Confused about f/stop Chart in NTP Learning Plan

[Quanita]

Ok, so I've read the f/stop chart page in New To Photography learning plan (http://www.ausphotography.net.au/forum/showlibrary.php?title=New_To_Photography:f_stop_chart)

I get that these are the magic numbers that equate to halving the diameter of each aperture (hole) as we go from 1.4 to (1.4)^2 = 2 to (1.4)^3 =2.8
and that if I don't touch my ISO and I want to maintain the same amount of light entering my image I will need to double the speed of my shutter
OR if I don't touch my shutter speed and I want to mainain the same amount of light entering my image I will need to double the sensitivity to light (my ISO)

I understand the relationship between the f/stop being a divisor of the focal length of the lens with the diameter of the aperture

What I don't understand is why I care?

Example:
in the chart -
what does knowing that I will let in the same amount of light if I leave my ISO as static
and I make aperture diameter half the size
as well as speeding up the shutter speed by doubling it
as I would if I left it alone mean to my photo?

I'm (so far) quite comfortable with the math's but I don't understand how understanding that relates to the actual photo?

If it's on the next page, I may regret this post, but I am going to post it anyway.

[Kym]

Aperture controls Depth of Field (DoF), i.e. how much of the subject is in focus.
So while one exposure is the same as another from the amount of light perspective
they have different aesthetic attributes, i.e.

shallow DoF (wide open, low number aperture) - blurred background
slow shutter speed (closed, high number aperture) - possible camera shake blur or moving subject blur

[Quanita]

so if I take a photo that I think has correct exposure but the depth of field is too large and I want background blur, I decrease the size of my aperture (higher number) and compensate for that with shutter speed (faster) to change the aesthetics of the photo but still have the same well exposed shot?


Ok it took me a while, but my brain likes that now :th3:

[ricktas]

so if I take a photo that I think has correct exposure but the depth of field is too large and I want background blur, I decrease the size of my aperture (higher number) and compensate for that with shutter speed (faster) to change the aesthetics of the photo but still have the same well exposed shot?


Ok it took me a while, but my brain likes that now :th3:

exactly! But remember that as you increase ISO you also increase noise, so its all a wonderfully creative balancing act that we play.

[OAKS]

I am thinking lower number for less dof? I might be wrong but if you have an aperture of say f11 you will have a lot more in focus than if you had a aperture of say f1.8 . so for buttery background you would be shooting with the small number (big hole) and for a scene where everything is to be in focus you would use say f11 (smaller hole). Maybe the pros could tell me if this is right........ but this is how i understand things :)

cheers,

[Kym]

The why is explained here... http://www.ausphotography.net.au/forum/showlibrary.php?title=New_To_Photography:Depth_of_Field_and_Aperture_-_why_is_it_so

f/1.4 has a much shallower DoF than f/11

[Quanita]

I am thinking lower number for less dof? I might be wrong but if you have an aperture of say f11 you will have a lot more in focus than if you had a aperture of say f1.8 . so for buttery background you would be shooting with the small number (big hole) and for a scene where everything is to be in focus you would use say f11 (smaller hole). Maybe the pros could tell me if this is right........ but this is how i understand things :)

cheers,

Yep taa... got all caught up and messed up - will edit to correct it thanks!

- - - Updated - - -


so if I take a photo that I think has correct exposure but the depth of field is too large and I want background blur, I increase the size of my aperture (lower number) and compensate for that with shutter speed (slower) to change the aesthetics of the photo but still have the same well exposed shot?


Ok it took me a while, but my brain likes that now :th3:

Erm so in my haste to get it I swapped the ideas around... and as per @OAKS comment have corrected it above.
Sorry If I have inadvertently confused anyone else (eek) :o

[ricktas]

Sorry If I have inadvertently confused anyone else (eek) :o

Nah..we all get it. Only confused one is you. :lol2::lol:

[Quanita]

Thanks Rick....:shh:

[arthurking83]

That's the simplistic way to look at it .. wait till you find out that aperture/shutter/ISO aren't the only elements that can determine the exposure.

Lens design(T-Stop) and even different sensors in the camera all make a contribution to the actual exposure.

Do you watch the meter level indicator in your viewfinder as you work on the composition .. before you take the shot?