Questions tagged [optics]

Optics is the science of light, and in photography often refers more specifically to to the properties and construction of lenses or the technical aspects of light sensors.

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64
votes
7answers
20k views

What is a “diffraction limit”?

I've seen the term used, but what is a "diffraction limit", when should I worry about it, and what undesirable effects are a result of it ?
17
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4answers
4k views

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

I've heard of: perspective distortion barrel distortion pincushion distortion mustache distortion What are these different types of distortion, and how do they relate? What causes them, and can they ...
27
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5answers
4k views

What is the shape of the focal plane?

This is something I just realised I don't entirely know the answer to, so I'm going to ask it here as I think it's interesting. In most non-scientific writing on depth of field, diagrams generally ...
121
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7answers
12k views

What is bokeh, exactly?

I understand that "bokeh" refers to out-of-focus areas of an image — but there is obviously more to it than that. What does the term mean exactly? How well is bokeh really understood? Is it purely ...
4
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2answers
3k views

Does wide angle equivalent in crop sensor skew image?

I see many posts on both this forum and elsewhere the discuss the use of a wide angle on a crop sensor. For example, they discuss how at 14mm lens is 14mm on a 35mm film or full frame, but with a 1....
31
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8answers
22k views

Technically, why is the out of focus area blurred more when using a bigger aperture?

I'm wondering, technically, why and how does the out of focus areas blur more when using a bigger aperture. I think it'd help a lot if I presented a problem that's been driving me nuts for a long time:...
7
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6answers
1k views

Does sensor size impact the diffraction limit of a lens?

My understanding of diffraction, is that with a small aperture the 'airy disk' (which I understand is the pattern light from a given direction relative to the lens will form on passing through the ...
46
votes
7answers
10k views

How do constant aperture zoom lenses work?

Cheaper zoom lenses usually are faster at the wide end and slower at the long end (for example, the $150 Canon EF-S 18-55mm f/3.5-5.6). More expensive constant-aperture zoom lenses have the same ...
26
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4answers
9k views

What is focal length and how does it affect my photos?

What is focal-length? Are focal-length and zoom synonymous? How does the focal length of a photo affect it? Are there common uses for different focal lengths, and how can I decide what to use when?
20
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3answers
2k views

What is Chromatic Aberration?

What is Chromatic Aberration? Is it a physical part of the lens, or just an optical illusion?
15
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4answers
18k views

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

By definition, a prime lens is a fixed lens system with a fixed focal length. Then, simple physics tells us that it should be able to focus only on one plane (at a fixed distance) in front of it. But ...
20
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2answers
5k views

Why do zoom lenses and compact cameras have varied maximum aperture across the zoom range?

Why does a camera's maximum (allowed) aperture get smaller when you increase its zoom?
16
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3answers
9k views

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

A friend of mine is thinking of buying a used medium-format film TLR camera (a Mamiya C330), and he showed me some of the test shots he'd taken with it. I was struck by the curiously non-uniform ...
29
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3answers
8k views

Does changing the focal length change focus?

When using manual focus or back focus on D60, I sometimes zoom in the lens, set the focus, and then zoom out. Does changing the focal length (zooming out), also change the focus? In case the answer ...
54
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8answers
34k views

Why do light sources appear as stars sometimes?

See for example this photo: From my experience, the longer the exposure the stronger can this effect be observed. Is this correct? Are there any other factors that influence the creation of these ...
17
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3answers
3k views

What is the “Circle of Confusion?”

I know that when I want to calculate Depth of Field by hand one of the variable elements in that equation is the Circle of Confusion. In layman's terms, what is the "Circle of Confusion," how do I ...
8
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2answers
3k views

Is it normal for focal length to change while focusing?

When I change the focus distance on my Pentax 55-300mm lens, the focal length appears to change. More specifically, the lens appears to zoom in as I focus towards the minimum focusing distance. This ...
15
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3answers
7k views

What causes lens flare?

