A new digital camera back for 'live' subjects
by John Henshall
We see new digital cameras almost every week. Most are low resolution models, intended for consumer and business use -- and many of them have life spans of no more than six months.
In contrast, the professional digital cameras are fewer, have longer product lives and are often supplied as digital backs for well-established professional bodies and lenses, originally designed for use with film. They are produced in much smaller quantities and are therefore much more expensive to buy.
Because of the expense of area array sensors, many of which were originally intended for military use, some professional backs use less expensive linear arrays, which traverse the image plane like a very slow focal-plane shutter, capturing a narrow strip of the image at a time, making them unsuitable for capturing 'live' subjects.
There haven't been many developments in 'instant' capture professional cameras since Dicomed introduced the Big Shot in 1996. Even Kodak, the most prolific developer of digital cameras based on 35mm camera bodies, enjoys long lives for its products. The four year old DCS460 is only just being replaced by the DCS560 (in Canon body) and forthcoming DCS620 (in Nikon body).
It came as something of a surprise, therefore, when no fewer than five high resolution digital cameras were launched towards the end of 1998: the Leaf Volare, Dicomed LittleBigShot, MegaVision S3, Phase One LightPhase and the Sinarback with Sinarcam -- the first digital front and back both from the same company.
Even area arrays are not without their problems when it comes to capturing 'live' subjects in colour. The original Leaf DCB makes three sequential exposures through red, green and blue filters, so it is no better than a scan back for anything which lives and moves. Manufacturers get round this problem by 'striping' the CCD with a mosaic of tiny colour filters, positioned over each pixel. The three colour channels are computed from adjacent pixels as the images are sucked into the computer. This makes instantaneous exposures possible in full colour.
Unfortunately there is a trade off. The adjacent colour pixel interpolation produces colour aliasing, an objectional artifact where the software cannot work out the correct colour, especially in areas of high contrast. So it makes up some colours. The problem is, they can often be the wrong colours , which stick out like sore pixels.
The reason for the sudden spate of new backs in autumn 1998 was the new 24 x 36 mm FTF3020 chip from the Dutch electronics giant, Philips (pictured right). Previous cameras had used large chips made by Loral Fairchild (USA) or Thomson (France). Philips make their 'building block' modular CCDs by 'stitching' together multiple 12 x 12 mm one megapixel blocks. Six block make up a 24 x 36 mm six megapixel sensor. This size just happens to be the same size as a frame of 35mm film, so lens focal lengths are exactly the same as in 35mm photography.
"So we can put them into existing 35mm film camera bodies, right?" I can sense your excitement already. Unfortunately not, because of all the connections and other gubbins around the photo-sensitive area. Of course, someone could design a special body which takes 35mm lenses. That would be a very expensive proposition so, instead, the digital camera manufacturers use slightly larger (medium format) bodies, such as the Pentax 6 x 4.5 or Hasselblad, into which the sensors fit easily. Of course, this means you get smaller viewfinder images and have to think of lens focal lengths as though they were on 35mm bodies. But it's a small price to pay.
LIGHTHASE IN ACTION
Just after Photokina 1998, Allan Hansen hand-carried a pre-production LightPhase and Macintosh computer on a flight from Phase One's headquarters in Denmark for the first test of the new back in the UK.
Neither Phase One nor Philips will say whether the CCD inside the LightPhase camera is the new Philips chip. This is understandable as it would preclude Phase One using any other manufacturer's sensors in the LightPhase. But look carefully at the picture of a Philips sensor (above) and you will see the tell-tale tiles of the stitching. I've seen a Philips chip, the chip inside the Leaf Volare (who admit they use the Philips chip) and the LightPhase chip. Let me just say that they look remarkably similar -- although the Leaf Volare is (at the moment) triple exposure. The pictures from the Leaf Volare have a remarkable tonal depth and -- guess what -- so do the pictures from the LightPhase.
How should we test it? What subject should we choose? A nice still life of old bottles and cans perhaps? No way, not when you can photograph live subjects with the LightPhase. These would soon show up any harshness which the interpolation imposed and we needed full professional feedback on any operational drawbacks. So I 'phoned Keith Thompson.
Keith's models were a young Russian woman and her son. He shot them high- and low-key, with and without the boy, using the back with a standard Hasselblad body and lenses. It was just another shoot for Keith, except that he was able to look over to the monitor a couple of seconds after each exposure and decide whether he liked the framing and expression. Keith found this particularly useful: when he got the child's expression he wanted, that was it. Next set-up. No overshooting was necessary, as with film.
Keith's fastest shooting rate was a shot every one and a half seconds. The camera was connected to the computer by a long, thin FireWire (IEEE1394) cable down which both power and images travel. That was the only imposition -- and a very minor one -- on Keith's freedom to roam. The quite slow relative ISO speed of around 50 caused a bit of concern about depth of field, though. Production models of the LightPhase will be able to fit onto the Hasselblad in either landscape or portrait mode, removing the necessity for a right-angled viewfinder prism -- or the right-angled neck joint which Keith quickly developed.
The images were 'developed' later -- a process that takes around couple of minutes each depending on the speed of the processing computer -- each to a full 36MB 48-bit (16 bits per colour) RGB file via a 14-bit analogue to digital converter. This allows a subsequent further level of processing, akin to being able to fine-tune the exposure, when the images are converted to 18MB 24-bit (8 bits per colour) files. The undeveloped files are 12MB.
Leaf employ cooling in the Volare to improve noise and dynamic range. There is no cooling in the LightPhase because the back is not powered between shots and therefore does not need to dissipate the power as heat.
(Above) low-key portrait (below ) two sections of the same shot at one-to-one
The processed images are exquisite. There is no other word to describe them. The dynamic range -- said to be eleven stops -- produces deep and lustrous images of superior quality. There is no noise in the shadows and -- incredibly when you bear in mind that this is a 'striped' chip -- there is no evidence of any colour aliasing. This really is a remarkable and stunning product.
The absence of colour aliasing is due to the superb software interpolation, about which I was unable to tease out any information. The images do not appear soft, as with the Kodak DCS5xx range. Instead they seem, on close inspection, to have had a slight amount of unsharp masking applied. This makes them look slightly harder that images from the (three-shot) Leaf Volare.
A LightPhase back would be able to eliminate the use of film in a makeover studio, perhaps used in conjunction with a Kodak Pegasus LED 20P printer. The quality is so good that we also have to consider the possibility that the LightPhase signals the beginning of the end for three-shot cameras. Why not have the increased versatility of this good single shot for £15,000 ($22,900)? If Phase One adopt the new high-capacity MicroDrives from IBM, making LightPhase completely portable, its versatility will increase even more.
Mother and child
This article first appeared in "John Henshall's Chip Shop", February 1999.