Questions tagged [lens-design]

Of and relating to the specifics of lens construction and manufacture.

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2
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1answer
731 views

Why don't all zoom lenses have variable f-numbers? [duplicate]

As I understand it, the f-number is a ratio between the focal length and the aperture diameter. A zoom lens can change focal length, but shouldn't the maximum aperture be a fixed size? If so, that ...
2
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1answer
1k views

How does a focus ring bring a subject in or out of focus?

When you manually adjust your focus ring on the lens, what actually happens inside the lens? Is this changing simply the point at which the lens is focusing, so that anything at this distance away ...
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1answer
355 views

Why do old-school catadioptric lenses have a fixed aperture?

Pretty much what it says on the tin. As far as I can tell, catadioptric telephoto lenses (operating on a similar principle to many telescopes; using mirrors rather than refraction) fell out of favour ...
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3answers
3k views

What does a megapixel designation on a lens actually mean?

I know that in a CMOS sensor the megapixels give you an idea of how many pixels are actually there to capture the light. In terms of a lens however, I cannot find any relation between the megapixels ...
22
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2answers
3k views

Are there any secrets in lens design?

Lens manufacturers usually share diagrams like this for their products. However, they conspicuously omit specifications that would allow one to completely analyze the optical system, like the power ...
15
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2answers
6k views

Retrofocus lens? What's that?

I saw that in Why do some people prefer 50mm to 35mm prime lenses, even for a crop sensor? , in @MattGrum's answer: ... The 50mm is a simpler design compared to the retrofocus 35mm ... What's ...
31
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2answers
6k views

What is a pancake lens?

I've read about a "pancake lens" but don't really understand what that means. What the pros and cons of having a pancake vs. another type of lens? I'm thinking of getting a Panasonic Lumix DMC-GF1 ...
12
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2answers
567 views

Does focus breathing make a lens slower when close focusing?

I've heard that focal length of some lenses will become noticeably longer when focusing to a close distance, an effect called "focus breathing". Since f-number is focal length divided by diameter of ...
9
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1answer
667 views

Why do certain lenses increase angle of view upon close focus?

I recently picked up a superzoom lens, the Nikon 28-300mm. Although I got it primarily for its versatility, my intuition was that a lens that can do 300mm focal length at 50 cm, as indeed it can, ...
8
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1answer
229 views

Can the method from the paper “High-Quality Computational Imaging Through Simple Lenses” compete with conventional lenses?

This answer to another question of mine linked to an interesting article: High-Quality Computational Imaging Through Simple Lenses. It proposes the use of simple optics and computational photography ...
5
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1answer
7k views

How to read a lens spot diagram?

How to read such a lens spot diagram?
14
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6answers
4k views

What is the Leica look?

What is the Leica look that fans of the company claim is unique to them? What concrete differences are there that are most obvious to a layman?
13
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4answers
4k views

How can a lens like a 18-55mm have more than one focal length?

How can a lens have a range of focal lengths? Shouldn't it be a single number? Isn't focal length supposed to be fixed for a lens of a particular shape and geometry? What am I missing? How many ...
12
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1answer
504 views

Can anyone identify this lens?

I read once, in a book, about a lens that was an "inverse fisheye". Basically a hemispherical mirror mounted at one end of a glass tube. I can't remember what it was called, nor can I find any ...
10
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3answers
5k views

Are all DSLR lenses made of glass?

This question is about lenses to "big" DSLRs, not system or compact cameras with interchangeable lens. Are all lenses made of glass in DSLR? And if not, is there a notable difference between: kit ...
9
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4answers
15k views

Which impacts the speed of focusing more, the lens or the camera body?

Speed is the larger concern, but a description of accuracy would be appreciated as well.
8
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2answers
10k views

What does “Flat Field Focus” mean?

Looking at lenses, specifically sigma macro lenses, I noticed that it had a ""Flat Field" front lens element". What does this mean? And how is it different to the norm?
7
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1answer
5k views

What are STF lenses?

What are STF (smooth transition focus) lenses? How much do they differ from other fast lenses? What artistic techniques are done with them? For example Sony has an a-mount 135mm F2.8 [T4.5] STF. What ...
5
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7answers
11k views

Does the Nikkor 50mm f/1.4g perform better than the f/1.8d?

Looking into these two lenses, I'm getting the impression that for my Nikon D-90 with DX camera sensor that the f/1.8d would waste light that is cropped by the sensor whereas the f/1.4g would not as ...
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2answers
145 views

How can a lens produce better (or worse) colors than another one?

So I was looking the Lomography Lomogon 32/2.5 Lens, which looks pretty cool. However in the copy they claim that it produces images with great color. Now if the lens glass is slightly tinted, then ...
0
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2answers
1k views

What are the advantages of Tamron SP 85mm f/1.8 over the Nikon 85mm f/1.8G?

