Aperture Question

I have a bit of a techinical question and hope someone can answer it.

How does an image become sharper when you make the aperture smaller? If less light is getting through how does the dof become clearer?

Many thanks

Mikey

Mikey,

It does not as far as I'm aware. Now if you are thinking of DEPTH OF FIELD thats a different story. The aperture has a direct bearing on that without question.

Lots of other things will affect how sharp an image appears. Things like camera movement (hand-shake), too slow a shutter speed if hand-held, quality of lens, light quality, image contrast (or lack of) etc, etc.

What exactly are you trying to shoot? and whats the problem?

Richard

1. The image doesn't get any sharper, only more of it appears to be in focus.

2. By limiting angle of incidence you're limiting the circle of confusion over a greater depth. Hence objects at greater depths appear to be in focus.

2A. You need the same amount of light to expose the same scene regardless of aperture. Of course, the smaller the aperture the longer the duration of your exposure (shutter speed) needs to be.

Richard,

there isn't a problem, I am just trying to understand how when you shoot at F4 you get dof and when you shoot at F22 you don't. How does changing the size of the aperture affect the dof?

Thanks

Mikey

The technicalities: Click.

dof= depth of field.

f4 (larger aperture) gives you a shallower depth of field than f22 (smaller aperture).

There are other factors that come into play at f22 that may reduce sharpness.

Lenses DO GET SHARPER when you begin to stop down the aperture from max...typically highest resolving power of the lens is about 2-3 f/stops from wide open! While a lens' aerial resolution is max at max aperture, resolution on film in an optical system will typically show better MTF 2-3 f/stops from max aperture

René Damkot wrote in post #5508372
The technicalities: Click.

...Mmmmath -_-

You want a graphic example, try:

mikeyjm26 wrote in post #5508250
I have a bit of a techinical question and hope someone can answer it.

How does an image become sharper when you make the aperture smaller? If less light is getting through how does the dof become clearer?

Many thanks

Mikey

Wilt wrote in post #5508477
Lenses DO GET SHARPER when you begin to stop down the aperture from max...typically highest resolving power of the lens is about 2-3 f/stops from wide open! While a lens' aerial resolution is max at max aperture, resolution on film in an optical system will typically show better MTF 2-3 f/stops from max aperture

Wilt, I don't believe the OPs question had much to do with maximum aperture.

shutterfiend wrote in post #5508999
Wilt, I don't believe the OPs question had much to do with maximum aperture.

He did state, "How does an image become sharper when you make the aperture smaller?" And the image qulaity does become higher in delivered resolution as you go from max aperture to around f/5.6 typically, then after peaking the resolution does start to decrease. So what other circumstance should we be trying to answer?!

Well, he did go on to ask

Jon wrote in post #5509837
Well, he did go on to ask

So, OP, were there two questions posed about single topic sharpness?

Or were they two difference questions...one topic about improvement on sharpness, and a second topic about improvement in DOF?

At a small aperature (f2) the lense opening is very big. This allows a light from the subject to enter the lense at many different angles which are focused onto the sensor. Light from objects that are farther than the subject will come in to the lense at shallower angles, and will be focused in front of the sensor. By the time the light from these objects reaches the sensor it is out of focus. Light from objects that are closer than the subject will enter the lense at steeper angles, and would be focused behind the sensor. So when the hit the sensor, they are still out of focus.

With a larger aperature (f22) the lense opening is very small... This means that light entering the lense from the forground or background will be more or less parallel to light from the subject, and will be focused at nearly the same distance from the lense (very close to the sensor) so the image on the sensor appears in focus.

A good diagram would go a long way in explaining this.

Wilt wrote in post #5509827
He did state, "How does an image become sharper when you make the aperture smaller?" And the image qulaity does become higher in delivered resolution as you go from max aperture to around f/5.6 typically, then after peaking the resolution does start to decrease. So what other circumstance should we be trying to answer?!

shutterfiend wrote in post #5508396
dof= depth of field.

f4 (larger aperture) gives you a shallower depth of field than f22 (smaller aperture).

There are other factors that come into play at f22 that may reduce sharpness.

Lens construction and diffraction do play their parts in image sharpness, however, such information may clutter understanding of basic concepts, IMO.