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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24
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4answers
9k 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 ...
56
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3answers
50k 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 ...
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4answers
142 views

Do chromatic aberrations change with distance?

I just saw the following claim on an amazon review and can't make much sense of it. Chromatic aberrations after 10 meters become significant. After 15-20 meters the picture becomes unusable. Is ...
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3answers
1k views

Why do mirrors give less sharpness, gamut, and contrast than lenses?

What is the scientific reason mirrors give less sharpness, gamut, and contrast compared to lenses? Ex. Is it an inherent property where light dissipates more when scattered compared to going through a ...
1
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1answer
92 views

What causes the frosted glass effect of out-of-focus areas?

I expect that the out-of-focus areas would look like smooth gaussian blur ideally. But I found that they look like looking through frosted glass. Colors around the edges are blending with a grainy ...
2
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3answers
184 views

What shutter can fit a lens element with large glass?

I am building a camera using a very large front glass element for the lens (diameter is 70mm). At first, I thought I should try to find a shutter that is 70mm in diameter as well, one that can ...
1
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2answers
482 views

Why is the image plane at Z = f in pinhole camera models?

Can someone show me the mathematical interpretation of why the image plane is at Z = f in the pinhole camera model? I found a possibly useful formula in Wikipedia, as shown in the figure below: My ...
2
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3answers
177 views

focal length to aperture relation while zooming - is my russian lens lying to me?

I have this old soviet/russian "Granit" 80-200mm lens, connected to my Canon 550d DSLR through M42 adapter. I also have "modern" kit 18-55mm lens. What I don't get is how aperture ...
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4answers
251 views

Does a lens with this zoom range exist?

I want to buy a zoom lens for a DSLR but I want its Focal length to start from a small number (18, 55, 100, 200) and end to a very large number (1300, 2600) so it can see near and far. Also I want it ...
0
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1answer
155 views

How to calculate height of camera and ground coverage via geometry?

I have a GoPro7 that I will mount on a pickup vehicle to capture ground images with video capture. The camera isn't top down but has about 20 (or 30) degrees inclination from the vertical axis. I want ...
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2answers
2k views

Canon EOS R or R5 with EF-S lens

Next month, I will buy a canon EOS R5 for concert photography. I will be short on money for some months or even a whole year because of this investment. I have a lot of EF-S lenses and some EF lenses ...
5
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3answers
2k 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 ...
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2answers
233 views

What's the best choice of lens from an optics surplus shop to get a Stanhope Lens-like magnifying function?

I am looking to do some experiments with my cellphone and a lens, holding the lens in contact with my cellphone lens. I'm looking for a lens that has the shortest back focal length length possible, so ...
4
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1answer
177 views

Would you consider this lens (Samyang 8mm CS II) defective?

I purchased a new Samyang 8mm F3.5 UMC Fish-eye CS II today. After I made my first shot with it I immediately noticed a flaw. At f/3.5 the flare of bright objects is shifted towards the bottom (and ...
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6answers
1k views

Aperture iris in front of lenses (in object space)

This question discusses the iris placed in camera body and this question does not reveal too much details about external iris. I recall from scattered information that I have read that iris placed in ...
3
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2answers
291 views

Calculating Lens Hood Dimensions

How can I calculate for a given lens, where in the periphery a theoretical lens hood would become visible? This seems dependent on the size of the front element, focal length, and possibly other ...
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6answers
2k views

What is the relationship between lens diameter and exposure?

All of the online calculators for exposure, I have seen, factor in time, film speed, and aperture (which is a function of the iris diameter and the focal length of the lens). However I would have ...
44
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4answers
40k views

What does the number of elements and groups in a lens mean?

All lens specifications include a statement of how many elements the lens contains, and in how many groups, for example: Nikon AF-S VR Zoom-NIKKOR 70-300 mm 1:4,5-5,6G: 17 elements in 12 groups (two ...
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4answers
296 views

Why is there an air gap between lenses and digital sensors, as opposed to continuous glass-like higher refractive index?

Thinking about ultra-fast lenses (ƒ<1), it would seem useful to have a solid+liquid medium between lens and sensor. This wouldn't have been very practical (presumably) at the time of film, but with ...
0
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2answers
222 views

How are wide angle lenses able to project an image onto a sensor?

The Nikon F-mount has a flange distance of 46.5mm. A 14mm lens for example has an horizontal angle of view of about 104°. How is a lens able to project an image from the rear element onto the sensor ...
4
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4answers
167 views

Seeming contradiction on wikipedia about rear nodal points and how the principal plane is related to focal length

There are two lines on the wikipedia pages for "cardinal points" and "focal length" that seem to contradict each other, and I would be extremely grateful if someone could explain ...
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2answers
2k views

How do I clean a Yashica Mat-124g taking lens?

I have disassembled the taking lens of my Yashica Mat-124g and tried to clean it. First, I used 99% isopropyl alcohol and it didn't help. Then I used a 1:1 solution of hydrogen peroxide and ammonia ...
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2answers
102 views

Estimating the optical resolution of a lens

In Tony & Chelsea Northrup's recent video titled 5 Lies Camera Companies Tell You, they mention that the optical resolution of a kit lens is often lower than the resolution of the sensor at around ...
40
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6answers
9k views

Why do stars appear as circles, not points?

Excluding the Sun, stars are so far away that their angular diameter is effectively zero. However, when you take pictures of them, brighter stars appear as circles, not points. Why? In theory, any ...
0
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2answers
119 views

What means lens optical characteristics?

