Alley in Pisa, Italy

by Lars Kotthoff

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84

Most importantly: It's not just the disks rendered from a point source, even though that's the simplest way to describe it and see it. The disk is just a shorthand; the lens characteristics that produce these disks are always present; they're what determines the look of the out-of-focus areas in every photo you take! On the one hand, it's quite ...


49

Yes. There is development in four areas: computer design, material science, features, and finally a category I'm going to call "not better just different". Computer Design Lens design has always been a mix of art and science. In the first part of the previous century, art was clearly primary (even for scientific lens designers). Now, lens design software ...


47

The main reason is that a 100% viewfinder requires extremely careful adjustment to assure that the framing in the viewfinder exactly matches what will show up on the sensor. In most cases (I'm pretty sure all cases, really) this means they have a little adjustable frame just below the pentaprism that gets adjusted by hand to match up precisely with what the ...


43

There have been some very good answers, however there are a couple details that have not been mentioned. First, diffraction always happens, at every aperture, as light bends around the edges of the diaphragm and creates an "Airy Disk". The size of the airy disk, and the proportion of the disk that comprises the outer rings, and the amplitude of each wave in ...


41

This appears to be a beautiful example of Fraunhofer diffraction. It is due to the wave nature of light. The effect depends on the wavelength (that is, the color). It is most pronounced when bright light from a practically infinite distance passes through narrow slits, causing the light to spread perpendicular to the slits. This spreads a point-like beam ...


38

It tells us that the aperture contains either three or six blades and that where these blades meet there is a corner which results in Fraunhofer diffraction. This is discussed mathematically in Physics SE. It also tells us that the lens was stopped down, as if it were wide open there would be no corners to cause diffraction, regardless of the number of ...


35

I think the best way to describe Bokeh is to show Bokeh: Reference: In the Spotlight by Healzo The blurry background "circles" are what we normally refer to as Bokeh, however in general it more simply refers to the quality of background blur. The picture above has some truly excellent bokeh, as the circles are truly round, generally evenly shaded across ...


34

The basic difference is that a pentaprism is a solid block of glass. This means it's fairly heavy. It has mirroring material on all but two sides, so the light enters one side, gets reflected around inside, and then comes out the one other un-mirrored side. This means there are only 2 air/glass interfaces involved: one where light enters the prism, and one ...


28

You probably didn't find much because you were searching on the wrong term. The phenomenon isn't commonly called 'The Newton Effect,' it's usually called 'Newton's Rings.' Briefly, Newton's Rings are an optical property of physics that occurs between two pieces of glass when one piece of glass is convex and the other piece is flat and there is airspace ...


25

There is no simple relationship between the physical length of the lens and its focal length. For example, a retrofocus wide angle is generally longer than its focal length, while a telephoto lens is shorter than its focal length. Inside a zoom, you have several lens groups that move independently. The focal length of the zoom depends on the relative ...


25

Your intuition is essentially correct but there are a few important points. When the lens is stopped right down, only light heading for the centre of the front element will make it into the picture, so the whole front element isn't used for every point of light hitting the sensor (though all of it is used for some point of light). Even when the aperture ...


24

Bokeh, in its most technical definition, is the shape produced by taking an out of focus picture of a single point of light. The overlapping bokeh from all the myriad points of light that make up a scene creates the blur in out-of-focus areas. People may have different preferences, but there are really just a few different measurable qualities of bokeh. ...


24

Why the wide aperture blurs the background more Let me start with Wikipedia figure: Above we have a wide open aperture. Only point 2 is in focus. Points 1 and 3 are out of focus. Due to wide aperture, the rays coming from them through different parts of the lens intersect the screen 5 (a film or a digital sensor) in different points. We may also tell ...


23

I was recently trying to figure this out myself, and found this question. I didn't feel the accepted answer was quite complete, so here's my shot (no pun intended!): The first thing to understand is that the light that reflects off any one point on a surface isn't one beam of light, but many, coming in at many different angles and reflected off at many ...