I heard a couple of years ago that only certain types of lens caused flare to appear, something related with the material and/or quality of the lens. Is this true? Which material/quality caused flare? ...
14
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3answers
6k views

What is the reference point that the focal length of a lens is calculated from?

I understand the idea of a focal length for a single lens, i e the distance from the lens to the point at which parallel rays of light converge. However, in the case of a photographic lens with ...
7
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2answers
1k views

What could cause this visible artifact which seems to a be a glowing inverse of something outside of the frame overlayed on this photograph?

An acquaintance recently posted an image to FB from his recent trip to the JFK Historic Site asking for an explanation of a visible artifact he states was not visible to the naked eye but was visible ...
37
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4answers
4k views

How do I interpret an MTF Chart?

As part of how Canon (and other lens makers) give technical information about their lenses, they supply an MTF (Modulation Transfer Function) chart. How do I read and interpret what the chart is ...
15
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5answers
33k views

What is “infinity focus”?

I have been reading a bit about astrophotography and the term infinity focus keeps coming up. What is infinity focus and how do you set the camera to infinity focus?
3
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2answers
3k views

What's the difference between real and effective aperture?

I understand that the simple idea that f-stop is focal length divided by aperture really applies to a simple single-glass lens, not the compound lens systems used to provide good image quality in ...
2
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5answers
1k views

Why does it seem like large sensors are necessary for good low-light performance?

Phone manufacturers have recently started advertising the size of the photosites on smartphone camera sensors. They argue that larger photosites lead to better low-light performance. I think a good ...
60
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5answers
2k views

Is there development in the world of lenses?

Now, I'm not an expert, so if this post makes you laugh, you're welcome. Still, as far as I know there are basically two components that determine the potential quality of a camera's photos: Sensor ...
52
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2answers
46k views

What is the difference between a pentaprism and a pentamirror?

Higher-end SLR cameras include a pentaprism to transmit the image from the lens to the viewfinder, whereas lower-end SLR cameras use a pentamirror to accomplish the same task. What are the ...
25
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13answers
44k views

How does the lens diameter influence photo quality?

I have tested two different 50mm lenses in my camera. One was a Nikkor 50mm ∅52mm. The other one was a Sigma 50mm ∅72mm. I took some pictures with both lenses using the same setup for aperture and ...
13
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3answers
16k views

What is the technical difference between focus and zooming?

This may look like a silly question but I don't know what the difference between zooming and focusing is. Zooming in will usually let me have fewer subjects in the scene while zooming out will allow ...
11
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3answers
4k views

What are the theoretical minimum and maximum apertures?

Is there such a thing as a maximum aperture that a lens can be open to? What about a minimum aperture that it can be closed to? Do these concepts even make any sense? Is there a lens with the ...
4
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2answers
2k views

Is the size of the entrance pupil the same as the size of the effective aperture?

I understand that the entrance pupil is the image of the aperture as seen from the front of the lens. However, is the size of the entrance pupil the same as the size of the effective aperture? In ...
41
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4answers
6k views

How does aperture work without “cropping” the image hitting the sensor?

I've been teaching myself the various settings in cameras and now have a much fuller understanding of how to use my camera effectively, but one thing is still bugging me. When the aperture size is ...
23
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4answers
8k views

How does the human eye compare to modern cameras and lenses?

A goal in most photography is to present a scene which resembles what a person who had been there at that moment would have seen. Even when intentionally working outside of that, human vision is the ...
19
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2answers
5k views

Why are cine lenses so much more expensive?

For example, compare a cine lens like the Zeiss Compact Prime CP.2 50mm/T2.1 ($3,900) to a high-end DSLR lens like the Canon 50mm f/1.2L ($1418). Both are EF-mount, have the same focal length, and it ...
16
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4answers
72k views

How does a spherical lens differ from an aspherical lens?

