photographic shutter

[tomlib]

Hi, I would like to consult someone to finally understand the problem. It is not entirely clear to me exactly how the camera aperture works. To be clear, by aperture I mean an opening that can be enlarged and reduced and, in the old fashioned way, determines how much light gets into the camera, similar to the human eye. It sounds nice but the image gets into the camera rather than just the light itself. It seems to me as a layman that by reducing the viewfinder, the recording area must also be reduced. Logically, I would see it as, for example, when I zoom out the lens, it is necessary to reduce the aperture so that ambient light does not pass through. But, for example, with the eye, it really depends on the direct amount of light.
Could someone explain it to me in a simple way or recommend some literature, because everywhere seems to be said that way about the light and I'm getting confused. I would like to explain it somehow. My camera really changes the aperture depending on how it zooms. But what about the eye or older cameras like the Flexaret?

I used google translator.

Tom.

 

[Strodav]

The camera body does not have an aperture. The aperture is in the lens. The shutter speed in the camera adjusts the time an image is on the camera sensor. The longer the shutter speed, the more time the sensor sees light. The shorter the shutter speed, the less time the sensor sees light. There are additional considerations. Fast shutter speeds freeze motion where slower shutter speeds can blur motion. Faster shutter speeds help reduce camera shake, which can blur an image. The aperture in the lens controls the amount of light getting to the sensor. There are additional considerations. Large apertures have a shallow depth of field, which can be used to separate your subject from the background. Smaller apertures have a deeper depth of field, which can be used to get closer and farther parts of your image in focus. The articles below contain good descriptions of how a camera works and about the exposure triangle of shutter speed, aperture, and ISO.

Understanding Digital Camera Sensors

www.cambridgeincolour.com

Camera Exposure: Aperture, ISO & Shutter Speed

www.cambridgeincolour.com

Hope this helps.

 

[480sparky]

Logically, I would see it as, for example, when I zoom out the lens, it is necessary to reduce the aperture so that ambient light does not pass through.

It sounds like you're thinking that a scene that requires a given exposure at, say 100mm, the exposure must change if the lens is zoomed to 50mm.

That's not how light and exposure works.

Perform this simple experiment: You're reading this post right now on some sort of device whether it be your phone or a computer monitor. The screen is at a set brightness. Now take your hand and cover up half the screen. Did the other half get brighter or dimmer?

 

[AlanKlein]

The aperture does not change the angle of view of the scene. It only changes how light or dark it is. Try this at home at night. Turn a light on and off. Notice that the scene from left to right and up to down covers the same area even though your eye's aperture is opening and closing to adjust to the light. Only how light or dark it is changes. That's how an aperture works. The field of view remains the same. Only the amount of light that enters changes.

Regarding zoom, when you zoom in to telephoto, there is automatically less light because of the way a lens works. So the maximum aperture f stop is greater at wide angle and the least at telephoto zoom setting. But this limitation of light has to do with more glass in the lens when zooming to telephoto. It's not related to how apertures work.

 

[wfooshee]

Aperture is not measured or expressed in absolute numbers, the way shutter speed is. A shutter speed of 1/250 exposes the film or sensor for 1/250th of a second, whether you have a 50mm lens or a 300mm lens. Where aperture gets weird is that the physical size of the aperture does need to change depending on the focal length of the lens... A aperture of say, 5mm (pulling a random number out of my butt) allows a certain amount of light to contribute to an exposure through a 50mm lens, but that physical-size aperture allows far less light to contribute to an exposure through a 300mm lens. The correct aperture is proportional to the lens's focal length, and that's where the f numbers come from. It works out that an aperture opening that is 1/8 the lens's focal length contributes the exact same amount of light to an exposure whether the lens if 50mm or 500mm. A physical aperture of 6.25mm in a 50mm lens (50/8) produces the same light gathering as a physical aperture size of 62.5mm in a 500mm lens (500/8.) We express that aperture value as f:8. We don't care what the physical size of the aperture opening is, but because of the way the optical properties of lenses works, The exposure value of f:8 is the same, regardless of focal length.

That's actually one reason you don't see very long lenses with very large apertures... The lens barrel of a common 70-300mm zoom lens simply isn't large enough to have an iris that can open to 75mm, which would be f:4. There are long lenses with large apertures out there, like a 600mm f:4, but they are expensive. By the way, when a lens is capable of larger apertures, we call it a fast lens; a large aperture lets in enough light to allow for faster shutter speeds.

Your question about changing the aperture with zoom has merit, but not the way you're thinking of it. You can't separate light from image. The aperture is not a "shade" in front of the lens, it's an iris between certain elements of the lens. A large iris lets in more light, resulting in more exposure, and a small iris lets in less light, resulting in less exposure. If we had to set aperture size by its physical dimension, we'd have to carry around a book of tables to match desired exposure settings to focal length, and photography would be far less fun than it is. the fact that the aperture behaves proportionally to focal length saves us that headache, and lets us express aperture as the simple fraction of the focal length. Remember, an aperture 1/8 (or 1/4, or 1/16) the size of the lens's focal length allows the same exposure of light through the lens, no matter the focal length, so we simply say f:8 (or f:4 or f:16.) That's also why large apertures have small numbers. An aperture of f:1.4 is a common maximum aperture for lenses in the 50mm range. A 500mm lens couldn't economically be built large enough to carry an iris capable of f:1.4! If you want an example of a cost-no-object fast, long lens, Google the Sigma 200-500 f:2.8 lens, yours for about $26,000!

