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Thread: Depth Of Field Question

  1. #1

    Default Depth Of Field Question

    Hi, I've read these lines from whitepaper from http://www.aakatz.com/whitepaper/ and I have a few question about things...

    To get the deepest depth of field - the sharpest photos:


    Use high f/stops (smaller apertures)
    Use wide-angle focal lengths
    Shoot subjects from a distance, even if you zoom

    To get shallow depth of field - to isolate subjects from backgrounds:


    Use low f/stops (larger apertures)
    Use as much telephoto zoom as you can (high focal lengths)
    Separate subjects from backgrounds
    Shoot from as close as you can get to the subject

    I don't really get the part "Shoot subjects from a distance, even if you zoom" Meaning if lets say I want to take someone in a picture together with a background and I want them both sharp, must I stand far away and take that picture? In this case, can I actually zoom in to that someone and still have a deep DOF? Or zooming in will cause it to have a shallower DOF?

    For the shallow depth of field, Use as much telephoto zoom as you can (high focal lengths) actually tells me to stand far away and zoom in all the way if possible, but the next line, Shoot from as close as you can get to the subject means I have to get close to my subject? :S I'm confused.. Sorry for being a noob man, guess tt's why I'm posting in the 'newbies corner'. :P

  2. #2

    Default Re: Depth Of Field Question

    Yes, the way it's usually describe is a bit contradicting! But it's correct.

    Aperture: big = shallower DOF, small = deeper DOF.

    Long focal length = zoom in, shorter = zoom out.
    Focal length: long = shallower DOF, short = deeper DOF.

    Focus point is the object/point you're focusing on/in focus/sharpest.
    Focus point: nearer = shallower DOF, further = deeper DOF.

    So to get the narrowest DOF, zoom too the max, go as close as you can, use widest aperture. Of course with max zoom, you can't go too close. Or compromise and zoom less, but go closer. Maybe some more experienced bokeh shooters can give better advise here =P

  3. #3
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    Default Re: Depth Of Field Question

    You had the theory lesson so now it's time for the practical. You won't understand fully till you go out for practise and experimenting.

    (Taken from your provided link)
    'It changes the depth of field itself. The closer to the camera you focus, the shallower the depth of field. The further away you focus, the deeper the depth of field. .... To keep it simple, depth of field is determined, to a large extent, by where you focus.'

    Qn:
    Shoot subjects from a distance, even if you zoom
    Ans: Whilst still using a WA lense, shoot from a distance.

    Qn: I want to take someone in a picture together with a background and I want them both sharp, must I stand far away and take that picture?
    Ans: That will depend on the subject to background distance as well. If background does not fall within
    subject DOF then the background would perceive to be not sharp.

    Qn:
    In this case, can I actually zoom in to that someone and still have a deep DOF? Or zooming in will cause it to have a shallower DOF?

    Ans: Yes and yes. How much you zoom in would give you how much DOF. However since long focal lengths give shallow DOF, you'll need to compensate for deep DOF by a narrower aperture thus requiring longer exposure. How smart that decision is, is another qn.

    Qn: Shoot from as close as you can get to the subject
    Ans: Did you read the entire article or just skip to the end?
    'Fig. 8-31 Extreme closeup using close-up lens.' It describes the author using a closeup lense on the subject.
    '
    The closer you get to the subject, the shallower the depth of field. Close up lenses let you get much closer at telephoto than you normally can....'

    2 important points which I didn't find in the link is firstly, apertures on different types of lenses give different DOF. f5.0 on a WA lense would give a reasonable DOF while f5.0 on a telephoto would be quite shallow.

    Secondly, the way to judge DOF on your subject is that it extends 1/3 towards the camera and 2/3 the distance towards the background from your focusing point. This is one way to help in deciding where to focus on the subject.

  4. #4

    Default Re: Depth Of Field Question

    Quote Originally Posted by Razorsharp87 View Post
    Hi, I've read these lines from whitepaper from http://www.aakatz.com/whitepaper/ and I have a few question about things...

