Sunday, September 13, 2009

Hasselblad 80mm f/8 Sharpness Comparison with Fuji Pro 160S Film

Medium format photography is a reasonable compromise when you want a very good image quality and sharpness with relatively low weight and efford (compared to view cameras). Therefore it makes sense to look at the sharpness of both, lens and film. I chose a high contrast subject – a tree lit by evening light against a bright background. The incident light meter gave me a reading of EV15. It was very windy and no tripod was used. But a 1/500 s shutter speed should compensate for this. Anyway, we want to look at images from real conditions in the field and not at test charts shot in a lab.
I shot it with a Hasselblad Zeiss 80mm Planar lens at f/8 and 1/500 s shutter speed set to a distance of approximately 40 m (the tree). Hyperfocal distance as given on the lens is 18 m at f/8 but this value is calculated for a huge circle of confusion. Do not believe depth of field scales, they only give you the acceptable sharpness for small enlargements!). The film was a Fuji Pro 160S with an ASA speed of 160. It gives natural colors, has a relatively low contrast and is thus ideally suited for portraits. According to the manufacturer's MTF graph, it should be about as sharp as Fuji Velvia 50. It has a response of 70% at 50 cycles/mm whereas Velvia 50 has only about 45%.

It was scanned with a Nikon Super Coolscan 9000 ED at 4000 dpi and 8 bit per color. The print would be 1.1 m times 1.1 m (43 feet wide) if you print it at 200 dpi. You would need a 75 megapixel camera in order to snap at least a comparable black and white image (for color, you would need approximately 3 to 4 times as many pixels).
The image on the left shows the center sharpness at 100%. The lens should be at peak sharpness here (in the center and at f/8, it might be even sharper when focused to closer distances). This corresponds to a 38 mm x 38 mm square at 200 dpi (1.5 inches). Note how the extremely fine details of the smallest branches are still resolved. At such high spatial frequencies, contrast on film is very low due to both, lens and film performance. With dark braches in front of a bright sky, at least subject contrast is large. Otherwise, no details would probably been resolved at this level.
No unsharp mask or any sharpening algorithm was applied. I think this would only enhance film grain and remove the nice analog look, which means that film and lens behave just the way as described above. Sharpness does not vanish suddenly at a certain frequency as it does with digital. It is a nice, smooth transition between parts with high and low sharpness. The image on the right shows another example at 100%, this time a little off-center (17 mm distance to the center of the negative). The background sky (and sea) is less bright here, but small individual branches are still easily seen. Overall sharpness does not look extremely good, but this is because no unsharp mask has been applied. We are used at looking at digital images at 100% magnification with an unsharp mask applied almost always. This effect partially compensates for the sudden drop in sharpness at the digital image's Nyquist frequency. As on the image above, a little noise is also visible, which originates from the film itself. 160 ASA film at 4000 dpi does not look as clean as images from a digital SLR at 100 or 200 ASA.
The last example is from the very top of the image (22 mm off the center), showing branches nicely lit by the evening low, orange evening sun. You almost see the transition between bright and dark on each individual branch.
Image sharpness of a scanned medium format film is much larger than anything from amateur digital cameras. But of course this sharpness is only visible in huge prints. But much more important than sharpness is color and the highlight capability. Look at the clouds -they are very bright but there are no washed-out highlights in this scan. I will look at the highlight capability in one of my next posts.

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