Aperture/F numbers

Jujitsu1

Jujitsu1

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Darren
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I se from looking through this site that people recommend shooting with a f number as low as possible to get great blurry backgrounds. I'm I missing something as I thought the Aperture/ F numbers were set by the len and what zoom you had EG my Kit lens is 18-70 3.5-5.6. So at 70mm I can get the f stop down below 5.6 . I can go a lot higher is I put the camera on the A mode. I can then turn it up to f36 but the photos then became pretty dark.
 
As there is less light passing through the sensor you will need to increase your exposure time to compensate.

Try increasing the ISO or increasing the exposure time
Both will result in more light passing through the sensor and exposing the image.
 
I think the confusion here is a 'low' or 'small' F number, eg 5.6 gives a large aperture.
However a 'large' F number gives you a smaller aperture, less light and more depth of field (ie less background blur)

Have a read here and take a look at the diagram here to see what i mean.
 
Jujitsu1 said:
I thought the Aperture/ F numbers were set by the len and what zoom you had EG my Kit lens is 18-70 3.5-5.6. So at 70mm I can get the f stop down below 5.6 .
Click to expand...

Your lens has a variable maximum aperture (the smaller the number the bigger the aperture) which is quite common for consumer type zoom lenses.

But thats only the maximum aperture, aperture size is adjustable (between maximum and usually f22 or f32 depending on lens) and this adjustment is essential as its one of the three things that effect exposure (the other two being shutter speed and film speed)

So aperture controls the AMOUNT of light hitting the film (size of hole basically), shutter speed is how long the light hits the film and film speed is how reactive the film/sensor is to the light hitting it.

Film is dark to start with and the more exposed it is to light, the more light it becomes so now you can see that a bigger hole opened for longer means the film will be more light at the end of the process.

Hope thats a simple explanation - and for the others, it doesn't need taking to pieces and analysing thanks. :thumbs:
 
To add more confusion for you "aperture" this has a few links contained that may help you .... or it just may turn you :cuckoo:
 
Thank you all for the advise
 
A good learning read is "understanding Exposure" by Bryan Peterson.
 
ki_user said:
Don't forget just to add to the confusion DOF is also governed by distance and focal length
Click to expand...

I suspect that it's better to reduce the confusion and simply state that DoF is governed by aperture and magnification.

Bob
 
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