On the right is a comparison between two images, one exposed using a 10-stop neutral density filter and the other without. The filtered image was exposed for 8 sec f/16 at ISO 200 while the unfiltered image was taken at 1/250 sec f/16 at ISO 200. The difference in exposure is actually 11 stops, since the filter’s light transmission is clearly not the amount stated on the box. For those interested, it was a Heliopan ND 3.0 filter. Mouse-over the top image to see the filtered image.


Aside from slight colour and contrast differences, the ND filter on the DP2m causes some annoying colour vignetting. The image is cyan at the edges and magenta at the centre, whereas my D700 shows only a magenta cast when using this filter.





The slider-image comparison on the the right will show actual-pixel crops of both the normal exposure (left) and long exposure (right). With this comparison, I saw no discernible loss in quality in the 8 second image.

Luminance noise reduction was on it’s lowest setting.

I think it’s a fairly pointless exercise to do ISO series and ISO comparisons with the DP2m. It’s been covered in enough detail in other online reviews. In summary, the mid to high ISO performance of the Dp2m isn’t good at all by today’s standards. For colour work, staying within ISO 100 to 400 is recommended, and at a push one can get away with shooting at ISO 800. For monochrome images, ISO 800 looks OK and ISO 1600 being my tolerable limit.


There are some things one can do to improve B&W image quality when shooting in low light at higher ISO values, or with long exposures. You would’ve noticed the increase of noise in the red-channel B&W conversions seen on the previous page’s comparison. Now, with a high ISO image open in SPP, but this time selecting the blue channel in SPP’s channel mixer, you’ll quickly notice that the image becomes much less noisy than the default setting. So, if one has to shoot at higher ISO values, just remember that a B&W conversion using the blue channel in SPP’s channel mixer, can go a long way to reducing noise and therefore improving the image quality.


Below is an ISO 1600 image taken indoors in terrible lighting conditions. Exposure: 1/13th sec, f/4 at ISO 1600.

On the left is the original colour image (mouse-over for actual pixels crop) which shows the strong colour blotches associated with all DP Merrill High-ISO images. On the right are actual pixel crops of two SPP monochrome conversions from this file, the image on the left representing a straight conversion with no adjustments, and the image on the right representing a conversion with only the blue channel selected. Again, luminance noise reduction was set to minimum for all images.

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NAVIGATION:

Image Quality

Page 3

Great care should be given to proper exposure and keeping the ISO values as low as possible. One must simply accept that this isn’t a camera for all situations, and it’s restrictions are much the same as shooting with low ISO film.


Moving on to long exposures, the DP2m is restricted once again. Annoyingly, but possibly for good reason, Sigma has limited the maximum exposure times of the Dp2m to 30 seconds. I would imagine that anything beyond that could quite rapidly influence image quality, however, the facility for a little longer exposures would be nice.


Long exposure image quality is very dependant on the light quality and how well the scene is exposed. Shooting long exposures in daylight conditions, using a strong neutral density filter, I see little or no loss in perceived quality. However, a long exposure in dim lighting can show raised luminance noise, with colours in shadow areas becoming a little more blotchy.


I recommend, when shooting long exposures, to expose as far to the right as possible. If the scene allows it, shoot multiple shots and use the median filter method described earlier, to reduce the noise.

Below is an image taken under poor conditions. The 30 sec f/2.8 exposure at ISO 200 wasn’t nearly sufficient, and the results were dark and colours were poorly handled by the camera. However, the resulting image isn’t unusable. The most annoying aspect of it would be the feint colour blotching.


Again, the image quality is greatly improved when using SPP’s monochrome conversion with the channel mixer set to blue. Much like the high-ISO comparison above, the luminance noise is greatly reduced.


Mouse-over the image to see an actual pixels crop, which will clearly show the increase in luminance noise and the colour blotching.