Monday, January 25, 2010

SIGMA DP1 – Impressions

After receiving my DP1 on Friday, these are my impressions of the camera.

Unboxing – In person, the DP1 has a very clean, neat, subdued and understated appearance, without going as far as being minimalistic to the point that it becomes inconvenient to use. I was pleased to find that the body was metal and not plastic. The camera has a certain heftiness to it but manages to still be comfortable to carry around. Unfortunately due to the size of the lens, it’s quite a tight fit to get into a pocket.

Controls – The controls are laid out pretty much conventionally. Before turning the camera on however, you need to remove the lens cap, which has to lined up to re-attach it to the lens, and doesn’t have anything tethering it to the camera. The focus wheel felt a lot more solid than I was expecting – I was worried it would be a loose wobbly affair, but it move smoothly. The shutter button is firm and responsive. The remaining buttons offer enough feedback when pressed and are for the most part unobtrusive. Having black text on black buttons may not be to the taste of some but I found myself preferring this. The digital zoom buttons can be customized and set to control menu items, such as changing ISO, picture quality, metering mode and so forth, which I found very useful.

Powering on – After removing the lens cap and turning the power on, the lens extends, and then the LCD turns on and the live view feed starts. The camera then continues to initialize, and eventually all the icons will appear on the screen. Only then can you start taking photos. Start up time will be a big problem with this camera if you need to take spontaneous shots. If you know you are going to be taking photos, it would be advisable to set the camera to not automatically turn off, and rather have only the LCD turn off.

Interface – The majority of settings are lumped under only 2 menus. Unfortunately the menus aren’t customizable, nor is there an option to use a custom menu with user arranged menu items. The on screen interface when shooting is standard fare, displaying battery life, shots left, current mode, ISO, White Balance, shutter speed and aperture, amongst others. In manual focus mode a focus distance scale is superimposed on the live view and a magnified live view is also available. Unfortunately there are no depth of field indicators on the focus distance scale.

Responsiveness – Before buying the DP1 I did a lot of research, and was well aware of the speed issues and general irresponsiveness of the camera. When changing settings there is a slightly noticeable delay between the time you press the button and the new settings being reflected on the screen. The camera’s live view seems to hail back to digital cameras of 5 years ago – it has a low frame rate, appears very grainy at times, and even goes monochrome in low light. If your subject isn’t moving then this shouldn’t be a problem, however problems might arise when trying to follow anything moving at more than a reasonable speed on the screen.

Autofocus – The focus on the DP1 is painfully slow. Focusing on anything moving is incredibly likely to be an exercise in frustration. For stationery objects in good lighting, the autofocus eventually finds it’s target and locks on accurately. However, in low light, or for moving objects, the autofocus struggles and gives up. The autofocus has two modes, 30cm to infinity and 50cm to infinity, the latter being slightly faster which helps a great deal. The autofocus contributes a great deal to the delay between pressing the shutter button and your photo being taken, so it’s a great benefit to learn about depth of field and hyperfocal distance to use manual focus to prefocus your lens.

Shutter Lag – The shutter lag (after focussing) is more or less on par with most other compacts.

Post-shutter Lag – Arguably the DP1’s biggest problem is the lag after taking a photo, while the camera saves the photo to memory. The camera completely locks up for a good couple of seconds after shooting, and ignores ALL input. When shooting in RAW mode, the camera continues writing even after that for a good while, but you can carry on taking photos. In Continuous drive mode, the camera only locks up after the 3rd photo.

Post shooting – The DP1’s review system is standard, offering the ability to zoom in and out of photos, display thumbnails in a 3x3 grid, and shooting information for individual photos, including a histogram with separate curves for red, green and blue. There is however no indication of highlight or shadow clipping.

Workflow – I admittedly didn’t spend much time in Sigma’s supplied software, as I already have a workflow in place using Lightroom. So I copy JPGs from the memory card onto my harddrive, and convert X3F (Sigma Foveon RAW files) straight to DNG (Adobe Digital Negative files) straight off the card, before importing into Lightroom.

Image Quality (prelude) – It’s important to note that the Sigma DP1 uses a Foveon sensor, which is different to the sensors used in 99% of digital cameras. In a conventional digital camera, a sensor is used which is made up of millions of photoreceptors, each recording how much light it receives. The camera then records these, and creates an image out of them.

