Another newbie aperture question: For almost all of the time I've been shooting Digital, I let the camera make all the decisions, so I never gave any thought to what was actually...

jerrypoller Loc: Huntington, NY

For almost all of the time I've been shooting Digital, I let the camera make all the decisions, so I never gave any thought to what was actually happening within the camera/lens. With the purchase last Dec. of a D7100 (an upgrade from a D90, upgraded from a D80), I decided to learn how to "take" photographs instead of letting the camera take them. My first lessons came from YouTube, and then shortly thereafter, from this forum. Which brings me to today's question. I bought a used Nikkor 35-70 f2.8 zoom on recommendation from a forum member. I've been shooting in Manual mode with Auto ISO now for a few weeks and wondered just recently what is going on physically in the camera and the lens when I set the
Aperture above f2.8 inasmuch as the lens is "fixed" at f2.8 throughout the zoom range. I guess this question also applies to any lens when the camera sets the Aperture for less than/greater than the lens min/max aperture. If there is a link in the forum describing this process, please direct me to it. Thanks.

tradio Loc: Oxford, Ohio

You may want to study the exposure triangle, sounds like you may be getting mixed up on aperture and ISO. ISO is the amount of amplification applied to the signal from sensor, Higher ISO is more amplification.
This tutorial does a fairly good job of explaining aperture.

http://www.alienskin.com/f-stop-lesson/

bsprague Loc: Lacey, WA, USA

"I set the ISO above f2.8 inasmuch as the lens is "fixed" at f2.8"

That has me confused. ISO is numbers like 100, 200, 400, 800,etc.

Aperture is f2.8, f4, f8, f16, etc.

Zoom effects neither.

Can you ask your question again? Maybe break it into pieces?

jerrypoller Loc: Huntington, NY

bsprague wrote:

"I set the ISO above f2.8 inasmuch as the lens is "fixed" at f2.8"

That has me confused. ISO is numbers like 100, 200, 400, 800,etc.

Aperture is f2.8, f4, f8, f16, etc.

Zoom effects neither.

Can you ask your question again? Maybe break it into pieces?

You're absolutely right - my newbie mistake. What I meant to say is when I set the Aperture to e.g. f11 on an f2.8 lens, what is going on in the lens itself since it's "set" to f2.8. Sorry for the mistake.

jerrypoller Loc: Huntington, NY

tradio wrote:

You may want to study the exposure triangle, sounds like you may be getting mixed up on aperture and ISO. ISO is the amount of amplification applied to the signal from sensor, Higher ISO is more amplification.
This tutorial does a fairly good job of explaining aperture.

http://www.alienskin.com/f-stop-lesson/

My mistake - I've corrected the OP to reflect what I really meant - setting the Aperture higher than the lens Aperture itself. Sorry.

BebuLamar

Your lens doesn't change the aperture when you zoom. Many zoom's do change the aperture when zoom. With these lenses the aperture gets smaller (bigger number) as you zoom toward the long end. If the lens isn't set at max or min aperture a modern camera like yours would automatically change the aperture to keep it constant.

jerrypoller Loc: Huntington, NY

BebuLamar wrote:

Your lens doesn't change the aperture when you zoom. Many zoom's do change the aperture when zoom. With these lenses the aperture gets smaller (bigger number) as you zoom toward the long end. If the lens isn't set at max or min aperture a modern camera like yours would automatically change the aperture to keep it constant.

How does the camera "change" the aperture. It can't be a physical change in a fixed f2.8 lens, can it? Is it just a "computed" aperture the sensor recognizes?

bsprague Loc: Lacey, WA, USA

jerrypoller wrote:

You're absolutely right - my newbie mistake. What I meant to say is when I set the Aperture to e.g. f11 on an f2.8 lens, what is going on in the lens itself since it's "set" to f2.8. Sorry for the mistake.

I'm still not sure I understand and it may already be answered. When you set it to f11, it stays at f11. If won't be set to f2.8 unless you set it there.

