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Thread: Understanding DOF vs. format size

  1. #21

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by windwaver View Post
    I understand where you're coming from buddy. What I need to know is how you guys get the correct DOF without the DOF preview button?
    i use the DOF scale on my lens to gauge.

  2. #22

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by flipfreak View Post
    i use the DOF scale on my lens to gauge.
    Yeap, that's 1 way but there's no DOF scale on my lens as well. There's no DOF preview as well. The only thing I have is my own feeling if I'm getting it right.

  3. #23

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by calebk View Post
    What camera are you on? I think you are not getting what everyone is saying here, to be honest.

    Why are you putting all emphasis on aperture, then using your focal length to control your DOF? You should be focusing on getting your shot right first in terms of composition, then worry about your exposure settings after your shot is composed.

    You are shifting focal length to fit f/2.8. You should be shifting aperture to fit your shot size.
    Yeap, tried that as well, didn't really work. Problem is, I'm not even sure if the DOF is correct cos I can't see.........

    On FZ20 anyway. Come on, there must be some way to gauge even without a DOF button or len gauge.

  4. #24

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by windwaver View Post
    Yeap, that's 1 way but there's no DOF scale on my lens as well. There's no DOF preview as well. The only thing I have is my own feeling if I'm getting it right.
    use the online dof calculator.

  5. #25

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by flipfreak View Post
    use the online dof calculator.
    , I tried remembering all the calculations but even then, it'll be difficult to judge in reality.

  6. #26
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    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by windwaver View Post
    Yeap, tried that as well, didn't really work. Problem is, I'm not even sure if the DOF is correct cos I can't see.........

    On FZ20 anyway. Come on, there must be some way to gauge even without a DOF button or len gauge.
    I don't quite understand you. You frame your shot, then open up your aperture to the max, and it doesn't work. What does "doesn't work" mean? What do you mean by "incorrect DOF"? What is the whole premise of your question?

  7. #27
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    Default Re: Understanding DOF vs. format size

    I suppose what windwaver is try to say is:

    Shot has been framed, taken, reviewed. At 50mm (35mm film equiv), f2.8, my depth of field is still a bit deep.. I can't open up any more, so I need to go to say 85mm (35mm film equiv) -- I sacrifice the framing to play more importance on getting a shallower depth of field.

    Just to highlight one point in the thread that might not be very clear -> Subject to background distance does not affect the Depth of field; the nearest to furthest distance in 'acceptable?' focus remains the same and is based on format size (~circle of confusion), focal length, focus distance and aperture. Rather what the poster meant was the further the background was from the subject the more off-focus it'll be.

    Eg. Distance scale: 0m to infinity
    Super blur ... blurer ... blur ... acceptable? focus ... sharp focus ... ... acceptable? focus ... ... blur ... ... blurer ... ... super blur

    *edit* this example is for easy understanding and is not meant to be 100% accurate... go read a book for that.
    sharp focus is the point where you focus
    acceptable focus would be the near/far distance of your depth of field;
    Last edited by alexj; 25th June 2008 at 01:15 AM.

  8. #28
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    Default Re: Understanding DOF vs. format size

    Hi windwaver, the FZ20 has a smaller sensor than a dSLR, so if you're comparing a f2.8 shot with a f2.8 from an dSLR, you're gonna get deeper depth of field on your Lumix. If you want a smaller depth of field, as in, u only want your subject to be focussed and everything else blur, set aperture to f2.8, step back back back back back then zoom in to your subject to compose. This will greatly increase your chances of a blurred background. You can also set to macro mode for lesser depth of field, I think. You can't really see it when you're composing because the FZ20's EVF has a low pixel resolution.

    About your not getting the focus right, select point focussing rather than let the camera decide. Then half depress your shutter release to focus on the subject in the middle, THEN recompose before you take your shot. This way, it's usually quite spot on for me.

    Hope this helps. Cheers!
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  9. #29

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by karnage View Post
    Hi windwaver, the FZ20 has a smaller sensor than a dSLR, so if you're comparing a f2.8 shot with a f2.8 from an dSLR, you're gonna get deeper depth of field on your Lumix. If you want a smaller depth of field, as in, u only want your subject to be focussed and everything else blur, set aperture to f2.8, step back back back back back then zoom in to your subject to compose. This will greatly increase your chances of a blurred background. You can also set to macro mode for lesser depth of field, I think. You can't really see it when you're composing because the FZ20's EVF has a low pixel resolution.

    About your not getting the focus right, select point focussing rather than let the camera decide. Then half depress your shutter release to focus on the subject in the middle, THEN recompose before you take your shot. This way, it's usually quite spot on for me.

    Hope this helps. Cheers!
    Ah! Spot on my friend! This is exactly what I was looking for!

    In other words, with a smaller sensor, the DOF will increase (deeper). What I don't understand is in order to compensate that, why do I need to move back and zoom back in? Yes, I've tried that before I post and it works but I don't understand why.

    So the problem why I can't see the DOF is the stupid low pixel lol, got it!

    And yes, I'm using spot focusing. Just that it's like lottery for me for outdoor shoots, end up always take a few shots at the same spot but I don't want to guess, I want to know the principle behind it .

    Has it got to do with focus length if I need to stand back back back and zoom back in to get the effect? Or can I set to macro+macro lens to decrease the DOF? (haven't try this though).

    Thanks for your post buddy!

  10. #30
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    Default Re: Understanding DOF vs. format size

    Actually, not being able to see the right DOF at a given aperture is not just due to the low pixel count of the EVF. Like [alternative] mentioned, when we're composing, the lens has its aperture wide open (i.e.f2.8) for a brighter image for easier composition. On the FZ20, I believe when you half-depress the shutter button, it does stop down the aperture to whatever aperture you've set, or the camera has decided on. So that is, in a way, the DOF preview.

