Photographers obsess about sharpness. Declaring an image "tack sharp" is one of the highest compliments on the technical execution of an image. So most photographers are surprised when they first learn that their expensive cameras have a built-in filter that deliberately blurs the image -- technically a low-pass, or anti-aliasing (AA), filter that blocks very high frequencies -- before it ever gets to the camera's sensor. This filter is needed because camera sensors are checkerboards of red, green, and blue, causing them to create artifacts called moiré patterns on certain subjects with fine detail, unless they are smoothed out.
When Nikon introduced its new high-end DSLR the Nikon D800(Opens in a new window) this week, the initial buzz was all about its amazing 36MP resolution full-frame sensor, professional 1080p video capabilities like real-time HDMI output and headphone audio monitoring, and seemingly limitless upgrades to autofocus, metering, white balance detection, and processing speed. The D800 is a unique blend of a full-frame camera with the pixel density of the very popular Nikon D7000 APS-C model, combined with many of the components of Nikon's new flagship D4 -- all at a price of $2,999, halfway between the D7000 and D4. Likely to instantly kill sales of any remaining Nikon D3X units priced at $7,999, just about the only "give-up" in the Nikon D800 is speed. At 4 fps it doesn't hold a candle to the 10 fps of the Nikon D4. The higher pixel density also means that those craving the ultimate in low light performance will still be happier shelling out the money for the bigger, although lower resolution, D4.
Now attention is turning to the D800's sibling, the D800e. In something of a revolutionary move, Nikon is giving photographers an option to purchase their new 36MP Nikon D800 without the low-pass filter, in a model called the Nikon D800e. This new option is causing a great deal of head-scratching among potential buyers as they attempt to decide which model is right for them. The truth is that there isn't an easy answer, but fortunately, since this isn't the first camera to go without the low-pass filter, there is a lot of data on exactly what the results will be to help buyers compare.
You can almost see the detail from this D800e sample image drip off the screen. Click-through for the full-resolution version if you dare -- it is a mind-blowing 33MB JPEG.
As background, the problem of moiré -- named for a finely patterned French textile -- arises when a photo subject has a repeated pattern that is fine enough so that each repetition falls on the sensor's Bayer filter array slightly differently. Surprisingly, despite this obvious shortcoming, camera makers have stuck with the Bayer array for decades, mostly just telling their customers to live with the problem -- most medium format digital backs don't feature a low-pass filter, as they are designed for the highest possible resolution -- or adding a filter which undoes some of the work they have put into sharp lenses and high-resolution sensors.
In a break with tradition, Fujifilm has just announced that its new X-Pro1 will use a radical 6x6 array, designed to reduce moiré and other artifacts. If it is successful, Fuji is likely to start a trend. In the meantime, DSLR buyers have mostly been stuck with the anti-aliasing filter, although the niche Sigma SD1 has one that is user-removable, which gives the photographer the best of both worlds. Aftermarket company Maxmax(Opens in a new window) will also remove the anti-aliasing filter in your DSLR, providing you with sharpness at the cost of a few hundred dollars and a camera which will no longer be serviced by the manufacturer.
My first experience with a filterless DSLR was after my Nikon D70 was converted to an infrared camera. As part of the conversion the anti-aliasing filter was removed, resulting in blisteringly sharp images like this one of a local vineyard:
Moiré: The dark side of pure sharpness
With results like that, it's hard to see why anyone would deliberately blur an image with a low-pass filter. Until you look at what happens when photographing a fine texture with a non-filtered sensor. This sample image from Maxmax shows the moiré effect that can result (look at the air conditioning vent in the sample from the camera with the filter removed):
Apples to apples: The Nikon D800 and Nikon D800e
For Nikon, removing the anti-aliasing filter in the D800 to create the D800e wasn't quite as simple as it sounds. The filter in the D800 is actually two layers, surrounding the infrared filter. The first layer blurs the image horizontally, and the second one blurs it vertically. To create the D800e Nikon has apparently swapped out the second filter with one which re-converges the image that the first layer blurs. This seems a little overly complex compared to just junking the filters all together, the way Maxmax does, but may have been a smaller manufacturing change or been needed to keep the IR filter functioning properly.
Since the two Nikon models are twins differing only in the composition of the filter, it is easy to show both the resolution enhancing and the potential moiré effects of changing the filter. This first pair of image samples show the increase in sharpness with the modified filter:
The next pair shows the downside of the modified filter, with visible moiré in the clothing:
Obviously, anyone spending a lot of time photographing finely patterned clothing would want to think twice about the D800e, but for anyone else the added sharpness and detail really kicks the performance of the camera up another notch. Nikon is charging a premium for the specialty version of the camera, with the D800 selling for $2,999 and the D800e for $3,299.
[Image Credit: Vineyard(Opens in a new window)]
