Depth of fields, apertures and the F number

Angi · #1 (**permalink**) 05-04-2008, 11:27 AM

Specially for Brittone.

This is how I understand it.
When you set your camera on manual mode you control all aspects of the image you are taking. The aspects you control include the aperture ( the F number), the shutter speed which is measured in fractions of seconds and the ISO.

Aperture

Inside your lens is a hole created by 6 metal blades, this is called the aperture and it is used to control the amount of light that reaches your film or digital media whilst taking a photograph. The F number is a fraction that indicates the diameter of the aperture. The smaller the F number the larger the aperture is, and the higher the F number the smaller the aperture. So by increasing and decreasing the aperture or F number you are contolling the light which will be shown in your photograph.

The aperture also affects the depth of field ( often referred to as DOF).
When using a large aperture ( small F number such as 2.8, 4 or 5,6) then the focus will be sharper only on the area you are focusing on, the background will appear more blurred.
Heres an example
I used an f number of 5.6 and focused on this plant, this made the background disappear into a blur, this is useful when you want to isolate a single item to photograph.

another example
To isolate the focus on the corner of the bookspulled out in this pile I used an aperture of F4.5 which blurred the rest.

When using a small aperture, which is a high F number such as 22, 36 then more of the photograph will be in focus. This will also help to capture more detail.

An example would be
I used F22 to get as much detail as i could in this rose

(If had I used f5.6 on the above photograph then only the area focused on would have detail and the rest would be blurred.)

For this one F22 was used so I would get more detail, plus the flower in the background was still recognisable as a flower rather than a total blur.

Increasing the F number and reducing the aperture again to F29 means even more is in focus in this image, plus detail is better. But other setting required altering to allow for the decrease in light allowed into the lens.

Closing the aperture even more to F36 (and altering the shutter speed, plus ISO etc) produced this with even more detail.

Now to help your image work you will also need to increase or decrease the shutter speed to allow more or less light. But first lets ask MacroJunkie to check over what Ive written and maybe add some more.

Hope this helps Brittone - like I have mentioned before the book " Understanding Exposure " is great for explaining it all.

macro junkie · #2 (**permalink**) 05-04-2008, 11:42 AM

putting it to f/22 wont give u more detail..your just have more dof..if anything your get less detail because of diffraction softening..the rest is spot on tho

brittone05 · #3 (**permalink**) 05-04-2008, 11:52 AM

Thank you both

I am now sat with the detailed instructions of how to change things actually on my camera - struggling but I will get there

Shall be going to my grans later and she has a gorgeous flowery garden so will have a play

Thanks again

x

macro junkie · #4 (**permalink**) 05-04-2008, 11:59 AM

Quote:

Originally Posted by brittone05

Thank you both

I am now sat with the detailed instructions of how to change things actually on my camera - struggling but I will get there

Shall be going to my grans later and she has a gorgeous flowery garden so will have a play

Thanks again

x

do a test..shoot the same flower at f/8 f/11 f/16 and f/22

at iso100
shutter speed 200
full flash

asm1006 · #5 (**permalink**) 11-05-2008, 02:21 PM

Hi Ange! Thanks for directing me to this-its in laymans terms

Can I print this out for personal reference?
Anna.xx

Angi · #6 (**permalink**) 11-05-2008, 08:15 PM

Of course you can, but its just how I understand it.

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