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 ...
- 32.1k
40
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 ...
- 174k
30
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 ...
- 174k
28
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 ...
- 32.1k
28
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 ...
- 32.1k
22
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 ...
- 143k
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:...
- 12.2k
22
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 ...
- 38.5k
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 ...
- 174k
21
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 ...
- 1,894
20
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 ...
- 174k
18
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 ...
- 38.5k
18
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 ...
- 174k
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 ...
- 174k
15
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 ...
- 8,504
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 ...
- 1,242
15
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: ...
- 38.5k
14
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) ...
- 241
14
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 ...
- 1,803
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 ...
- 102k
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 ...
- 51.1k
12
votes
Why do mirrors give less sharpness, gamut, and contrast than lenses?
Mirrors are better than lenses in that they are inherently free of chromatic aberrations, and are reflective over very wide spectral bandwidths. For these reasons, they are very attractive design ...
- 2,435
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 ...
- 174k
11
votes
What could cause this visible artifact which seems to a be a glowing inverse of something outside of the frame overlayed on this photograph?
What you are seeing in the photo is a specific type of lens flare known as ghosting. It is an inverted and reversed reflection of the brightest highlights of the scene. If you were to draw an x and y ...
- 174k
11
votes
Accepted
Is a two-prime lens possible? E.g. 35mm and 50mm
Yes it is technically possible. The question is whether this will have practically same limitations as a zoom or not.
There are two objectives from Leica with stepped focal length adjustment: the 16-...
- 4,597
11
votes
Accepted
What can cause double-vision effect in slightly out of focus areas?
A cheap filter (uncoated or poor coatings) can reflect some of the light which is always reflected off of the front element surfaces.
The primary reflection (blue in the drawing) will be stronger than ...
- 13.8k
10
votes
What happens if anti-reflective coating is fully ruined or removed from lens' most outer surface?
Up until the late 1940s and into the 1950s, camera lenses didn't have coatings. The result was much higher incidence of lens flare and reduced contrast in the presence of bright light sources.
...
- 11.5k
10
votes
Is a two-prime lens possible? E.g. 35mm and 50mm
It is possible and Canon has done it, although in a different way than you'd expect - their EF 200-400mm f/4L IS USM Extender 1.4x. It's a zoom lens with a built-in teleconverter that could be toggled ...
- 2,044
10
votes
Accepted
Are there any 24-70 2.8 lens with no length change in zooming?
You need to look for a lens that uses internal zoom so that the length of the lens will not change during zooming. You also want a lens with internal focusing so that the length of the lens doesn't ...
- 174k
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