Bsrhrki

What if a revenant (monster) gains fire resistance?

What are some good ways to treat frozen vegetables such that they behave like fresh vegetables when stir frying them?

How to say when an application is taking the half of your screen on a computer

Why should universal income be universal?

How could a planet have erratic days?

How should I respond when I lied about my education and the company finds out through background check?

Is there a way to get `mathscr' with lower case letters in pdfLaTeX?

Temporarily disable WLAN internet access for children, but allow it for adults

PTIJ: Haman's bad computer

Invalid date error by date command

Redundant comparison & "if" before assignment

Are Captain Marvel's powers affected by Thanos' actions in Infinity War

Is there a RAID 0 Equivalent for RAM?

Store Credit Card Information in Password Manager?

What are the advantages of simplicial model categories over non-simplicial ones?

Has any country ever had 2 former presidents in jail simultaneously?

Open a doc from terminal, but not by its name

What is the highest possible scrabble score for placing a single tile

The IT department bottlenecks progress, how should I handle this?

Why does the Sun have different day lengths, but not the gas giants?

Why is the "ls" command showing permissions of files in a FAT32 partition?

Do we have to expect a queue for the shuttle from Watford Junction to Harry Potter Studio?

Does the UK parliament need to pass secondary legislation to accept the Article 50 extension

Strong empirical falsification of quantum mechanics based on vacuum energy density?

How do apertures which seem too large to physically fit work?

Size of the entrance pupil vs size of the apertureHow do constant aperture zoom lenses work?Does the size of the front glass mean anything?How do different apertures affect photographs?Why aren't lenses designed with extra large apertures for autofocus beyond what's used for imaging?Who tells my camera which apertures my lens hasWhy do landscape photos with large apertures have dark corners?Which filters will fit Voigtlander 15mm?How can I use flash with large apertures?Why are large zoom ratio constant apertures lenses not generally available?Can too-tight lens hoods become accidental apertures?

8

1

A 400mm f4.0 lens is supposed to have a maximum aperture diameter of 10cm. Looking at such a lens they don't seem big enough to fit that kind of aperture including all the mechanics for control inside them. Do modern lenses have a way of focusing light into a smaller aperture to behave like a bigger one or are they really always the size that the formula (fstop = focal length / aperture diameter) suggests?

lens aperture lens-design physics

share|improve this question

edited 4 hours ago

mattdm

122k40357653

asked 5 hours ago

LuLeBeLuLeBe

432

New contributor

LuLeBe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

8

1

A 400mm f4.0 lens is supposed to have a maximum aperture diameter of 10cm. Looking at such a lens they don't seem big enough to fit that kind of aperture including all the mechanics for control inside them. Do modern lenses have a way of focusing light into a smaller aperture to behave like a bigger one or are they really always the size that the formula (fstop = focal length / aperture diameter) suggests?

lens aperture lens-design physics

share|improve this question

edited 4 hours ago

mattdm

122k40357653

asked 5 hours ago

LuLeBeLuLeBe

432

New contributor

LuLeBe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

A 400mm f4.0 lens is supposed to have a maximum aperture diameter of 10cm. Looking at such a lens they don't seem big enough to fit that kind of aperture including all the mechanics for control inside them. Do modern lenses have a way of focusing light into a smaller aperture to behave like a bigger one or are they really always the size that the formula (fstop = focal length / aperture diameter) suggests?

lens aperture lens-design physics

share|improve this question

edited 4 hours ago

mattdm

122k40357653

asked 5 hours ago

LuLeBeLuLeBe

432

New contributor

LuLeBe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 4 hours ago

mattdm

122k40357653

asked 5 hours ago

LuLeBeLuLeBe

432

New contributor

LuLeBe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 4 hours ago

mattdm

122k40357653

asked 5 hours ago

LuLeBeLuLeBe

432

New contributor

LuLeBe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 4 hours ago

mattdm

122k40357653

edited 4 hours ago

mattdm

122k40357653

asked 5 hours ago

LuLeBeLuLeBe

432

New contributor

LuLeBe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 5 hours ago

LuLeBeLuLeBe

432

2 Answers
2

active

oldest

votes

10

Your observations of the lens leads you to both a correct, and incorrect, conclusion.

1. Correct: the aperture (i.e., mechanical iris) of the lens is substantially smaller than the 10 cm it supposedly should be. Only the front element is anywhere near 10 cm diameter. Where the iris mechanism is in the lens barrel, the diameter is substantially smaller than 10 cm.




2. Incorrect: the stated aperture size is not actually 10 cm in diameter. In reality, it is the the apparent size of the wide-open aperture (the iris), when viewed through the front of the lens, that is 10 cm in diameter.