Many lenses (like the Pentax DA 15mm f/4 Limited, or the Nikon AF-S 35mm f/1.4G) are described as having "aspherical lens elements". Does this mean that regular lenses are spherical lenses? What's the ...
4
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4answers
6k views

Do lenses affect color fidelity?

It seems to me that my costlier (Tamron 90 f/2.8 macro) lens gives better colors than my cheap Canon 18-55 IS kit lens. So does lens matter for color quality? What physical processes are involved in ...
37
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3answers
4k views

When you zoom in with a lens on an SLR why does the lens go in then out?

I guess this is more a question of optics than photography but I just got an SLR with a basic 18-55 lens. I noticed that when going from 18 to 55 or 55 to 18 the lens physically comes back in and ...
30
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3answers
15k views

What is a zone plate?

I was looking into alternative methods of photography and I happened upon something called a 'zone plate.' Three questions: What is a zone plate? How does it work? What can I do with it?
9
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5answers
10k views

Do bigger focal lengths capture more light? [duplicate]

I never understood what the f really stands for in the f-stop values, like f/1.8. Wikipedia explains it in various articles, but I still find it very confusing. What I understand, though, is that it ...
4
votes
1answer
583 views

Do lenses have focal planes or focal spheres/ellipsoids?

The title says it pretty much all. I'm asking this because I find myself always using the focus point in the center, and after I focused, I rotate my camera to make the framing right. However, if ...
3
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4answers
772 views

Why does illuminance stay the same for a given f-stop even when focal length changes?

I'm trying to wrap my head around the math/physics of how illuminance on the film/sensor plane remains equal for a given f-number regardless of the focal length of the lens. Since a longer lens will ...
10
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1answer
6k views

What are Barrel and Pincushion distortion and how are they corrected?

I have some questions regarding barrel distortion and pincushion distortion. Since they are related I have put them in single post. I am aware that barrel distortion occurs more in wide-angle lenses,...
56
votes
4answers
8k views

Why aren't all viewfinders 100%?

We often see that a manufacturer's high-end (D)SLR models offer a "100% viewfinder," which shows the entire exposed frame, and allows precise composition with regard to objects near the edge of the ...
14
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3answers
9k views

How does an apodization filter improve bokeh?

The new Fujifilm Fujinon XF56mmF1.2 R APD has an "apodization" filter, which Fujifilm says "smoothes the outline of the subject to create a more natural bokeh effect". The Wikipedia article on ...
20
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5answers
3k views

How does a circular lens produce rectangular shots?

Is it something like the sensor captures a circular image and then what we get is the cropped version? Something like this: Or did I get it completely wrong?
11
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4answers
7k views

How many optical aberration types are there in lenses? And what are they?

Everyone hears something about chromatic aberration but are there any other types? What causes them?
9
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2answers
8k views

What are ED elements?

I find that some lenses are indicated with the letters "ED", referring to some special type of lens element. What are ED elements, and what advantages do they bring? Note that this question isn't ...
8
votes
4answers
6k views

How does a short flange back distance improve image quality?

In the description for the new lens mount for their X-Pro series, Fujifilm says: 1: Specifically designed to maximize the mirrorless design of the body, the X-Mount has a short flange back distance ...
8
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5answers
2k views

Why not have the diaphragm in camera body instead of the lens?

Why is the diaphragm to control the amount of light entering the camera typically in the lens and not the camera body itself?
4
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1answer
1k views

How can I calculate the effect of a supplementary close-up lens (a.k.a macro filter)?

If I have a +1, +2, +4, or +10 close-up lens which attaches to the front of my regular lens, how can I calculate its effect on close focusing distance, figure out how much magnification I can get from ...
22
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4answers
4k views

What are good advanced books on the physics and science of photography?

I am looking for books about the physics of DSLR, including modern photography optics and sensor electronics. If I already have some books on optics and electronics, I have found fairly hard to find ...