DLA is Nonsense! It should be deleted from the reviews.

[pin008]

Everybody knows small aperture means strong diffraction, but there is no limit from the pixel size and density.


According toDigital SLR Camera Reviews here, so-called DLA (Diffraction Limited Aperture) is the aperture where diffraction begins to visibly affect image sharpness at the pixel level. It says as sensor pixel density increases, the narrowest aperture we can use to get perfectly pixel sharp images gets wider.


This theory assumes the image is a perfect dot and nothing else, and compares its airy disk with pixel size. If the airy disk is larger then pixel size, then the diffraction is visible.
<p class="last"]But actually, the photo image is not a dot, but a continuous surface. When diffraction occurs, the whole the image, every part, every dot gets some kind of blur. So each pixel is definitely affected by some degree of diffraction. There&rsquo;s no such thing called perfectly pixel sharp images. Diffraction could be visible at any aperture, any pixel size theoretically. The size of pixel doesn&rsquo;t limit anything. Digital sensor and film have no difference here.

[Keith B]

Hello, Poop...this is Fan.


Fan...this is Poop.





I'm ducking!

[ShutterbugJohan]

Are you advocating that we all use pinhole cameras with f/800 lenses? [:P]

[pin008]

Read the 1st sentence and understand it.

[Sean Setters]

Read the 1st sentence and understand it.
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pin008 - We're generally a very friendly and helpful forum community here, and if there's a misunderstanding about anything (or disagreement), those who know generally try to help and weigh in. However, your first post seems a bit aggressive and your second post a bit sarcastic. If you'd like to have a meaningful discussion about DLA, I'm sure those that understand it best will be glad to explain its generally accepted significance in greater detail (or else link to information that has already been covered, as above).


Try to keep an open mind, and if you still disagree with something, explain your position in a respectful manner.

[pin008]

If you think I have some aggressive or sarcastic attitude, I hereby formly apologize! i didnt mean it.


as a non-native speeker, to express my debate is already hard. I can hardly arrange noble words.


Pleasefollow my debates, ignore my words and expressioins.





[:P]

[wickerprints]

Daniel better chime in here before this thread gets out of hand...or perhaps it is already too late.


In any case, diffraction is an intrinsic physical phenomenon of passing a wave through a hole. It's there no matter how big or small the hole or wavelength is.


But the ability to observe the extent of diffraction depends strongly on the resolution of the device that is used to measure it. While it is true that a real-world image is not composed of discrete, collimated point light sources, it is also irrelevant. If one acknowledges the two basic principles that (1) diffraction exists, and (2) the degree of diffraction is inversely proportional to the size of the aperture, then it doesn't matter what the object space looks like. Your ability to see the diffraction basically depends on the highest spatial frequency that your imaging device is able to capture.


What do we mean by being able to observe the diffraction? After all, if some degree of diffraction occurs at any f-number, then there is some even at f/1.0 (assuming the lens is otherwise ideal). But what does it mean to have a sensor with such high resolution that we can "see" the effect? How do we know when we do see it? One way to think about it is to say that one is diffraction limited at the spatial frequency at which increasing the sensor resolution further confers no additional advantage, yet reducing the resolution causes you to lose detail. But that's counter-intuitive because we don't usually think of sensors as being of variable resolution.


Thus, we usually phrase DLA in terms of loss of sharpness at a fixed sensor resolution when stopping down further; i.e., a particular sensor "starts to show" a loss of sharpness at the DLA and this softness increases as f-number increases. Opening the aperture faster than the DLA doesn't make it sharper, either (again, assuming an ideal lens).


But a word to the OP: the reason why your post came across as "aggressive" is that your first post basically called the diffraction-limited aperture model nonsense, and dismissed it without providing any real evidence to support your claim. You didn't even introduce yourself or engage in those usual polite pleasantries that are considered essential to demonstrate good social skills.

[clemmb]

This has been discussed at length here before. Here is some light reading on the subject.


LOL


Mark

[Jon Ruyle]

I think what DLA needs is a little more understanding and kindness, not agression and hate.

[clemmb]

I think what DLA needs is a little more understanding and kindness, not agression and hate.






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I do not see it, aggression and hate that is.