Is this sharp?

[camerapapi]

I know most of you are well aware of this but it is so important that it merits to repeat it if just to refresh knowledge.
Except for the new Leica, the M9, all digital cameras have a blur filter. The filter is known as AA (anti-aliasing) filter and, as very well you know, it is positioned by the manufacturer ON TOP of the camera sensor.

The filter is said to filter UV rays but its primary purpose is to avoid moire and perhaps, and I am not absolutely sure on this, to control noise at high ISO settings. Moire is not always evident and in many applications, landscape photography is one of them, the filter is not necessary. Although sharpness improves without the filter, it seems that at high ISO settings noise is more evident and so it has been reported by others.

With the introduction of the D100 Nikon used a pretty strong filter. Immediately those using the camera complained that the files did not have an acceptable degree of sharpness. They were right! Being so old in technology, applying sharpness in camera caused a significant deterioration of the images to the D100 due to artifacts and this was most evident when shooting JPEG. RAW were better files but still it was a wise movement to keep sharpness as low as possible and add it during post processing.

I admit that I learned that early when I owned the D100 and my files had excellent quality if I did my part. The AA filter blurs the image and sharpness, as you know very well, has to be added during editing. Many photographers sold their D100 because of that and when Nikon introduced the D70, well aware of what the filter was doing, a new AA filter was introduced and this time it was weaker than the filter used by the D100. The immediate result of that was that the files out of the D70 were superior when it came to sharpness but under certain circumstances moire was more evident. I have not seen that with my D70s though, perhaps because of the type of subjects I usually photograph.

We never had this issue with film. Film renders sharpness according to the quality of the lens in camera and the grain structure of the film in use. Films in the ISO 200-400 handle grain reasonably well. Fuji did very well with their Fuji 800 although Kodak did not share well with their version. Photographers went beyond ISO 400 rarely because of grain and I remember perfectly well that Kodak film with that ISO 400 speed using medium format cameras, still showed ugly grain in the enlargements. That is what I saw using a Hasselblad.

With digital things have changed radically in the past 3 years after the introduction of the D3 and D300. When Nikon introduced the D50 we could see hints that Nikon was already working to control "noise" with digital cameras, something Canon has been doing for years although at the expense of loosing some details. The AA filters used in more modern cameras are weaker and the quality of the files are better. The D300 is a very acceptable camera for those shooting often at ISO 1600 but many photographers will tell you the D90 is better. I have not used any of those cameras at high ISO so take my words with a grain of salt. The D7000 seems to be excellent in that respect and I have already seen reports of its awesome noise performance at ISO 3200, although it is still early to say. You know that noise is not the only parameter to measure in a camera. AF, colors and image quality, along with dynamic range, are important factors photographers keep in mind when they are buying new cameras. If lower noise is the result of using weaker AA filters it is something I do not really know.

The lowly D3100 is an excellent camera when it comes to image quality and noise control. I have seen outstanding pictures out of it when the lens used was of good quality. Files shot at ISO 3200 are very good considering the price of the camera. Another case of a weaker AA filter!

So, is this sharp? I see that question often in the forums and the answer is very simple, use a camera with a weak AA filter and most modern cameras do use one. Use sound photographic techniques, use a tripod and whenever possible, shoot at the lowest ISO setting your camera offers. I could add USE FILM, but I am afraid I could start a war!
One day all manufacturers will get rid of the AA filter in their cameras. I am sure the time is coming.
Good shooting.

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William Rodriguez
Miami, Florida.

 

[Lurker]

http://en.wikipedia.org/wiki/Nyquist_frequency

Of course you can leave out the filter. Just as you can drive around without seat belts. It will be fine 99% of the time and who cares about that 1% right? I've seen examples of sampling artifacts and it wasn't pretty. We're not talking about "some moiré" here, we're talking about an picture that is totally different from the actual image.

As the resolution of the sensor goes up, the strength of the anti-aliassing filter can go down. If the current trend of megapixel madness continues we can indeed get rid of the anti-aliassing filter completely because diffraction effects (even at f/2) will yield a lens resolution that is less than that of the sensor anyway.

Edit:
A webpage called Scanners and sharpening gives some background information on the need of an anti-aliasing filter in image digitalization. On that page you can find this sample image:

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(source: Sergio Lovisolo)

Note the weird "maze" that's right of the center - that is aliasing. Also note the moirées - the anti-alias filter isn't there to prevent moiré, it's there to prevent aliasing (which is why companies that offer removing the AA filter shouldn't show the "look, less moiré" pictures because moiré isn't the issue).

If the image the sensor is trying to digitize has a higher resolution than the sensor aliasing will take place. The tendency of Nikon to use weaker filters has less to do with Nikon engineers experimenting with weaker filters, but more with the fact that higher resolution sensors require less AA filtering (and as we hit diffraction limits, no filtering)

 

[ddietiker]

Or you can just send your camera to a company that removes the AA filter...

 

[camerapapi]

Thank you Lurker for your interesting comments. When you talk to manufacturers about the AA filter they mention the word MOIRE more than anything else. I do not have the technical expertise to discuss aliasing or moire or the potential effect of the filter on noise at high ISO settings. The Leica M9 shows moire under certain conditions but it could very well be aliasing.
We are beginning to learn about the new sensor in the D7000. Unquestionably, because of its denser megapixel count I am sure Nikon had a few problems to handle. Preliminary tests and photographs from the D700 are encouraging but I have to agree with you, there is some kind of madness about the megapixels race. In my humble experience I would dare to say that a camera with 10 megapixels should be very capable and perhaps it has all the pixels we really need. My D2H, with only 4.3 megapixels is very capable of beautiful enlargements due to its big and fat pixels so well distributed over the LCAST sensor.
I did not want to talk about film but when using film sharpness is something that will not suffer because no conversions are necessary, assuming sharpness is there to begin with.
Douglas I am well aware of the few companies that remove the AA filter. I have to be honest with you when I say the AA filter never has been a concern for me with the new cameras. I am sure you know very well that sharpening a file during editing is an easy job that we tend to overdo but in general the results are excellent.
I posted this information with the purpose of helping those new to photography that still do not understand why their pictures sometimes are not as sharp as they should be.
Although it is true that the AA filter is actually a blur filter, modern filters are very efficient and the files can be sharpened beautifully in Photohsop assuming sound photographic technique have been used.
Thank you for your comments.

