nikon D7100 - how will Canon respond?

Started Feb 21, 2013 | Discussions thread
Severian The Lame Contributing Member • Posts: 550
Re: Hopefully with no AA filter on the 7D II...

noirdesir wrote:

bobn2 wrote:

noirdesir wrote:

And is this an option in reality? Do we know AA function exactly and does have LR a tool where I can input the parameters of the AA function?

No, but I believe that DxO does have one where they have already put in that correction. There are several ways to do it in practice and theory, if you wish. First step is to find the MTF of your AA filter. The way to do this is to project a slanted edge on the sensor (I would suggest a knife edge held close to the sensor illuminated by a laser pointer) and use a slanted edge MTF program (quite a few available) to find the MTF. Actually what you want is the PSF. When you find the PSF, you apply a deconvolution to the image to correct out the filter. You can get plugins for ImageJ which do both the PSF analysis and the deconvolution.

Good luck with that. Hope your sensor survives its laser bath! Commonly available high power laser pointers have a spot irradiance of about 625 W/m^2 and low power ones about 125 W/m^2. That's somewhere in the neighborhood of 1 to 3 stops less bright than the sun at zenith on a clear day. Moreover, I think your slanted edge test might fare better in incoherent light.

Roughly since the D800E came out (but probably also before in reference to Leica or MF) people here (including you) have discussed the MTF of an AA filter. Somebody then posted MTF curves for one or two AA filters in a thread where you also participated. But that was about it, until Marianne showed some of her results. So, while it is naturally measurable, essentially nobody beside DxO has ever done it.

Of course others have done it, but they're not inclined to make this information public. Canon, Nikon, and all of the other manufacturers have all done this as part of their design process. Canon has finally made a little bit of this knowledge available to us to use (but not to actually know) in the form of its Digital Lens Optimizer . Obviously Canon has measured the properties of the AA filters in (representative samples/prototypes of) each of it sensors and has detailed mathematical models of those sensors and filters as well as of each of its lenses (or at least the modern ones). This allows them, via DPP with DLO, to correct the major lens aberrations, AA filter blurring, and diffraction blurring, to the extent that such things are amenable to correction by software.

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