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Archive 2013 · AA filter discussion ....

  
 
Photon
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p.4 #1 · p.4 #1 · AA filter discussion ....


veroman wrote:
...
The t1i/500D, however, was equipped with a much thicker filter than any other Canon camera I'm aware of. Why? I don't know. What I DO know is that the t1i was significantly less sharp than its predecessor, the xsi, and not as sharp as its successor, the t2i. The t1i has been heavily and justifiably criticized for its loss of detail. It is otherwise an excellent piece of gear, with good dynamic range, auto-focus accuracy, very good handling and construction, and an easy-to-use control layout.
...
- Steve

Interesting discussion. I have to say my impression is that it would be cheaper and simpler to replace a T1i with a T2i in order to gain sharpness (though I'm not familiar with any of the Rebel series, and don't know what other tradeoffs may be involved within the various bodies). I'm always interested in the possible ramifications of technical issues and the kinds of future designs we may see, but I'm glad that the AA filter in the bodies I shoot is not at all a concern (for my purposes). Still, kudos to you for doing the experiment and posting results.



Apr 12, 2013 at 10:11 PM
snapsy
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p.4 #2 · p.4 #2 · AA filter discussion ....


Here's a good article+demonstration on aliasing artifacts.

http://www.dvxuser.com/articles/article.php/20



Apr 12, 2013 at 10:16 PM
Photonic
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p.4 #3 · p.4 #3 · AA filter discussion ....


Steve,

I am happy that you are enjoying the investment you made in your camera to remove the AA filter. It is clear that you find the images it now produces to be very pleasing to your eye. Others may agree.

My concern is that your posts seem to suggest that you believe you have created a "better", higher resolution camera in so doing. All I can tell you is that there is no getting around Nyquist. If you don't properly low pass filter the optical path in front of the sensor then you will produce aliasing which represents false detail.

This said, not all low pass (AA) filters are created equally. It is impossible to make a perfect LPF and as with most engineering challenges you can trade performance for cost. I can imagine that the original filter on your camera was of the less expensive variety and perhaps used a lower cut off frequency to compensate for other non-ideal attributes. If that is the case it might make more sense to replace the AA filter with a better one rather than removing it completely.

Your post has motivated a good and useful conversation. I think that many will find the article linked by snapsy to be very informative on the entire subject of aliasing.




Apr 13, 2013 at 05:58 AM
veroman
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p.4 #4 · p.4 #4 · AA filter discussion ....


Photon wrote:
Interesting discussion. I have to say my impression is that it would be cheaper and simpler to replace a T1i with a T2i in order to gain sharpness (though I'm not familiar with any of the Rebel series, and don't know what other tradeoffs may be involved within the various bodies). I'm always interested in the possible ramifications of technical issues and the kinds of future designs we may see, but I'm glad that the AA filter in the bodies I shoot is not at all a concern (for my purposes). Still, kudos to you for doing the experiment and
...Show more

Thank you for your comments. Actually, what led me to the t1i was, in fact, my first purchasing a t3i ... same 18MP sensor as in its predecessor, the t2i. I didn't like its output AT ALL. To me, it was yet another example of squeezing too many photo sites into too small a space. I know there are many who are quite happy with their t3i, t4i, 60D and 7D cameras. I prefer to use cameras with the largest photo sites possible, which leads me to routinely use cameras like the 1Ds, 5D and 40D. I simply prefer their output.

I thought the t1i, with "only" 15MP (I know; the difference between 18MP and 15MP is somewhat negligible) might be what I was looking for in a light, travel body. So I found a used one via KEH at a very good price. The ONLY thing about the t1i that seemed to me to be a problem was the AA filter. In the end, I can say that I prefer the output of the t1i to the t2i and all the APC 18MP Canons.

- Steve



Apr 13, 2013 at 08:32 AM
veroman
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p.4 #5 · p.4 #5 · AA filter discussion ....


Photonic wrote:
Steve,

I am happy that you are enjoying the investment you made in your camera to remove the AA filter. It is clear that you find the images it now produces to be very pleasing to your eye. Others may agree. My concern is that your posts seem to suggest that you believe you have created a "better", higher resolution camera in so doing. All I can tell you is that there is no getting around Nyquist. If you don't properly low pass filter the optical path in front of the sensor then you will produce aliasing which represents false detail.

