Lens aparture question

roddur

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Jun 3, 2013
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hi,

what does it mean when you can set "f" number in camera that is different from what is written on the lenses? for example my kit lens has f3.5-f6.3. but in aperture mode i can set eg. f7.1, f22

i'm learning :), so go easy on me
 

~tc~

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f3.5 and f6.3 is simply the widest aperture at the either end of the kit zoom.
F stop is the focal length divided by the iris opening diameter, and it determines the depth of field in your image and, along with shutter speed and ISO, determine your exposure.

A smaller number = larger opening = shallower depth of field, faster shutter speed, and/or lower ISO

Larger number = smaller opening = deeper depth of field, slower shutter speed, and/or higher ISO
 

alfogator

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Alfonso Caschili
The number written on the lens is the lowest aperture number (the scale is reversed, a lower value indicates a larger aperture). Each lens can be set to any number of values, usually starting from 22 and then going to smaller values: the number on the lens indicates your bottom, you can't set the aperture to a value smaller than that.
Some lenses, like your zoom, have variable maximum aperture at different focal lengths, so you can go to 3.5 at the widest angle but when you zoom in the lowest number you can set increases to 6.3.
 

roddur

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Jun 3, 2013
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14
thanx, appreciate your answers.

i fully understand what f number means. but i wanted to know, suppose i'm using a prime lens with f2.8, when i'm taking photo if i change the aperture in the camera to f22 or f6.3. what does than mean? will the aperture be 2.8 or the one i set in the camera.

i hope i'm not asking anything stupid :)

@pdk42, thanx for the link, will read it.
 

Cruzan80

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Aug 23, 2012
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Sean Rastsmith
What you set in camera will dictate. The part on the front of the lens is simply a quick reference on how wide it can go. Using a 50mm f1.4 vs a 50mm f2 won't have a difference in metering (aka shutter-speed and ISO, as far as brightness of the shot) at f4.

If it helps, ask around and see if someone has an older manual lens. Great way to "see" the aperture change (as you move the aperture dial, the blades will contract, restricting light through the lens).

BTW, no stupid questions. Everyone starts out at the same point, and if you don't ask, you don't learn. You will find people here are fairly informative to new photographers, especially with helping illustrate various things that we take for granted with digital.
 

RevBob

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When using an autofocus :43: lens setting the aperture in the camera will physically change the aperture in the lens. Older (legacy) manual focus lenses had a ring that allowed you to change the aperture by turning the ring on the lens. Either way the "iris" in the lens opens or closes depending on the aperture chosen. Hope that helps. :smile:
 

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