Do you feel the aa-filter in your D3/D700 is too strong ...?

Started Aug 14, 2008 | Discussions thread
Thom Hogan
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Re: substitute filter
In reply to Octane, Aug 17, 2008

Octane wrote:

really? I thought they just take the "cover". So after the
modification the protective glass is still on the sensor?

It has to be, for two reasons. First, the AA filter is part of the optical formula. Nikon counts on the refraction in calculating where the sensor is positioned. Without some glass over the sensor, you're going to have focus at the wrong point. Second, the AA filter also filters UV/IR. If you let that light through to the sensor you're going to get the same problems that made pros hate the D2h: near IR pollution.

I have done some experiments with sharpening a while ago.

Sharpening is not the same as resolution. This is an age old issue that many don't understand: there's real acuity and faux acuity.

My assistant and I have been doing a number of tests with various lenses and various cameras (AA removed, AA in place) lately, and it's convinced me that if you want maximum pixel density and acuity with the current Nikons you MUST have a D300 with the AA removed. This is a problem in more ways than one, though. First, you lose sensor cleaning. Second, the only replacements I've seen get the filtering wrong--white balance is now wrong (the camera has assumptions about spectral transmissions). Third, Nikon generally won't repair a modified camera, so you end up having to keep and restore the AA if the camera has to go back. And, of course, moire now can be a serious issue with small, repeating detail. Indeed, on the test charts when moire was produced by the AA camera it was the typical diagonal color bars you'd expect, but with the non AA camera color pattern interference is a mess when it occurs (random, stronger, and often adds chaotic element that is impossible to remove).

The plus side is this: a significant resolving increase. For example using an ISO 12233 chart and shooting with a top performing lens (300mm f/2.8), the AA D300 was resolving the 400 lines/height bars while the non AA D300 was clearly resolving the 500 lines/height. This is very similar to the difference between a really good lens and a cheap lens (indeed, testing the new Nikkor 500mm f/4 versus the Sigma 150-500mm f/5-6.3 wide open produces a similar result).

You can't sharpen a sharp photo and expect it to get better.

Well, if you always use the same sharpening recipe, I'd agree with you. But I have yet to see any out-of-camera photo that can't be improved. Moreover, most of us have long felt that there are three stages to sharpening: input sharpening, acuity sharpening, and output sharpening. The first removes AA and the digital aliasing impact, the second improves edge (and only edge) definition, and the latter makes up for deficiencies in output technology, such as ink bleed.

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Thom Hogan
author, Complete Guides to Nikon bodies (18 and counting)
http://www.bythom.com

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