bpulv Loc: Buena Park, CA

Picture Taker Loc: Michigan Thumb

Thank you burkphoto. I always find your input with reading.

fotobyferg

“Who’s on first...”

frankraney Loc: Clovis, Ca.

This is what I've read and understand, as an amateur that does not understand a lot of what goes on. I just use the aperture and SS at lowest ISO to get the photo.

tropics68 Loc: Georgia

Very interesting and informative. Thanks

John_F Loc: Minneapolis, MN

The edge zone as I used it has a width over which diffraction effects are noticeable. This width is not a function of the radius of the circular aperture.

editorsteve

The explanations given here and linked to are roughly true. As a physicist who has designed and built (simple) astronomical optical systems, let me put it this way.

1. There is ALWAYS diffraction at the edge of a lens or aperature iris-stop.

2. The diffraction pushes some light waves (photons if you are quantum-oriented) into the entire field of view.

3. As they interact with the light waves that are SUPPOSED to be in the field of view, they can degrade the imge we're trying to capture -- looks sort of like flare but the interaction can produce lighter or darker spots. The interaction appears random but it is not -- it can be calculated with difficulty from the wavelengths and the lens/aperature/iris geometry.

4. As the aperature is reduced, the amount of diffracted light stays roughly the same but it increases, relative to the light that is SUPPOSED to be there. This degrades contrast and resolution. When the aperature is VERY VERY small, as roughly noted by the first commenter, the image you finally see or record on the sensor is said to be diffraction-limited.

5. Usually, this has little effect and is hard to notice. But as the scene gets darker, diffraction's mischief is easier to notice. If I use my 3" f/13.3 refractor (with excellent doublet lens) on a dark night to view a star cluster, each star (which should be a tiny point) will appear as a tiny DISK due to the resolving limit of the lens. But the light from the other stars in the same field will obscure a faint ring around each star. I can see the faint ring when I look at a bright solitary star or binary star on a clear, dark night. The ring is mainly diffraction. There is some diffraction in the disk as well.

6. Moral: A really wide-aperature lens of really high quality will have good resolution at full aperature, great resolution as it is stopped down, and somewhat diffraction-limited resolution as you get to the smallest aperatures. But the point at which that happens depends on the sensor size, brightness of what you are imaging, and the quality of the lens. True, f/11 or f/16 or even f/22 or f/32 may be the limit, as you struggle to gain depth of focus. You can play with lens tilt, camera placement and sensor size to get the best result, but it can never be perfect with optics alone. Software that can calculate and "cure" the diffraction and other abberations is getting better and better though. We are heading for software-envy attacks that will replace gear-envy attacks!

Anhanga Brasil Loc: Cabo Frio - Brazil

You got me lost here. The distance in wavelength is given on linear metric
measures, e.g., 10 meters or 100 nanometers. Hertz is a unit for Frequency,
i.e., Cycles per Second. Electric current is usually 50 or 60 Hertz (Hz) depending
on where one lives. The same goes for radio waves and light waves. In the case
of Light, I am leaving the "Photons" out of the equation (they did work for Einstein, though).
IIRC, that is the way it is. I do not know if anyone mentioned that, but I did not
reach the end of the topic, yet.

Picture Taker Loc: Michigan Thumb

I all so majored in physics ant two points as I see it 1) your lens is the sharpest the middle range (f8 or may be f11) and 2) I love my picture talking and sell them as a picture mot as a technical marvel. But love this conversation.

Uuglypher Loc: South Dakota (East River)

Elmslie’s citation of Cambridge in Color in no way proves any aspect of my comments on diffraction relative to relative apertures to be incorrect in either relative or absolute terms. I may have been remiss in failing to emphasize that although the focal length and distance to sensor conspire to render the resolution effect of the significantly different diffraction occurring to a slight degree with a large f/16 aperture in a telephoto lens and to a much greater degree with a much smaller f/16 aperture with a wide angle lens may or may not be indistinguishable related to airy disc diameter and the pixel sizes of the sensors in use. For those of a more classic bent, the characteristic grain size of different photosensitive emulsions enters into consideration.

