f/16 Isn't Equal to f/16 (Page 2): qi Hi, Bob, Interesting discussion.As you state it is important to remember that the functional system of relative apertures is that two lenses of...

Uuglypher Loc: South Dakota (East River)

qi Hi, Bob,
Interesting discussion.As you state it is important to remember that the functional system of relative apertures is that two lenses of different wave length will have differently sized apertures of f/16. The aperture diameter is relative to the focal length.
The f/16 aperture diameter is 1/16 of the lens’ focal length and will deliver proportionately the same intensity of light to the film or sensor served by lenses of differing focal lengths but each with the same aperture.

As for diffraction, it occurs with light rays passing intimately by the edge of the aperture. Let’s keep in mind that the f/16 aperture of a 400mm. lens has a greater circular area with proportionately less relative aperture edge than does the much smaller F/16 aperture of an 18mm lens. The smaller the diameter of an f/16 aperture, the greater the proportion of the light passed will have to pass intimately by the edge of the aperture. Hence, a smaller f/16 aperture will c@use more diffraction than will a larger f/16 aperture.

So your thematic question requires the answer that no, not all F/16 apertures are (functionally) equal regarding their inherent capacity for diffraction.

Dave

R.G. Loc: Scotland

Whatever theory suggests, I think we've all seen the photos showing the gradual softening which we get above f/11 on a FF camera. It has been suggested that the effect becomes significant in practical terms only once the affected area is three or more pixels wide, so it depends on the resolution of the sensor as well.

burkphoto Loc: High Point, NC

R.G. wrote:

Whatever theory suggests, I think we've all seen the photos showing the gradual softening which we get above f/11 on a FF camera. It has been suggested that the effect becomes significant in practical terms only once the affected area is three or more pixels wide, so it depends on the resolution of the sensor as well.

That sums it up nicely. Compare different sizes of 20MP to 24MP sensor (Micro 4/3, APS-C, full frame) and you change the f/stop where diffraction comes into play. Compare 16, 32, and 50MP full frame sensors, and diffraction becomes noticeable at different apertures, too.

ken_stern Loc: Yorba Linda, Ca

Very interesting
Thanks for posting & yes testing camera & lens (s) is all important -- something i'll start doing

User ID

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John_F wrote:

............... Aperture diffraction would seem to
become more noticeable at small apertures
(high f stops) because the edge zone makes
up a larger fraction of the entire aperture area.
.............

You said:
".......... at small apertures (high f stops)
because the edge zone makes up a larger
fraction of the entire aperture area ..... "

The so called "edge zone" is the circumference
of a circle. The circumference can NEVER vary
as a "fraction of the entire aperture area". The
ratio of diameter to area to circumference are
fixed ratios. Some of us slept thru 3rd grade
and some of us are old enuf to have forgotten
stuff from those days .... and some of us are
just way too vulnerable to frequently parroted
popular misinformation.

But the ratios never vary. You can look it up.

And acoarst f/16 is always f/16, as Monday
is always Monday. But "Monday" can be the
worst day of the work week, or a paid day
off attached to a 3-day-weekend ! But it IS
ALWAYS "Monday" :-)

.

Uuglypher Loc: South Dakota (East River)

Uuglypher wrote:

qi Hi, Bob, br Interesting discussion.As you state... (show quote)

A clarifying point I should have included is that the circumference of the aperture increases arithmetically ( 2x pi x r) while the area of aperture’s circle increases geometrically (pi x r squared). Thus as an aperture increases in area (geometrically) the increase of its circumference is disproportionately slower (arithmetric). Thus, less diffraction with a large f/16 aperture than with a small f/16 aperture.
Dave

selmslie Loc: Fernandina Beach, FL, USA

Uuglypher wrote:

.... Let’s keep in mind that the f/16 aperture of a 400mm. lens has a greater circular area with proportionately less relative aperture edge than does the much smaller F/16 aperture of an 18mm lens. The smaller the diameter of an f/16 aperture, the greater the proportion of the light passed will have to pass intimately by the edge of the aperture. Hence, a smaller f/16 aperture will c@use more diffraction than will a larger f/16 aperture. ...

No, a larger f/16 aperture for 400mm (400/16=25mm) travels further (400mm) than the smaller (18/16=1.125mm) which travels only 18mm to reach the film/sensor.

This is also explained in LENS DIFFRACTION & PHOTOGRAPHY Cambridge in Colour, "Independence of Focal Length Since the physical size of an aperture is larger for telephoto lenses (f/4 has a 50 mm diameter at 200 mm, but only a 25 mm diameter at 100 mm), why doesn't the airy disk become smaller? This is because longer focal lengths also cause light to travel farther before hitting the camera sensor -- thus increasing the distance over which the airy disk can continue to diverge. The competing effects of larger aperture and longer focal length therefore cancel, leaving only the f-number as being important (which describes focal length relative to aperture size)."

