Aperture question

[ant]

Hi guys how are ya? Im relatively new to digital photography - especially my EOS 300D, and have a question regarding aperture values. i understand that the larger the aperture the more blurred the backgrounds in photos will be and vice versa, but what im asking is on the camera, when selecting the aperture value, is it the smaller the number the smaller the aperture, or the other way around - smaller the number larger the aperture? also, what are the smallest and largest aperture values i should be able to select on my camera? thanks for your help guys,

ant :?

[nosquare2003]

Welcome.

The smaller the number, the greater the aperture.


(Scottes, please confirm the above. :P )

[Jesper]

nosquare is right... :P

What the minimum and maximum apertures are that you can select, depends on your lens, so look it up in the specifications of your lens. For zoom lenses, it often depends on the focal length. Look at the 28-135 f/3.5-5.6 IS USM for example. At 28mm, the max. aperture is f/3.5; at 135mm, it is f/5.6. In between 28 and 135mm, the max. aperture gradually goes from f/3.5 to f/5.6.

Note that most lenses give you the sharpest possible results at around f/8. Most lenses are not optimally sharp wide open, and at smaller apertures (f/16 and above) the image may become less sharp because of diffraction (http://photonotes.org/cgi-bin/entry.pl?id=Diffraction).

[Scottes]

The smaller the number, the greater the aperture.


(Scottes, please confirm the above. :P )

I have no idea. I've proved that too many times in the past, so I no longer take part in Aperture questions.

ROFLMAO!!

[scottbergerphoto]

The f stop number is a ratio between the focal length of the lens and the diameter of the lens actual aperture opening. The larger the f stop the smaller the actual opening in the aperture. That allows you to use the same numbers for all different lenses.
Scott

[DaveG]

Hi guys how are ya? Im relatively new to digital photography - especially my EOS 300D, and have a question regarding aperture values. i understand that the larger the aperture the more blurred the backgrounds in photos will be and vice versa, but what im asking is on the camera, when selecting the aperture value, is it the smaller the number the smaller the aperture, or the other way around - smaller the number larger the aperture? also, what are the smallest and largest aperture values i should be able to select on my camera? thanks for your help guys,

ant :?

The smaller the aperture (i.e. the hole) the greater the depth of field will be. A real life example of this is watching a little kid who's nearsighted squint. Without having any idea about the cause and effect they squint , which essentially narrows the amount of light entering their eyes, the depth of field increases and they can see better.

The numbering of aperture openings is what usually gets the beginning photographer. 2, 2.8, 4, 5.6, 8, 11, 16 ... And when they learn that 16 (usually referred to as f16) is the SMALL hole it looks unnecessarily complicated.

Well first off understand that you treat these numbers as whole numbers. 2.8 doesn't get rounded off to 3 for example. Then understand that there's one "unit" difference between each of these numbers. If we go from f4 to f5.6 we have let one unit LESS light into the camera since we've made the aperture (lens opening, hole, whatever you want to call it) smaller. In photography the "units" are called "stops" and since shutterspeeds and ISO numbers are also measured in stops we can use them to create different effects while maintaining the correct expsosure.

The numbering by the way - big hole, small number - is messed up becasue there is not enough room to write the number out completely. If you look at shutterspeeds you'll see read outs like 60 or 125 and you know that they really are 1/60 or 1/125. Well apertures should really be writtern as ratios. 1:2, 1:2.8, ... 1:8, and THEN it makes at least a little more sense. There isn't room to write them and the only place you'll ever see them written like this is on the end of the lens where you'll see something like "Canon 50mm 1:1.4"

[Shakespeare]

OK, here's my newbie question...let's say I'm using the 18-55 f/3.5-5.6. When I'm out shooting on the porch and zoom out, the camera reads f/3.5. When I zoom in it says f/5.6. But when I point up to the sky, the number keeps getting bigger...f8, f/11, f/22.

The same thing happens on my 70-200 f/4 L. When I shoot a bright shot, the number gets bigger. I thought it was supposed to stay at f/4 all the time?

S

[Jon]

What it sounds like you're reporting have two different causes. But they both reflect that the viewfinder display isn't of the lens' maximum aperture, rather it's the aperture it will stop down to to take the picture.
1) the 18-55, as you zoom out, changes from f/3.5 to f/5.6. This is because the 18-55 has an f/3.5 aperture only at 18 mm. At 55 mm, it's an f/5.6 lens. If you were looking closely, you'd see the shutter speed changing too (getting longer, like from 1/60 to 1/30, say) to maintain a constant exposure.
2) When you point the lens at the horizon, then raise it toward the sky (without zooming), the aperture indicator changes from f/4 through f/5.6 to . . ., to f/22. You won't see the shutter speed change in this situation (until the aperture stops changing). This is because the with brighter subject, the camera needs to use a smaller aperture to keep from overexposing.

[DaveG]

OK, here's my newbie question...let's say I'm using the 18-55 f/3.5-5.6. When I'm out shooting on the porch and zoom out, the camera reads f/3.5. When I zoom in it says f/5.6. But when I point up to the sky, the number keeps getting bigger...f8, f/11, f/22.

The same thing happens on my 70-200 f/4 L. When I shoot a bright shot, the number gets bigger. I thought it was supposed to stay at f/4 all the time?

S

You must have the camera on some type of an automatic setting. When you point it at the very bright sky the camera wants to close down the aperture in the lens (to let less light in) in order to compensate for the additional brightness, compared to your darker first shot. A PROGRAM setting of some kind will do this, as well as Tv, where you pick the shutterspeed and the camera will pick the aperture.

The camera is thinking this: "He has me on Tv. That means he's picked a shutterspeed [1/125] and he wants me to pick the correct aperture. He's pointed the camera at that bunch of trees and the aperture [in this example] that is correct is f4. Now he's pointed me up at the sky. Wow there's a LOT more light. I'm going change the aperture to f22 to compensate and keep the exposure correct."

If you have the camera on MANUAL, the "needle" will move but the aperture and shutterspeed will stay right where you left them. You will then have to manually change the aperture or shutterspeed until the "needle" is centered, which indicates the exposure is now correct. If you don't centre the needle the shot will be either over or under exposed, depending on what side of centre the needle indicates.

[ejwebb]

What mode are you shooting in? The camera automatically changes the aperture and/or shutter speed to get the proper exposure, depending on the shooting mode. If you were shooting in manual or aperture priority you would set the aperture to what you wanted and it would not change unless you changed it intentionally.

The f/ stop indicated on your lens represents the size of the maximum opening - not the only opening. You can still adjust the aperture to make it smaller, resulting in larger f/ stop numbers. Of course, to get the same exposure you have to compensate by increasing exposure time or ISO.