Hot answers tagged

65

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 ...


42

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 ...


36

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 ...


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

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, ...


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 ...


25

The loss of contrast is due to the central obstruction; that is, the "hole of the donut" that blocks light from getting through the center of the lens. In a diffraction-limited telescope or lens, the point spread function—basically an image of a point source, like a star—is the Fourier transform of the aperture. For a circular aperture, like ...


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 ...


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


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

Pretty sure I answered this one before but I cannot find it. As focal-length gets longer, the angle of view gets smaller. With a smaller angle of view, rays forming the image are closer to being parallel. With less variation of angle between rays, light has to travel more before being sufficiently out of focus. This is a little oversimplified but I hope it ...


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.


20

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 ...


19

The two generally control two different aspects of the image projected by the lens. Focusing sometimes has the effect of changing "zoom" a little as well, however its purpose is different. To keep it simple: Focus adjusts the Focal Plane The focal plane is the thin plane of reality that is focused clearly on the imaging medium Focusing moves this plane ...


17

Speaking from the world of amateur astronomy, there's quite a bit of development happening with lenses. Eyepieces and objectives are all using new, exotic glass and computing resources to design well-corrected refractive devices. New glass mixes don't come along very often and the proper effort to better mate the shapes and characteristics still requires ...


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

The pupil (aperture opening) area is proportional to the square of the focal length (at the same f-stop). So 105mm being about twice the focal length of the 50mm, it would need 4x the pupil (area) to be f/1.2. In other words f/1.2, or any f-stop, doesn't correspond to a fixed diameter - it increases for larger focal lengths. That also assumes both lenses ...


15

The f-number is in use to express how much light a lens can capture, so the 85mm f/1.8 and 24mm f/1.8 can capture the same amount. Here, f is the focal length, and f/1.8 means that maximum aperture diameter is 47.2mm in first example and 13.3mm in second. What you have to consider here is that the 85mm lens has a much narrower field of view, therefore it ...


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