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Old Mar 14, 2006, 3:39 PM   #151
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Lets all bow in the presence of such knowledge.
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Old Mar 14, 2006, 3:58 PM   #152
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I am afraid this subject is over your head. Memorizing things that you read somewhere does not allow you to comprehend it, as you obviously dont. I gave you what is clearly a fictitious demonstration thinking that anyone with even the slightest degree of intelligence would see it as such. It is like when you were in school learning math and they used baskets of apples. You didnt stand there asking the teacher inane questions such as how did the apples get there. It is just a way to make it easier to visualize. Of course you could not use a particle accelerator the way I desrcibed; "why waste time with spelling mistakes"? Reason because you have no argument, so all you do is find faults whereever you can rather than address any real points.

style="BACKGROUND-COLOR: #000000" I have no more time to waste on you. You are ignorant just like the scientists that wrote in American science how the Wright brothers would never get off the ground, or the ones that laughed at penecillin, the ones that laughed at matter transportation. All ignorant people that are unable to grasp the simplests of comments no matter how it is explained to them because they simply dont want to, they block it out, prevent it from entering their head. 2095809745+02228-36578=220088 you cant know if the answer it correct simply by reading the numbers can you? You cant understand something simply by reading it. You will make an interesting and amusing case study for my book, that among other things explores this bizzare human ability to self deceive and ignore the obvious. That is what ignorance is all about, ignoring. So as you and grizzly have ignored what I have written I shall ignore you. Will I read your response to this? No, I learnt that long ago, you just walk away, turn, and dont look back. Enjoy your delusion.
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Old Mar 14, 2006, 4:21 PM   #153
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Keep it Civil Guys.

Debate the issues, and don't throw flames.

Keep personal comments out of it.


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Old Mar 14, 2006, 4:30 PM   #154
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who let the nun in?
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Old Mar 14, 2006, 4:34 PM   #155
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I can see that you have a point your trying to make, I can see its relevance, but you examples are goofy your descriptions are flawed and every post contains inflamitory remarks. Its really HARD to see through all that.

You want to say something about interfering light, what? I've seen plenty of remarks regarding your posts (the on-topic portions) and it looks like everybody has misunderstood you so far. When everybody around you is crazy, its time to look inward.
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Old Mar 14, 2006, 7:28 PM   #156
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Damn, this is going back and forth.
I just wanted to say that I'm starting to read things (just so you know I'm not ignoring you. I've been "accused" of ignoring threads because I don't always have the time to read the long ones. I still find it interesting.

I was also thinking about the bumblee bee example when I wrote my post, actually. I've always viewed it as an example of mans huberous. We *think* we know a lot (or everything) when clearly we don't. Science at the time said the bumblbee couldn't fly, but clearly it could. I do engineering for a living (not physical, though... Computer Science), so I'm constantly dealing with trying to maximise knowing what I know, and minimizing the things that I think I know but don't.

Mark47,
That nun, as you put it, helps run the place. If you don't like it, then please leave. They have the choice to run it as they choose. Personally, I agree with him. You can disagree with tmoreau as you want, but don't insult him and expect it to get by. As I've said before, go to the forums on www.dpreview.com if you want to attack people personally. That is accepted over there, it isn't here.

Eric
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Old Mar 14, 2006, 7:38 PM   #157
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Alright, back to my previous posts. (I left some loose ends, its time to tidy them up)

To sum things up, lenses can not be defined simply by focal length, you must also consider angle of view and maximum aperture. Using the f/d ratio you can estimate the aproximate minimum size of the front element, for example a 200mm f/2.8 lens will be at least 71.4mm in diameter. Varying the focal length and angle of view will change the image circle, and therefore maximum sensor size. The so called "crop factor" comes in when a lens designed for a larger sensor is used with a smaller sensor, thus not utilizing the whole image circle.

Refering to such measurements as the airy pattern of diffraction and numerical aperture we find some measure to the theoretical limits of lens resolution. Whats interesting is that for a given angle of view a lens resolves detail of a certain size on the focal plane. We can vary this 'number of pixels' if we use a longer focal length to increase the size of the image circle (physical 'pixel size' remains the same). These limits apply to all optical systems, and real results can be assumed to be less. There are probably additional factors to consider with how these minimum details overlay onto an image sensor, but at least we have a general outline of what to expect.

