Wednesday, September 30, 2009

Film Highlight Rendition

Sunset Velvia
For many people, color is more important than sharpness. Velvia might have a lower contrast range and exposure latitude than negative film and maybe even good digital cameras. But film's highlight capabilities are still unbeaten. Look at the sky, the clouds and the sun are naturally rendered. There is no color cast (hue) from bright to very bright areas and no blown-out highlights. If you click at the image above, you see the 4000dpi scan scaled down to 10%. It was shot with a 150mm f/4 lens focussed at 65 meters at f/16 and 1/4s (EV10) on Velvia 50 film. I pointed the light meter to the sky and added 2 stops, so the sky appears bright and the sea appears not too dark. This exposure was just right, I also made a shot at EV9 but it was slightly to bright.
I love the section underneath the sun where the sea looks like magma or lava:
Sunset crop shot with velvia
Digital cameras tend to clip highlights which results in strange color casts, usually making skin appear orange or yellow and this bright orange and yellow sky appear white and greenish. I have tried to simulate the digital image. The following image shows a 200% simulated digital image with a mouse over comparison to the 50% analog image.

The digital image is of course not as sharp but also has clipped highlights but is brighter in the shadows. The sun is completely white and has greenish surroundings. The image from the film appears to have lower contrast but looks much more natural.

Sunday, September 20, 2009

4000dpi Medium Format Scan vs. 2000dpi Scan

Today I would like to compare 4000dpi vs 2000dpi scans. Tree shots are perfectly suited for sharpness comparisons. The shot was made by my friend Philipp with a Zeiss 50mm lens on Fuji Velvia 50 probably at EV 14, which is f/11 at 1/125s. It was shot hand-held. Its a beautiful subject in beautiful light. And the slight underexposure and vignetting helps to keep the attraction centered to the main subject. In 100% view the image is sharp, but not extremely sharp. It is a typical medium format sharpness. The image above shows the original scan rotated by 0.4 degrees and scaled to 5 percent. It was rotated in order to keep the black frame lines straight.
I used the original, non-rotated file and an image downsampled to 2000dpi (also not rotated) for the first comparison. I compared the original version at 100% and the downsampled file at a 200 % view and it was impossible to see a difference. I also did not see any difference between the 400 percent and 200 percent view.
Then I brought rotating into play. I rotated the original file and I rotated the downsampled file by the same amount. Then I enlarged both versions to 200 and 400 percent respectively and was finally able to see a difference (mouse over for the 2000 dpi version):

It is mainly the film grain which makes the first image appear sharper. No real details are lost but anyway the 2000dpi looks less sharp. Please consider that this is not a 100 % view but a 200 % and 400 % view. It is hard to see anything at 100 % here. I recommend 2000dpi scans when file size is critical and the shot is not extremely sharp from the beginning. You will still get top-quality compared to an image from a digital camera or a scan from 135 film. You will still get a good quality after rotating or other transforming but the quality of a transformed 4000dpi scan is clearly better - at least when you plan to make huge prints of it.

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.

Monday, September 7, 2009


Welcome to my blog. In the following posts, I would like to share my experience with converting from digital photography to analog medium format (6x6, 120 film). I will try to answer questions like
  • why should you upgrade to 120 film?
  • what are the drawbacks?
  • what do you gain?
But mainly I will share results from scanning medium format photographs and I would like to encourage you to share your thoughts, too.
Ahrenshoop Velvia 50 EV9 IMG004I chose as a URL because this is easy to remember. I will not only cover Velvia film, but Velvia is of course very popular - for me and many other photographers.

The image above shows a 6x6 photo shot with Velvia 50 film. I shot it a couple of months ago at an EV of approx. 9 at f/16 and 1/2 s. I read the sky with a light meter and added two stops (which was a bit too much). Unfortunately, Flickr does not show its original resolution of 8525x8525 pixels. Thus, I show a 100% crop here (click to enlarge):

Not really impressive, is it? But this is film at f/16 and 4000 dpi. Moreover, the subject is backlit. But the highlights look good, altough the overall image is slightly overexposed. Please do not forget that this is only 0.71% of the original image area! For comparison, I rescaled the image to one third in order to simular a typical resolution of a 12 MP DSLR and sharpened it very slightly. The sensor of the simulated digital camera has about 4260 x 2840 pixels. Of those, only 2840 x 2840 pixels are usable with a square!). This in not really fair because a Bayer interpolating DSLR can resolve brightness with 12 million pixels but every pixel can see only either red, green, or blue. It needs four pixels to see the original color! A better way would be to rescale only luminance to 12 MP, but color to 3 or 4 MP. But anyway, we ignore that for now and give digital a little unfair advantage. What does it look like?
Well, this is difficult to compare ... It's much smaller ;-) Let's compare the cropped image with the crop of the blown
up image from a simulated digital camera. The digital image (mouse over) looks sharpened, more grainy and has much less detail and fewer real colors.

Conclusion: This is a very brief comparison but the difference is obvious.