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Tagged Questions

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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4
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2answers
802 views

How can I get the image/sensor dimensions in mm to get Circle of Confusion from EXIF?

I need to get calculate some formulas based on Circle of Confusion and/or image dimensions (diagonal) in millimeters based on EXIF data only. IOW, I cannot say "this photo was shot with Canon 5D3 ...
-1
votes
1answer
644 views

How to calculate the magnification factor of an object to its image?

I have an object of size 37.5um x 37.5um, and captured a 640 x 480 resolution image of the object with a CMOS sensor. I see that the object is around 200 x 200 pixels in the image. How do I calculate ...
3
votes
0answers
148 views

Is this a Fata Morgana? [closed]

I took this photo. Above the horizon there is a thick line that looks like a cloud, but it surely isn't. Is this a Fata Morgana? What do you think? The Image
11
votes
4answers
627 views

Why aren't lenses designed with extra large apertures for autofocus beyond what's used for imaging?

Historically, designing large-aperture lenses has been difficult because correcting the optical aberrations that arise from large apertures requires complex designs and very large amounts of glass. ...
4
votes
3answers
442 views

What does it mean that a lens is x millimeters?

Every lens has different focal length in terms of millimeter so if I have a 100mm lens, what does that refer to? Does it mean the length of the lens itself is going to be 4 inches long, or does this ...
4
votes
1answer
108 views

Why do focusing aids darken when not looked at directly?

Many users of (D)SLRs equipped with a split image rangefinder or, to a lesser extent, with microprisms will notice how they have a tendency to appear dark in less than optimal conditions, such as ...
3
votes
2answers
563 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 ...
1
vote
2answers
392 views

What does it mean for a telecentric lens to be focused to infinity?

I have a question about a telecentric lens Ive been studying (for physics research!) and was wondering if you guys could help clear some cobwebs in my head. For starters, I am simplifying the TC lens ...
19
votes
2answers
454 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 ...
7
votes
5answers
713 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?
3
votes
1answer
132 views

Does lens focus affect the appearance of sensor dust?

I know that aperture affects the appearance of dust on a camera's sensor (or, technically, the filter in front of the sensor), but does focus matter at all? Since the dust is behind the lens, I ...
15
votes
2answers
859 views

Does a specific f number across all lenses denote same amount of light?

When we say a light source emits 1500 lumens of light, it does not really matter if the light source is incandescent, CFL, diode etc. Similarly, when I say f/1.8 can I assume that all lenses pass the ...
5
votes
2answers
185 views

Why do the Nikkor non-AI 135mm vs 50mm f/1.8 work differently when I look directly through the lens?

I recently purchased an old Nikkor 135 f/2.8 non-AI lens. Beautiful lens, but the closest focal distance is about five feet. I noticed that it will 'focus' at about 4 inches as well. If I hold the ...
4
votes
2answers
770 views

Why does calculated distance of an object in an image vary when zooming?

I would like to calculate the distance of an object from my camera, so i used the formula given in this question and I got a very good answer, but I've found that when I zoom and take the picture and ...
5
votes
1answer
136 views

Is diffraction an issue with macro lenses?

I'm looking to try out macro photography and have a rental of the Canon 100mm 2.8L IS and the MT-24EX flash to try out on my Canon 7D. I've been reading that with the flash, you can stop down to ...
1
vote
1answer
121 views

Macro mode: Should I make sure the lens is all zoomed out?

It appears that on most compact digital cameras, the macro mode (flower symbol) works best (or only) when the zoom lens is at the widest setting (comparable to e.g. 35 mm). What is the reason? ...
1
vote
2answers
258 views

Is it worth it to read The Book of Optics

Is it actually worth it to read the Book of Optics by Alhazen to get basic knowledge about Optics? I know it's way too old but this book was important in the optics field. Also where can I find it ...
2
votes
1answer
167 views

How Do DxO Lens Ratings compare between systems?

Looking for new camera system with changing lenses (DSLR or SLD) I find DxOMark also has rating for lenses: http://www.dxomark.com/index.php/Lenses/Camera-Lens-Ratings What do the results numbers ...
0
votes
1answer
393 views

Where are the principal planes located in a camera lens?

I want to find locations of the principal planes of a camera lens. I have looked at the specification for my lens here and here, but did not find what I need. But there are many other parameters in ...
7
votes
3answers
980 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 ...
7
votes
5answers
770 views

What would be a good book for optics?

I would like to refresh my knowledge about optics. I studied optics back in the university but I almost forgot everything. What would be a good book to do that?
6
votes
1answer
134 views

Is there a correspondence between Tilt-Angle and the angle of the Focus-Plane?

Tilt lenses have their tilt-range specified in degrees, typically around ±8°. It seems that this number corresponds to how much a lens physically tilts along one axis. The effect is to tilt the plane ...
11
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3answers
534 views

How does the D800E reverse the effect of an antialiasing filter by adding another filter?

