14 years ago
There are several answers here about F Stop that are correct in most respects but none have addressed the essence of your question(s); the first is why some lenses are marked f4-5.6 and so on. On zoom lenses, there is a minimum and maximum zoom, shown in terms of millimeters-a 100-300 mm zoom lens has that telephoto range, for example. If in this example the lens is marked f4-5.6 that means that at 100 mm zoom, the maximum lens opening is f4 and at 300 mm the maximum lens opening will be f5.6.
To answer your second question, the lower the f stop doesn't necessarily mean it is 'better' for the lens or means the lens itself is better, but it is a commonly used indicator of lens quality. Lenses that will stop down more-i.e. to f2.8 instead of just to f4-are most costly to manufacture, provide better low-light performance, and are generally considered 'better.'
However, the way you use the lens and the optics-the quality of the glass-is actually more important than the numbers themselves.
For an example of the importance of glass quality, if there is significant distortion in the glass or dropoff in sharpness at the edges of the photo in a lens, you wouldn't want that lens even if it did have a 'better' maximum f stop. Contrast ratios are also important. There are many factors that are involved in making the choice and decisions about lens quality, but if the glass itself isn't good, it doesn't matter what the other specifications are.
If, for an example of 'use,' you are shooting a lot of action-like sports-with available light, a zoom lens that opens up to f2.8 might be very useful when it gets later in the day or evening. Even more useful might be a lens that will STAY at a set f stop regardless of the zoom setting, so you can stay at a certain shutter speed to freeze the action, or use flash at a consistent exposure. There are many other examples of how you might use a lens that would impact the importance of the f stop range.
You can tell a little bit about any lens you see at a glance-the larger the front element, the more light gathering ability it has; in the example of sports photography above, that's why you see so many photographers on the sidelines at games using those lenses with huge diameter barrels-they need the low light performance those big front elements provide. If you're doing mostly portraits and still life closeups of flowers you usually want another type of lens.
Finally, if you are shooting manual, all lenses have a 'sweet spot' where the sharpness and quality of the image they deliver is the best. For most lenses, this 'sweet spot' is in the f5.6 to f8 range, so again, just the ability to open up to a wider f stop to let in more light does not necessarily mean better performance. Once you find that 'sweet spot' you might want to shoot most of your pictures around that f stop, unless you are shooting for a particular depth of field or certain other special effects.
And one other note-while it is true that the measure of light is halved or doubled by fstop, that means FULL f stop and not all the markings on lenses represent full stops. For example, f5.6 allows twice as much light as f8; on many cameras you will also see a setting for f6.3 and f7.1. Those aren't full stops, so don't be fooled by that. What IS useful about the half as much/twice as much rule when it comes to light is it also applies with shutter speed and ISO or film speed. Learn that and you can manipulate images to get precisely what you are looking for when shooting manually.
Hope this helps-good luck and enjoy your camera!
14 years ago
The F stop or aperture is how wide open the hole in the lens is. A larger number means that the hole is smaller (it's a bit counterintuitive). With a manual camera, you adjust the F stop to determine what your focus will be in the picture.
A large number/smaller hole (i.e. 16) means that more in the picture will be in focus (think of it like squinting your eyes). A smaller number (i.e 4) means that there will be more depth of field--one thing will be in focus while the background or foreground is blurred. It's on a scale so the smaller the number the blurrier everything will be except what you've focused on, and the larger the number the more in focus everything will be.
The F stop works in conjunction with the shutter speed to determine the level of exposure in your pics. If it's bright outside and you have a small F stop (lens wide open) you'll need a quick shutter speed so too much light doesn't overexpose the picture. On the flip side, if it's dark and you have a large F stop, you'll want a slower shutter speed to allow more light.
It's technical and definitely takes some time to get the hang of!
14 years ago
The f-stop (aka aperture) is what determines how much light is admitted through the lens. Its an inverse relationship - f1.4 would be the largest opening - the lens would be said to be "wide open" while f16 would be the smallest opening - the lens would be said to be "fully stopped down".
Correct exposure is determined by the available light, ISO, f-stop and shutter speed. On a sunny day a "wide open" lens would give you a fast shutter speed. A "fully stopped down" lens will give a much longer shutter speed.
Each f-stop going up the scale (f1.4 to f2 to f2.8, etc) decreases the amount of light by 1/2. So f2 admits 1/2 as much light as f1.4; f2.8 admits 1/2 as much light as f2; f4 admits 1/2 as much light as f2.8, etc. With less light admitted the shutter has to stay open longer.
I hope this example doesn't confuse you. It is purely hypothetical for illustration only to show the shutter speed-f-stop relationship. We are shooting on a sunny day with ISO 100.
f1.4 @ 1/1000 sec.
f2 @ 1/500 sec.
f2.8 @ 1/250 sec.
f4 @ 1/125 sec.
f5.6 @ 1/60 sec.
f8 @ 1/30 sec.
f11 @ 1/15 sec.
f16 @ 1/8 sec.
Since ISO is a measure of the sensitivity to light of an imaging surface - film or digital - the less light admitted the longer the shutter has to be open to expose the imaging surface for correct exposure at a given ISO. In our example using ISO 100 we have an imaging device that is slow to respond to light.
If, in our example, we were using ISO 200 our shutter speed would change as shown in this example:
f1.4 @ 1/2000 sec.
f2 @ 1/1000 sec.
f2.8 @ 1/500 sec.
f4 @ 1/250 sec. etc.
If we change to ISO 400:
f1.4 @ 1/4000 sec.
f2 @ 1/2000 sec.
f2.8 @ 1/1000 sec.
f4 @ 1/500 sec. etc.
As you can easily see the more sensitive our imaging surface the faster the shutter speed at any f-stop.
The f-stop also controls Depth of Field (DOF) but that is a topic best left for another time.
5 years ago
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14 years ago
"This is the number assigned to determine the aperture, or size of the lens opening. A high f-stop number means a small amount of light is allowed in, which would be used to avoid an overexposed image. A low f-stop number means a large amount of light is let in, as you might use to shoot at a high shutter speed without getting a dark image.
Examples: I used a high f-stop setting to avoid my image being too bright and sunwashed."
basically its about how much light your lens lets through. the brighter you want the pic the lower the f-stop. it just depends on wat type of pic ur planning on taking and the lighting
5 years ago
High F Stop
5 years ago
My instructor told us that the lower f-stops are sometimes orange or pink because you can't handhold the camera at those settings.
14 years ago
"i see lenses with f4.-5.6" + "doesnt the camera have the f stop" - ah dont those two quote seem odd?
"this does not make and logic" - your correct
Fstops are the opening of the lens refer mr aces answer, shutter speeds are what the "camera" have - more correctly the "body"