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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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76 views

Is there theoretical limit on the minimal focal length for a given sensor size?

There seems to be a limit, around 0.33, on the fastest possible aperture. Is there a theoretical limit on how wide a non-fisheye lens can be? That is, what is the minimal possible focal lens for a ...
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1answer
68 views

What defines an “objective”?

I'm not experienced in photography and would like to get some knowledge about the terminology. My question is: What defines an objective? Or: When would you define something as an objective? I mean, ...
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27 views

Focus Issues Using a C mount Filter on a CS Lens

I'm trying to use the Arducam 8mp with CS mount with a 25.4 C-Mount Filter, but I am unable to focus the picture. The filter fits perfectly and still leaves room for the lens to screw in. It says in ...
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4answers
2k views

Is camera lens focus an exact point or a range?

I have often wondered if the focus of a lens at a particular focal length is an exact point or a range within a few millimeters. This becomes all the more important when manually focussing. How far ...
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1answer
63 views

Rainbow flare effect on Industar 50-2

I am reproducibly getting the kind of rainbow-streak flare seen in the attached image on my copy of the Industar 50-2 (a russian 50mm f3.5 tessar-ish M42 pancake). The pattern does rotate when ...
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2answers
448 views

Camera image in pixel to real image in meters size relation [closed]

first post so please be nice. I am doing an image processing project and my problem is now that I would like to know how big my digital image is in the real world. I have: digital image: 336x256 ...
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3answers
97 views

Does field of view change for different lens model for the same focal length?

I am using two lenses - Tamron 75-250mm F/3.8-4.5 Model 104A and AF-P DX NIKKOR 70-300mm. When shot with lenses set to 250mm of focal length, the field of view for the Tamron lens is greater than the ...
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5answers
212 views

Why is low chromatic aberration considered important in the digital era?

I have read many lens reviews. It seems that low chromatic aberration is considered an important property of lenses. However, film is a dead dinosaur today. Practically everyone is using digital ...
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2answers
77 views

Does the T-number account for lens vignetting, or only for glass/coating transmission?

Surprsingly I could not find information on this. Many lenses have vignetting profiles available. Vignetting changes if you use a cropped sensor, or, in case of zoom lenses, can change with zoom. ...
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1answer
116 views

What is lens astigmatism?

Can someone simply explain astigmatism and its different types? How are they caused in lenses, and how can they be identified in images? I'm looking for a simple, understandable explanation. I've ...
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3answers
98 views

Light falloff - until lens surface, focal center, or camera sensor?

Preface: if there is a better-suited forum for this question, please direct me. I figured it'd be better to post into Photography and not Physics as some of you might have already examined this ...
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1answer
143 views

How wide does the front element of a lens have to be, given the focal length and the aperture?

Clearly, a lens with focal length F and aperture 1/f has to be at least F/f mm wide. Maybe a little more to accommodate the angle of view. However, lenses tend to have wider front elements than F/f. ...
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2answers
64 views

Does adding a lens with a higher MTF50 in front of a lens with a lower MTF50 increase the MTF50 of the entire system?

I know that the MTF of an entire imaging system can be modeled by multiplying the MTF of each component (possibly because multiplication in spatial frequency domain is convolution in space?) So, let'...
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2answers
75 views

What kind of lenses with a “slightly different diffraction behaviour” were used in “large format photography in the 1980s”?

Referring to an interview with a lens expert (Krolop&Gerst Objektivreihe 17/32), discussing diffraction limits. "Es gibt ein paar Spezialobjektive die haben ein bisschen anderes Beugungsverhalten,...
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3answers
176 views

A projection of a real-image is one fixed perspective, but looking through the lens with my eye, I see many perspectives. Why?

Assume that I have a camera obscura (with a large lens - something like a magnifying glass) setup projecting an image of some still life. I look at my projection on my projection plane and I see one ...
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2answers
139 views

Why can my eye focus on the real image of a convex lens at many distances from the lens, but a projection only works at a specific distance?

