Manual aperture vs. automatic

Discussion in 'Nikon' started by christian_stahl, May 10, 2008.

  1. I got a D40x and am getting aquainted to it/digital photography. I used to believe (at least with
    classic cameras) that a higher aperture makes landscape in the distance sharper. It doesn't with
    the D40. I chose an aperture of 20 for a landscape, and it turned out less sharp then the auto
    aperture. Maybe I'm mistaken about what manual aperture is for - what do I need it for?
    I'm not very happy with the lowest aperture (5.6) and the kit lens in "tele"-mode (55) for portraits -
    the background is still quite sharp. At least that's different from classic cameras!
    This must sound very naive, but apart from practice - where do I get appropriate information about
    setting the aperture manually on my camera?

    Thank, Christian
     
  2. probaly diffraction that starts to interfere above f11.
     
  3. Indeed, the kit lenses don't generally provide a wide/fast enough aperture to eassily isolate your portrait subjects from a nearby/intermmediate-distance background. And as you've seen, the longer you push the lens, the tighter that widest aperture becomes. That's just a fact of life with the less expensive lenses, and you'll have to work with distances between you, your subject, and the background in order to make the most of that withoug buying a faster lens.

    As Hans mentions, much past f/11, and you'll be seeing the effects of some diffraction that will cause some visible softness on certain types of detail. That's sor of a laws-of-physics problem that's a little more pronounced on digital sensors that it is on film. I have noted that being a bit less of a problem when the lens is of better quality in the first place. Meaning, I can stop a good prime lens at 60mm down to f/22 and see less trouble with diffraction than I'll see at f/16 (at the same focal length) in a more consumer-grade zoom. Optical sins and complexity in lenses are cummulative, so every little thing counts.

    Your urge to shoot in aperture priority is a good one. You're just up against two limitations (slower lens issues when wide open, and diffraction that impacts all lenses - but some worse than others - when stopped down). It takes some time to find your sweet spots, there, as they apply to your subjects and style. Of course, new lenses are always fun!
     
  4. There is no difference in the effect of an aperture if it is selected manually or automatic.

    "Manual aperture" just mean that the camera selects the aperture diameter automatically. A smaller aperture results in less light hitting the sensor and also results in an increase in "Sch䲦entiefe" . Less light hitting the sensor must be compensated by longer exposure time to get the same level of brightness in the final image. There are many factors that could give you less sharp images and a long exposure time could be one of them.

    I recommend reading the manual and a basic introductory book on photography. I am certain your local library will have plenty to offer :)
    See it this way: Looking at an image of an old flute will not make you an expert in playing the instrument. There is much more to it. Once you found out which end to play it still requires training.
     
  5. The only time I shoot above f16 is when I'm deliberately wanting a less sharp look to the photo.


    Kent in SD
     
  6. The problem with small apertures reducing sharpness is created by a phenomena called
    diffraction. Ken Rockwell recently wrote an excellent and practical article that will help
    you to determine the 'sharpest' aperture yielding the maximum depth of field for your
    shooting situation. The article is freely available, here:

    http://www.kenrockwell.com/tech/focus.htm
     
  7. What was the shutter speed in both cases?
    A small aperture (large f no.) requires a correspondingly slower shutter speed to achieve the correct exposure.
    I suspect your reduced sharpness at f20 is due to camera shake, not diffraction.
     
  8. Shutter speed is the more likely answer. Diffraction exists but it's fairly subtle, and would rarely be noticed by novices on casual inspection.
     
  9. Thanks a lot. I used a tripod + "2 seconds-mode" (in English??? the camara waits
    two seconds , then takes the picture).
    "As Hans mentions, much past f/11, and you'll be seeing the effects of some
    diffraction that will cause some visible softness on certain types of detail." Thanks,
    that's what I saw, I just didn't konw why.
    "you'll have to work with distances between you, your subject, and the background
    in order to make the most of that withoug buying a faster lens."
    OK, that's a compromise.

    I just don't see the difference using different apertures with this lens/camera, but I
    guess I'm expecting too much - it's not medium format after all.
     
  10. It's not just that it's not medium format. It's that the lens is not very fast. By that. I mean that the smallest aperture is rater small and so you won't see the really out of focus backgrounds with f5.6 as you would with an f2.8. For the f20 shots, you have chosen, the shutters speed may need to go quite low which can be affected by some camera shake. You really do not need to go all the way to F20 to get a nice sharp landscape shot. F8, f11, f16 are was wide as I've seen published photos, to be honest.

    Is auto aperture the same as aperture priority on film cameras ?
     
  11. I don't believe you mentioned what lens you were trying but for a typical lens one would use for a camera like this you will probably find your sharpest fstops from around f6-f11. Anything on either side of these values will tend to be on the soft side. I'd suggest reading up on depth of field, circle of confusion. These will lead to other terms and techniques that will be of help to you.

    Frankly for landscapes with digital I rarely stop down less than 8-11 depending except with 4X5 but that's a bit different.
     
  12. I use the kit lens (18-55 mm, 1:3,5-5,6). I am a bit concerned about aperture of the
    lens. As far as I know, the only single lens lens available for the D40x is the 'Sigma
    30mm f/1.4 EX DC for Nikon', and and there seem to be some issues with quality
    consistence. Maybe by the time I'm used to the camera, Nikon has some more lenses
    for the D40.
    Here are some pictures I took, all of them unedited, exept for the "konzert" picture:
    http://gallery.mac.com/stahlchristian#100120
     

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