    If you're using spot focussing and it's still not usually in correct focus, it could be because where you're focussing is an area of low contrast, so the camera is having a hard time to focus. As to why a longer zoom will decrease DOF, I'm not too sure. Read it somewhere but the technical aspect didn't really matter to me at the time, so I guess it didn't register in my head. =)

    Anyways, I don't feel it's a really big problem to take more shots. It is, after all, digital. Always take more to be safe. Even in the film days when people couldn't delete a frame, they still shoot like nobody's business, because they know that when you get that one shot, it is more than worth the rolls of "wasted" film.
    incywincyspider climbup the waterspout...

  11. #31

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by karnage View Post
    Actually, not being able to see the right DOF at a given aperture is not just due to the low pixel count of the EVF. Like [alternative] mentioned, when we're composing, the lens has its aperture wide open (i.e.f2.8) for a brighter image for easier composition. On the FZ20, I believe when you half-depress the shutter button, it does stop down the aperture to whatever aperture you've set, or the camera has decided on. So that is, in a way, the DOF preview.

    If you're using spot focussing and it's still not usually in correct focus, it could be because where you're focussing is an area of low contrast, so the camera is having a hard time to focus. As to why a longer zoom will decrease DOF, I'm not too sure. Read it somewhere but the technical aspect didn't really matter to me at the time, so I guess it didn't register in my head. =)

    Anyways, I don't feel it's a really big problem to take more shots. It is, after all, digital. Always take more to be safe. Even in the film days when people couldn't delete a frame, they still shoot like nobody's business, because they know that when you get that one shot, it is more than worth the rolls of "wasted" film.
    Haha, yeah that's why I shoot many times on the same place but humans are not that patient at times. If stepping back & zooming in decreases the DOF, that can only mean that as it gets more telephoto, the DOF decreases. As for focus, I never had a problem with spot focus. It's how far from the subject do you usually shoot with the correct DOF that I'm concern (with a certain aperture).

    The correct way is of course compose/frame, focus, adjust aperture for DOF, shoot. In my case, it's not that easy for I can't 'see' the DOF neither thru a DOF button or Viewfinder.

  12. #32

    Default Re: Understanding DOF vs. format size

    OK folks, this is what I'm trying to get at.

    400mm200mm
    100mm50mm

  13. #33

    Default Re: Understanding DOF vs. format size

    28mm17mm

    So is this a perspective change or changes in depth of field?

  14. #34

    Default Re: Understanding DOF vs. format size

    at smaller focal lengths bokeh will be gradual
    and at longer lengths bokeh will be "immediate"
    thats how it is i dunno exactly how to explain

    if you want a blurred background from a pns/prosumer with a small sensor you either have to really step back and get telephoto or just use photoshop
    no other ways i think
    Last edited by Raied; 27th June 2008 at 05:08 PM.

  15. #35

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by windwaver View Post
    28mm17mm

    So is this a perspective change or changes in depth of field?
    both. notice the 2 structures behind mogwai changes with the focal length? dof naturally is different with the different focal length but the same aperture.

  16. #36

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by windwaver View Post
    28mm17mm

    So is this a perspective change or changes in depth of field?
    Perspective change would mean the background is changed between pictures. DOF change would be the changes in the area of focus in the picture. In this case, both is changed.

    Let me apologise for misinterpreting your query. I assumed that you were using an SLR and that's wrong of me. For a PnS, the camera does stop down when you half press the shutter (it also AF in this period) before taking the picture, but it's hard to see the changes in your LCD screen, hence why SLRs are useful. Your only tactic would be to memorise the depth of field for a particular focal length and aperture for your camera.

    Samuel
    f/8 and be there.

  17. #37

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by windwaver View Post
    OK folks, this is what I'm trying to get at.

    400mm200mm
    100mm50mm


    wow...i never realized tat different focal lengths can affect te background by so much!!! i assume u din crop te photos right??
    I have a near-mint Olympus E-620 Underwater Case for Sale. PM me for a great deal!

  18. #38

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by flipfreak View Post
    both. notice the 2 structures behind mogwai changes with the focal length? dof naturally is different with the different focal length but the same aperture.
    Actually I've assumed as it gets more telephoto, the DOF decreases but somehow, there're people in the net that stress that DOF stays the asme even at different focal length. Seriously, I'm not sure how true is that.

    Once I understand this point, it'll be easy to me to get everything right

  19. #39

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by windwaver View Post
    Actually I've assumed as it gets more telephoto, the DOF decreases but somehow, there're people in the net that stress that DOF stays the asme even at different focal length. Seriously, I'm not sure how true is that.

    Once I understand this point, it'll be easy to me to get everything right
    then u have to assume a few things. are u going to stay wit the same subject to camera distance? if so, the 2 different focal length will definitely have a difference in the resulting DOF.

    for eg, if i am shooting with my 55mm on a subject 5m away and then i swap to my 150mm, the dof from the 150 will be alot more shallower than the 55mm.

    but take into consideration the fov as well.

  20. #40

    Default Re: Understanding DOF vs. format size

    Quote Originally Posted by flipfreak View Post
    then u have to assume a few things. are u going to stay wit the same subject to camera distance? if so, the 2 different focal length will definitely have a difference in the resulting DOF.

    for eg, if i am shooting with my 55mm on a subject 5m away and then i swap to my 150mm, the dof from the 150 will be alot more shallower than the 55mm.

    but take into consideration the fov as well.
    Well, it's been a hot topic even in other forums on DOF vs focal length. As a tele lens compress the image, it may seem that DOF has decreased but in actual fact, it's only compressed rather than decreased. To me, the DOF seems rather reduced but it's interesting to see it from another point of view

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