For any lens, the aperture when viewed through the front of the lens is known as the entrance pupil. It is the entrance pupil that is 10 cm in diameter.

See also:

• Size of the entrance pupil vs size of the aperture

share|improve this answer

edited 3 hours ago

answered 3 hours ago

scottbbscottbb

20.5k75895

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  That made it so clear, even better than the first answer. I think I understood it now, hopefully! Thank you very much!
  
  – LuLeBe
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Or to flip the description around: the light that gets through the aperture formed a 10 cm disk where it met the objective lens. When you increase the f-stop you start intercepting some of that light.
  
  – dmckee
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @dmckee Absolutely, great way of stating it from the iris's viewpoint! =)
  
  – scottbb
  2 hours ago
  

  
  
  
  

add a comment | 

2

Lens designers have a few tricks up their sleeves. As an example, zoom lenses change focal lengths but the aperture diameter does not physically change with the zoom. This is an oddity because as the focal length changes, so does image brightness. In fact, if the focal length is doubled, image brightness falls off 4X. Conversely, if the focal length halves, image brightness will increases 4X. How do you think the optician compensated and maintained the exposure? The front group of lens elements acts as a magnifier. In other words, the diameter of the iris as seen by the outside world appears expand and contract with the zoom when in fact it is fixed as to diameter. It is the apparent diameter of the iris and not the actual diameter that determines the light gathering power of the lens. Note: most inexpensive zooms give up the ghost as the user zooms towards max magnification. A more costly zoom will likely maintain a constant exposure throughout the zoom.

share|improve this answer

answered 4 hours ago

Alan MarcusAlan Marcus

25.7k23060

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Right yes I know about constant aperture zoom lenses. I originally thought they'd have a larger aperture and just close it down when zoomed out. But that makes much more sense the way you explained it, thanks!
  
  – LuLeBe
  4 hours ago
  

  
  
  
  

add a comment | 

Your Answer

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "61"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

LuLeBe is a new contributor. Be nice, and check out our Code of Conduct.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fphoto.stackexchange.com%2fquestions%2f106099%2fhow-do-apertures-which-seem-too-large-to-physically-fit-work%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

10

Your observations of the lens leads you to both a correct, and incorrect, conclusion.

1. Correct: the aperture (i.e., mechanical iris) of the lens is substantially smaller than the 10 cm it supposedly should be. Only the front element is anywhere near 10 cm diameter. Where the iris mechanism is in the lens barrel, the diameter is substantially smaller than 10 cm.




2. Incorrect: the stated aperture size is not actually 10 cm in diameter. In reality, it is the the apparent size of the wide-open aperture (the iris), when viewed through the front of the lens, that is 10 cm in diameter.

For any lens, the aperture when viewed through the front of the lens is known as the entrance pupil. It is the entrance pupil that is 10 cm in diameter.

See also:

• Size of the entrance pupil vs size of the aperture

share|improve this answer

edited 3 hours ago

answered 3 hours ago

scottbbscottbb

20.5k75895

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  That made it so clear, even better than the first answer. I think I understood it now, hopefully! Thank you very much!
  
  – LuLeBe
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Or to flip the description around: the light that gets through the aperture formed a 10 cm disk where it met the objective lens. When you increase the f-stop you start intercepting some of that light.
  
  – dmckee
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @dmckee Absolutely, great way of stating it from the iris's viewpoint! =)
  
  – scottbb
  2 hours ago
  

  
  
  
  

add a comment | 

10

Your observations of the lens leads you to both a correct, and incorrect, conclusion.

1. Correct: the aperture (i.e., mechanical iris) of the lens is substantially smaller than the 10 cm it supposedly should be. Only the front element is anywhere near 10 cm diameter. Where the iris mechanism is in the lens barrel, the diameter is substantially smaller than 10 cm.




2. Incorrect: the stated aperture size is not actually 10 cm in diameter. In reality, it is the the apparent size of the wide-open aperture (the iris), when viewed through the front of the lens, that is 10 cm in diameter.

For any lens, the aperture when viewed through the front of the lens is known as the entrance pupil. It is the entrance pupil that is 10 cm in diameter.

See also:

• Size of the entrance pupil vs size of the aperture

share|improve this answer

edited 3 hours ago

answered 3 hours ago

scottbbscottbb

20.5k75895

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  That made it so clear, even better than the first answer. I think I understood it now, hopefully! Thank you very much!
  
  – LuLeBe
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Or to flip the description around: the light that gets through the aperture formed a 10 cm disk where it met the objective lens. When you increase the f-stop you start intercepting some of that light.
  
