quick question about the iris?

[lawrenceots]

I just have a quick question -

Is the iris in the human eye compared to the shutter or aperture in a camera?

The irus expands and contracts the let in or reduce the amount of light, as does the shutter in the camera. Then again the aperture in the camera does allow more light in, but also increases/decreases depth of field.

If some kind person would 'put me wise!'

Mucho thanks

 

[StewartR]

I just have a quick question -

Is the iris in the human eye compared to the shutter or aperture in a camera?

The irus expands and contracts the let in or reduce the amount of light, as does the shutter in the camera. Then again the aperture in the camera does allow more light in, but also increases/decreases depth of field.

If some kind person would 'put me wise!'

Mucho thanks

The iris in the human eye corresponds to the iris in a camera. Both open up and shut down to alter the intensity of light coming in.

The human eye doesn't have any feature analogous to the shutter in a camera.

 

[StewartR]

PS ... The iris in the human eye also controls depth of field, in exactly the same way as in a camera.

This isn't at all obvious, because it's virtually impossible to perceive the depth of field produced by your eye directly. But there are secondary effects which are perceptible. the most obvious of these is that your eyes get more tired more quickly when you're reading in poor light than when you're reading in bright light; and black text on a white computer screen (the standard since Windows came out in the 90s) is easier to read than light text on a black screen (the previous standard).

What's happening here is that, when the light is poor, your iris opens up the pupil in order to let more light in. But, as with a camera, a large aperture means a shallow depth of field. This means that the muscles in your eye have to hold the focus much more accurately, and hence you get tired faster.

 

[lawrenceots]

Many thanks Steware the aperture bit is what confused me most!

 

[onform]

WoW..saved me some time.. Great explanation Stewart

 

[Tracer]

PS ... The iris in the human eye also controls depth of field, in exactly the same way as in a camera.

This isn't at all obvious, because it's virtually impossible to perceive the depth of field produced by your eye directly....

I have become long-sighted with increasing age and need reading specs - about 2.5 diopter. Without them I can no longer read a newspaper even if I hold it a arm's length - except in very bright summer sunlight outdoors when I can read it quite comfortably at normal distance.

 

[PerfectSpeed]

I have become long-sighted with increasing age and need reading specs - about 2.5 diopter. Without them I can no longer read a newspaper even if I hold it a arm's length - except in very bright summer sunlight outdoors when I can read it quite comfortably at normal distance.

This is happening to me I'm only 43

 

[Greenninja]

The human eye doesn't have any feature analogous to the shutter in a camera.

I can blink 5.9 times per second for a maximum of 90 blinks low quality or 18 high quality.

 

[dan d]

The "shutter speed" of the eye is about 25Hz. This is the kind of refresh rate of the retina. And although the iris stops down to control the amount of light getting in there's a far greater compensation possible by changing the gain of the retina - bit like changing it's ISO number.

And you don't strictly become long-sighted with age you become presbyopic. The lens gets stiffer (makes up for other things not getting stiffer as you get older) so can't re-focus on near stuff.

 

[PerfectSpeed]

And you don't strictly become long-sighted with age you become presbyopic. The lens gets stiffer (makes up for other things not getting stiffer as you get older) so can't re-focus on near stuff.

Took me two reads, but I got there lol

 

[Flashman]

The human eye doesn't have any feature analogous to the shutter in a camera.

The eyelid perhaps?

PS ... The iris in the human eye also controls depth of field, in exactly the same way as in a camera.

Further to this... we also control depth of field, to a point, with the eyelids. If we can't see a distant object clearly we squint, the narrow slit between the eyelids when we squint has the same effect as reducing the aperture and brings things into clearer focus.