Need for Speed
by Bjørn Rørslett 

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I possess a number of candidate lenses for shooting soft, shallow-focus images. Although the intuitive approach would be selecting long focal lengths, the largest apertures are more easily attained with lenses in the 50-85 mm range. An added advantage is that these shorter lenses lend themselves for hand-held photography. This in turn leads to more easy-going and enjoyable shooting for the photographer and eventually might unleash a creative power all of its own.

Need for Speed

Very Large Apertures

© Bjørn Rørslett/NN

A broad selection of the large aperture lenses applied in my high-speed, close-up photography. (More have been added after this picture was taken, amongst them the famous Repro-Nikkor 85 mm f/1 and a Rodenstock TV-Heligon 42 mm f/0.75. A Kowa 55 mm f/0.8 and a MATI 86 mm f/1.2 are the newest additions to my collection, plus several Rodenstcoks, such as 64 mm f/1.25, 95 mm f/1.4 and 100 mm f/1.5 lenses. All of these are carried in a metal case which now doubles as weightlifting dumbells ).

Depicted from left to right: Rodenstock XR-Heligon 75 mm f/1.1 and Noct-Nikkor 58 mm f/1.2, and in front row, Rodenstock TV-Heligon 50 mm f/0.75, Ultra-Micro-Nikkor 55 mm f/2, and Nikkor-O 55 mm f/1.2 CRT lens. The Noct-Nikkor lens needs an extension ring to bring it into the close-up range, and a matrix chip-equipped E2 ring is just the appropriate means to this end. The XR-Heligon has been updated with a matrix chip, too, and the TV-Heligon will be next on the upgrade path.

The selected lenses all have different maximum effective aperture and image magnification. I have compiled the relevant data for these lenses in the table below. Please note that for such close-up shooting conditions, there can be a great discrepancy between nominal and effective aperture. Remember f-numbers are specified for infinity focus. Moreover, due to the various optical designs, even greater variability is introduced. Thus, when the pupil magnification (p) is factored into the equation, some of the seeming blindingly fast lenses fade into the not-so-extreme category. However, any of these lenses still are much faster than a Micro-Nikkor set to an equal magnification.


Image magnification* m

Pupil magnification**

Effective aperture***

Field Curvature

55 mm f/2
0.39 ~ 1 2.8 Negligible (+)
75 mm f/1.1
0.5 ~ 0.4 2.5 Intermediate (+)
58 mm f/1.2
plus E2 ring
0.3 - 0.4 ~ 0.8 1.6 - 1.8 Intermediate (+)
Nikkor-O 55 mm
f/1.2 CRT lens
0.26 ~ 0.9 1.6 Strong (-)
50 mm f/0.75
0.62 ~ 0.4 2.0 Strong (+)
85 mm f/1
1.0 1.0 2.0 Zero

* m = ratio of recorded object size to actual size

** p = (exit pupil diameter)/(entrance pupil diameter)

*** Neff = N (1 + m/p)

The advertised large-aperture value of fast lenses is valid only for infinity focus and when they cover their designated image format. Step way outside these parameters and the effective aperture may be significantly reduced (as shown in the Table above).

Also note that many of these lenses lack a focusing mechanism so they act as fixed-focus lenses only. Since none of them are general-purpose lenses, I find this draw-back of less importance in practice. I simply have to think and plan ahead for my photographic assigments which in itself is a bonus.

Need for Speed

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Last Update 15 March, 2005