What is going on inside the lens is like an eyeball. In bright light, the iris has to shrink in diameter. In dim light it grows in diameter. Inside the lens is a set of plates or blades that form a near circle and does the same thing. Unfortunately, left over from the dark ages of film, is the idea that big numbers like f16 are the little holes and small numbers like f2 are the big holes.

bsprague Loc: Lacey, WA, USA

jerrypoller wrote:

How does the camera "change" the aperture. It can't be a physical change in a fixed f2.8 lens, can it? Is it just a "computed" aperture the sensor recognizes?

My understanding is that lens makers have trouble explaining a special feature where the aperture can remain constant throughout the zoom range. It is easy at the tiny range (f16) and harder at the wide settings (f2.8). Lens can be cheaper, smaller and lighter if they compromise and allow the aperture to shrink as you zoom to a higher magnification.

The idea is that on some lenses you can set f2.8 and it will stay "fixed" at f2.8 throughout the zoom range. If you set f2.8 and some shutter speed and ISO to match for exposure, the setting remain constant or "fixed" through out the zoom range.

DWU2 Loc: Phoenix Arizona area

When you look through the viewfinder, the lens is always at its maximum aperture - in this case, f2.8. Otherwise, what you would see through the viewfinder would be dark. But, if you've selected, say, f11 for the shot, when you take it, the camera's diaphragm partially closes to restrict the aperture. So, the lens' maximum aperture is "fixed" in the sense that it can go no wider, but the diaphragm enables the aperture to be made smaller.

Erik_H Loc: Denham Springs, Louisiana

jerrypoller wrote:

You're absolutely right - my newbie mistake. What I meant to say is when I set the Aperture to e.g. f11 on an f2.8 lens, what is going on in the lens itself since it's "set" to f2.8. Sorry for the mistake.

F/2.8 is the largest aperture your lens will open up to, the smaller the number the larger the opening. So, when you stop your 35-70mm lens down to say, f/8 or f/11, the aperture still closes down, allowing less light in, but you can still attain f/2.8 @ 70mm. With a variable aperture zoom, e.g. Nikon's 70-300mm f/4.5-5.6, the largest aperture changes from f/4.5 to f/5.6 as you zoom the lens out. A fixed aperture (prime) lens maintains the same aperture throughout the zoom range.

mwsilvers Loc: Central New Jersey

jerrypoller wrote:

How does the camera "change" the aperture. It can't be a physical change in a fixed f2.8 lens, can it? Is it just a "computed" aperture the sensor recognizes?

Your lens aperture is NOT really "fixed" at f/2.8 in the way you're suggesting. F/2.8 refers to the widest aperture your lens is capable of, not the only aperture. The term fixed is a bit of a mosnomer. All it means is that the maximum aperture is f/2.8 on your lens regardless of the focal length you have it set to. You can always make the aperture smaller. I'm not sure of the minimum aperture on your lens but it's at least f/16 and probably smaller. Variable aperture zoom lenses will have a different maximum aperture depending on the focal length being used.

Rich1939 Loc: Pike County Penna.

bsprague wrote:

Unfortunately, left over from the dark ages of film, is the idea that big numbers like f16 are the little holes and small numbers like f2 are the big holes.

Fortunately, left over from the age of enlightenment, aka the days of film :) , is the idea that aperture numbers like f16 and f2 are expressed as the ratio between the aperture diameter and the lens diameter.
Or to help your understanding, consider the f to equal 1/

JOEADDOTTA Loc: Rotonda West,florlda

There is a wonderful book for you to read it is"photography for dummies"It covers almost everything........

jerrypoller Loc: Huntington, NY

mwsilvers wrote:

Your lens aperture is NOT really "fixed"... (show quote)

Oh, now I see. I thought a single aperture lens (e.g. f2.8 vs f3.5-5.6) meant it was always at that size opening. Thanks for clearing it up for me.
:thumbup: