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09-29-2008, 10:29 AM   #1
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How can a lens "outresolve" a sensor?

I've come across the term "outresolve the sensor" to describe some lenses. I'm not sure what it means.

Is there "too much" lens for some sensors? Is it qualified by sensor size -- too much lens for a 6mp , but ok for a K10, and best on a K20? I realize that a K20 is going to bring more detail at the same size to an image than a K100 will, but how does the lens figure into that.

By "too much" I mean is the cost of that lens not justified because the output images won't benefit from the lens' ultimate resolving power, e.g. a 31mm on a K100D?

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09-29-2008, 10:52 AM   #2
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Hmmm. I know what it means. . .difficult to explain. You might start by reading this:

1951 USAF Resolution Test Chart - Wikipedia, the free encyclopedia


But there is a physical limit to the amount of detail a piece of glass can project onto an image plane. Typically, a good, expensive, lens will have more resolving power than a cheap lens.

A Pentax Limited is going to capture more detail than a plastic Holga lens.

. . .but now, we can record more detail than even a good lens is physically capable of projecting.

A more in depth answer

http://www.luminous-landscape.com/tutorials/resolution.shtml

Last edited by konraDarnok; 09-29-2008 at 11:07 AM.
09-29-2008, 11:41 AM   #3
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The lens doesn't figure out anything. It's a passive optical system. All it does is form an image on the focal plane.

See it this way : if you smear oil on a window, it's harder to see through it, so the resolution it gives you is lower. If the window is dirty, same story. If you get a better, clearer window, the resolution you can see is better. Replace "window" by lens and you get the same interpretation.

Now, the sensor is like our eyes, they can be better or worse, but they have no impact on the performance of the "window".

The sensor's role is to record the image created by the lens. Both are working together, but each has its role.
09-29-2008, 02:14 PM   #4
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QuoteOriginally posted by FHPhotographer Quote
I
Is there "too much" lens for some sensors?
Not in the sense of actually producing worse results than a lesser lens - just in the sense of not actually demonstrating its superiority.

Simple example: consider viewing thumbnails only. No way could you tell the difference between any two lenses looking at a picture the size of a postage stamp. View the images at typical web dimensions (say, 400x600) and maybe you could tell the very worst lenses from the very best, but most would basically look the same, somewhere in the middle. View at 100% and then you can see everything there is to see.

QuoteQuote:
too much lens for a 6mp , but ok for a K10, and best on a K20?
In the sense described above. A 6MP camera might not have enough resolution show the difference between two given lenses, just as is the case when viewing thumbnails. Move up to a 10MP sensor and some difference become more apparent, just as viewing at web dimensions might. Move up to 14MP and maybe now it's more like viewing the images at 100%.

QuoteQuote:
I realize that a K20 is going to bring more detail at the same size to an image than a K100 will, but how does the lens figure into that.
If the lens is not *capable* of that kind of detail, more pixels won't help. Tape a Coke bottle to your camera instead of a lens and see if the K20D gets you any more resolution than the K10D. More pixels will display more details only if your lens is capable of produing details that your current sensor is not showing because it lacks the pixels. Which is to say, if it is outresolving the sensor in the sense we talking about.

Actually, in practice, it's probably never that simple - it's not like resolution is constant across the frame, or the same at all apertures or subject distances. But conceptually, that should help clarify things.

QuoteQuote:
By "too much" I mean is the cost of that lens not justified because the output images won't benefit from the lens' ultimate resolving power, e.g. a 31mm on a K100D?
There can easily reasons other than resolution why a lens might be worth it. If you're going to shoot at f/8 all the time, the 31 might not beat the kit lens at all in resolution on a K100D in the center. It might beat the kit lens in the corners, though. And it will beat it more and more in resolution as you go to wider apertures. But if it also has better color, contrast, bokeh, or whatever else, that's going to hold regardless of whether it is outresolving the sensor or not.

09-29-2008, 04:03 PM   #5
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Its become a real concern as camera technology and larger digital capture capability are revealing faults, chromatic aberration, distortion and sharpness issues in modern lenses that were not as much as a concern in the past.

Some users now wish that the manufactures focus less on the camera body megapixel arms race and instead build better lenses. Quite a few shooters are no longer as happy with their zoom lenses and are going back to collection quality prime lenses as a result...

Max
09-29-2008, 04:28 PM   #6
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Marc, I think I followed that, thanks. I just want to drag the "output" issue in here...

I really think the ouput/print is the final arbiter of the image quality. When I look at the dpreview test images for the k100d and k200 at 100% crops I see no appreciable IQ diffence between them on the screen; true, the 10mp will allow a larger 100% print, but at 10x14" I can get a 180dpi print that is virtually identical to the naked eye to the 11x14" 240dpi print from the k200. The real value in the additional mp is in cropping and that's where a 50% crop of the k100 will be different than the k200 at the larger sizes.

thinking out loud, now... a great lens mounted on a K20, in my hands, will probably give me pretty much what I can get with my 28-105 lens on my humble K100. It isn't a question of the lens outresolving the sensor, it's a question of the lens outresolving the photographer.
FHPhotog

Last edited by FHPhotographer; 09-29-2008 at 04:34 PM.
09-29-2008, 05:08 PM   #7
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the bad thing about better sensors is they also demand higher quality glass too

the more dense the pixels are in the sensor, the need for more resolution from the lens
for FF, also need to consider corner performance
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