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 ...
- 33.2k
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 ...
- 176k
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 ...
- 33.2k
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 ...
- 33.2k
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:...
- 12.3k
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 ...
- 39.5k
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 ...
- 176k
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 ...
- 176k
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 ...
- 176k
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 ...
- 176k
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 ...
- 1,252
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: ...
- 39.5k
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 ...
- 1,823
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 ...
- 103k
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 ...
- 2,455
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 ...
- 176k
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-...
- 5,525
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 ...
- 18.8k
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.
...
- 12.6k
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 ...
- 2,055
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 ...
- 176k
10
votes
What's the opposite of a fisheye lens?
A fisheye lens isn't designed to have extreme barrel distortion -- the distortion is the result of trying to map a sphere onto a plane.
A regular lens follows the equation ...
- 2,455
10
votes
Why is the hole in a pinhole camera usually a circle?
The pin-hole casts (projects) tiny image circles on the back wall of the camera. This is also the place we position photo sensitive material so that we can replica this image on film or paper or ...
- 39.5k
10
votes
Why can't my custom camera body focus to far distances?
If not, do I move the lens away or closer to the optical plane to fix the problem?
If the lens will focus on near subjects, but not on a subject at "infinity," then that means that the lens is too ...
- 635
9
votes
Accepted
Determining the size of the smallest resolvable detail for a given camera
If you want tens to hundreds of pixels per 50 micron area, you need a microscope. Based on your object size, with that resolution, you want at least 10px/50um * 3000um/50um a 600px wide view of your ...
- 2,455
9
votes
Do convex lenses make parallel light rays of different wavelength converge to different points?
Yes, they do. This is the cause of chromatic aberration. It happens in two ways, actually. Axial chromatic aberration (also known as longitudinal CA) happens because different wavelengths focus at ...
- 143k
9
votes
What's the practical difference between two Canon 50mm f/1.2 L lenses?
They're two totally different designs that just happen to be the same (nominal) focal length and apertures.
The New FD 50mm f/1.2 L debuted in 1980 with 8 elements in 6 groups. As with all FD lenses, ...
- 176k
8
votes
Accepted
What causes lens flare along specific axes?
What causes lens flare along specific axes?
This answer assumes the 1st and 3rd images are caused by the same phenomenon, and image 2 is caused by something different.
Image #2
To my eyes, this ...
- 33.2k
8
votes
How can I test that the image is inverted in a pinhole camera?
Make a simple, non-photographic pin-hole camera. Start with a cardboard tube. The round Quaker Oats breakfast box is perfect for this job. You can use any cardboard mailing tube. Cut off both ends, ...
- 39.5k
Only top scored, non community-wiki answers of a minimum length are eligible