Have I worked this out? Advice req'd.

Bristol Pete

Well-known Member
Right, been reading up and practicing. Is this right?

So, the 'higher' the aperture number the smaller the opening, hence a blurred background behind the subject? So, example 5.6 would mean a tight focus with a blurred background/depth of field and and say 36 would give an even spread of focus?

In effect, higher is lower and lower is higher?

Thanks,

Pete.
 

Jazz Monkey Jr

Distinguished Member
You are correct, a smaller number means a larger opening (apeture) which means a smaller depth of field (or focus)
The larger apeture also means you get more light in, so you can have a faster shutter speed.

Apetures range from f1 (very very very fast) up to f91on my camera (very very very small)
In reality unless you have a really expensive lens you may only see values between f4 and f27.

The values of the shutter speed and apeture are linked, say you had the correct exposure for a scene and you then changed the apeture to a higher number, to get all the scene in focus, to get to correct exposure again you would have to let more light in, because yopu have made the apeture (hole) smaller. You would do this by keeping the shutter open for longer (a slower speed).
The values of both are measured in stops, and each stop lets in twice, or half, the light in. This is easy in shutter speed, because if the shutter speed is double (1/50th second to 1/25th second) then it will let twice as much light in.
In the apeture it is more difficult because the numbers don't really mean that much, here are the apeture f-stops:

f1.8 f2.8 f4 f5.6 f8 f11 f16 f22 and so on.

So the following combination of shutter speed and apeture will give you EXACTLY the same exposure, but will have different depths-of-fields.

F1.8 at 1/250th second
F2.8 at 1/125th second
F4 at 1/60th second
F5.6 at 1/30th second
F8 at 1/15th second
F11 at 1/8th second
F16 at 1/4 second

I hope I have explained this right, it has been a while since I learnt it all.


This might also help:

http://www.photoxels.com/tutorial_aperture.html
 

Bristol Pete

Well-known Member
Is this a better attempt than last night?

Forget the quality, just looking at the depth. Both shot at 5.6 by hand.
 

Attachments

  • Picture 060 (Medium).jpg
    Picture 060 (Medium).jpg
    43.8 KB · Views: 69
  • Picture 061 (Medium).jpg
    Picture 061 (Medium).jpg
    42.2 KB · Views: 69

Jazz Monkey Jr

Distinguished Member
Try a different apeture, as high as it will go and focus one-third into the picture (you will need a tripod as the shutter speed will slow down to compensate)
If you haven't got a tripod, sit it on some books.
 

Bristol Pete

Well-known Member
OK, will do. Also, is that right is that

5.6 can be called a higher aperature and that say 36 is lower?

Seems odd, and makes it far more confusing initially :rolleyes:
 

Jazz Monkey Jr

Distinguished Member
Captain Benefit said:
Is this a better attempt than last night?

Forget the quality, just looking at the depth. Both shot at 5.6 by hand.

They have a shallow depth-of-field, because the apetures big, and you are fairly close to them.
Try exaclty the same picture with a different apeture, turn the dial to Av and move the dial to around f16 or higher and focus one third in to the picture.
 

Bristol Pete

Well-known Member
Try a different apeture, as high as it will go and focus one-third into the picture (you will need a tripod as the shutter speed will slow down to compensate)

As a guess will that give an even picture?
 

Jazz Monkey Jr

Distinguished Member
Captain Benefit said:
OK, will do. Also, is that right is that

5.6 can be called a higher aperature and that say 36 is lower?
5.6 is a LARGER aperature and 36 is a SMALLER aperature

Seems odd, and makes it far more confusing initially :rolleyes:

Just think of 5.6 as a large opening (aperature) with a small f-value
and 36 as a smaller opening (aperature) with a high f-value, this will help to understand how much light it is letting in.
 

Bristol Pete

Well-known Member
Here we are, taken in F16. As hand held for now I had to raise the iso to catch them but there is a big difference.

Seriously, thanks a lot for your input! :thumbsup:
 

Attachments

  • Picture 063 (Medium).jpg
    Picture 063 (Medium).jpg
    51 KB · Views: 63
  • Picture 064 (Medium).jpg
    Picture 064 (Medium).jpg
    54.8 KB · Views: 60

Jazz Monkey Jr

Distinguished Member
Another way of thinking of it, the apeture is the same as your iris, if the sun is bright, it closes up, a bit like f36.
When it is night time, your iris opens up to let more light in, a bit like f2.8.

Hope I haven't confused you any more.
 

Bristol Pete

Well-known Member
Its starting to make sense but slowly. As I said, why lower is higher makes it harder to get the old nuggin around but learning slowly.
 

Jazz Monkey Jr

Distinguished Member
Captain Benefit said:
Here we are, taken in F16. As hand held for now I had to raise the iso to catch them but there is a big difference.

Seriously, thanks a lot for your input! :thumbsup:

There is more in focus, but they are a bit blurry because you handheld.

A quick rule to work out of you need a tripod or not, use the same or faster shutter speed as your focal length.

If you are using your camera at 28mm, you need at least 1/30th second or faster to get a sharp image.
If you are zoomed right up to 125mm, you will need 1/125th second or faster.

You can usually get away with slower, but it is a rough guide.
 

penumbra

Active Member
Hi,
this Might help, the f no. of a lens is calculated by dividing the diameter of the front element by the size of the aperture formed by the internal 'iris' blades.
ie say the front element is 50mm dimeter and say the max aperture is 25mm, this wuold be an f2 lens, as you stop down the lens the aperture gets smaller so the same lens 50mm but now with the aperture set at 12.5mm would give you f4. thats why the f no. goes up!
hope that helps (should if ive explained it properly):smashin:
 

Bristol Pete

Well-known Member
Last ones taken at F5.6 with shutter speed at 1/125 @45mm. Much sharper, hand held too. It is getting there.

Definately going to myself a tripod....

Pete.
 

Attachments

  • Picture 072 (Medium).jpg
    Picture 072 (Medium).jpg
    49.2 KB · Views: 59
  • Picture 073 (Medium).jpg
    Picture 073 (Medium).jpg
    44.9 KB · Views: 55

barongreenback

Active Member
Yup - a good demo of depth of field there.

BTW, do you have an odour problem? lol ;)
 

The latest video from AVForums

Star Wars Andor, Woman King, more Star Trek 4K, Rings of Power & the latest TV, movies & 4K releases
Subscribe to our YouTube channel

Full fat HDMI teeshirts

Support AVForums with Patreon

Top Bottom