Peak Sharpness of Lens

Discussion in 'Beyond the Basics' started by pm63, May 21, 2008.

  1. pm63

    pm63 TPF Noob!

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    I keep reading about how certain lenses acheieve their peak sharpness at certain apertures. I was wondering if:

    1. I should be paying special attention to where my lenses achieve their peak sharpness? Obviously, I'd like to be able to control DOF but if this also controlls sharpness there is another factor to throw in, another compromise to be made.

    2. Will I notice a big degredation in sharpness if I am not at the "peak" f-stop?

    3. How important is peak sharpness generally. Kinda the same as #1.

    4. My lenses are the D40 kit lens (Nikkor AF-S DX 18-55 f/3.5-5.6), as well as the 55-200 f/3.5-5.6. Does anyone know whereabouts they achieve peak sharpness?

    Any help would be very much appreciated.
     
  2. Alex_B

    Alex_B No longer a newbie, moving up!

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    It is always a compromise. But I would say composition and the effect you want to achieve with your image comes first. So to me that also includes control of DOF. If DOF however does not really matter, then you can think about peak sharpness.
    Depends on the lens. With wide apertures you get all the problems of the lens projection, with apertures too small you get diffraction problems. The former strongly depends on lens design, whereas the latter is similar for all lenses.
    Depends on how bad your lens is if you are not in peak sharpness, and it depends what you want to use the images for.

    sorry, never owned that lenses. but usually you will find graphs online somewhere telling you about the optimum aperture.
     
  3. goodoneian

    goodoneian TPF Noob!

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    i'd have say worry about dof first, cause you can sharpen and image in post processing easier than produce you can depth of field
     
  4. Early

    Early TPF Noob!

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    Lenses are usually at their sharpest 2 to 3 stops down from their wide open position.

    There's also a thing called optimization. Lens #1 may produce better results at a distance than lens #2, and be just the opposite close up.
     
  5. AndrewG

    AndrewG TPF Noob!

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    You may not always be able to use your lens at its optimum performance aperture-very low light might involve maximum aperture where the lens might not be performing at its best. If you are using your lens creatively with variable depth of field then, as Alex says, you will be very slightly compromised.
    If your lens is good quality to begin with, you'll barely notice any image degradation except, possibly at the extremes of the aperture range. Some wide angle lenses will have noticeable vignetting at full aperture.
    Also I believe that too much emphasis is placed on image sharpness; if you look at the work of a master like Henri Cartier-Bresson many of his pictures made with a Leica and 5cm lens are anything but sharp, in the accepted sense. It's the final composition of the image which is important.
     
  6. pm63

    pm63 TPF Noob!

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    Thanks for your input everybody,

    As Alex and Andrew say, creative effect and getting the 'vivion' right is more important to me than minute differences in sharpness, and I am willing to sacrifice it. Guess I'll not worry about it then.
     
  7. Dubious Drewski

    Dubious Drewski TPF Noob!

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    I have looked at LOTS of lens data and I've found that as a general rule, you'll get the sharpest results from your lens if you're a couple stops from maximum, as stated (That's around f5.6 or f8). But some lenses are strange, like the kit Canon 18-55; The wider open you are, the sharper it gets. You are also going to get the best sharpness at about 1/3 into the zoom range. For example My Pentax 18-55 is sharpest at 24mm (At f5.6, it out-resolves the K10's sensor) PM63, with your 18-55, your sharpest point is at 35mm and at f8. Exactly that. But don't let it dictate your shots, just keep it in mind.

    For example, the Canon 70-200 f2.8 and the Nikon 70-200 f2.8 are both sharpest between 100mm and 130mm. And then they both drop off significantly the further you zoom in. (The Canon drops off ALOT. And it's an L lens, I don't get it.)

    Also keep in mind that peak CA and fringing seems to be sometimes independent of the optimal sharpness. Sometimes you'll have excellent resolution but be susceptible to fringing and vice versa.

    Actually no, I'm going to have to contradict you on that. It is much easier to create bokeh than it is to create sharpness.

    When you sharpen, you're taking minimal visual information and trying to create the illusion of more detail with it(Simply by exaggerating contrast at edges). With blurring, you're just taking away information, so that's easy to do in a way that looks good(and believable). Especially so if you have access to CS3 and can use the lens blur feature. But if not, plain Gaussian will do it too.
     
  8. Samriel

    Samriel TPF Noob!

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    www.photozone.de

    If it helps, you have some lens tests and reviews, and you can compare lab performance and sharpness at certain apertures.
     
  9. Garbz

    Garbz No longer a newbie, moving up!

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    I wouldn't even worry about it.

    I have never judged the quality of an image by it's sharpness or it's noise (unless the noise is really distracting from an image). The sharpness fetish is something born with the digital cameras and the constant zooming in on pictures.

    Go to the local library and grab Time Life's best photos of the 20th century, and have a look at just how many stunning photos in that book would be considered sharp by the twisted standards some of the members of this forum put on images.
     
  10. passerby

    passerby TPF Noob!

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    Generally I am satisfied with clear enough photos where the objects I aimed is/are in the frame, since the pictures are just for me myself. But lately I am start becoming a pixel peeper where I many times engrossed by it. I believe this is a sign that I am starting to expect only the best.

    Anyway. There are seem to be more than just lens that make the photo sharp:

    Camera movement,
    subject movement,
    subject not in focus,
    changing brightness of the lighting,
    the distance of the object from the camera.
    And also the ISO.

    I assume here you are talking specifically your own lens. I have seen number of times photos taken by the Nikkor 55-200 vr like yours are really sharp. Maybe the VR has good influenced to it - I don't know. I have the 18-55 like yours and most of the photos produced are quite good considering this is a mere plastic kitlens. I am satisfied with the result from f5.6 to f11. To be honest I have never tried slower or faster aperture than that. But mostly I just use f8.

    I may upload couple pictures for sample in the general gallery some other time if/when I am in good uploading mood.:wink:
     
  11. chris

    chris TPF Noob!

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    Either obtain a test chart and photograph that at various settings or select a static object (buildings are good - they don't usually move very much) set your camera on a tripod or firm support and photograph at various apertures, focal lengths and subject distances. If you want to check out the lenses at short distances then newsprint makes a good subject but try to ensure that it is flat otherwise shallow depth of field may mask sharpness of the image. For best results pick a time when the illumination is constant so that variations in contrast do not affect interpretation of the results. Check the results and identify what range of apertures give the best results.

    You can look up reviews and tests but these are typically carried out on just one sample and you don't know whether it was specially selected because iot would give good results or whether it was a good, bad or average example of the lens. Only you have the actual lenses that you will be using so just get on and do it yourself using your equipment.
     
  12. Joves

    Joves No longer a newbie, moving up!

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    I have to agree totally. Just look at any of the old publications, they wouldnt pass the new standard of some today for sharp. Really if the image has the right content you never notice the finer details.
     

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