The above is not, I freely admit, germane to Bob’s original question, and for that I do, most abjectly, apologize for attempting to introduce a personally considered practical aspect into the conversation. Mea culpa maxima est! (with chest beating).

I should have been more pointed in emphasizing the basic fact that diffraction is, always, forever, and without exception, greater with smaller apertures than with larger apertures and that this incontrovertible fact is of significance only to those with the practical desire to get the best performance out of each of their lenses. To bring home the significance of this requires only that each, newly acquired prime lens be routinely and easily tested to determine, within the series of available smaller apertures, the aperture at which the obvious softening effect of diffraction actually becomes unacceptable. Zoom lenses must be similarly tested at different focal lengths.
It will be discovered that the particular aperture at which diffusion becomes critically objectionable will differ among different lenses (and will be judged differently by different observers).

We ought not forget that many of our modern cameras function with modes of various degrees of automation. Some exposure modes fail to take into consideration the phenomenon of the onset of unacceptable image “softness” due to diffraction with progressively smaller apertures. If you want a silky waterfall in bright sunlight, and choose shutter priority at a very long shutter duration and fixed ISO, you are taking your chances with your camera choosing a minuscule, diffraction-rich aperture.

And lastly, unacceptable “softness” is a highly personal criterion! Since having my old, well-used, cataractous lenses that had done yeoman service over almost eight decades replaced with new, crystal clear polymer ones, I am repeatedly discovering the need to re-evaluate a number of images from the more recent decades of my archives regarding the “sharp-soft dichotomy”. It is thus very much a case of “each to his own” or, as Miss Bibiana Stark, my high school Latin mentor would intone:
“De gustibus non est disputandum”.

...and so it goes!

Dave

fourg1b2006 Loc: Long Island New York

I don't know if i learned something or just wasted my time. Im not going to bother trying to figure it out.

broncomaniac Loc: Lynchburg, VA

Hahahaha. Ditto.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

User ID

The two posts above about leaf shutters and apertures
are backwards. Referring back to the thread title, with
a leaf shutter, "f/16 is [still] f/16"... BUT ..."1/500
sec slows down to 1/250 sec".

The "leaf shutter effect" does nearly nothing regarding
effective aperture. The effect is that size of the aperture
influences actual shutter speed, only at 1/250 or 1/500.

The shutter speeds are calibrated [using that term quite
charitably] to include the time spent opening and closing,
and NOT just the time spent "paused" at fully open. So
the time it takes to clear the aperture is figured into the
nominal shutter speed.

Clearly, this formula is inconsistent at high shutter speed
comparing the time-to-clear-the-aperture at both large
and small apertures. The result is that at about f/16 and
smaller, the 1/500 may effectively be actually 1/250 so
that the exposure will be 1EV over.

This info used to be plainly stated in the user manuals
that shipped with 'Blad leaf shutter cameras.


A revealing side note is that there were a very few leaf
shutters that claimed 1/1000 sec or 1/1500. These were
for real, but limited to smaller than f/8 or f/11 at those
speeds. The "magic" was a special mechanism that would
limit the maximum opening of the blades to about half of
their normal full open diameter, thus shortening the time
it took to execute the reciprocating motion of the leaves.

Soooo .... the leaf shutter effect can be either a problem
or offer a benefit. For the price of 'Blad lenses, Compur
should have licensed the beneficial design from Copal [or
Seiko ... don't recall exactly].

Anywho, if you wanna use maximum shutter speed with
a leaf shutter, don't stop down past about half way ;-)


`

tbrad57 Loc: Cottonwood, AZ

I have to chime in on this just because I see a lot of information being thrown around and although that information is valid does it matter. Most lens have a sweet spot for what f stop works best with it. A favorite photograph of mine is Edward Weston's Pepper #30 shot with an f stop of 240 with a very long exposure in the order of 4 to 6 hours. Granted he was using a view camera and they typically can be stopped down to f 64 hence the name Studio 64. Don't think there was a problem with refraction in his work.