Rongnongno Loc: FL

When I read this I have a question....

Wavelength has to do with the distance between crests in a wave before the wave repeats itself (Hertz). Frequency determines if we are able to perceive the wave (Hertz per second) or not. And there we get not only into light perception but also into sound among many other things.

Frequency is directly tied to the wave length and the amplitude tied to the intensity or volume of the wave (Loudness in sound by example). Frequency is basically the pitch. The lower the deeper the sound, the higher the sound (30Hz~20KHz). The amplitude has to do with loudness.

When it comes to light the human light goes from ultra violet to infrared (I do not know the frequency limits here). I assume, perhaps wrongly, that the amplitude affects the brightness.

[Edit]
Oh, something else... The medium is also important. A wave transmitted in the air takes longer to propagate than in water or a solid. (Might be irrelevant but still, worth noticing)
[/end edit]

That is my understanding anyway.

Aperture in all that???? What the heck? Apples and oranges?

PeterBergh

Rongnongno wrote:

... The medium is also important. A wave transmitted in the air takes longer to propagate than in water or a solid. ...

As far as electromagnetic radiation (EMR) is concerned, the facts are the exact opposite. EMR is at its fastest in vacuum and slower in any other medium. An example: in glass, visible light (EMR within some specific wavelength range) is around 30 % slower than in vacuum. As you surmise, the amplitude is directly related to the brightness. (I won't go into wave-particle duality, but brightness is the number of photons per second hitting the target.)

With sound waves, your observation is correct; generally speaking, sound moves slower in less dense media. As you state, pitch is frequency and amplitude is loudness.

TriX Loc: Raleigh, NC

Rongnongno wrote:

When I read this I have a question.... br br Wave... (show quote)

So the question is what does aperture and diffraction have to do with the wavelength of the light? Per Cambridge in Colour: “Light rays passing through a small aperture will begin to diverge and interfere with one another. This becomes more significant as the size of the aperture decreases relative to the wavelength of light passing through, but occurs to some extent for any aperture or concentrated light source”. That pretty well sums it up...

Pablo8 Loc: Nottingham UK.

Years ago, a 'Theory' was bandied about, regarding the leaf-shutters having an influence on the actual aperture during an exposure. The opening and closing of the shutter blades, acting as an added changing aperture IE. not allowing the full area of the actual aperture allowing light through the lens (during the whole length of the exposure) to the film. EG. If f/5.6 was set on the aperture, the shutter blades opening and closing, would effectively make the actual aperture, from a pinhole-size, to f/5.6, and back to pinhole as the shutter blades were opening and closing.Cannot remember what the conclusions were. Just a 'Kite Flying Theory'.

R.G. Loc: Scotland

Uuglypher wrote:

....as an aperture increases in area (geometrically) the increase of its circumference is disproportionately slower (arithmetric).....

You see the same divergence when you compare surface area to volume, which is why single celled organisms can breathe through their skin whereas if an elephant or a whale tried doing the same thing it would suffocate.

R.G. Loc: Scotland

Rongnongno wrote:

....Frequency is directly tied to the wave length.....

The other factor is speed. Sound travels much slower than light (which is electromagnetic radiation), so the wavelength of a 10KHz sound wave is measured in millimeters or inches whereas the wavelength of a 10KHz electromagnetic wave would be measured in kilometers. Electromagnetic radiation travels much farther in 1/10,000 of a second than sound. Where visible light is concerned, its frequency is measured in THz (terahertz) which means that the wavelengths are measured in nanometers. The frequency range of visible light covers less than one octave.

It's interesting to note that in the case of both sound and light, as the frequency increases they both become more directional (i.e. less prone to dispersion). However, the difference between the lowest and highest frequencies of visible light isn't large enough to make major differences where apertures are concerned. What does make the difference is that longer wavelengths are affected differently from shorter wavelengths when passing through glass, which is why we get fringing.

selmslie Loc: Fernandina Beach, FL, USA

Pablo8 wrote:

Years ago, a 'Theory' was bandied about, regarding the leaf-shutters having an influence on the actual aperture during an exposure. The opening and closing of the shutter blades, acting as an added changing aperture IE. not allowing the full area of the actual aperture allowing light through the lens (during the whole length of the exposure) to the film. ...

A leaf shutter can manage 1/500 sec but they aren't that accurate at that setting. They open and immediately close without pausing.

At lower speeds they open and close at the same speed but pause while open to provide the longer exposures.

If the speed of opening and closing were to have any effect it would occur at only the highest shutter speed and widest aperture which for medium format is about f/2.8 and for larger formats f/5.6 or smaller.

But since medium and large format lenses are almost never used both wide open and at the highest shutter speed, there is no real reason for concern.

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

rmalarz wrote:

Well, actually it is, or is it? br br Let's get o... (show quote)

I don't mind technical posts. I find them sometimes interesting. But for me, the emotional and artistic appeal of a photograph will always outweigh technical considerations.