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  1. #11

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    Try photographing a black circle on a white background at various shutter speeds hand held. You will discover once the images are enlarged, that the circle becomes slightly oval at the slower speeds.
    The longer focal length will make this even more pronounced. Try using a tripod if the situation allows, to get the best image quality out of your lenses
    Last edited by Marcus S; 02-21-2011 at 07:43 PM. Click to view previous post history.

  2. #12
    Markster's Avatar
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    I see that I'm in for another round of test shots. I think I need a focus test. The tape measure is a good idea (or a yard stick).

    I was using a shutter release with a tripod to take some test shots in lower light with Ektar 100 and noticed that it wasn't as crisp as I imagined it should be. It's a slightly older tripod, so it's a bit heavier. Not heavy duty mind you, just old. I thought it might be better off than a lighter flimsier one you might find on sale nowadays. The camera didn't seem to vibrate or move at all.

    I guess I need to get some more film!
    -Markster

    Canon AE-1P 35mm | 50mm/f1.8 FDn | 28mm/2.8 FD | 70-200mm/f4-5 FD | 35-70mm/F2.8-3.5 Sigma FD

  3. #13

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    No need for a test chart, but a tripod is a necessity for the test. Lock the camera down on the tripod and focus on an "infinity" target & make an exposure, a second or third exposure if you like at different distance. Then duplicate the test with another of your lenses. Compare the negatives
    Heavily sedated for your protection.

  4. #14
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    You do see kind of what you get, but keep in mind that a viewfinder has much, much less resolution than the negative you're shooting. The other thing is that many cameras vignette inside the viewfinder optics (it's mostly a matter of how the viewfinder screen is ground and only a narrow range of incident angles showing up, which means an effectively smaller aperture), which means that you will perceive a deeper DOF in the viewfinder than you achieve on film, especially if shooting wider than f/4. So it might be misfocused yet appear to be sharp due to a combination of the viewfinder being low res and showing more DOF.

    If you have a split-prism, that should never be in error.

    Never focus then recompose, it will cause focusing errors due to rotation of the focal plane. Don't focus then zoom out unless you know for certain that the lens is parfocal. Most are not.

    If you're sharpness-testing, a tripod, release cable, stationary high-contrast subject and MLU are mandatory.

    It might just be a cheap, soft lens - even the cheapest crap optics will still look sharp in the finder, which kind of demonstrates that you can't judge final image sharpness from the finder. Even crap lenses should give you sharp results at f/11, so test at a range of apertures to see if there's an improvement.

  5. #15

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    What you see is what you should get but if you have a plain screen then it can be tricky to get critical focus. Some plain screens are better than others for getting focus.

    Anyway, you seem to have other lenses. Do you have an issue with the other lenses? If not, then this particular lens is just not that sharp.
    Hasselblad, Mamiya RB, Nikonos, Canon EOS

  6. #16
    markbarendt's Avatar
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    Quote Originally Posted by holmburgers View Post
    28mm at f/3.5 is going to have lots of DOF, so focusing errors might be harder to spot in the viewfinder. I'd recommend zooming in to 70mm on the subject, focusing, and then backing off.
    Well DOF depends a lot on subject distance.

    I have a Tokina 28-80 2.8 that is truly finicky about focus anywhere near wide open even at the wide end. Tends to end up focusing oddly if I'm not being careful.

    It also focuses at different points in the focus ring's rotation at 80 and 28 so zooming to focus doesn't normally help.

    It is WYSIWYG though.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  7. #17
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    Quote Originally Posted by holmburgers View Post
    28mm at f/3.5 is going to have lots of DOF, so focusing errors might be harder to spot in the viewfinder. I'd recommend zooming in to 70mm on the subject, focusing, and then backing off.
    I would agree with this, I find it better with zoom lenses to focus on the maximum focal length then zoom back to required one, because they are less subject to "Focus Shift" this way.
    Ben

  8. #18
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    The zoom has a macro focus at the 70mm stop. Would you suggest testing the short DOF that the macro has? Or would you think this might be in focus but the normal ranges could still be soft?
    -Markster

    Canon AE-1P 35mm | 50mm/f1.8 FDn | 28mm/2.8 FD | 70-200mm/f4-5 FD | 35-70mm/F2.8-3.5 Sigma FD

  9. #19
    Lee L's Avatar
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    There are two types of zoom lens designs. Parfocal zooms are designed to stay in focus at the same distance at a given setting throughout their range of focal lengths. Varifocal zooms need to be adjusted for focus as focal length is changed. Parfocal zooms are often 'close enough' (manufacturer's/designer's call), but not dead on focus as the focal length is changed. Parfocal zooms are more difficult to design and more expensive to produce. Ever look at the prices for cine zoom lenses, which need to be more accurately parfocal?

    My impression is that as auto-focus came into wide use, this distinction became of less concern and so attention to varifocal vs. parfocal lenses in marketing and reviewing was dropped, and you don't see it mentioned much anymore, to the point that many who entered photography in recent years are completely unaware of the design differences. The distinction between varifocal and parfocal zooms was an often-discussed design feature before autofocus, especially among news and sports photographers who needed the parfocal feature for speed in use.

    Lee
    Last edited by Lee L; 02-22-2011 at 10:58 AM. Click to view previous post history.

  10. #20

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    I've been out of focus most of my life!

    Jeff

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