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| p.25 #13 · Still no love for the Ricoh GXR? |
As with all things photographically related, there's some trade-offs YOU have to decide on.
Image noise vs artificial light. DoF vs shutter speed (when there's not enough light to get both). The list goes on forever...
If your main interest is wide angles and available light shooting, then an AA-less camera certainly adds more value than what it detracts. For me, that mostly shoots in a studio (often) or in good weather with good medium/long tele lenses, I find being without an AA filter "not worth it", but that's my personal choice.
The main negative things about corners and AA filters is that:
a) the material isn't supposed to work that way - everything goes out of whack. Birefringency, which is the physical effect that makes an AA filter "work" is also ray angle dependent to quite a large degree. On the whole you can see the AA filter as a combined beamsplitter/collimator, separating one singular ray of light into two rays at slightly different angles as it enters the filter, and then on exit makes them run perfectly parallel again - as a PAIR of rays. As a ray passes "straight through" one layer of AA filtering it's "spread" buy a certain fixed amount when exiting. If the ray passes through at an angle, it's spread by quite a lot more - as the run-length for the ray through the plate is longer. To spread in both X and Y directions you use two layers of AA filter material, with a phase-plate (to remove polarization) in between. One spreads in "Y", the other in "X".
b) Like any flat slab of transparent material placed in the optical path, it affects the focusing of rays. Astigmatism increases (if the lens wasn't astigmatic in "the other direction" before - then it gets better...) and if I remember correctly it also effects the flatness of the focusing field. I could be wrong about the focusing field. This is why you should keep the internal filter mounted in a super-tele if it says you should do so. It is optically corrected for the filter, and might actually give worse results if it's not there...
If it wasn't so prohibitively expensive, the absolutely best solution would be an AA filter that has weak strength in the middle, and then tapered off to no strength at all on the edges. This would on the other hand make the filter into a convex lens, with all the effects that includes.
The second best solution (but also expensive) is to increase resolution on the sensor. The NEX7 is right there on the edge of actually not needing an AA filter.
It's to bad Ricoh didn't have time to wait for the IMX071 16MP sensor in stead - it would have had slightly less of the negative effects you can get from not having an AA filter.