William.

 

[mnp13]

I know in terms of technology, 10 years is "stone age" but this was one of the things we tested at Kodak - and at that time Kodak was the only game in town for high end digital. The very very first D1 was recalled after it's first launch because they stole 4 (or 6?) international patents from Kodak, I was part of the reverse-engineering team that found those thefts.

Moire is very different from anti alaising, as Lurker showed in his image. I know that "moire" is the excuse that is given, but it's a very different issue than alaising.

The prototypes didn't always have AA filters on them, and we saw lots of those little mazes during our testing. And it's not just the pattern, it's the color shift and little rainbows that cause problems. It's an interesting effect until it ruins a beautiful photo.

I see the problem - lose sharpness or get the filter taken off and risk those little patterns and color shift deciding to show up. Personally, I'll take the hit in the sharpness.

And I completely agree with you - that is one of the ways that film beats digital hands down (there are a few more too :wink: )

 

[ddietiker]

.....Douglas I am well aware of the few companies that remove the AA filter. I have to be honest with you when I say the AA filter never has been a concern for me with the new cameras. I am sure you know very well that sharpening a file during editing is an easy job that we tend to overdo but in general the results are excellent.
.......

Since my last camera, it hasn't been a concern for me either William. Todays camera's can take perfectly sharp photo's. There is a huge difference between my old D100 unsharpened RAW file and the RAW file I get out of my more recent camera. I find I barely add much sharpening in PP at all now.

 

[Taco2575]

So, to interject this massively technical (to me anyway) discussion with a bit of learning opportunity, can you guys and gals briefly (as possible, anyway) explain the terms you're using.

I know I can google and such, but I find it easier to learn from people who can define a term and offer a clearly-observable example of it.

The 2 that jump out are Moire and aliasing?

Also, how common is it for a "great shot" (as seen on here, for example, in the Night Shots of the National Mall thread) to have been THAT great as-shot?

Meaning, I suppose, how often are GREAT shots really captured, and how many "really good" shots are made great with PS, etc?

 

[Lurker]

So, to interject this massively technical (to me anyway) discussion with a bit of learning opportunity, can you guys and gals briefly (as possible, anyway) explain the terms you're using.

Nyquist frequency: if the resolution of your lens exceeds that of your sensor then there is a chance that you get "aliasing artifacts" - funny shapes that aren't really there but visible anyway.
To prevent this from happening, a "blurring filter" is mounted in front of your sensor that blurs the details to a level roughly similar to what your sensor can handle. "The theory" prescribes actually to blur it to a pixel size half of what the sensor can handle, but that isn't always necessary - picking the right strength for the anti-alias filter (sounds much better than "blur filter") is a bit of witchcraft and Nikon has improved over the years. This is why the D50 is so much sharper than the D100 (same sensor, different filter).

As the resolution of the sensor increases, the strength of the anti-alias filter can decrease as the image that the sensor sees needs less and less blurring.

Diffraction: an optical effect that is caused by light forced through a (small) opening. Diffraction causes both unsharpness and lack of contrast. If the unsharpness is contained within one pixel you won't see it. But as pixels get smaller and smaller it's easier and easier to spot diffraction. The diffraction effect gets worse at small apertures (large numbers). But as sensors improve we do not only see more detail, but also more diffraction. The diffraction at f/11 that was invisible at 12MP might become visible at 16MP.

Diffraction causes the lack of resolution that the anti-alias filter is trying to achieve. So, if the sensor is big enough (say, 24MP at DX) the diffraction effect is that even at ultra wide apertures (f/1 and f/1.2) the image is blurred at pixel level. On a positive note, at that point an anti-alias filter is no longer required.

Pre-emptive snark: yes, techheads, I took a few shortcuts here. But Taco wanted an explanation in simpler terms.

 

[TetonTom]

Or you can just send your camera to a company that removes the AA filter...

Is this what they do when they "HR", or "hot-rod" a camera?
I don't remember where exactly I saw it, but samples from a HR'ed D200 were sharper to the eye than a D700. Not just a little, either...

 

[camerapapi]

I am so glad I made mention to the AA filter. I have also learned a little in the process and the comments have been superb and I thank you all for that.
Douglas, I am walking on the same steps of Michelle. Even with cameras as old as my D2H, when I shoot RAW I can keep sharpening during editing to a minimum so it does not seem we are sacrificing much on regard to quality with modern AA filters. It was interesting Michelle to hear about the D1 and your research with Kodak. I still use and love film. I guess old habits are hard to break.
Tom, you are exactly right, when the AA filter is removed images are sharper but I hope you have read the other posts, especially that of Michelle. The D200 also had a moderately strong filter giving the impression that the images were soft but I found, during the brief period I used one, that RAW files from the D200 were excellent and sharpened beautifully.
I sincerely believe that modern cameras are doing very well and as I mentioned in the original post, there is a good chance cameras in the future will control aliasing better to the point that the filter will not be necessary, but this statement is only a guess.

William.

Addendum: The sunset was shot with my D2H and the lowly 18-55 non VR platic lens.