A&P Understanding F Stop DOF on a Canon 50mm f/1.8

Discussion in 'Lifestyle' started by FindersKeepers, Jul 13, 2008.

  1. FindersKeepers

    FindersKeepers New Member

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    EDU: Understanding F Stop DOF on a Canon 50mm f/1.8

    I've seen quite a few threads in the past year or so where people either

    A. Complain that people are taking shots wide open with their 50mm 1.8 or 50mm 1.4

    or

    B. Don't understand why they can't keep proper focus on a 50mm f/1.8 or f/1.4, at wide open aperture.


    Since my 50mm f/1.4 is not yet here I'll use my newly acquired 50mm f/1.8 (backup for on an xti) as a demonstration...


    First with the 50mm f/1.8 you have these options for aperture.
    Highlighted in BOLD are the examples I'm using

    1.8, 2.0, 2.2, 2.5, 2.8, 3.2, 3.5, 4.0, 4.5, 5.0, 5.6, 6.3, 7.1, 8.0, 9.0, 10, 11, 13, 14, 16, 18, 20, 22

    What this means is that at F/1.8 your aperture blades are WIDE OPEN, allowing the most light through, at F/22 they are closed as far as they can go, allowing the least amount of light through.

    ADDITION: One of the important things to remember when shooting in MANUAL mode though, is you will have to change your shutter speed to match your aperture change... For example, the F/1.8 photo had a shutter speed of 1/3200 at ISO 100, and the f/22 photo was a shutter speed of 1/20 at ISO 100... I'll add the shutter speed per photo to the photo description...

    I shot these in AV (aperture priority) the camera auto adjusted the shutter speed for close tot he same exposure, again I did nothing besides a resize and RAW to JPG conversion



    At F/1.8 your Depth of Field is very shallow, meaning whatever is focused on is pretty much all you'll see IN focus in somewhat of a straight line as below.

    Meaning, if you focus to your center focus point, which I did, above and below the subject will tend to be more blurry
    50mm f/1.8, 1/3200 shutter at ISO 100
    [​IMG]


    At f/2.2, it's still fairly wide open but the slight change does affect DOF quite a bit
    50mm f/2.2, 1/2000 shutter at ISO 100
    [​IMG]


    at f/4.0 the change shows even more apparent
    50mm f/4.0, 1/640 shutter at ISO 100
    [​IMG]

    50mm f/7.1, 1/200 shutter at ISO 100
    And at f/7.1 you see quite a bit of change in the DOF
    [​IMG]

    50mm f/13 1/60 at ISO 100
    Then as we step down futher to F/13 it looks even more in focus
    [​IMG]

    and finally at f/22, your smallest aperture your subject and its surroundings are as in focus as they can get
    50mm f/22, 1/20 sec at ISO 100
    [​IMG]


    Here is a good link on understanding how the aperture affects what you are shooting.
    http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

    Some cameras have a DOF preview button, which allows you to see what your image will look like at different apertures through the viewfinder, play with AV setting on your canon and set different apertures focus on something and you'll see how much the background changes focus as your subject usually stays the same.



    Anybody have any corrections :o
     
    Last edited: Jul 14, 2008
  2. iDrive

    iDrive OTAP crew. Muradadog crew. GO GATORS!

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    Thanks!
     
  3. Bloke

    Bloke Banned

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    um its clearly marked on the scale on the lens
     
  4. FindersKeepers

    FindersKeepers New Member

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    Thats not the point of this thread...


    The point is to visually show the people that are visual learners, not hands on learners, what the aperture does to your photos.
     
  5. Perkwunos

    Perkwunos Dog Bones OT Supporter

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    Thanks I like this, helped me realize what is going on.
     
  6. xSteveO

    xSteveO Guest

    [​IMG]

    side by side >
     
  7. iDrive

    iDrive OTAP crew. Muradadog crew. GO GATORS!

