Aperture question

[gothra]

I'm looking at vaious reviews of some P&S cameras, mainly the ones with fast lens like Fuji X10 and Olympus XZ1. Seeing the sample pictures, I don't understand how some of the picutures were listed with a high f-number. For example, the X10 has f2.0-2.8 lens (f2.0 for wide angle; and 2.8 for telephoto), but I see sample pictures stating f/5.6 and f/8? I'm confused.

 

[Netskimmer]

The 2.0-2.8 is the Maximum (widest) it will go depending on how far you have 'zoomed' out. At it's shortest focal length it can go from f2.0 to f11.0 and when 'zoomed' it can go from 2.8 to f11.0.

 

[gothra]

I'm very sorry but I still don't get it. If I don't zoom at all, the camera will be at f 2.0, and when I zoom way in to the subject, it will reach f 2.8? I thought that's what the range means...so where does the f 11 comes from? I currently have a S100, its f 2.0 - 5.9; when I zoom in, the number will only go to 5.9?

 

[Judobreaker]

Aperture is set separate from your zoom.
The 2.0-2.8 is however (like Netskimmer said) your maximum aperture depending on which zoom you use.
This basically means that when you're not zooming at all your maximum aperture will be 2.0. You can still set your aperture smaller at no zoom,never larger though.
At full zoom the maximum aperture decreases to 2.8. You can't get it up to 2.0 anymore because of the way the lens is built. You can still set it smaller though.

If you're at no zoom and have your aperture wide open (at 2.0) and you start zooming in the aperture will automatically change to 2.8.

 

[Netskimmer]

Are you shooting in manual or auto? If you shoot in manual there should be a way to change your aperture setting. When zoomed all the way out that option will give you a range of numbers from f2.0 to lets say f11.0. If you zoom all the way in to get the most magnification that range of numbers will be f5.9 to f11.0.

 

[chris]

The f stop is a dimensionless number that describes the size of the aperture (entrance pupil) within the lens through which light passes and which can be regulated by adjusting the aperture blades. The f number is the ratio of the focal length of a lens to the aperture diameter; this means that the smaller the f number is the greater the aperture.

For a zoom lens if the diameter of the aperture is kept constant then the f number will increase as the focal length of the lens is increased. It is quite expensive to design and build a zoom lens so that the maximum (smallest) f number remains constant over the full range of focal lengths for the lens

For the maximum aperture (smallest f number) of a zoom lens to remain constant over the full range of focal lengths the physical size of the aperture must increase in proportion to the focal length; it is expensive tt build a lens that can do this and many zoom lenses are designed to have a variable maximum aperture across the zoom range so that the cost of producing the lens can be kept to a minimum. This is why the cheaper zoom lenses are marked with a range of f numbers such as f2.0 – f2.8 (the smaller number is for the wide end of the zoom range and the higher number is for the long end) and why lenses with a constant maximum f number are expensive (they require more glass and more design effort). The apertures of zoom lenses can be adjusted to be smaller than the maximum value, with a consequent increase in the f number, which is why you see images taken at f 5.6 or f8 using a f2.0 – f2.8 lens. The minimum aperture for a lens can typically be within the range f11 to f32 though some, particularly those used for large format, can go down to f128.

 

[Helen B]

For the maximum aperture (smallest f number) of a zoom lens to remain constant over the full range of focal lengths the physical size of the aperture must increase in proportion to the focal length

That's a little misleading perhaps - as the elements in front of the iris move in relation to the iris, the size of the entrance pupil can change even if the physical diameter is unchanged. That's why the minimum aperture of a variable aperture zoom does not vary in proportion to the focal length - the iris size may be fixed but the entrance pupil size isn't. It is also why constant maximum aperture zooms need not have the physical size of their iris variable over the full zoom range.

 

[DiskoJoe]

These are some jacked up answers.

Aperture is simple. Its how wide the opening is for the shutter. It has a range that it can go through f2 is the largest opening and the higher numbers would be a smaller opening. Its how the camera changes the amount of light coming in. Most camera lenses can do this.

Just buy the point and click you think looks cool and go have fun shooting pictures.

 

[Judobreaker]

These are some jacked up answers.

Aperture is simple. Its how wide the opening is for the shutter. It has a range that it can go through f2 is the largest opening and the higher numbers would be a smaller opening. Its how the camera changes the amount of light coming in. Most camera lenses can do this.

Just buy the point and click you think looks cool and go have fun shooting pictures.

Our point is that when you're zooming in the maximum aperture is not 2.0 anymore.
It's still nothing to worry about as this is the case with any compact camera I know and it doesn't necessarily make them bad. ^^

 

[prodigy2k7]

For the maximum aperture (smallest f number) of a zoom lens to remain constant over the full range of focal lengths the physical size of the aperture must increase in proportion to the focal length

That's a little misleading perhaps - as the elements in front of the iris move in relation to the iris, the size of the entrance pupil can change even if the physical diameter is unchanged. That's why the minimum aperture of a variable aperture zoom does not vary in proportion to the focal length - the iris size may be fixed but the entrance pupil size isn't. It is also why constant maximum aperture zooms need not have the physical size of their iris variable over the full zoom range.

I love you Helen but I still get confused with aperture/entrance pupil/iris etc... Is the entrance pupil the aperture when looking through the front of the lens? And because of the optics, the size of the entrance pupil can change while the physical aperture does not?

Also: iris vs aperture?

 

[KmH]

Aperture is simple. Its how wide the opening is for the shutter..

Say what?

 

[gothra]

Thanks to everyone! You're awesome! I had been using the same setting (set up in custom on day one: maximum aperture, highest acceptable ISO) for my camera for years, because I'm always shooting under the same condition. Stupid me, I had never touched that button to decrease the aperture, or maybe I have just didn't realise it...I just tried it on my camera and I see it now, duh. This is embarassing even for a newbie question...ale:

 

[Tiberius47]

I'm very sorry but I still don't get it. If I don't zoom at all, the camera will be at f 2.0, and when I zoom way in to the subject, it will reach f 2.8? I thought that's what the range means...so where does the f 11 comes from? I currently have a S100, its f 2.0 - 5.9; when I zoom in, the number will only go to 5.9?

The aperture that the camera has written on the side of the lens is just the widest apertures that are available. It doesn't mean that the camera will be using them.

 

[Helen B]

Is the entrance pupil the aperture when looking through the front of the lens?

Yes.

And because of the optics, the size of the entrance pupil can change while the physical aperture does not?

Yes.

Also: iris vs aperture?

Yes, well, that's just my questionable habit - I wanted a word for aperture that people will associate only with the physical thing, and never the image of it or the size of it, so I decided on 'iris'. Maybe diaphragm would be better. I'm not sure. I would welcome opinions.Best,Helen