However, each photoreceptor only records HOW much light - how bright the light is that it’s receiving. It does not record colour. For the camera to record colour, each photoreceptor has a coloured filter in front of it. Most digital still cameras use a Bayer colour filter array, with 25% of the photoreceptors having a red filter, 25% having a blue, and 50% having a green one. When light passes through a red coloured filter, only the red light goes through, and the photoreceptor records, and so on for green and blue.

Without getting too technical, a 10 megapixel camera (which has 10 million photoreceptors) will then have 2.5 million red values, 2.5m blue ones, and 5m green ones. However, an image on the screen needs one red, one green, and one blue value per pixel to display a colour image, whereas the camera only has one value per pixel. The camera then guesses the other 2 values for pixel it has from neighbouring cells, using a Bayer demosaicing algorithm. These 2 values are interpolated from surrounding cells, and were not actually recorded by the photoreceptor.

The sensor in the Sigma DP1 (and the rest of the Sigma cameras) uses a Foveon X3 sensor. The Foveon sensor uses 3 layers of photoreceptors: one layer of green photoreceptors, one of blue, one of red, and stacks them together, so that light falling on the sensor will pass through a photoreceptor recording red, a photoreceptor recording blue, and a photoreceptor recording green, to get a pixel with a value for each of red, green and blue. The Foveon has approximate 4.6 million photoreceptors of each colour. As it does not interpolate values from neighbouring photoreceptors, it produces a 4.6 megapixel image.

At first glance a 4.6 megapixel image might sound a lot smaller than a 10 megapixel one, but it is important to note that the Foveon sensor has 14 million photoreceptors producing a 4.6 megapixel image, whereas a conventional camera has 10 million photoreceptors that produce a 10 megapixel image by guessing more than half the data in that 10 megapixel image. The Foveon sensor is recording 4.6 million red values, whereas the 10 megapixel conventional camera is only recording 2.5 million.

Image Quality – The Sigma DP1 produces files 2652x1768 pixels in dimension, as it does not use demosaicing to upscale it’s images. At 100% or 1:1 view, the images are sharp and clear, and don’t have the blurriness or smudginess of having been upscaled. At ISO 100 and 200 there is a very distinct absence of noise. Unfortunately at ISO 400 and 800 noise gets significantly worse.
When resized to 900x600 pixels, the DP1’s photos are for most intents and purposes, indistinguishable from my Canon 350D with the 18-55mm kitlens set at 18mm (for the same field of view), which I found very impressive for a compact camera. This is most likely due more to the fact that the Foveon sensor is physically in size almost as large as lower end digital SLR cameras. (Foveon 286mm², Canon APS-C 329mm², most compacts having sensors in the 25 to 43mm² range)

While straight out of the camera, the DP1’s colours look quite different to how the scene actually looked, it is easily corrected in post processing. The images recorded texture, detail, and colour transitions very well.

Lens – The DP1 has a 16.6mm lens (which has a field of view equivalent to a 28mm lens on 35mm format). It has a maximum aperture of f/4, slightly slower than most dSLRs kitlenses having a maximum aperture of f/3.5 at 18mm (which would be equivalent to the DP1’s 16.6mm). The DP1 has a prime lens which cannot zoom or be interchanged. While I have not done any proper tests or shots of resolution charts, I didn’t notice any major vignetting while taking actual photographs. The lens was quite sharp, even wide open, and wasn’t found to be noticeably soft in the corners.

Flare can be problematic when shooting with the sun in the frame. In some circumstances, the DP1 exhibits a strange phenomenon where blown out highlights (such as flare from the sun) go from white to bright magenta/pink.

Conclusion – The DP1 is most definitely a niche camera, aimed at a small percentage of photographers who need a camera that is small, but still has the image quality of their bulkier cameras, and are willing to put up with any quirks the camera has.

The DP1 is dreadfully slow in comparison to a dSLR due to a combination of both it’s glacial autofocus and the delay after taking photos. The former can be eliminated by prefocusing the lens, which luckily isn’t a problem with both a dedicated focus wheel, on screen focus distance scale, and magnified live view. Unfortunately, not much can be done for the latter. The DP1 is a camera where you can’t afford to press the shutter button carelessly.

The DP1’s image quality is excellent. Images are sharp and clear, with detail and texture showing well, and smooth transitions between colours, with practically no noise at ISO 100 and 200 in daytime outdoor conditions.

While I am more than satisfied with my Sigma DP1, new buyers could do well to research and find out whether the camera’s drawbacks are worth the image quality.