BetterPhoto Q&A
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Macro Accessories

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August 22, 2002

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August 22, 2002

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August 22, 2002

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August 22, 2002

Jeff has mentioned the downside of extension tubes, light loss occurs as extension is increased. However, the "diopter" auxiliary lenses also have a downside. The inexpensive single element ones have poor optics that introduce aberrations. Uncoated, they're also very susceptible to flare. The better ones with at least two elements to provide aberration correction and a single anti-reflective coating on all element surfaces to combat flare are as expensive as extension tubes, sometimes more.

Extension tubes have zero optics in them; they are hollow tubes that go between lens and body, and couple the lens/body linkages or connects between the two. By extending the lens away from the film plane, its focus range is shifted to a closer one. Because they do not introduce any additional optics, they do not introduce any additional aberrations or increase susceptibility to flare. They can increase the magnitude of aberrations that already exist in the lens. This is due to increased subject magnification, not the tubes, and would occur even with perfect diopter auxiliary lenses.

Having used both types, I greatly prefer extension tubes in spite of some light loss. The camera is on a tripod and a cable release is used for making macros if at all possible. Macros are highly susceptible to camera shake and focus accuracy problems if hand held. Shutter speeds longer than can be hand held are therefore not a concern to me.

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August 24, 2002

Also (last question!) does the use of the extension tube alter your TTL meter readings i.e. would I have to use a lightmeter?
cheers and thanks for your (anticipated!) help
eilen_j

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September 03, 2002

If you use the camera body's TTL metering, it will compensate automatically for the reduction in light that occurs at extreme close focusing. I occasionally work with studio lights and that requires using a "flash meter" as the camera has no control over the lights except to trigger them. It's similar to using a hand held meter with available light (no flash). In these cases an exposure compensation must be made based on either magnification or on total lens extension (the two are related). Kodak's Pocket Photoguide has a nifty wheel in it that can be used to find the exposure compensation using either magnification or total lens extension. With available light I've found it easiest to use the camera body's TTL metering (as with TTL controlled flash when it's possible to get the desired lighting that way).

Most zoom lenses use internal focusing and their physical length does not change as the lens is focused at some distance closer than infinity. Most prime lenses use a "helical" for focusing which moves the lens farther away from the film. Their physical length increases as the lens is focused from at distances closer than infinity.

Nikon makes three extension tubes, the 8mm PK-11A, 14mm PK-12, 27.5mm PK-13 and 52.5mm PN-11. The size given is their length, which tells you how far it moves the lens away from the camera body. These are all "AI" type rings with meter coupling and automatic operation of the lens aperture. You will have to manually focus the lens though. They were designed for the manual focus lenses (AI and AIS). Unlike a couple other camera systems though (most notably Canon), Nikon has kept compatibility of its lens mount between manual focus to auto-focus bodies and lenses. With macro work, manual focusing is nearly always a necessity. Depth of field is very shallow at close focusing and setting it where you want it can be critical.

Rings can be stacked and depending on the size and weight of the lens added onto the end. The limit would usually be the three shorter "PK" tubes: 11A+12+13 (49.5mm total). Don't know if the PN-11 can be stacked with the others (I don't believe it should be). Stacking too many together can create mechanical problems, especially if the lens is long or heavy.

A bit of history behind the rings and why these lengths were chosen:
The specific lengths of the three shorter "PK" tubes were chosen for compatibility with the 55mm f/2.8 Micro AIS manual focus lens, although they can be used with any lens from 20mm to 300mm. The longer PN-11 tube's length was similarly chosen to make it compatible with the older 105mm f/4 Macro for 1:1 magnification (lifesize on film). It was kept in the system as it allows the same with the newer AIS 105mm f/2.8 Macro. The "PN" tube includes a tripod mounting ring for better balance of lens, tube and camera body.

Setting up to shoot a macro with a zoom lens can be a bit trickier. You will have to adjust how much extension you are using, camera distance from subject, focal length of the zoom and lens focus. The longer the lens focal length, the more extension required for the same magnification (size of subject in the film frame). Using longer focal lengths is typically used to gain more "stand-off" distance from lens front to subject, not higher magnification. I typically work with 85mm and 135mm prime lenses in the field (outdoors) or when I must use flash indoors. Too short a lens requires it to be too close and the camera/lens can end up blocking light reaching the subject. Too long a lens requires too much tube length to get desired magnfication (I've used a 200mm with tubes, but not very often). Be patient with learning how to use them and work methodically. Shooting macros has a learning curve.

If you have more questions about macros or the Nikon rings, just ask.

-- John

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September 06, 2002

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September 06, 2002

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September 10, 2002