether you need the longer working distance, or if you need the wider angle of view. For many years my choice was the famous Micro Nikkor 55 mm F 3.5 macro lens. I used this exceptionally sharp, macro lens in my bag in place of a “normal” lens and could move in for real close-ups when needed. If I was doing an interview with an artist or chef for example, I could get pleasing environmental portraits and detailed close ups of their work with the same lens.

With tiny wild plant material, frogs, snakes, and scorpions the 200 mm macro lens is ideal. But sometimes, the 200 mm macro may be just too much lens. Remember, the angle of view is like a 300 mm lens on smaller, DX sensors. And its depth of field is very shallow.

If in doubt, try the mid-range lens: the AF-S VRII Micro-Nikkor 105mm f/2.8G IF-ED macro lens. It is one of the better lenses around and is a most useful tool.

© 2011 Brian Loflin. All rights reserved.

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