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    those pics are almost too small to even see a difference.

    but i do like the side by side comparison
     
  8. xenon supra

    xenon supra OT Supporter

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    Kinda basic but probably helpful to some :coold:
     
  9. alexromo

    alexromo New Member

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    helpful thread!

    It wouldve made things much easier for me months ago when i was just getting my feet wet
     
  10. FindersKeepers

    FindersKeepers New Member

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    :doh: Yeah didnt think of that part or I could have made arolling gif



    I made it very basic, with simple explanations so people could 'get' it
     
  11. e.pie

    e.pie Active Member

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    :werd::coold:
     
  12. mobbarley

    mobbarley Active Member

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    how about mentioning the change in shutter speed to get the right exposure?
     
  13. iDrive

    iDrive OTAP crew. Muradadog crew. GO GATORS!

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    because he was talking about DoF and not exposure?
     
  14. FindersKeepers

    FindersKeepers New Member

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    edited to reflect.
     
    Last edited: Jul 14, 2008
  15. Jcolman

    Jcolman OT Supporter

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    Anytime you change aperture you have to change exposure if you want to keep the same exposure value. That's why he mentioned exposure.
     
  16. Jcolman

    Jcolman OT Supporter

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    Change your "f/13" example from " then as we open it up further...." to "then as we stop down further".

    oh, and nice write up. I should copy this and put it my EDU.
     
  17. FindersKeepers

    FindersKeepers New Member

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    will do :)


    I'm making another for Polarizers at the moment as it seems to be another question I see a lot (not so much here, but in other places).


    use it if you like.
     
  18. Perkwunos

    Perkwunos Dog Bones OT Supporter

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    yeah you should. :bigthumb: :wavey:
     
  19. mobbarley

    mobbarley Active Member

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  20. spahndirge

    spahndirge Scumbag Member

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    Good explanation, but one thing I can't understand yet is why close down the aperture? Here's some pics I took at the weekend.... (Some level change in PS)


    ISO 100 - 50mm - 1/400sec
    [​IMG]

    ISO 100 - 50mm - 1/320sec
    [​IMG]


    ISO 100 - 50mm - 1/100sec
    [​IMG]

    All the images are at 100%, shot with 40D + Tamron 17-50mm in manual, so my questions are....

    Why does f9 appear sharper?
    Would the shot appear even sharper if I used something like 5.6?
    When would I use f22 if it's going to come out that blurry? (Why not just increase shutter speed?)
     
  21. Jcolman

    Jcolman OT Supporter

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    Every lens has it's maximum sharpness aperture. Usually it's about 4-5 stops from wide open. When you're shooting far away landscapes, you won't really notice much of a difference between apertures. It's only when you have objects closer to the camera, and you focus on that object, that depth of field becomes apparent.
     
  22. FindersKeepers

    FindersKeepers New Member

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    What "dad" said.

    which is why you notice a different between exposures.

    had that been a closer object it would be more apparent.


    I find when explaining to friends that tend to use P&S and XT/XTI etc is that an easy thing to do is shoot a distant subject at a range of apertures until you find what you like as your "sharp/comfort area". But it should be listed on your lens paperwork too :)

    And then do the same with a close subject.
     
  23. jared_IRL

    jared_IRL OT Supporter

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    I like your edu's.

    :h5:
     
  24. spahndirge

    spahndirge Scumbag Member

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    Ahh, i get it now, thanks. I think the sharpest aperture for the tamron is around F/5.

    When I shoot landscapes, should I stick to around F5? I've seen some photos on here using F22, what kind of conditions would require an aperture as small as that? Is it dependent on the lens? Like, 300mm 2.8 lens should be sharpest around F5-6?

    I'm still experimenting with aperture and it takes a bit of getting used to on the tamron, will it take a while to get used to another lens once I get it (ie, zoom lens)?
     
  25. FindersKeepers

    FindersKeepers New Member

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    Thanks I'm doing my best to cover some of the ultra basic constantly asked stuff that most people answer or get annoyed and answering over and over, but there are no EDU's for :)
     

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