Hot answers tagged

45 votes

Why do stars appear as circles, not points?

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 ...
user avatar
  • 31k
39 votes
Accepted

Why can't my custom camera body focus to far distances?

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 ...
user avatar
  • 168k
29 votes
Accepted

Why is infrared light's focus point different from that of visible light?

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 ...
user avatar
  • 168k
27 votes
Accepted

Do convex lenses make parallel light rays of different wavelength converge to different points?

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 ...
user avatar
  • 31k
27 votes
Accepted

Why is the hole in a pinhole camera usually a circle?

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 ...
user avatar
  • 31k
23 votes
Accepted

In what way does the lens mount limit the maximum possible aperture of a lens?

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 (...
user avatar
  • 3,335
22 votes

Is a two-prime lens possible? E.g. 35mm and 50mm

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:...
user avatar
  • 11.4k
22 votes

Is camera lens focus an exact point or a range?

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 ...
user avatar
  • 168k
21 votes
Accepted

Why is my large format lens so much smaller (in length) than my 35mm-format lens?

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 ...
user avatar
  • 140k
21 votes

Do convex lenses make parallel light rays of different wavelength converge to different points?

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 ...
user avatar
  • 36.2k
20 votes
Accepted

What is the shape of the focal plane?

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 ...
user avatar
19 votes
Accepted

Why do prime lenses have multiple lens elements?

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 ...
user avatar
  • 168k
17 votes

Why is infrared light's focus point different from that of visible light?

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 ...
user avatar
  • 36.2k
17 votes
Accepted

How to choose a good smartphone if the top priority of the user is photography?

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 ...
user avatar
  • 168k
17 votes
Accepted

Why doesn't an extension tube "crop" the picture?

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 ...
user avatar
  • 168k
15 votes
Accepted

How does an apodization filter improve bokeh?

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 ...
user avatar
  • 117k
15 votes

Why are large zoom ratio constant apertures lenses not generally available?

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 ...
user avatar
15 votes

How can I test that the image is inverted in a pinhole camera?

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 ...
user avatar
  • 1,183
14 votes

What is the cause of this non-uniform bokeh effect?

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 ...
user avatar
  • 140k
14 votes
Accepted

How can a super tiny iPhone 6 Plus lens produce significant DOF?

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 ...
user avatar
  • 1,644
14 votes
Accepted

What model does Lightroom use for lens correction?

Does anyone know if this software uses the Brown-Conrady model to achieve the lens correction? Yes they do use those very common camera calibration coefficients. I added some copyable text versions ...
user avatar
  • 8,334
14 votes

How do manufacturers get to high (83x) zoom levels on hybrid cameras?

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: ...
user avatar
  • 36.2k
13 votes
Accepted

Why are superzoom lenses small but giant telephoto lenses huge?

The 1200mm lens you cite is something of an aberration, since it's built-to-order, not a general-market lens — see Why are some big telephoto lenses so expensive compared to telescopes? and Why are ...
user avatar
  • 140k
13 votes
Accepted

What's the opposite of a fisheye lens?

The opposite of a fisheye is a rectilinear lens. You probably did not find one because your definition is wrong. Distortion of a fisheye lenses is not barrel distortion, it is that a different ...
user avatar
  • 101k
13 votes

What is the farthest a camera can see?

If you simply want visual examples with commonly available lenses and resolutions the webpage: "Guide to Identifying or Recognizing a Face: Resolution, Focal length, and Megapixels" has a number of ...
user avatar
  • 1,743
12 votes

How can a lens with a single focal length focus on more than one plane?

First, focal length is a property of a lens (by lens I mean a piece of plastic or glass that's inside your camera's photographic lens system). If you just have a single lens (think magnifying glass) ...
user avatar
  • 221
12 votes
Accepted

Categorization of 14mm lens as rectilinear?

Unlike most other digital cameras, Panasonic micro four-thirds cameras record lens correction information (distortion and CA, iirc) into the EXIF information of their RAW files (and will bake in the ...
user avatar
  • 49.1k
12 votes
Accepted

What is the difference between perspective distortion and barrel or pincushion distortion?

Perspective is determined by the position of the camera relative to the scene. When a camera position produces a perspective that makes an object or scene look different than we might expect it to ...
user avatar
  • 168k

Only top scored, non community-wiki answers of a minimum length are eligible