Tagged Questions
3
votes
3answers
209 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 ...
3
votes
2answers
108 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
131 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 ...
7
votes
5answers
425 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?
15
votes
2answers
390 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 ...
4
votes
2answers
130 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 ...
0
votes
1answer
215 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
330 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 ...
15
votes
2answers
529 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 ...
11
votes
4answers
1k 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
2k 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
100 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 ...
2
votes
2answers
659 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 ...
7
votes
2answers
760 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 ...
7
votes
3answers
327 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
654 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, ...
6
votes
1answer
237 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 ...
19
votes
3answers
1k 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 ...
6
votes
4answers
508 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 ...
44
votes
5answers
884 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
...
4
votes
2answers
630 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 ...
5
votes
2answers
3k 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 ...
23
votes
3answers
5k 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 ...
9
votes
2answers
1k 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?
4
votes
1answer
456 views
Are mirror lenses appropriate for DSLR astrophotography?
There's a whole host of inexpensive mirror lenses available in the 500 mm - 800 mm range (this for example). They have slow max apertures (f/5.6-8) and a donut shaped bokeh (not a problem ...
15
votes
5answers
690 views
How do I find the aperture that produces the highest-quality images for a given lens?
I'm not talking about large aperture (f/1.8, f/2.8...), rather, about small apertures (f/18, f/20, f/23...). I read somewhere (actually I think it was on this site, but I don't exactly remember which ...
4
votes
1answer
229 views
What is the camera's influence on lenses' optical properties?
I installed my 50mm f/1.4 Nikon lens on my Olympus E-P1. I notice some properties of the lens changed — namely, magnification and DoF both increased.
I understand magnification increases because of ...
21
votes
2answers
2k 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
votes
4answers
334 views
Why are some zoom lenses “soft” at either end of the focal length range?
As one reads about zoom lenses, a relatively common comment that comes up in reviews of some lenses (especially lower-priced lenses) is that the lens is not as sharp ("soft") at one or both ends of ...
10
votes
1answer
1k 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
...
11
votes
3answers
4k 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 ...
13
votes
6answers
1k views
Can a smaller sensor's “crop factor” be used to calculate the exact increase in depth of field?
If APS-C and similar crop-sensor digital cameras have a focal length multiplying effect such that a 50mm lens has an apparent focal length closer to the field of view of an 80mm on a full frame ...
26
votes
3answers
2k views
What does a hexagonal sun tell us about the camera lens/sensor?
In this picture, we see that the sun comes out as a hexagon. I am sure it is not arbitrary. What does the hexagon tell us about the instrument that captured the image?
27
votes
5answers
4k views
How do constant aperture 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 ...
16
votes
3answers
1k views
What makes a Carl Zeiss lens so special in a smartphone?
There are smartphones on the market that have a focus towards photography. Some are equipped with a Carl Zeiss lens. I have looked into Wikipedia, which tells me that they are a brand who produces ...
16
votes
11answers
9k 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 ...
26
votes
2answers
2k 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 ...
12
votes
6answers
459 views
Does lens speed still increase meaningfully when the physical aperture is larger than the sensor size?
This question came to me this morning, thinking about 50mm lenses. I have the Pentax 50mm f/1.7 (manual) and it's a very nice lens, but would be considered (relatively) slow on 35mm film, and many ...
16
votes
5answers
899 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?
10
votes
3answers
2k 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?
12
votes
3answers
367 views
What is Chromatic Aberration?
What is Chromatic Aberration? Is it a physical part of the lens, or just an optical illusion?
