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45

Whenever light passes a boundary, it diffracts, or bends, due to the wavelike property of light interacting with that boundary. An aperture in an optical system, typically circular or circle-like, is one such boundary. How light interacts with the aperture is described by the point spread function (PSF), or how much and to what degree a point source of ...


43

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 ...


40

If I have built my device with the correct distance between the flange and the optical plane, does this mean the (inexpensive) lens I am using is bad? If you had built your device using the proper specified flange distance of 17.526mm instead of rounding it off to 18mm you probably would not be asking this question. 0.474mm doesn't seem like much, but it ...


28

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 ...


28

It is for the same reason that chromatic aberration occurs at all: different wavelengths of light will bend at slightly different angles when passing through the same refractive medium such as a lens element. Chromatic aberration in most well designed photographic lenses will be less severe because the lens has been designed to correct for it at the various ...


27

Do convex lenses make parallel light rays of different wavelength converge to different points? Yes. The separation of different wavelengths of light is called dispersion. Different wavelengths of light refract at different angles because the refractive index of a transparent medium is frequency dependent. We often describe different materials, such as ...


26

From Wikipedia's Pinhole camera article, The best pinhole is perfectly round (since irregularities cause higher-order diffraction effects), and in an extremely thin piece of material. Industrially produced pinholes benefit from laser etching, but a hobbyist can still produce pinholes of sufficiently high quality for photographic work. There is a ...


22

There are two hard limits on how fast a lens can be: The first is a thermodynamic limit. If you could make a lens arbitrarily fast, then you could point it to the sun and use it to heat your sensor (not a good idea). If you then get your sensor hotter than the surface of the Sun, you are violating the second law of thermodynamics. This sets a hard limit at f/...


22

Yes, it is possible and a "Lens Turret" is one way of accomplishing it. It was very common to use a "Lens Turret" on film and movie cameras in the 1950's before zoom lenses became practical. Source: Bolex 16mm Source: Macro lens turret Source: 8mm film camera with lens turret


22

There's only one distance that is in sharpest focus. Everything in front of or behind that distance is blurry. The further we move away from the focus distance, the blurrier things get. The questions become: "How blurry is it? Is that within our acceptable limit? How far from the focus distance do things become unacceptably blurry?" What we call depth of ...


21

The focal length is the distance from the (theoretical) center of the lens to the image plane. On the large format camera, there's a lot more camera between the lens and the film. The lenses are also often relatively simple — there's no need for a focusing mechanism in the lens itself, for example. @osullic gives the example of the Schneider PC TS Makro-...


21

Light from a far distance object, like a star, arrive at the lens, as parallel rays. As they transverse the lens, they are forced to change their direction. They bend inward, we call this refraction from the Latin to bend backwards. We can draw a trace of these rays; they trace out the shape of a cone. What we find is, the apex of the violet cone of light ...


20

There is a clear difference in intent and design philosophy. The Canon 50 f/1.2L is a bokeh machine, offering not only shallower depth of field (due to the ultra wide f/1.2 aperture) but also a smoother background blur on account of the decision to leave a certain amount of spherical aberration in the design. It's a lens with character and a distinct look, ...


20

The effect is called field curvature. A good discussion comes from Nikon. It is a lens aberration that can reduce the resolution of the lens when coupled with a flat sensor. In the old days, the film could be bent a little to try to follow the image plane and reduce the effect, but our sensors today are rigid. It can be reduced with lens design.


17

If you're on a tight budget and want to get the best "bang for the buck" you need to select the phone that has a camera with strengths in the areas you need them the most while letting go of other features or capabilities that won't affect the kinds of photos you wish to create. Which is more important, sensor size or focal length? Image stabilization or ...


17

The extension tube does change the field of view. Specifically, it enlarges the image circle size at the sensor/film plane. Light as it is projected by the rear of the lens onto the film/sensor plane is like the light coming out of a projector: the further away the screen is, the larger the image that is projected. Since the sensor/film does not expand as ...


16

No, this is not the case. Aperture F stops are calculated on pupil size and focal length of the lens. From wikipedia In optics, the f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture1) of an optical system is the ratio of the lens's focal length to the diameter of the entrance pupil.2 It is a dimensionless number that is a ...


16

The diaphragm is not at the back of the lens but in between optical elements. Forcing it to be at the back would be severely restrictive in terms of lens design and wide-angle lenses would become impossible on most a sensor-size and flange distance combinations.


16

The ideal lens would cause light beams of every color to come to a focus at the same distance from the lens. That would be the focal length of the lens when the lens is imaging at infinity (∞ as far as the eye can see. When we image objects that are closer than infinity, they come to a focus further away from the lens. That is why we must cause the camera ...


15

Bokeh is formed by many points of light spreading out, passing through the aperture and being projected onto the image plane as series of overlapping discs (assuming a round aperture). This can lead to harsh textures and effects when there are strong contrasts in the out of focus parts of an image, especially when lenses feature overcorrected spherical ...


15

The main reason we don't have "super zooms" with a large constant aperture is size/weight/costs. Roger at LensRentals recently blogged about this in the post: About That 25-300mm f/2.8 You Wanted About How Big is that? The lens is in a video housing, so that makes it a bit larger than an SLR designed lens of the same specifications would be. But it'...


15

Replace the back wall of the camera with a sheet of tracing paper, ground glass (or similar translucent material) and observe the resolved image from behind the camera. You may need a dark sheet over your head (and the rear of the camera) to allow the dim image to be visible. This should remind you of how very old cameras were operated (for exactly the ...


14

This is field curvature. Simple lenses naturally project a curved field, not a flat one to match film or digital sensors. Modern lenses attempt to correct for this, but many older designs do not. In fact, it's sometimes called the "Petzval effect" after a classic design famous for this look. Interestingly, just this week Sony showed prototypes of a curved ...


14

I think the use of the term 83X while true, is most misleading. The Coolpix does a remarkable job when it comes to its optical range which is 83X. This is actually called the zoom range. The math is: The power of the camera’s lens is adjustable from 4.3mm wide-angle to 357mm telephoto that’s 357 ÷ 4.3 = 83. In other words the span of the zoom is 83X.To ...


14

Single lenses with real thickness refract the different wavelengths of light at slightly different angles. For anywhere other than the exact optical center of the lens, this causes a prismatic effect that gets more noticeable as one moves further from the optical center of the lens. This is what we refer to as chromatic aberration. It isn't the only optical ...


13

Every lens forms an image at a certain distance for a certain subject. In order for a lens to be "focussed" on the subject this image must land on the sensor. For an object at infinity, the lens forms an image at a distance of f, where f is the focal length. For an object close enough for 1:1 magnification the lens forms an image at a distance of 2*f, double ...


13

The fundamental driver of cost in a lens is not the correction of aberrations, although the correction of aberrations does add to the cost of a lens, and may be a more significant factor in wider angle lenses. Generally speaking, the primary cost of a lens is the "glass". I put glass in quotes, because sometimes it is other materials, such as Fluorite or a ...


13

Many older or cheaper phone cameras use a "fixed focus" lens. ie it is always set to focus a specific distance away from the camera. This is usually set to the "hyperfocal distance", ie everything from half that distance out to infinity is in focus. This depends on just what is acceptable as 'in focus'. But most photos from these cameras will be sharp ...


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