This
...Show more

I really don't think I've created a "better" t1i. What I've done is make the camera more applicable to my needs, i.e. it's closer to what I see in my larger, full frame cameras and can therefore substitute for them when I travel. The real acid test is when I actually use it on a long trip and see how it's done when I arrive back home. So far, the issue of false detail has yet to be seen as any kind of a serious problem, and moire has not shown up at all as far as I can see.

The snapsy article, I think, is overall a good one, but full of caveats and contradictions, particularly when the author qualifies his stance on the subject of false detail by saying things like, "Rarely will you see such obvious image contamination as on a resolution chart. In a real-world image, it may be much harder to spot what's 'real' and what's aliased 'fake' detail. To an untrained eye, a heavily aliased image might even look good." I mean, come one ... either he believes false detail in a still image makes for a poor image or he doesn't. It seems to me he hasn't made up his mind or is too insecure in his observations to stand firm on false detail.

Anyway, I will post images from time to time with my filter-free t1i, including those where the filter removal hurt an otherwise good shot.

Best,
Steve



Apr 13, 2013 at 08:51 AM
Monito
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p.4 #6 · p.4 #6 · AA filter discussion ....


veroman wrote:
come one ... either he believes false detail in a still image makes for a poor image or he doesn't. It seems to me he hasn't made up his mind or is too insecure in his observations to stand firm on false detail.


Beware of false dichotomies and binary thinking. Things are very rarely all one way or the other. It is a slam to accuse him of being "insecure".

False image data is present in all DSLR images. This is an example where we actually can say something is all one way. It is a direct consequence of the Nyquist theorem and the fact that camera manufacturers do not put strong and truly effective AA filters on.

However, whether or not the false data in a given image makes for a poor image is sometimes a matter of debate and taste and even then a person can rate one image as poorer or better than others without saying it is all the way 'good' or all the way 'bad' for false image data.




Apr 13, 2013 at 09:12 AM
veroman
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p.4 #7 · p.4 #7 · AA filter discussion ....


Monito wrote:
Beware of false dichotomies and binary thinking. Things are very rarely all one way or the other. It is a slam to accuse him of being "insecure". False image data is present in all DSLR images. This is an example where we actually can say something is all one way. It is a direct consequence of the Nyquist theorem and the fact that camera manufacturers do not put strong and truly effective AA filters on. However, whether or not the false data in a given image makes for a poor image is sometimes a matter of debate and taste and
...Show more
Sorry, but no matter how you look at it, the article represents poor writing. On the one hand he speaks of aliasing and other false detail as, "Yikes! Fake! Invented! Completely inaccurate! Wrong! Misrepresentation! Shouldn't be there!" He even draws the analogy of a female who embodies "natural beauty" (whatever that means) and one who's had work done, ie face lifts and the like. Pretty strong feelings about the subject of aliasing/false detail. But then he injects qualifiers and caveats throughout the piece, as if to say, "It's not all that bad." Poor writing. Poor way of exploring a topic.
- Steve



Apr 13, 2013 at 09:50 AM
AJSJones
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p.4 #8 · p.4 #8 · AA filter discussion ....


Steve - I think the article is doing two things: 1) presenting the facts : it is "false detail, wrong, inaccurate" etc and 2) allowing for variability in personal reactions to their appearance and how that reaction may be influenced by subject matter or taste or both. The writing style is quite conversational (presumably attempting to make the subject more accessible to folks who flinch at pure tecnical style) but presents a good, ahem, picture of the whole issue.


Apr 13, 2013 at 11:20 AM
veroman
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p.4 #9 · p.4 #9 · AA filter discussion ....


AJSJones wrote:
... presents a good, ahem, picture of the whole issue.

Glad you included "ahem." Would have been pretty punny otherwise. :-)
- Steve



Apr 13, 2013 at 12:46 PM
veroman
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p.4 #10 · p.4 #10 · AA filter discussion ....


Another sample, photographed with my 24-105. First shot is full scene, 2nd shot is 100% crop:












Apr 14, 2013 at 10:57 AM
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