  – dmckee
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @dmckee Absolutely, great way of stating it from the iris's viewpoint! =)
  
  – scottbb
  2 hours ago
  

  
  
  
  

add a comment | 

Your observations of the lens leads you to both a correct, and incorrect, conclusion.

1. Correct: the aperture (i.e., mechanical iris) of the lens is substantially smaller than the 10 cm it supposedly should be. Only the front element is anywhere near 10 cm diameter. Where the iris mechanism is in the lens barrel, the diameter is substantially smaller than 10 cm.




2. Incorrect: the stated aperture size is not actually 10 cm in diameter. In reality, it is the the apparent size of the wide-open aperture (the iris), when viewed through the front of the lens, that is 10 cm in diameter.

For any lens, the aperture when viewed through the front of the lens is known as the entrance pupil. It is the entrance pupil that is 10 cm in diameter.

See also:

• Size of the entrance pupil vs size of the aperture

share|improve this answer

edited 3 hours ago

answered 3 hours ago

scottbbscottbb

20.5k75895

share|improve this answer

edited 3 hours ago

answered 3 hours ago

scottbbscottbb

20.5k75895

answered 3 hours ago

scottbbscottbb

20.5k75895

answered 3 hours ago

scottbbscottbb

20.5k75895

2

Lens designers have a few tricks up their sleeves. As an example, zoom lenses change focal lengths but the aperture diameter does not physically change with the zoom. This is an oddity because as the focal length changes, so does image brightness. In fact, if the focal length is doubled, image brightness falls off 4X. Conversely, if the focal length halves, image brightness will increases 4X. How do you think the optician compensated and maintained the exposure? The front group of lens elements acts as a magnifier. In other words, the diameter of the iris as seen by the outside world appears expand and contract with the zoom when in fact it is fixed as to diameter. It is the apparent diameter of the iris and not the actual diameter that determines the light gathering power of the lens. Note: most inexpensive zooms give up the ghost as the user zooms towards max magnification. A more costly zoom will likely maintain a constant exposure throughout the zoom.

share|improve this answer

answered 4 hours ago

Alan MarcusAlan Marcus

25.7k23060

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Right yes I know about constant aperture zoom lenses. I originally thought they'd have a larger aperture and just close it down when zoomed out. But that makes much more sense the way you explained it, thanks!
  
  – LuLeBe
  4 hours ago
  

  
  
  
  

add a comment | 

2

Lens designers have a few tricks up their sleeves. As an example, zoom lenses change focal lengths but the aperture diameter does not physically change with the zoom. This is an oddity because as the focal length changes, so does image brightness. In fact, if the focal length is doubled, image brightness falls off 4X. Conversely, if the focal length halves, image brightness will increases 4X. How do you think the optician compensated and maintained the exposure? The front group of lens elements acts as a magnifier. In other words, the diameter of the iris as seen by the outside world appears expand and contract with the zoom when in fact it is fixed as to diameter. It is the apparent diameter of the iris and not the actual diameter that determines the light gathering power of the lens. Note: most inexpensive zooms give up the ghost as the user zooms towards max magnification. A more costly zoom will likely maintain a constant exposure throughout the zoom.

share|improve this answer

answered 4 hours ago

Alan MarcusAlan Marcus

25.7k23060

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Right yes I know about constant aperture zoom lenses. I originally thought they'd have a larger aperture and just close it down when zoomed out. But that makes much more sense the way you explained it, thanks!
  
  – LuLeBe
  4 hours ago
  

  
  
  
  

add a comment | 

Lens designers have a few tricks up their sleeves. As an example, zoom lenses change focal lengths but the aperture diameter does not physically change with the zoom. This is an oddity because as the focal length changes, so does image brightness. In fact, if the focal length is doubled, image brightness falls off 4X. Conversely, if the focal length halves, image brightness will increases 4X. How do you think the optician compensated and maintained the exposure? The front group of lens elements acts as a magnifier. In other words, the diameter of the iris as seen by the outside world appears expand and contract with the zoom when in fact it is fixed as to diameter. It is the apparent diameter of the iris and not the actual diameter that determines the light gathering power of the lens. Note: most inexpensive zooms give up the ghost as the user zooms towards max magnification. A more costly zoom will likely maintain a constant exposure throughout the zoom.

share|improve this answer

answered 4 hours ago

Alan MarcusAlan Marcus

25.7k23060

share|improve this answer

answered 4 hours ago

Alan MarcusAlan Marcus

25.7k23060

answered 4 hours ago

Alan MarcusAlan Marcus

25.7k23060

answered 4 hours ago

Alan MarcusAlan Marcus

25.7k23060