If we look at this another way, we can see that it is in fact a limitation in optical systems and not a limit in the light availible. This can be proved by considering the example I gave of a 28mm 12 degree FOV lens compared to an 825mm 12 degree FOV lens. They took in the same "composition", and resolved detail at the same size on the focal plane, but due to the larger image circle of the 825mm lens we have more of those fixed size details. The difference was that the 28mm lens could not distinguish between the three colored pixels of the TV, but the 825mm lens could, even though both were in the same location and had the same field of view.

The differences in field of view, sensor size, and focal lengths can be summarized in this chart. Consider that the Minolta A1 has a 2/3 sensor and a 7.2-50.8mm lens, we can reference the chart and see that its field of view compares to a 35mm camera with a 28-200mm lens.



We know there are limits (with todays technology) to how small you can make an image sensor. Compact digicams often use photosites that are as small as 3 microns, but with high amounts of noise. DSLR's use photosites that are 6-8 microns, sometimes larger. At all fields of view, the theoretical resolution limit is well beyond the accepted limits to sensor design.

There is much more to consider in lens design, though. Lens abberations come in many types and are only one of the limits to achievable resolution.

Still, even if the exact numbers arent achievable it gives a point of comparison. Since the aperture value (f-stop) dosent seem to factor (as far as I can tell [edit] it seems my calculations are just based on f/1, using a smaller aperture will degrade max resolution more than what I've shown) we could have a 100mm 12 degree fov lens with f/2.8 (35.7mm minimum diameter) and a 200mm 12 degree fov lens with f/5.6 (35.7mm minimum diameter) that have different image circles and different theoretical maximum resolutions. Since they are gathering light from the same area, it seems that resolution is limited by the lens (and not, or much less so, by the availible light). Sure, youd need to vary the shutter speed or sensetivity to maintain the same exposure, but its an interesting point.

I'm quickly tiring of this, since it seems I'm talking only to myself. Its been a lot of fun disecting what limits we are up against, and an eye opener in a few cases. I hope that there is at least somebody reading this who isnt a photographic phd and finds it interesting. Working the numbers will only get you real world results when you really know everything that goes into the problem (ala bumblebee, where the figures were based on a model too rudimentary to apply to reality), but its also how I make a living so of course its where I'm going to focus my efforts. Another approach might be to compare measurements of actual lenses and chart the results, and that would be just as valid and potentially more accurate since it dosent rely on 'knowing all the variables'. This post was to put my point into conversational terms, which I really couldnt do without making the more technical posts this weekend to substantiate it.

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Old Mar 14, 2006, 9:25 PM   #158
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Very interesting stuff.
There are some things that I don't claim to understand fully... my physics classes didn't go into optics much (I took a full year of college physics, but optics at this level is taught later.) So some of that was over my head.

I also found this link very interesting:
http://www.cambridgeincolour.com/tut...hotography.htm
Maybe others will too.

tmoreau, like you, I don't see where your argument contradicts much of what I read... although I must admit that I skipped a lot of the name-calling posts and therefor probably missed some of the meaningful portions of what people said.

I'm unclear on something about N.A., which maybe you could answer for me. The answer wasn't in the wikipedia entry you linked to. "θ is the half-angle of the maximum cone of light that can enter or exit the lens" What is a "half-angle" in this context? How is it calculated? And how does that vary per lens?

Thanks, I've enjoyed the factual non-name-calling portions of this thread.

Eric
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Old Mar 14, 2006, 9:39 PM   #159
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If the lens gives a 12 degree FOV across the image circle, and the whole image circle is used, your sensor captures 12 degrees diaganolly (thats not what you asked, just trying to be complete) the half-angle is simply six degrees. Its measuring from the center axis, rather than the whole cone. Its also useful to note that the angle of view is probably always a bit more than the aov captured by the sensor, throwing things off a little.

The more I poked through wikipedia, the more entries I found about this topic (in general). Very interesting stuff indeed, that link looks quite interesting I'll have to read it in detail. I like the interactive bit about the airy disk.
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Old Mar 15, 2006, 1:08 PM   #160
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I thought that interactive part was very helpful in understanding it (once I really thought about what I was seeing. Damn, you mean I gotta think in off-work hours!)

Maybe it was just the wording that threw me. The use of "is the half-angle of the" instead of "is half the angle of the". The second is much clearler to me that its a simple 1/2'ing. Saying it the way that they did made me wonder if there wasn't something else going on.

Eric

ps. I think we actually strayed from the original topic quite a lot... as it was if the 35mm equivalent information listed for digital cameras is a good or bad thing. But some of the information in the digression is relevent to that point (sensors out resolving lenses is an issues as the sensor size gets smaller.)
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