21

There is a really good tutorial that explains all the details at luminous-landscape.com. If you don't want to read the whole article, this section covers the basics: Here are some rules of thumb for reading a chart... — the higher up the chart the 10 LP/mm line is (the thick lines), the higher the contrast reproduction capability of the ...


21

Summary A zone plate is a way of focusing light, like a lens, but using Fresnel diffraction instead of refraction. This is cool from a theoretical point of view, because it demonstrates the wave nature of light. And it's cool from a photography point of view, because the images produced have a unique glow, with a impressionistic almost-painted look. If ...


19

Carl Zeiss is a very well respected lens maker, and very literally one of the reasons "German engineering" conjures images of precision and care. Camera phone manufacturers license the name (and, maybe but not necessarily, actual lens technology) from Zeiss in order to borrow some of that high-end image. This isn't necessarily all chicanery: companies who ...


19

Cine lenses do have to overcome certain limitations that don't really apply to still cameras. Still lenses will usually exhibit the phenomenom of "breathing" during focus. Breathing will cause the image to appear to get larger when the focus shifts, a non-issue for a still camera, but a big issue when doing motion picture recording. Fixing that isn't free, ...


18

Chromatic Aberration is a distortion that occurs when a lens focuses different colours slightly differently. It is caused by the refractive index of the lens (the amount that the lens bends light) being slightly different for different colours, so I suppose you could say it is caused by physical properties of the lens. It is possible to produce higher ...


18

f1.4 will always be 2/3rds stops faster than f1.8. The diameter has nothing to do with whether or not part of the sensor is hidden. That is a separate measurement referred to as vignetting, and not the image circle's light level. The image circle's light level/brightness is directly affected by the aperture of the lens design. FF lens simply means the ...


18

This is often a source of confusion which most people get backwards, so understanding this is delicate: When a light entering a lens is not in focus, a point on the subject is focused into a circle on the image plane (sensor/film). This circle IS the circle of confusion. The more out of focus a point is, the larger the circle of confusion becomes. This ...


18

Uncontrolled light causes lens flare. This can be light that's reflected from internal lens surfaces, or that's scattered by imperfections in the glass. If the flare is badly controlled, it will produce the dramatic lens flare artifacts which you've probably seen. More controlled flare will be diffused over the entire image, reducing contrast but not ...


17

Lenses don't shine light directly through, they focus it, if you forgive the lousy ray-tracing: The green lines represent the cone of light striking the lens with a narrow aperture, the red is the cone of light allowed by a wide aperture. In this case you can imagine the aperture immediately in front or immediately behind the lens (there's not much ...


17

And for a visual: Pentamirror Pentaprism


17

I'm going to crib from my answer to an earlier question on aperture: When the aperture is very small, the admitted light is highly "collimated", which is a fancy way of saying "all the rays are nicely parallel to each other". This results in a sharp focus for all the light that comes in. When the aperture is more open, only the rays which closely match ...


17

The short answer is because it is cheaper to manufacture such lenses. The longer the lens and the wider the aperture, the larger the optical elements in the lens - thus larger the expense to produce them. A lens like 70-200/2.8 must have a front optical element of 200mm/2.8=72mm, which is quite a chunk of glass. On the other hand, the 70-300/4-5.6 needs to ...


16

Focal length is a measure how the lens focusses the light into a point. When light enters a 50mm prime lens, the light converges into a point the camera sensor after 50mm. In addition the focal length determines the magnification of the object you photograph. A long lens (e.g. 300mm) magnifies the images a lot (useful for birding) while a short (wide angle) ...


16

No, you are correct and the reason photos are the size and shape they are just has to do with the size and shape of the film or digital sensor used to capture the image from the lens. The rest of the image that falls to the top, bottom, and sides of the film or sensor are just not recorded. ...interesting thought, I never really realized the circular ...


16

The areas which are out of focus are blurred in a shape matching that of the lens opening. The final shape is usually circular when shooting wide open, but when stopped down, the aperture blades modify the shape, for instance, with 6 blades, the bokeh would probably be hexagonal. One example of circular bokeh: To really show this effect, you can use a ...



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