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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How do sensors "focus" on the bottom of the lens (flange distance)?

I know that when a camera sensor is used with a lens there is a specific distance between the sensor and bottom of the lens (aka "Flange distance" or "flange focal distance") in a ...
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How do I determine the focal length of a simple meniscus lens empirically?

I have a camera (Bolta Photavit IV) with a simple reverse Galilean finder that is missing the rear element (this is a common problem, they fall out). If I have a complete finder and disassemble it, ...
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How does using more spherical lenses compensate for spherical aberration?

I've heard of three common ways to compensate for spherical aberration: Small aperture (fewer non-paraxial rays). Aspheric lens (compensate with lens shape/material). Corrective spherical lens ...
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Why smaller AoV APS-C has same aperture as larger AoV FF lens?

I am quite confused, FF focal length 50mm f/2.0 has aperture diameter 25mm APS-C lens 50mm f/2.0 has aperture diameter 25mm Then both lenses have same size front glass. However Angle of View for lens ...
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Decrease FF lens focal length for use on APS-C and still have it focus?

Need to convert very cheap vintage FF 50mm f/2.8 lens to work as 35mm lens for for APS-C, for having wider angle of view. Its kind of works by simply placing lens closer to camera sensor (without ...
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Samyang 10mm F2.8 UNKNOW ADAPTER? [duplicate]

I want to use this Samyang 10mm F2.8 lens on my fujifilm X mount camera. What kind of adapter I need to mount on my fujifilm X mount? Was used with a sony nex adapter: After a searching on the ...
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3 answers
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Projecting image on camera

I have an optical system that forms an image at various distances (25cm range) as shown in the figure here: What kind of optics is required to project this image onto a CCD camera but without having ...
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A spot on the lens inside the camera

Hello! Is there someone who has experience with this kind of "spot-on-the-lens" stuff? :) I bought a used 35 mm camera and discovered a "spot" on the lens inside. Of course, it ...
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Motion tracking/VFX: How to get needed info for iPhone camera?

Basically, I want to do VFX with my iPhone SE 2nd Generation front-facing camera. The software being used is Blender up-to-date. I'm not sure what to set Blender for in the track camera settings field,...
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Does it exist?: a Coronagraph-style LCD panel mask inside the optical lens to pass dark and block bright pixel segments?

So we know coronagraphs are just a circular mask in the center of a telescope to block the sun's bright light and allow our eyes to see into the dark around the sun. But what if this coronagraph could ...
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APS-C + speedbooster vs full frame

I own a Nikon in DX-format (Nikon name for APS-C sensor, crop factor ~1.5) and I'm considering buying a 50mm prime lens soon for it. (To be complete, my camera is a D5200, although I don't think the ...
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Telephoto lens for camera whose lens cannot be removed

Is it possible to add a lens in front of another lens to make it a telephoto lens? I have a few "fisheye" adapters that I can put in front of any lens to take a fisheye photo, but I wonder ...
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There are many f2.8 zooms for FF. Why are there so few f2/f1.8 zooms for APS-C?

APS-C/Super35 cameras are less staple for film than they were before, but are still widely used. Besides, there are quite a few semi-professional APS-C DSLRs on the market. As far as I understand, a ...
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2 answers
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Is there an optical/photographic reason for the difference between product and its product image?

I recently bought this wristwatch from a major online store, which was advertised with the following image: One of the reasons I picked it is were the black pointers and markers. The watch I actually ...
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6 answers
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How do I calculate f/stop change for teleconverter that increases lens magnification?

I'm trying to calculate the f/stop change of attaching a x2 teleconverter to a 80mm f/2.8 lens. In this instance, the teleconverter attaches to the front of the lens, and has a larger opening than the ...
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What's the practical difference between two Canon 50mm f/1.2 L lenses?

I've got an RF 50mm f/1.2 L lens for my R system. I've recently been playing with an F-1, and picked up the FD 50mm f/1.2 L lens. Obviously some of the different size is the autofocus and other ...
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4 answers
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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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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 ...
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3 answers
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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 ...
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3 answers
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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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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 ...
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1 answer
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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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4 votes
3 answers
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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 ...
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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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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 ...
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4 votes
1 answer
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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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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 ...
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4 votes
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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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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 ...
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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 ...
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2 answers
138 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 ...
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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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1 vote
2 answers
269 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....
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2 votes
3 answers
766 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 ...
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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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2 answers
247 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 ...
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1 vote
3 answers
488 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 ...
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1 answer
962 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 ...
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1 answer
525 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 (...
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5 votes
2 answers
150 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 ...
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1 answer
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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 ...
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16 votes
5 answers
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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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3 answers
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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 ...
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1 answer
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I have a Nikon D60 and two lenses: 70-300 and 18-135. Should I get a 50mm 1.8 prime? [closed]

I have a Nikon D60 and two lenses: a Tamron 70-300 mm f/4-5.6, and a Nikon 18-135 mm f/3.5-5.6. I got all of these things really cheap, and now I want to buy a prime lens. I was thinking about a 50 ...
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1 vote
1 answer
219 views

Are front lens focusing and unit focusing equivalent in triplet/tessar style lenses?

Some vintage tessar or triplet type lenses (eg such intended for viewfinder cameras) implement focusing by merely moving the front element or front cell. When adapting such lenses to other cameras, ...
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2 votes
2 answers
158 views

How can a subject stay in focus if the shot is recomposed afterwards?

I have a doubt about a procedure that I see many photographers continuously apply and they taught me. I see that, when they want to take a picture with their reflex, they do this sequence of steps: 1)...
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Lumix G85 - Black Corner regardless of lens and no hood - please help

I have owned a Panasonic Lumix G85 for about a year. This month, I've started getting a black area on the left corner of my images, which you can also see on the EVF. I can't see anything on the ...
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1 vote
1 answer
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How to get close to 180 degrees with minimal fisheye look on iPhone X or 11?

I'm trying to film my rugby practices with my iPhone and wondering what is the best lens to use to capture the entire field without much that fish eye look? I noticed that the new iPhone 11 (Pro) ...
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How do i find the distance required to resolve a point on a page from a mobile camera?

Given all details such as focal length , aperture etc , how can i find the size of a point on a paper that is at a given distance from a mobile camera ? Or vica versa , the distance required to ...
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1 vote
1 answer
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Ghosting artefacts in narrow DOF photographs

Snapping with a Canon EOS 600D in narrow DOF situations (for example with low f-stop numbers at long focal lenght), I get ghosting artefacts on the parts of the photograph which are out of focus. ...
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