    To get the deepest depth of field - the sharpest photos:


    Use high f/stops (smaller apertures)
    Use wide-angle focal lengths
    Shoot subjects from a distance, even if you zoom

    To get shallow depth of field - to isolate subjects from backgrounds:


    Use low f/stops (larger apertures)
    Use as much telephoto zoom as you can (high focal lengths)
    Separate subjects from backgrounds
    Shoot from as close as you can get to the subject

    I don't really get the part "Shoot subjects from a distance, even if you zoom" Meaning if lets say I want to take someone in a picture together with a background and I want them both sharp, must I stand far away and take that picture? In this case, can I actually zoom in to that someone and still have a deep DOF? Or zooming in will cause it to have a shallower DOF?

    For the shallow depth of field, Use as much telephoto zoom as you can (high focal lengths) actually tells me to stand far away and zoom in all the way if possible, but the next line, Shoot from as close as you can get to the subject means I have to get close to my subject? :S I'm confused.. Sorry for being a noob man, guess tt's why I'm posting in the 'newbies corner'. :P
    You're spot on. It's indeed confusing because what's in theory is not practical in real life.

    If you shoot a subject with focal length 50mm and you stand 2m away, then you would need to stand 8m away with a 200mm focal length for the same main subject size.

    If both uses the same aperture, the DOF of 50mm at 2m way is the same as the DOF of 200mm at 8m away. This can easily be verified with any online DOF calculator.

    So while the theory says that use a longer focal length and stand nearer to achieve a shallower DOF, it's not very practical in real life and it is this part which causes the confusion. In real life, if you use a longer focal length, you definitely need to stand further away to have the main subject the same size within the frame.

    So practically, the key to DOF is the aperture.

    In this regard, a large aperture in longer focal length may be harder and more expensive to come by than a large aperture in a shorter focal length.

    Notwithstanding the above, the DOF may be the same but the bokeh and the field of view are different for different focal lengths used and they may make a great difference in what is included in the background and how the relative subjects' distances may appear (i.e. photography term : perspective difference due to the difference in shooting distance with different focal lengths. 50mm from 2m away will have a very different perspective from 200mm from 8m away even though the main subject appears the same in size in the picture and the DOF is technically the same at the same aperture F number). A longer focal length has a narrow angle of view and therefore helps in isolating the main subject by keeping much of the background (messy and a distraction) out of the frame. The Bokeh for longer focal length also tends to be creamier.

    How shallow the DOF you're able to achieve is therefore also very much dependent on the subject size. If the subject is very small (e.g 10cm), you can shoot from extremely close distance (less than 30cm) with 70mm lens or less (assuming APS-C size sensor with 24mm in length for simplicity) and still have it within your frame and able to have a very shallow DOF with a wide aperture. However, if the subject is large (e.g. 2m tall) and you want to include it within your APS-C size sensor (for simplicity of illustration), you would need to demagnify it 24mm/2m = 24mm/2000mm = 1/83x. So even if you use a wide angle 20mm focal length, you would still need to stand at least 20x 83 = about 1.7m away. If you use 200mm instead, you would need to stand about 17m away and your DOF would be even more than shooting a small object at 30cm away with a much shorter focal length such as 50mm at the same F aperture number.
    Last edited by Clockunder; 23rd March 2008 at 03:15 AM.

  5. #5
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    Default Re: Depth Of Field Question

    to sum it up in simple english

    - the smaller the aperture (bigger f number) the greater the DOF
    - the bigger the aperture (smaller f number) the narrower the DOF

    - the longer the focal length of the lens the narrower the DOF
    - the shorter the focal length of the lens the greater the DOF

    - the greater the subject to camera distance the greater the DOF
    - the shorter the subject to camera distance the narrower the DOF

    so you have 3 variables that you can manipulate to control the DOF

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    Default Re: Depth Of Field Question

    so, basically to get the best combo for max bokeh would be biggest aperture, longest focal length, as near to the subject as possible ?

    am i rite to say this?
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    Default Re: Depth Of Field Question

    i think the background has to be as far away from the subject as possible as well..

    correct me if i'm wrong.. =)

  8. #8

    Default Re: Depth Of Field Question

    Quote Originally Posted by adiknaim View Post
    so, basically to get the best combo for max bokeh would be biggest aperture, longest focal length, as near to the subject as possible ?