According to http://mansurovs.com/nikon-d800-vs-d800e the D800E differs from the D800 in that one of the layers of the filter reverses the effect of the initial low-pass filter. How does this work? ...
11
votes
5answers
9k 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?
14
votes
1answer
248 views

What lens design limits derive from the width of the lens mount?

I'm familiar with the lens design limitations imposed by the flange-to-focal-plane distance. But what constraints are caused by the width of the lens mount (that is, the size of the hole in the ...
6
votes
3answers
1k 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 ...
17
votes
2answers
823 views

Do rounded edges on aperture blades improve image sharpness, and how?

In the description for the XF lenses for its new X-Pro system, Fujifilm crows: The [XF lenses] all offer precise control over depth-of-field and deliver excellent out-of-focus bokeh thanks to the ...
2
votes
1answer
1k views

How does the quantity of elements and blades in a lens affect the optics?

I am trying to get a greater understanding of how lenses work. Basically I bought this lens, the Sigma 10-20 f4-5.6: The construction has really fascinated me. 14 Elements in 10 Groups?! What ...
10
votes
1answer
466 views

How do I design a conceptual lens schematic?

I would like to attempt to create a schematic for a simple or small compound lens, but the process seems very daunting. I have thoroughly read 'Science for the Curious Photographer: An Introduction to ...
11
votes
1answer
396 views

Why do mirror lenses have poor contrast?

I was reading this question on mirror lenses and the answers taught me a lot about mirror lenses. It is pretty obvious to me why they have donut bokeh (central obstruction) and why they are fixed ...
12
votes
4answers
2k 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 ...
5
votes
3answers
5k views

Why are objects far away inverted through a lens but not through the viewfinder?

When I look through a lens the image of objects far away are inverted but when looking the the viewfinder on my camera they are not. Why is this? I am having a hard time understanding why objects far ...
2
votes
1answer
128 views

Why does an aperture crop the image when you look through a lens itself but not when you look through the viewfinder?

I have been studying lenses for two days now and the aperture is very confusing. Based on the question here it appears that the aperture should not crop the image at all but when I look through a lens ...
7
votes
4answers
1k views

Do bigger focal lengths capture more light?

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 ...
2
votes
2answers
2k 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 ...
14
votes
2answers
2k 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 ...
8
votes
3answers
445 views

What is the limiting factor in lens construction when it comes to f-stop values?

This widely praised Nikon 105mm macro lens has a maximum f-stop value of 2.8. I've held it in my hands, it's a big lens. Meanwhile, this 50mm Nikon lens can go up to f/1.2, despite being 25% cheaper ...
8
votes
1answer
1k views

How do straight edges end up curved in photos?

In the standard model for a lens straight lines in the subject of a photograph will always end up straight. However I have seen a variety of photographs in which straight lines end up being curved, ...
11
votes
4answers
2k views

Is overall light gathering of a lens only dependant on aperture?

My impression is that the aperture value of a lens determines its light gathering ability, but I'm not sure I understand how it works... When considering light gathering in telescopes, it is ...
6
votes
1answer
459 views

What does “distortion <XX%” mean in lens specs?

I'm going to buy a lens and I would like to understand what "distortion <XX%" means. It's a vari-focal 10-60mm lens, and mentions distortion <12-1%. According to my understanding, at 10mm focal ...
8
votes
3answers
5k 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 ...
24
votes
3answers
2k 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 ...
9
votes
4answers
939 views

Is it possible for a lens to produce too much contrast?

I came across a complaint that a certain lens produces too much contrast. The lens was described as rendering "cartoonish" contrast when shooting a portrait with diffused light from a window, where ...
50
votes
5answers
1k 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 ...
5
votes
2answers
1k 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 ...
10
votes
2answers
3k views

Why is depth of field affected by focal length?

As the focal length decreases, the depth of field increases as well. Why is this? I'm not so much interested in a physics lesson as I am interested in a simple, down-to-earth explanation.
5
votes
2answers
5k views

Is the difference between a good 50mm vs 85mm lens just your distance from the subject?

I was wondering: is the difference between a 50mm f/1.8 lens and a 85mm f/1.8 lens just your distance from the subject? Let's assume that distortion is minimal; both lenses are of high quality. Does ...
0
votes
0answers
58 views

Different sources of noise and ways to avoid/correct those [duplicate]

Possible Duplicate: What types of noise can be present in digital photographs? I've few questions related to noise found in digital images. There are topics on this forum on underexposure ...
5
votes
1answer
286 views

What's the history of neutral density filters instead of aperture diaphragms in compact cameras?

Some compact cameras use neutral density filters to control light rather than aperture blades, to avoid the effects of diffraction in tiny sizes. I first heard of this as a feature of the Nokia N8 ...
6
votes
2answers
839 views

How are neutral density filters in compact cameras implemented?

I've read here on this very site that some compact cameras don't use aperture blades to stop down the lens and limit the amount of light hitting the sensor. Stopping down increases diffraction. ...