With no colour filter array, the 18-million-pixel sensor in Leica’s new M Monochrom rangefinder captures highly detailed black & white images. Richard Sibley considers the advantages of using the Monochrom and finds out if it really is like shooting on film. Read the Leica M Monochrom review...
We have talked about the Leica M9 on a number of occasions, and in terms of specification, the new Monochrom is virtually identical, except for the changes that were necessary to convert the sensor for black & white use.
The sensor is the same KAF-18500 model originally produced by Kodak, though Kodak’s sensor production division is now owned by Truesense Imaging. This full-frame, 18-million-pixel (effective) CCD sensor would usually have a Bayer pattern colour filter array placed above its photosites. However, in the Monochrom this array is absent. So rather than each photosite being specially filtered for red, green or blue light, they are sensitive to the entire colour range. The resulting image is a pure luminance map of each photosite on the sensor.
The lack of this colour filter array therefore means that more of the available light is able to reach the sensor. For example, a blue filter will only allow the blue light spectrum to pass through, blocking all other colours. With the filter removed, the entire colour spectrum can be gathered by each photodiode, which increases the sensitivity of the sensor.
As a direct result of this design, the base ISO sensitivity of the 18-million-pixel CCD sensor is increased from ISO 160 to ISO 320, with the maximum sensitivity also increasing from ISO 2500 to ISO 10,000. The reason for the increase at the high-sensitivity end is that colour image noise is non-existent. Potentially, this allows more detail to be recovered from shadow areas, and means that the luminance noise should look far more speckled and akin to film grain.
Another important part of a standard sensor block that has been omitted from the Monochrom (as it has from the M9) is the anti-aliasing filter. We have talked about this quite a lot recently, with the recent Fujifilm X-Pro1 and Nikon D800E both lacking low-pass filters.
These filters sit above the sensor and ever so slightly blur the path of the light reaching the photodiode. Part of the reason for doing this is to help the colour demosaicing process and prevent false colour and moiré patterning. As the Monochrom does not have any colour information to demosaic, there is no need for the anti-aliasing filter. As a result, you would expect to see images that are much sharper and more detailed than those from conventional 18-million-pixel cameras.
There are a couple of features on the Leica Monochrom that are not present on the M9. The highlight and shadow clipping warnings have been made more advanced with the inclusion of a percentage adjustment setting that displays a warning when the set percentage is clipped. For example, with highlight clipping set to 100%, only completely blown-out highlights will be displayed. At 99%, any tones that are almost clipped will be added to the warning. This allows the photographer to ensure that detail is retained in highlights, which users of the Monochrom will find an important benefit. It is quite common to find in cameras with Bayer pattern sensors that only one of the colour channels becomes completely blown out, which means recoverable detail is often present in the other two colour channels. As the Leica Monochrom doesn’t have a colour filter, when the highlight becomes clipped, all detail is completely lost.
With absolutely no colour information produced by the Monochrom, any colour-related settings from the M9 have been completely removed. There is no setting to switch the colour space between sRGB and Adobe RGB and, more importantly, there are no white balance settings.
Contrast and sharpness adjustments are available to edit the look of the camera’s black & white JPEGS, though these are also found in the M9. The only other image adjustments are new toning options, which add sepia, cold or selenium effects to images, in either standard or strong settings.
Image: With only default sharpening applied, the Monochrom’s DNG raw files reveal a great deal of very fine detail