Friday, 23 November 2012

105mm f/2.5 AI-S: Another old skool Classic



The Nikkor 105mm f/2.5 coupled with a Nikon FM2, was reportedly the combination used to capture one of the most recognised portraits of recent times: Steve McCurry's "Afghan Girl". But how does this lens perform when not in McCurry's hands?


Continuing my digging of old 1980s film equipment, I came across the gem shown up top.

The lens has a long history, as noted in Nikon's inhouse "Thousand and One Nights" online magazine and also at the fantastic MIR site.

A general application for this lens and particularly the focal length is portraiture and across various internet forums, it is still held in high regard. From a gearhead perspective, what are it's basic characteristics?

The f/2.5 lens is nice, solid and compact with a built in retractable lens hood - the size however is deceptive given ultimate weight. The focus ring is wide with a long throw and being a Japanese made AI-S lens from the early 1980s, it's build is stunning. The lens is shortest at infinity focus and has a 52mm filter thread.

[updated at various times as I've had access to different/newer cameras - images below ranging from FX D750 and DX D7000/D300/D40]


Consider this mundane setting as the basis for examination - a Nikon RAW, converted to jpeg in CNX2 with standard sharpening. The focus target is about 1.5m/5ft away with the background extending another 4m to the window. Typical tight head/shoulders distance for FX. Images were shot with a full frame Nikon D750 on a tripod with the focusing via full magnification on liveview and captured with shutter release on selftimer.


D750 | f/2.5 | f/2.8 | f/4 | f/5.6 | f/8 | f/11

You may also get a feel for the colour rendition of the lens - the image above has been colour corrected with the WhiBal in the shot; in short the colours should be accurate. The scene was backlit with early winter sun and a slight mix of tungsten light from up above.

Sharpness

This is a series of 100% crops of the focus point, wide open f/2.5 and then stopped down to f/2.8, f/4 .. all the way to f/11.

D750

Wide open I've consistently found that the lens is a little soft although it could be my ability to focus. Even stopping down 1/3 of a stop to f/2.8 improves but only marginally. Going to f/4 and down yields significantly better results than the apertures around f/2.5. On the 24mpx D750 we can see the diffraction effects softening the images from f/8 onwards.


D40 | f/11 ISO400



Contrast is reasonable but I think the more modern lenses such the Nikkor 85mm f/1.4D are better in this regard.

A set of quick and dirty resolution/sharpness tripod'd, liveview focused images (DX D7100) all at 1.4m for reference:


D7000 | f/2.5 | f/2.8 | f/4 | f/5.6 | f/8 | f/11

Chromatic Aberrations

Purple fringing is common with most fast lenses, especially with older lenses.


D40 | f/2.5 ISO200 | 100% centre/focus crop

This image is backlit from overcast sky to exagerate high contrast areas.

D40 | top left (CA corrected) | bottom left (uncorrected) | top right (CA corrected) | bottom right (uncorrected)

As seen above, mild CAs can be reasonably well corrected in CNX2. However, extreme conditions are less successful as seen in the 100% center crop below.

Bokeh

I find the out of focus areas are pleasant overall, although I'm not so sure how I feel about the rendition of point light sources as they can seem a little jittery and especially when stopped down past f/2.8 but that may be due to the non-rounded aperture blades.


D300 | f/4 ISO200


D750 | f/2.5 ISO6400 | no vignette correction

We can also see that on FX there's also no real problem with vignetting - whilst it's there and visible I haven't found it overly objectional.


Focusing is assisted with the size and throw of the focus ring and of course it has a physical aperture ring which is invaluable for those who want dual use on digital and film bodies. I still however find it difficult to manually focus this with good results wide open, particularly with the higher resolution bodies (D7100,D750,D800 etc) - this is probably a problem for me, although seasoned/long time film SLR users tell me that the image will 'snap' into focus so I need more practise.


Overall the lens is very good, particular for the price that these can be found on auction sites when compared to the other portrait primes. However, it's maximum f/2.5 aperture does not make this a particularly fast prime so its not necessarily suitable for low light situations but neverless it's still a fun lens to use.

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