Say I have a single convex lens. I set it up like a camera obscura, shine a light on my object and project the image onto a projection plane. Given the focal length of my lens, the projection plane, ...
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4answers
373 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 ...
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2answers
128 views

Taking Photograph Through Beamsplitting Glass so the object photographed cannot see camera lense back

I am new to beam splitting glass & its properties and possibilities, but I would like to think that it should be possible for me to some sort of beam splitting glass in order to be able to take a ...
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3answers
153 views

Can too-tight lens hoods become accidental apertures?

There is frequently the suggestion to use tighter lens hoods than specified for some lenses when they are used with smaller sensors than they are designed for. The idea is that the vignetting ...
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2answers
91 views

Are bokeh (ball) shapes a result of vignette or aperture action?

The effect of getting shaped out-of-focus highlights (bokeh balls) from both non-circular apertures inside the lens, and masks applied in front of it (where an external aperture would presumably also ...
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1answer
79 views

What is a good reference for the technological aspects of modern digital photography? [closed]

What is a good readable, technically detailed reference on the technology involved in modern digital cameras, raw file conversion, and digital image processing? (Possibly a complete a complete answer ...
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1answer
213 views

Is this lens decentered?

I bought a second hand lens yesterday, but I'm not sure if it's decentered or not. When buying it, I did some tests to make sure it was not decentered, but when I repeated the test at home I'm not ...
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1answer
85 views

Why do CCTV and pro camcorder lenses often have vignettes, and apertures that can be fully closed?

I noticed this on both CCTV and "TV lens" C-mount lenses. Is this for manual black level calibration, or protecting some early sensor or *icon tube style from wear, or entirely another reason? It ...
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3answers
248 views

How exactly is “flange” defined in the term ''flange distance"

The concept of a flange distance is something I understand on a theoretical level, but not so much on a practical level. It is debatably the most important measurement in the camera, determining the ...
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4answers
422 views

Why do prime lenses have multiple lens elements?

If I look up the specifications of my 50 mm lens, it says that it has 8 lens elements, in 7 groups. Why is this, why not just a single lens element with a 50 mm focal distance?
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5answers
441 views

Why use ultra-wide with short focus?

I have a Samyang F/2.0 12 mm for the Sony E Mount, so the 35-mm equivalent focal length is 18 mm (crop sensor 1.5×). I use it mainly for landscapes and architecture in order to fit more in my frame ...
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2answers
380 views

Does on-sensor phase detection autofocus need adjustment for accuracy?

Is autofocus adjustment actually no longer required with on-imaging-sensor autofocus that's phase-detection only i.e. not relying on contrast detection? If not, why? How does lens autofocus adjustment ...
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1answer
157 views

How do extension tubes affect the image circle? [duplicate]

If you abuse your lens by just stacking a bunch of extension rings one on top of the other, will this start to affect your image circle? For instance, you have a lens that can just about cover your ...
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3answers
172 views

What does the value of 'exit pupil' represent on a lens datasheet?

On this datasheet of the Kowa LM25HC lens I have access to, there is a number called exit pupil, which equals -57.9 mm. What does this number represent? This is not a question about what the exit ...
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4answers
3k views

How do manufacturers get to high (83x) zoom levels on hybrid cameras?

Obviously the biggest hybrid zoom on the market (Nikon Coolpix P900 I think) does not range from actual 24 mm to 2 meters in physical length, but what kind of optical systems do manufacturers use to ...
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3answers
745 views

Can I force the aperture to stay open on macro lens?

I have a sigma 180mm f/2.8 lens, which I bought because it was the largest aperture I could find that focuses around 0.5m See this question for why this was important.. Upon arrival, however, the lens ...
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2answers
407 views

Is this a bubble in my lens element?

Both images show the same artifact.
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2answers
436 views

What is the cause of inclusions in my bokeh?

I was doing a lens review an two of my lenses showed these rather unsightly inclusions in their bokeh. There are two different lenses. EDIT: The third lens I have tested also seems to have this ...
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3answers
1k views

How to calculate stops of light lost from a teleconverter?