What are the advantages of Tamron SP 85mm f/1.8 Di VC USD over the Nikon AF-S 85mm f/1.8G and why Nikon is about $200 cheaper than Tamron? They are both similar on the specs. except for elements/...
9
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1answer
450 views

What kind of mirror in a mirror lens?

A normal mirror, that we see for example in an elevator, is a glass sheet with thin metal coating on the backside, so light reflecting from the metal surface goes first thru the glass. Metal mirror (...
9
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3answers
944 views

Does the imaging circle size change when a lens zooms?

When a zoom lens is designed for a cropped (APS-C) imaging circle, does the imaging circle necessarily stay that small throughout the zoom range? It is easily understandable that a prime lens ...
9
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4answers
628 views

Were lenses for film designed to focus different colors at different depths, and what does that mean for digital?

I was reading the book Adobe Photoshop CS5 for Photographers: The Ultimate Workshop by Martin Evening & Jeff Schewe (Focal Press. 2011) and read this paragraph about film lenses and DSLRs: … ...
8
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3answers
2k views

What are groups and elements in lenses?

I hear people talking about groups and elements in lenses, but I am not sure what they mean. Could someone please explain?
7
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3answers
4k 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 ...
6
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4answers
2k views

Why do lenses for larger sensors tend to have shallower angles?

Why do different (mirrorless) cameras + provided lenses all seem to end up with a 24 mm 35-mm-equivalent focal length? The fixed-lens Canon Powershot G5X has a 1" sensor (actually 8.80 mm high) with ...
6
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1answer
583 views

Which lenses show focus shift?

Some lenses, because of a design that includes uncorrected spherical aberration, shift their plane of focus backwards as the aperture is narrowed. This is most apparent at close focusing distances and ...
6
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1answer
1k views

What makes the Zeiss Otus 1.4/55 so special?

The new Zeiss Otus 55mm f/1.4 is nearly $4000. With faster lenses from Canon (50mm f/1.2L) with autofocus, why is the zeiss lens more than twice that of the Canon counterpart?
5
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1answer
98 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,...
5
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2answers
379 views

How does the Sony 135 F2.8 [T4.5] STF twin aperture lens design work?

I stumbled across the Sony 135 F2.8 [T4.5] STF other day. I have read through the review but I can't for the life of me figure out what the twin-aperture setup is supposed to do!
5
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1answer
197 views

Where exactly would the focal length of a lens in the ray diagram fall?

If a lens is specified as (EF 50mm f/1.8), where exactly is the 50mm distance if I were to show it in a ray diagram? Considering that a lens is made up of multiple elements, I could not find a ...
4
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3answers
1k views

How can the focal length of a lens be many times greater than the lens's physical length?

I bought a Tamron 16-300. Question is: how can it have a focal length 0f 300 mm when it is only about 30 mm long? Doesn't the lens have to be 300 mm from the sensing element?
4
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2answers
2k views

What influences the shape of a lens flare?

Most of the time the shape of the flare is close to a circle, but recently I saw a movie where the lens flare was elliptically shaped. The stills below, taken from the movie Die Hard, show the effect ...
4
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4answers
268 views

How small can current SLRs get and still give comparable photo quality?

Let's take the full-frame Canon 5D as example. How small can this camera be and still give comparable picture quality? What are the design constraints? Besides the sensor, the body, can the lenses ...
4
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3answers
159 views

How commonly do constant-aperture manual zooms actually influence the aperture mechanically when zooming?

I have seen a few examples of constant aperture zooms (eg a 28-100mm f/4 Ricoh.) in the secondhand markets where the aperture appears to be not fully open (visibly non-round hole) at some zoom ...
3
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2answers
339 views

Is having a lens with vignetting a real world negative for portrait lenses?

After reading this answer for another post: I don't mind the vignetting as it actually improves the look of portraits however if you're doing astrophotography what's the point in a lens that's f/1....
2
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1answer
2k 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 exactly ...
2
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2answers
1k views

How effective are the rear weather sealing rings on lenses?

I am kinda torn between buying a Sigma 18-35mm f1.8, Nikkor 17-55 f2.8 and Sigma 17-50 f2.8 for my D3100 and D7100 cameras. The reason for confusion is that the Nikkor one has a weather sealing ring ...
1
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1answer
191 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. ...
1
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1answer
7k views

What are screw drive lenses?

Are lenses known as screw drivers actually available?If so what are their features and why are they called so.Name some of the lens and their manufactures.
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3answers
3k views

Are there any 24-70 2.8 lens with no length change in zooming?

I'm planning to buy a 24-70 f/2.8 lens for my Canon 7D. I need a lens that won't increase its length while zooming (like the Canon 70-200mm series). Is there such a lens in any brand?
0
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3answers
155 views

Does a camera have to have a contiguous housing?

The lens group in this picture would have its own protective lens tubes like the one on a camera but one for each lens group. What would be an issue having a gap between the lens group and stray light ...