Aperture in lens and camera


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Camm

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#1
Hi,

I have a newbie question about aperture, hope someone can enlighten.

Given a lens of 18-55mm with aperture 3.5 -5.6. My understanding is that 3.5f at 18mm and 5.6f at 55mm. By adjusting the focal length changes the aperture settings as well.

OK my question - is the aperture range the minimum for that specific focal length? The camera itself allows adjusting of aperture as well, and I'm confused between the aperture in the lens and the camera.

Hope you understand what I'm trying to say...:dunno:
 

Galdor

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#2
Hi bro,

"Given a lens of 18-55mm with aperture 3.5 -5.6. My understanding is that 3.5f at 18mm and 5.6f at 55mm. By adjusting the focal length changes the aperture settings as well."

This is correct.

Aperture of a lens can be changed. If you are using a lens at 18mm the largest aperture it can open up to is f3.5 however, you can change the value to f8, f11, f16 and so on. Of course, when you change the aperture size, the DOF and shutter speed will change accordingly too.
 

cantaresg

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#4
The DOF can be changed by a few factors. The zoom size of your picture, the focal length that you used, the distance between you and your object and the distance between your object and the background are some compositional factor that affects the DOF. When you have composed your frame (or achieved the perspective that you wanted), the aperture is the only factor that can change your DOF.
 

zac08

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Feb 21, 2005
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#5
Hi,

I have a newbie question about aperture, hope someone can enlighten.

Given a lens of 18-55mm with aperture 3.5 -5.6. My understanding is that 3.5f at 18mm and 5.6f at 55mm. By adjusting the focal length changes the aperture settings as well.

OK my question - is the aperture range the minimum for that specific focal length? The camera itself allows adjusting of aperture as well, and I'm confused between the aperture in the lens and the camera.

Hope you understand what I'm trying to say...:dunno:
This is a variable aperture lens. And with a limited size of the front element, when you zoom out (at 18mm), the aperture requires only to be z size, but when you zoom out to a further length, say 55mm, then the aperture diameter WOULD need to be almost doubled to still give you the same f stop which you were using (i.e. 2 x z size)

The range you were talking about is actually the maximum aperture of the lens that it's capable of. Not the minimum, the minimum should be something about f22 or so.

As for control of aperture, these days, it's controlled on the camera by electronics. In the old days, they were adjusted by means of a aperture ring on the lens itself.
 

zac08

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#6
how do you change the DOF?
Taken from the web :

There are a few elements that will affects Depth of Field in a picture:

  • 1. the lens opening (the bigger the apertures, the zone of sharpness is shallower or vice versa);
  • 2. the focal length of the lens (the wide angle lenses have extended field of sharpness than a longer focal length lenses and vice versa), and;
  • 3. the distance from the lens to the subject (the nearer the subject is, the shallower the zone of sharpness and vice versa)
 

Camm

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This is a variable aperture lens. And with a limited size of the front element, when you zoom out (at 18mm), the aperture requires only to be z size, but when you zoom out to a further length, say 55mm, then the aperture diameter WOULD need to be almost doubled to still give you the same f stop which you were using (i.e. 2 x z size)

The range you were talking about is actually the maximum aperture of the lens that it's capable of. Not the minimum, the minimum should be something about f22 or so.

As for control of aperture, these days, it's controlled on the camera by electronics. In the old days, they were adjusted by means of a aperture ring on the lens itself.

Oh ok...so the aperture indicated on the lens is the max for that focal length and I can still change it in the camera to reduce the aperture ya.....I think I got it now.

Thanks guys
 

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