Discussion in 'General Gallery' started by sobi, Dec 7, 2003.
back to apeture 101 for me.
It's damn confusing. you always wonder if what you're saying is what you think it is or the opposite...
Boy, this thread has gotten confusing really quickly. Let me confuse you even more.
Depth of field: area of your photo that is in sharp focus. If you focus on your subject the DOF will extend in front of and behind the point you are focused on. In most cameras the DOF is parallel to the film plane. With view cameras and shift lenses you can alter the position of DOF in relationship to the film plane. This would allow what appears to be a greater DOF (it is actually just a repositioning of the DOF, you are using the height or width of the DOF rather than the depth (HOF? WOF??)). This is useful in close focusing situations.
Besides aperture, DOF is also affected by lens focal length and distance to subject. Wide angle lenses have greater DOF than telephoto lenses at a given aperture; the DOF at f/8 on a 28mm lens is huge (measured in feet), while the DOF at /8 on a 200mm lens is pretty small (measured in inches). The closer the lens is focused the shorter the DOF. With the lens focused at 20 feet f/16 is very deep; focused at 3.5 feet f/16 is very shallow.
Aperture: the hole in the lens. Controls exposure and DOF. The smaller the aperture, the greater the DOF. A non-photographic example of this is folks who need glasses for night driving: in the daytime when it's bright their pupils close down (small aperture/greater DOF), at night when it is dark their pupils open up (large aperture/less depth of field). Aperture size is refered to using f/number.
The f/# is arrived at by dividing the focal length by the actual aperture size. Example: a lens with a focal length of 100mm is at f/2 when the aperture is 50mm wide, it is at f/4 when the aperture is at 25mm wide, it would be at f/22 when the aperture is set to 4.5mm wide. So the larger the f/#, the smaller the actual aperture size, and the greater the DOF.
Old school lenses went from widest to smallest: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64.... Each number was approximately one stop (a halving or doubling of the amount of light). This standard helped the photographer doing math in the field. Auto-focus SLRs have built in computers and can do the everchanging math of the big zoom lenses so you will often see non-standard f/#s in the viewfinder such as f/9 or f/13.
Modern lenses are designed to stay wide open while you are looking through the viewfinder composing and focusing. When the shutter button is depressed the aperture closes down to the selected size a split second before the shutter opens, and returns to wide open when the shutter closes. Some cameras have a DOF preview feature. This allows the photographer to close down the aperture to the selected size, and DOF can be assesed through the viewfinder.
Fixed focal length lenses used to always come with a built in DOF scale on the focusing ring so that even without DOF preview the photographer knew their DOF. Zoom lenses would require something akin to a slide rule to figure it for all the possible combinations of focal lengths, aperture sizes, and distance to subject. Fortunately you can find websites that will show you how to build this device (search for "depth of field calculator").
While you're at it, search for "hyperfocus".
^^ What he said. That's all you'll ever need to know about DOF and apeture.
Pilgrim: you gave me a headache.
Sobi: next time just explain your theme was animal noses, and everyone will say what a perfect shot it was.
You can also say "soft focus". In my opinion the photo seems to be a tender cat moment revealing it's elusive tender side. oh yea, the license plate of my jeep is F64.
ok... so my 2.8 was on the right track, but that is referred to as greater DOF. At least I would have gotten the right results.....
took another one of him the other day and thought i would share. not sure why i liked this one so much, but i do. :?
I wanna try and say this aperture thing in simpler terms. The first thing to clear up is a common misconception. When someone talks about the smallest possible aperture they can mean two different things. Either the number of the stop or the size of the opening.
In this situation sid was talking about hte size of the opening. The larger the size of the opening the smaller the number. (If you ever get ocnfused take a lense off and look through it while you move the aperture ring.
If that confused you to, no fear, I've got a simpler explanation that leaves the technical stuff out and simply says the results. The smaller the number the small the DOF (the distance of what is in focus in your picture). So an aperture of 22 is almost infinity DOf while 2.8 is very small. the actual distance of this depends on other factors. Hope this helped.
P.S. - Heres another little tid-bit to help ya out. What do you do when theres something out in the distance you can't see? You squint your eyes, thus increasing the depth of field. Therefore the smaller the size of the hole in the lense (bigger number) the bigger the DOF.
Good luck to yall
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