    am i rite to say this?
    yes, and the background is reasonably far away.

    if you see macro photos, the f stop used is usually quite a large number, because you need details, and the distance to subject is phenomenally close for the focal lengths used.

    also, if the background is too close, i.e. your subject is plastering itself/herself/himself on a wall, then well, the background won't be too "bokehed"

    nothing will help you understand this better than taking pictures

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    Default Re: Depth Of Field Question

    Quote Originally Posted by ssping83 View Post
    i think the background has to be as far away from the subject as possible as well..

    correct me if i'm wrong.. =)
    yes i forgot about that one

  10. #10

    Default Re: Depth Of Field Question

    Ohhh.. Thanks for all of your extensive reply! I really appreciate them. Really did great help to me! I'm now trying around different settings to get different DOF and am learning alot from it.

    But I still have a question though.. Because while playing around, I realised my camera can't really do shallow DOF(eg, shooting full size people with blurred background), which I really want it to acheive.. Will an add-on lens actually work? After thinking about it alot.. I doubt right? :S Because I realise if I zoom in all the way to get a shallower DOF, I couldn't get a full size image of the person I want to capture. So in order to get the full size image of the person into the picture, I have to stand further away from the subject which means I 'm back to square zero again with the same DOF but worse still because my aperture size is slightly smaller due to the zooming in... am I right to say this? Is there any other way to do it or am I stuck with this limitation of the camera?

    If both uses the same aperture, the DOF of 50mm at 2m way is the same as the DOF of 200mm at 8m away. This can easily be verified with any online DOF calculator.
    By the way, I'm using a Sony DSC-H1.. Not a DSLR sadly...
    Last edited by Razorsharp87; 25th March 2008 at 12:56 AM.

  11. #11

    Default Re: Depth Of Field Question

    Quote Originally Posted by Razorsharp87 View Post
    Ohhh.. Thanks for all of your extensive reply! I really appreciate them. Really did great help to me! I'm now trying around different settings to get different DOF and am learning alot from it.

    But I still have a question though.. Because while playing around, I realised my camera can't really do shallow DOF(eg, shooting full size people with blurred background), which I really want it to acheive.. Will an add-on lens actually work? If it does, do I get a telephoto lens or wide-angle lens?
    what camera are you using? most prosumers can do certain amount of dof, you can amplify this with pp

    telephoto will help with bokeh more than wide angle

    but note that teleconverter tend to chop your aperture also, if i'm not wrong, whcih will defeat the purpose.

  12. #12

    Default Re: Depth Of Field Question

    what camera are you using? most prosumers can do certain amount of dof, you can amplify this with pp
    I'm using a Sony DSC-H1. And.. what's a pp?

  13. #13

    Default Re: Depth Of Field Question

    Quote Originally Posted by Razorsharp87 View Post
    I'm using a Sony DSC-H1. And.. what's a pp?
    post processing

    h1 eh, zoom to max, and then open up your aperture, make sure your subject is far away from background, sure got bokeh

    this was taken with h2, almost the same as h1.
    another bokeh photo from h1.
    yet another one

    definitely not as versatile as 50mm f/1.4 lenses, but you definitely can get bokeh if you want to, and have the know how
    Last edited by night86mare; 25th March 2008 at 01:49 AM.

  14. #14
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    Default Re: Depth Of Field Question

    Here's some examples...

    The following pic was taken using the Nikon D40x + 55-200mm lens at 200mm f/5.6. So this is an example of long focal length bokeh, and not using a fast lens.



    The next pic is taken with the same setup at 55mm f/5.



    The next pic is taken with the Nikon D40x + 18-55 lens at 55mm f/8.

    Last edited by geraldkhoo; 25th March 2008 at 11:51 AM.
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  15. #15

    Default Re: Depth Of Field Question

    That's some nice shots over there, geraldkhoo! But I guess that's only possible with animals or something small for my cam. I will have to do PP to get similar job done for humans. Thanks alot night86mare!