I have 12-60 Panasonic lens for mft system. I'm about to buy 12-60 Leica for the same camera, because the photos I do with my current lens feel, smartphone-ish. Depite the lenses are similar in ...
2
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2answers
1k views
1
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1answer
125 views

What explains a lens flare “streak” on only one side of light source?

We know than an axial streak can be caused by a smudged lens that has been wiped in one direction. The following image shows both lens flare and a lens "streak." But what could explain the one-sided ...
0
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1answer
244 views

Can you calculate lens thickness from knowing focal length and diameter?

I'm not the best at math, but I'm wondering if there is a formula to figure out the thickness of a lens from only knowing the focal length and diameter.
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2answers
206 views

Lens Magnification vs Pixel Magnification

Scenario: I take a picture with a camera that has a crop factor of 3.19. I use a 55 mm focal length equivalent for taking the photo. In the resulting image file header, it says a magnification of 0....
30
votes
4answers
11k 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?
3
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2answers
618 views

What does lens flare from a catadioptric (mirror) lens look like?

Can one get lens flare with a mirror lens? What does it look like?
14
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3answers
2k views

What is the pre-computer version of Photoshop's blending modes?

Before computers, to blend two pictures into one, I'd imagine they'd have used some sort of mirror setup to reflect the one picture onto a mirror containing the reflection of the other picture. Does ...
27
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15answers
49k 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 ...
2
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3answers
575 views

What is the necessary recess on an enlarger lens board?

I have recently acquired a Meopta Belar 75mm/f4.5, to use with my Durst M605 enlarger. I was remiss in not checking the mount of this lens (M23.5) before I bought it, and have therefore ended up with ...
12
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3answers
3k views

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

I'm starting to study cameras and lenses. By reading explanations and watching videos on convex lenses, I learnt that they make parallel light rays converge to a single point called the focal point. ...
4
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5answers
656 views

Is there an optical filter that reduces the film's contrast?

As far as I know, the change of the exposure moves the negative' density curve left or right only (moves the objects to the different zones), and to shrink or enlarge overall contrast, one has to ...
0
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2answers
155 views

No more turn left to get focus at infinity (hit the lens limit) [duplicate]

Academic question: If I run out of turn attempting to achieve an infinity focus (close, but no cigar) would I: Move the lens away from the sensor? OR Move the lens closer to the sensor?
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3answers
456 views

Why are adapters for slightly too-short backfocus lens mounts not made with just a thick glass window instead of a lens element?

Infinity-correcting adapters tend to incorporate a weak teleconverter usually. It would appear that a thick, planar optical glass window is also capable of lengthening back focus - and would probably ...
13
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6answers
1k views

What lens characteristics contribute to attractive lens flare?

Some lenses give really harsh and unwanted flares. Some gives beautiful flares that add depth to an image. What's the science behind this?
46
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7answers
12k 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 ...
5
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2answers
132 views

Which is better in lens hoods, felt-like material or sawtooth surface?

I have noticed that many1 Canon lens hoods contain a felt-like matte black material designed to reduce reflections. The material probably does so admirably, but tends to get dusty over time. On the ...
20
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2answers
597 views

How do graduated ND filters actually work?

My question stems from the fact that the surface of the filter is completely out of focus. My understanding is that light from any one point of the subject hits the lens all over... some of it ...
0
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1answer
690 views

How can i calculate the direction vector of a pixel? [closed]

So if you take a pinhole camera and make it as the origin of our plane(3D) and a pixel from the image plane and connect the two with a straight line it should make a vector, which has direction and a ...
0
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1answer
376 views

Why is there a maximum focus distance when using an extension tube? [duplicate]

I am using the Nikon D850 together with the Sigma 50mm/1.4 Art and the MEIKE MK-N-AF1-A extension tube(s). During first shots I found out that the combination not only has a minimum focus distance (...
0
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1answer
240 views

How do focal reducers affect image quality?

I have a bunch of lovely old full frame K mount lenses (like the 50mm f1.2 and the 135mm f2.5) and the idea of using them in a proper mirrorless body (I have the K-01 and that's a hell of a brick) ...
7
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3answers
6k views

What's the opposite of a fisheye lens?

A fisheye lens is an extremely wide-angle lens that is purposely designed to have extreme barrel distortion. Is there such a thing as a lens purposely designed to have pincushion distortion? What ...
4
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3answers
2k views

Which formula for f-numbers is correct: f/D or 1/(2NA)?

I've seen two different definitions for the f-number of a general-purpose lens. Are they consistent ? I'm assuming that subjects are distant (not macro, magnification is small), and we have a lens ...
0
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3answers
110 views

What techniques do higher-end lenses use to reduce astigmatism at high apertures?

I own a few lenses with a maximum aperture of f/2.8. For this question, I'll focus on two specifically: A Rokinon 14mm f/2.8, which retails around the $500 CAD mark; and A Sigma 24-70 f/2.8, which ...
10
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3answers
202 views

What useful information can one gain from a lens element diagram?

On many photo gear review sites, cutaway diagrams of lenses are featured which show the layout of the elements in each lens. Here's the style of diagram I'm talking about, taken from Nikon's website ...
16
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5answers
4k views

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

I have built a custom optical device that uses a standard C-mount lens as found on CCTV cameras. Wikipedia states that the flange-to-film distance of a C-mount lens is 17.526 millimetres. I have ...

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