sharp images at close aperture

[prasad_apte]

<p>I just want to know that why you can get the sharper images on lower f stops?</p>

[bobatkins]

<p>Sharpness is lowered by Spherical Aberration at large appertures (e.g. f1.4) and by diffraction at small apertures (e.g. f22). Somewhere in the middle (usually around f8) you get the sharpest image since SA has decreased a lot while diffraction still isn't large enough to significantly blur the image (at least with SLRs)</p>

[tommyinca]

<p>In an "over simplified" way, a good amount of lens errors (aka: aberrations) are caused by difference of how light(s) bend between the center and the edges of the lens. When you close down the aperture Iris, some of the light from edges of the lens are blocked off there by improves image sharpness and reduce internal flare (contrast). Not all lens errors can be corrected this way so it is also not a fix all solution. </p>

[peter_mckone]

<p>I may not understand your question correctly... In addition to what Bob said, the focal plane is VERY thin at f 1.8. So even though a sharp image is theoretically possible, your camera's auto-focus has no margin for error. At f 22, everything is in focus.</p>

[gorasinski]

<p>Have you ever had eye drops applied? Well, if you did then you probably remember that they open your pupil wide open and you could not see sharply in daylight, only at night.<br>

However, if you create a little tiny hole with your fingers and put it aginst your eye, the sharpness drastically improves, but the image becomes darker.<br>

This is the best example when trying to explain what do those f numbers do :)<br>

This is exactly how cameras work.</p>