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    Default Re: Depth Of Field Question

    hey guys.

    just to comment and share some of my experiences..

    i'm using a nikon p5000. it should be considered as a prosumer cam. i find that the bokeh is not really shown.
    even if im at widest angle with f/2.7 the DOF still seem to be quite great. unlike DOF in dslrs where the focusing on the subject is better?

    i tried using telephoto, but the minimium aperture will become f/5.6. then DOF will become so great, almost background n foreground n subject n everywhere can be seen clearly. lol

    so i guess i have to rely on pp?

    also sometimes, how to determine an optimal DOF? like the 2nd pic from geraldkhoo, is it a lemur? i realise bokeh was present on the hair on the body. what happens if i want the body hair to be focused too?

    thanks.

  17. #17

    Default Re: Depth Of Field Question

    your subject to background distance has to be great

    you can don't need pp as gkhoo has shown

    i think what you guys are doing is

    CAMERA ----SUBJECT -- BACKGROUND

    it should be

    CAMERA ----SUBJECT -------------------------------BACKGROUND

    if don't have dof means your aperture is spoilt

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    Default Re: Depth Of Field Question

    Quote Originally Posted by gymak90 View Post
    hey guys.

    just to comment and share some of my experiences..

    i'm using a nikon p5000. it should be considered as a prosumer cam. i find that the bokeh is not really shown.
    even if im at widest angle with f/2.7 the DOF still seem to be quite great. unlike DOF in dslrs where the focusing on the subject is better?

    i tried using telephoto, but the minimium aperture will become f/5.6. then DOF will become so great, almost background n foreground n subject n everywhere can be seen clearly. lol

    so i guess i have to rely on pp?

    also sometimes, how to determine an optimal DOF? like the 2nd pic from geraldkhoo, is it a lemur? i realise bokeh was present on the hair on the body. what happens if i want the body hair to be focused too?

    thanks.
    do rmb that the DOF is controlled by the actual focal length. for most PnS, the sensor size is actually very small. the actual focal length might be 6mm (but FOV is equiv. to a 36mm on a 35mm camera). thus, the DOF is actually very great, as compared to a focal length of 36mm on a full frame camera like the EOS 5D.

    to get a shallow DOF on a PnS for a full body shoot of a human, i tink its pretty difficult. can try half body or head shots then u'll get more background blur.
    else do PP.

    regarding the qn on the blurring of the hair as seen in the 2nd pic posted by geraldkhoo, he shot that with f/5, so the only way to increase the DOf is to stop down to maybe f/8 or f/11 (assuming he dosent change the focal length and dosent move further away frm the subject)
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  19. #19
    Senior Member geraldkhoo's Avatar
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    Default Re: Depth Of Field Question

    Quote Originally Posted by Fragnatic View Post
    do rmb that the DOF is controlled by the actual focal length. for most PnS, the sensor size is actually very small. the actual focal length might be 6mm (but FOV is equiv. to a 36mm on a 35mm camera). thus, the DOF is actually very great, as compared to a focal length of 36mm on a full frame camera like the EOS 5D.

    to get a shallow DOF on a PnS for a full body shoot of a human, i tink its pretty difficult. can try half body or head shots then u'll get more background blur.
    else do PP.

    regarding the qn on the blurring of the hair as seen in the 2nd pic posted by geraldkhoo, he shot that with f/5, so the only way to increase the DOf is to stop down to maybe f/8 or f/11 (assuming he dosent change the focal length and dosent move further away frm the subject)
    Yep... it is difficult to get a DOF with a PnS camera but depending on how you do your placement, you can achieve something. The following picture is just a shot done over dinner using a Nikon P5100, no flash, just max aperture...

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    Default Re: Depth Of Field Question

    Quote Originally Posted by geraldkhoo View Post
    Yep... it is difficult to get a DOF with a PnS camera but depending on how you do your placement, you can achieve something. The following picture is just a shot done over dinner using a Nikon P5100, no flash, just max aperture...
    haha... not only max aperture. but also shooting at (or almost at) the min. focusing distance

    but for full body human shots as mentioned by Razorsharp87... lol..
    don't think its achievable for PnS to get a nice background blur (if there is any bkgrd blur achieved at all)
    tt's y i suggest shooting at the most tele end + half body shots or head shots.
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