Technical Information

Getting high magnifications:

There are four ways to get more magnification than your prime lens allows:

1) Add a positive diopter close-up lens to the front of the prime lens.   This produces the equivalent of a shorter focal length lens, but the helicoid focusing mechanism still makes the lens the same distance from the film, so it can focus closer and greater magnification can be had. For a discussion of the Nikon positive accessory lenses, click here.

2) Using an adapter, attach a regular camera lens to the front of the prime lens, so the two lenses front elements are facing each other.  This is another way to accomplish the same result as in 1).  This technique can produce vignetting at the corners of the image, and is only useful when high magnifications are required.  The subject distances are so short that this approach is hardly ever useful underwater.

3) Add extension tubes or a bellows between the camera body and the prime lens.   If you use this technique underwater, you'll have to invent or purchase some mechanism to control the lens aperture, or you'll be stuck with a single aperture for each dive.  You'll have to compensate in your exposure for the extra extension, but you can calculate that by the magnification.  1:2 costs 1 stop, 1:1 costs 2 stops.   If you use TTL flash, the camera will compensate for the extension. For a discussion of the Nikon extension tubes, click here.

4) Add a negative diopter lens, such as a tele-converter, between the camera body and the prime lens. If you use this technique underwater, you'll have to invent or purchase some mechanism to control the lens aperture, or you'll be stuck with a single aperture for each dive.  A 2X tele-converter will double the magnification of the prime lens, without changing the subject distance.  You'll lose a stop with a 1.4X tele-converter, and two stops with a 2X.  If you use TTL flash, the camera will compensate for this.  The tele-converter is the only approach that will give you greater magnification without affecting the lens' ability to focus to infinity.    For a discussion of the Nikon tele-converters, click here.

3) and 4) can be combined.  1) or 2) can be combined with 3) and/or 4). 

For a discussion of sharpness, click here.

For a discussion of vignetting, click here.

The tables here apply to the first and second, and third situations.  Click on the links below for magnification and subject distance for the following lenses with various auxiliary lenses:

60 mm f/2.8 AF Micro-Nikkor

105 mm f/2.8 AF Micro-Nikkor

105 mm f/2.8 MF Micro-Nikkor

200 mm f/4D AF Micro-Nikkor

200 mm f/4 MF Micro-Nikkor

Click on the links below for magnification and subject distance for the following lenses, some common extension tubes with only the Nikon compound accessory lenses:

60 mm f/2.8 AF Micro-Nikkor

105 mm f/2.8 AF Micro-Nikkor

105 mm f/2.8 MF Micro-Nikkor

200 mm f/4D AF Micro-Nikkor

200 mm f/4 MF Micro-Nikkor

Click here to see magnification and subject distance for various ways to get to twice life-size with all five lenses, including the use of tele-extenders.

Everything reference above is pretty factual.  While some people would disagree with my emphasis, few would say that any of the above is wrong.  There's plenty of room for opinion in photography, though, and I have at least my share of opinions.   Click here for a personal discussion of the technical side of underwater macro photography:  the things I've tried, what worked best, what didn't work very well, what I'm working on now.

Notes

There are three groupings in the table:

1) The first set shows what focal lengths are achieved with the standard integer diopter correctors.

3) The second set shows what you get if you use inverted camera lenses of common focal lengths:  28mm,  35mm, and 50mm.

4) The third set shows the results of using some Nikon compound close-up lenses.

In each case, the magnification and subject distance are shown for each extreme of the helical focus.  The subject distance is measured to the front nodal point, which is close to the front of the lens glass, which is right behind the front of the mechanical assembly except in the case of the AF 105, in which case the glass is recessed about half an inch when the helicoid is at either extreme.  The addition of a single- or dual-element accessory lens will not change this much, but if you reverse a regular camera lens, the nodal point of the combination will probably be inside the reversed lens, and you will get less working room than indicated in the table.

All five lenses employ internal focusing to some extent (I think -- I'm not sure about the 60mm, but it looks to me like the focal length is 55 mm when it's focused as close as it will go), which means that the focal length of the lens varies with the focus. The inscribed focal length applies when the lens is focused on infinity -- when the lens is focused as close as it will go, the focal length is less.  Since Nikon doesn't supply this information, I calculated the actual focal length at close focus by measuring sum of the subject and object distances when the lenses are focused as close as they will go, and calculated the movement available in the helicoid from the resulting magnification.  The calculated numbers are included as notes.

The increased subject distance afforded by using the lenses underwater is not considered here.