Finally, an explanation of why f-numbers for apertures aren't sequential. Exposure stops are discussed as doubling or halving the exposure; a 1-stop difference is half the exposure or double the exposure, with "exposure" being the amount of light collected by the film or sensor. Shutter speeds is easy: double the shutter speed, say from 1/125 to 1/250, you get half of the exposure, i.e. a one-stop change. Aperture stops are f:1.4, f:2, f:2.8, f:4, f:5.6, f:8, f:11, f:16, etc. Now aperture work by the area of the iris opening, which involves a squaring factor. If I want to move 1 stop of aperture, I don't double or halve the f-number, I have to multiply or divide it by the square root of 2. Doubling or halving the f-number changes your exposure by 2 stops, not one. That's why the sequence of f-numbers on the lens seems... odd. 1-stop differences in f-stops are measured as 1.4 times the next one.

 

[AlanKlein]

Aperture is not measured or expressed in absolute numbers, the way shutter speed is. A shutter speed of 1/250 exposes the film or sensor for 1/250th of a second, whether you have a 50mm lens or a 300mm lens. Where aperture gets weird is that the physical size of the aperture does need to change depending on the focal length of the lens... A aperture of say, 5mm (pulling a random number out of my butt) allows a certain amount of light to contribute to an exposure through a 50mm lens, but that physical-size aperture allows far less light to contribute to an exposure through a 300mm lens. The correct aperture is proportional to the lens's focal length, and that's where the f numbers come from. It works out that an aperture opening that is 1/8 the lens's focal length contributes the exact same amount of light to an exposure whether the lens if 50mm or 500mm. A physical aperture of 6.25mm in a 50mm lens (50/8) produces the same light gathering as a physical aperture size of 62.5mm in a 500mm lens (500/8.) We express that aperture value as f:8. We don't care what the physical size of the aperture opening is, but because of the way the optical properties of lenses works, The exposure value of f:8 is the same, regardless of focal length.

That's actually one reason you don't see very long lenses with very large apertures... The lens barrel of a common 70-300mm zoom lens simply isn't large enough to have an iris that can open to 75mm, which would be f:4. There are long lenses with large apertures out there, like a 600mm f:4, but they are expensive. By the way, when a lens is capable of larger apertures, we call it a fast lens; a large aperture lets in enough light to allow for faster shutter speeds.

Your question about changing the aperture with zoom has merit, but not the way you're thinking of it. You can't separate light from image. The aperture is not a "shade" in front of the lens, it's an iris between certain elements of the lens. A large iris lets in more light, resulting in more exposure, and a small iris lets in less light, resulting in less exposure. If we had to set aperture size by its physical dimension, we'd have to carry around a book of tables to match desired exposure settings to focal length, and photography would be far less fun than it is. the fact that the aperture behaves proportionally to focal length saves us that headache, and lets us express aperture as the simple fraction of the focal length. Remember, an aperture 1/8 (or 1/4, or 1/16) the size of the lens's focal length allows the same exposure of light through the lens, no matter the focal length, so we simply say f:8 (or f:4 or f:16.) That's also why large apertures have small numbers. An aperture of f:1.4 is a common maximum aperture for lenses in the 50mm range. A 500mm lens couldn't economically be built large enough to carry an iris capable of f:1.4! If you want an example of a cost-no-object fast, long lens, Google the Sigma 200-500 f:2.8 lens, yours for about $26,000!

Finally, an explanation of why f-numbers for apertures aren't sequential. Exposure stops are discussed as doubling or halving the exposure; a 1-stop difference is half the exposure or double the exposure, with "exposure" being the amount of light collected by the film or sensor. Shutter speeds is easy: double the shutter speed, say from 1/125 to 1/250, you get half of the exposure, i.e. a one-stop change. Aperture stops are f:1.4, f:2, f:2.8, f:4, f:5.6, f:8, f:11, f:16, etc. Now aperture work by the area of the iris opening, which involves a squaring factor. If I want to move 1 stop of aperture, I don't double or halve the f-number, I have to multiply or divide it by the square root of 2. Doubling or halving the f-number changes your exposure by 2 stops, not one. That's why the sequence of f-numbers on the lens seems... odd. 1-stop differences in f-stops are measured as 1.4 times the next one.

How does the aperture size on a large format lens work since the same let's say type 0 shutter can be swapped among lenses with different focal lengths?

 

[wfooshee]

I have no large format experience, couldn't tell you... From what I'm reading (because you got me curious,) the photographer has to do some measurements of the aperture, starting at wide open, based on the lens's true focal length, note where that falls on the shutter's aperture scale, and adjust from there for smaller apertures. Might be fun to play with, but I don't have any such stuff!

 

[AlanKlein]

I have no large format experience, couldn't tell you... From what I'm reading (because you got me curious,) the photographer has to do some measurements of the aperture, starting at wide open, based on the lens's true focal length, note where that falls on the shutter's aperture scale, and adjust from there for smaller apertures. Might be fun to play with, but I don't have any such stuff!

The aperture is set just like other lenses according to the f/stop inscription on the shutter-aperture device that is swappable among difffereent focal length lenses. One unfortunate issue is there are no hard stops to make it easy. You have to be careful to line up the setting to the hash marks of which there are three per "soft" stop.

 

[AlanKlein]

See picture showing the aperture and shutter settings on the ring device in the middle of the lens. This is typical and the part that can be swapped.

[Near Mint] Fuji Fujinon W 150mm f/5.6 Large Format Lens COPAL from Japan | eBay

Total Condition Near Mint. Serial Number 534187. Appearanc Tiny scuffs from normal use.

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