AF-S Micro Nikkor 60mm F2.8G ED Arrival     Back to Notes on Photography
by Makoto Honda     April 7, 2008   


A new Nikon macro lens that I ordered from Adorama arrived today (4/1). The official name of this lens is a long alphabet soup: AF-S Micro Nikkor 60mm F2.8G ED. The AF means auto-focus, S means it has a silent motor in it for fast and quiet auto-focusing. The G designation is for the lens lacking a mechanical aperture ring. The ED means the lens contains a lens element made of “extra-low dispersion” glass. This lens has a 9-leaf diaphragm. Along with the “rounded” blades, the opening of the lens aperture maintains a fairly good circular shape for the first few stops. This macro lens also focuses to the magnification of 1:1 without needing any extension ring. The lens size, however, is huge compared with my good old Ai Micro Nikkor 55mm F2.8 lens.

I personally do not like a lens that does not have the traditional aperture ring, but many new lenses are designed as G lenses. I do not know why this lens has to be this huge. Also, why does it have to take a large 62mm filter size when the front element of the lens is much smaller. I have some extra 52mm filters but I have to buy 62mm filters for this lens. On my second thought I may consider using a step-down ring (62-->52), which should not compromise any light collecting capability of this lens.

Also, this is an FX lens, meaning its image circle covers the full 35mm format. So I can use this for D3 series cameras if I get one. Thus lens can be also used for 35mm film cameras, but unfortunately, I do not have any 35mm film Nikon cameras that support the CPU connection. For DX format cameras such as a Nikon D300, the adjusted focal length is 90mm.

I just tried only a few shots using my D300, but I have every reason to believe this is a very useful lens for me. The lens has an excellent MTF chart (provided by Nikon). That is the main reason I decided to get this lens.

Some Observations:

This lens has F2.8 - 32 apertures. In the Manual or Aperture-priority mode (using D300/D200), the aperture display on the camera LCD changes from F2.8 to F4.8 as I turn the focusing ring from infinity to the closest setting. Also, at the closest, I can set the aperture to F54. Initially I thought this lens is showing the "effective" F-aperture, because the closest focus for this lens is 1:1 magnification. But then, if I set the aperture to F5.6, for instance, the displayed aperture value never changes as I turn the focusing ring. Based on this, I erroneously concluded that this lens did not maintain the same F2.8 lens speed throughout its focusing range.

After exchanging emails with Nikonians, I learned that newer Nikon cameras do display (in their LCD display) the effective F aperture. Since I am a long-time Nikon F3 user, I did not know that. With a program controlled LCD, it is quite easy to display the exposure-factor-compensated effective aperture. I question the wisdom of doing so, however. (More on this later.)

This lens has a so-called internal focusing (IF). That is, the lens does not lengthen as you focus on a close-up subject. (The total lens length remains unchanged.) They tweak the positioning of lens elements to achieve focusing. In so doing, the focal length of the lens is changed also. That is, the 60mm focal length is not maintained throughout its focusing range. This is a bit of a "zoom" lens in effect. And, it does not keep the same F2.8 aperture, either.

Well, this is a trick all lens manufacturers play. They can alter two things: the focal length and aperture. Sometimes this is clearly stated in their lens spec, sometimes implied, and sometimes hidden.

As it turned out, in the case of an AF-S Micro Nikkor 60mm F2.8G ED lens, as you focus near 1:1 magnification, the focal length gets shorter (to around 50mm), and as a consequence, the lens gets brighter to around F2.4. (This relationship between the wide-open aperture and focal length does not have to be always inverse; some zoom lenses maintain the same aperture throughout their zoom range.) Since the 1:1 close-up imposes the exposure factor of 2 stops (see photomacrography), the camera's LCD display shows F4.8 when the lens is set wide-open.

In the case of AF-S DX VR Zoom Nikkor ED 18-200mm F3.5-5.6G (another lens I own), the lens epithet tells you that the lens aperture gets F5.6 towards the 200mm telephoto end. What they don’t tell you is that the focal length also changes as you focus. This is what I mean: Suppose I am using this lens at 200mm. I focus on a subject, say, 20 feet away. I expect my lens to be 200mm, because that’s how it is being set. Comparing with my fixed focal length Nikkor 180mm, I have noticed that the view angle of my 18-200mm (set at 200mm) is barely that of 180mm. (I felt a little bit cheated.) I can get the exact 200mm focal length only when the lens focus is very close to infinity.  

Coming back to the AF-S Micro Nikkor 60mm lens, I noticed the aperture transition chart in the user's manual. This chart tells us how the LCD display of the aperture changes according to the focus setting of the lens. The manual does state the LCD displays the effective aperture. Previously, I said I did not like this behavior. The reason is not so much the effective aperture display per se as it is their transparent behavior to alter the physical aperture setting.

Let me explain what I mean. If I set the lens at wide-open at infinity and then focus at 1:1, the LCD display changes from F2.8 to F4.8. This is the correct effective aperture. I do not like this, but I can live with it (for now). If I set the lens at F5.6 at infinity, and then focus at 1:1, the display remains F5.6. This behavior confused me and led me to the initial (but erroneous) conclusion stated at the beginning. This display of F5.6 is the effective aperture, not the F5.6 I had set. Did you get it? The camera changed my actual setting from F5.6 (2 stops down from wide-open) to around F3.5 (only half a stop down), without my knowing it. Many photomacrographers would not appreciate this. Nikon may argue that the aperture was opened accordingly to compensate for the exposure factor imposed so as to maintain the same shutter speed.....  Hold it! I am doing this test using my D300 in Manual or Aperture-priority mode, not Shutter-priority mode!

What we are talking about here is a complex subject, but we made it more confusing by mixing two issues together. So I will try to separate them.

1)  LCD aperture display - Nikon's LCD display is the effective aperture. This is a Nikon's design decision. This has a true value. If this was all Nikon is doing, I would not have any complain (maybe a little). This means, at 1:1 magnification, the display should show F4.8 if the lens is wide-open. This is indeed what I see. By the same token, if the lens is set at F5.6 at infinity, I should see F9.5 (give or take) on the display. However, what I see is F5.6. This leads to 2) below. Before I leave here, let me say that the effective aperture display is useful, but I am also interested in knowing the actual aperture, so that I can easily see how many stops it is from wide-open. Guessing that from the effective aperture display is difficult. An obvious solution is to show both (as an option). Actually, I am more interested in seeing the exposure factor (the number of stops), rather than the actual effective aperture value.

2)  Changing the aperture - In Shutter-priority and Program-mode, the lens aperture is changed automatically. So the concept of auto-adjusting the aperture is nothing new. But when your camera changes the lens aperture when you are focusing, you may feel uncomfortable. I do. This physical aperture change is effected by the macrophotography exposure factor. This is an intentional design on the part of Nikon. Some people may like it. I do see some benefit of this kind of behavior, but this should also be an option for the user. I will turn it off.

The current Nikon implementation combines 1) and 2) and transparently opens the lens aperture by 1.5 stops (at 1:1) until wide-open is reached.

I do not know if all the behaviors described above are controlled by the program resident on the camera, or some lens behavior is hard-coded in the lens itself. If the former, a change can be made in a future firmware updates.....