How would I be able to take the multiplication value of a teleconverter (1.7, 1.4, 2, etc) and find out how many stops of light are lost when using it just based on that number?
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2answers
192 views

Why is the aperture of this old lens showing as centered blue glare?

I just bought a old Minolta MD Zoom 35-135mm 1:3.5-4.5 lens together with two old Minolta SLRs to get into film photography. Before using actual film I adapted it to my Canon 600D (using a no-name MD-...
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4answers
230 views

Does a macro lens have a smaller DOF in 'real-world' distances at the same focal length and aperture as other primes, why?

This question IS about: Does a macro lens have a shallower DOF at the same settings and focal length as another prime? If so, what in the optics is responsible for this? Using a Macro lens as a ...
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3answers
252 views

Why would lens be much longer than its focal length?

I accidentally saw Nikon 17-35mm f/2.8 lens and noted that it is rather large for its focal length. Here's the first review of this lens search offered - looks like it's 107 millimeters long. Given ...
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2answers
654 views

What function does C1, C2, and Off mean on Sigma 120-300mm f/2.8 Sports lens?

I am using a Sigma f/2.8 120-300mm lens. How does the C1 and C2 affect pictures? Also, what about the Off, 1, and 2 switch on the OS feature?
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1answer
89 views

Are focus and resolving power optically equivalent?

Limited "resolving power" or "sharpness" is a problem one can see with many lower-quality lenses, especially with higher-resolution camera bodies. Playing with my cheap 500mm mirror lens, I often get ...
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1answer
169 views

What causes this pattern? [closed]

What causes the pattern seen on the image (it is a still from a video)? This doesn't seem to be a Moiré. It seems to be largely related to the camera or the filter (the pattern is fixed and aligned ...
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4answers
302 views

A thin camera and a thin lens with a large glass element

After seeing these 3D designs, I was wondering if a camera that is thin could possibly have such a large piece of glass in the lens (given the lens piece doesn't expand when powered on). As far as I ...
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4answers
264 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 ...
5
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1answer
211 views

Is there an easy way to tell the size of an image circle a lens has?

I know that lens can come in many formats, e.g. crops vs. full frame. However, someone recently told me that the Zeiss Otus has an image circle that is larger than the intended format. This is one ...
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3answers
178 views

If a camera has two lenses, where is the focal plane? In the sensor or in the second lens?

For example, this exercises asks where is the focal plane. Is in the sensor or in the second lens?
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3answers
121 views

What limit do lens manufactures come upon first when making a wide range lens with large aperture (besides economics)? [duplicate]

Economies of selling such a lens would be my first guess to why a lens doesn't exist but I am more interested in the physical characteristics of a lens. How do the characteristics of a lens affect ...
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3answers
1k views

Understanding focus distance of Nikon f/1.8D lens with D5600 Camera

I took some sample photos using my Nikon D5600 camera with Nikon f/1.8D lens. I had to set the focus manually since this lens doesn't provide AF with my camera. My Question: The album of my sample ...
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1answer
139 views

How do phone attachment lenses affect depth of field?

Let's take, for example, the Moment Tele Lens. This lens is pitched as a 60mm lens that allows you to get 2x "closer" to the subject. The iPhone 6s uses a f/2.2 lens. Does the mounting of the tele ...
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3answers
123 views

Design and Fabricating My Own Lens

I have a small business (just me) selling an inspection machine. The camera and lens work well, but I've had to print my own camera mount to get the lens further away from the CCD to get a good focus....
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2answers
410 views

Does the sensor size matters in the size and weight of an equivalent lens? Why?

In other words, does the size of projected image circle matters in the size and weight of two lenses with the same aperture/DOF (different f-number) and field of view (different mm)? All other things ...
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3answers
5k views

Why is the hole in a pinhole camera usually a circle?

I know that for pinhole cameras and camera obscuras the holes are usually round (they are circular). But I don't see the link between the shape of the hole and the formation of the image.