Apature

[Razr]

Oh dear.

First of all: Razr - you're a complete idiot.

And I'm turning you in for abuse of forum protocol.

(SNIP) In a 'variable aperture' zoom lens (such as a 75-300/4-5.6) then the aperture itself may not change - by this I mean the actual aperture's diameter, not the aperture value.

That makes no sense.

However what does change is the maximum aperture value, which is a function of both the diaphragm's diameter and the focal length of the lens.

Still nothing coherent.

So while the actual diaphragm's diameter may not change when zooming, the aperture value most certainly will in the above example.

Please Google "aperture priority".
Never mind. Here's one about "A":

Coolpix 995's Way of Achieving "Constant" Aperture.
To partially overcome the problems caused by the variable aperture feature, Coolpix 995 can maintain aperture within 1/3 stop in effect before zoom operation started, if possible. More precisely, the camera will do its best to keep the selected aperture with 1/3 stop as you zoom.
However, if the camera can maintain this 1/3 stop error range, aperture changes. Consequently, constant aperture while zooming may or may not be maintained. Note that this fixed aperture is only available in the Aperture-Priority mode and Manual Exposure mode when you can set aperture manually.

A CANON EOS fellow explains it better than me:

a constant f/# zoom does *not* stop down at shorter focal lengths. look through any lens as you zoom for proof. the iris doesn't move.

the f/# of a complex lens system is the ratio between the size of the entrance pupil (what you see when you look through the front of the lens) and the focal length. this means that the magnification of the lenses in front of the actual iris dictate just how "fast" the lens is (i.e., they dictate how big the opening looks).

constant f/# zooms do not change the iris as they zoom. instead, this magnification is what changes. in fact, this goes for all zoom lenses really, but for constant f/# zooms, the magnification changes fast enough to keep pace with focal length, keeping the ratio between them constant.

This is junior maths(SIC) Razr. I assume you are older than a junior so therefore you are an idiot.

As I noted before, your post here will be forwarded to the administrators.

[BBPhoto]

OK, I'm really late into this thread but I had to come see what all these posts were about. I've always tried to be as polite as possible and avoid these controversies but enough is enough.

Razr, you are attacking everyone else's points but are either incapable or unwilling to define exactly where you stand. Your posts, more and more, are taking on the life of some sort of virtual chameleon; very bizarre looking but somehow able to blend in with the background.

One of two things is going on. Either you are completely glib or you are completely inept when it comes to expressing yourself. Either way, you are being unnecessarily disruptive by arguing nonsensically against some very knowledgeable people who are absolutely correct if my interpretation of this whole mess is accurate.

My suggestion is that you take a deep breath before your next post and then clarify your argument. If there is a misunderstanding, great. We'll get it cleared up. If you are in fact saying that when using a f/3.5 - 4.6 lens, the widest available aperture at the short end (f/3.5) is available to the user at the long end of the same lens by using Av mode, way too many people are paying too much money for fast glass when they could just be using Av mode and you would be very, very wrong.

EDIT: I want to be completely clear here. In my above paragraph, I am asking if you are saying that I can put a 3.5-4.6 lens on my camera, let's take the 10-22 for this example, dial in an aperture value of 3.5 @ 10mm, then zoom to the long end - 22mm and in Av mode, I would be able to dial in an aperture of 3.5 so the camera effectively has the same shutter speed and the aperture is letting the same amount of light in the camera at both the 10 & 22 ends? Is this what you are saying?

Maybe your initial comment was a mistake through unwillingness to admit it, this has snowballed into a compete mess? Who knows? Either way, I invite you to clarify your argument so that maybe we can end this and some of these guys here can post in a thread more worthy of the effort.

[DonSchap]

Look ... here is an "optimum" aperture shot ... that aperture was f/13 to make sure most of the object was in focus, front to back ... shot in Av Mode, with a 90mm f/2.8 lens.

EXIF: 90mm - f/13 - 1/125 sec - ISO-400 - Aperture Priority

Sorry about my choice of subjects ... how tawdry, eh?

Did I wan't f/2.8 ... no, I opted (<- operative word, here) for f/13.

The SONY A100 camera worked out the rest of the exposure for itself, using the built-in flash.

Had I stayed at f/2.8 ... I would get something that looks a lot like this:

EXIF: 90mm - f/2.8 - 1/125 sec - ISO-400 - Aperture Priority

Note the unwanted f/2.8 bokeh ... definitely NOT "Optimum" Aperture.

[TenD]

http://www.uscoles.com/fstop.htm

http://www.paragon-press.com/lens/lenchart.htm

http://www.digital-slr-guide.com/maximum-aperture.html

http://www.dpreview.com/learn/?/key=aperture

Yes I know they are all wrong and you are right.

[Razr]

(SNIP)I seriously suggest you learn to read. "Optimum aperture" (or aperure as you quoted it) does not mean wide open at the arbitrary number of your choosing, it means wide open at the mathematical ability of the lens at the given focal length. Optimum and imaginary aren't the same word. Sorry.

"Optimum" aperture means "best" aperture at any given focal length with any given lens. Your unnecessarily convoluted (self-serving) asked and answered statement does not say that.

There are two possibilities here. 1. You're mentally retarded and you need a great deal of help because of your learning disability, or 2. You have never owned an SLR or SLR lens. Either way, I feel sorry for you.

Your post here will be reported to the admins.

Finally, why would every lens manufacturer list their lenses as "f/3.5-5.6" or "f/2.8-4" if they could be used at f/3.5 or f/2.8 throughout the entire focal length?

I am saddened that you do not know enough about lenses, lens markings or how lenses function in Av mode to even ask the proper questions.
Worse, you don't seem to comprehend that the markings denote the largest and smallest aperture settings.
They serve another purpose: to mark the f/stops for the photographer.

What possible reason could there be aside from the fact that you're wrong

I'm wrong for the way they mark their lenses?

for them to inform people that at the telephoto length, they'll only be getting f/5.6?

that makes no sense.

Why wouldn't they just list their lens at the maximum aperture that you have found a magical way to invoke despite the fact that physics deem it impossible?

"Asked and answered" as they say in court. "Maximum (and median and minimum) apertures" are attained in Av. and full manual mode throughout the zoom range.

[Rooz]

i doubt you've ever owned a camera or lens in your life. no one with practical experience with a dslr could possibly be this foolish.

someone please close this thread.

[Razr]

http://www.uscoles.com/fstop.htm

http://www.paragon-press.com/lens/lenchart.htm

http://www.digital-slr-guide.com/maximum-aperture.html

http://www.dpreview.com/learn/?/key=aperture

Yes I know they are all wrong and you are right.

Please, point me to the one that talks about "aperture priority"?

[Rooz]

Note the unwanted f/2.8 bokeh ... definitely NOT "Optimum" Aperture.

well...it's kinda optimum really cos it hides how ugly the a700 is.

[TenD]

Please, point me to the one that talks about "aperture priority"?

You have no understanding of the basics of aperture and f/stop, first learn the basics of what you are talking about. I haven't seen a single quote by you supporting your claims.

[TenD]

http://www.cs.mtu.edu/~shene/DigiCam...-priority.html

"Over the available range"
http://www.cs.mtu.edu/~shene/DigiCam...-priority.html

I suggest you read all of my links, and please supply one...one link that supports your "thesis".