DOF questions

Discussion in 'Photography Beginners' Forum' started by julie32, Jan 7, 2008.

  1. julie32

    julie32 TPF Noob!

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    Is it possible that someone could post a few shots with explanations of the DOF terms which are still confusing me. (i.e shallow, longer, shorter, tighter, deep etc). I recognize some people may use different terms that mean the same thing, but I'm having trouble visualizing it. I need to see photos.
    Anyone not feel like working, so they'll take some time and post a few for a nice girl?

    thanks
    julie
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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  3. Tighearnach

    Tighearnach TPF Noob!

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    Yeah them links MIke posted are really helpful and help to visualise it. If you still need photos to see then take a look at the first photo in your LIFE category on your website(amazing shots by the way). This is shallow depth of field as everything in background is blurry. If this green blur were in focus then you would have a longer DOF. I think (but am only learning myself) that that is it. All those terms you mentioned might well be people using different words to explain the same thing.
     
  4. julie32

    julie32 TPF Noob!

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    excellent big Mike, thank you!
     
  5. Mav

    Mav TPF Noob!

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    My daughter on a swing having a blast...

    [size=+1]f/6.3[/size]
    [​IMG]

    [size=+1]f/1.8[/size]
    [​IMG]
     
  6. nicfargo

    nicfargo TPF Noob!

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    Notice on Mav's pics there with the smaller aperture the background is nice and out of focus (called a Bokeh I believe). Lenses with more aperture blades, 6 instead of 5, will give better bokeh if there are lights in the background (lights will look circle with 6 blades, somewhat like a pentagon with 5 blades. Play around with low apertures to get a feel for this. If you don't have any lenses with low aperture, you can usually buy a Canon 50mm f/1.8 for under a hundred bucks. This is a great prime lens. If you have the money get the 50mm f/1.4, it has a better Bokeh, lower light ability, and just all around better quality.
     
  7. julie32

    julie32 TPF Noob!

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    ok, I think I'm getting it. (Tighearnach, thanks for the compliment, btw). So, when determining the DOF, you're looking at what's IN FOCUS, as to whether you say the DOG is shallow or long, is that correct to say?
     
  8. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Just to clarify...the background is more out of focus on the one with a LARGER Aperture and SMALLER F Number. F1.8 is larger than F6.3.
     
  9. julie32

    julie32 TPF Noob!

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    thanks mike
     
  10. nicfargo

    nicfargo TPF Noob!

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    yeah, thanks Mike...my bad. I always forget larger is technically smaller number and smaller is technically larger number (does that make any sense?). I just know my smaller number lets in more light, which means it is opened up more and becomes larger...ug...terminology is confusing!
     
  11. Mav

    Mav TPF Noob!

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    Yeah, sorta counter-intuitive isn't it, lol.

    BTW the first f/6.3 photo was taken with the 18-55 Nikon kit lens which has a 7-bladed diaphram. The f/1.8 photo was taken with the Nikkor 85mm f/1.8 which has a 9-bladed diaphram. Both lenses actually have crappy looking bokeh, which refers to the specific out-of-focus rendering of the lens, which also has to do with the optical design.

    Depth of field is just DOF. But the bokeh is how the out of focus area actually is rendered. Some lenses can give you a nice tight depth of field, but can actually have ugly and distracting out of focus area rendering leading to a very odd looking image.

    Here's a narrow crop from my 85mm f/1.8 at or near wide-open. The light points have ugly rings around them. Now compare this to my 18-135mm f/3.5-5.6 (@ f/5.6, full image) and the bokeh in that is very smooth. The light points are more neutral and don't have hard edges which leads to a much smoother looking and less distracting background. A lot of Nikon primes have UGLY bokeh unless you buy the super expensive f/1.4 versions which have a much cleaner look. In contrast, I think I've read that the Canon EF 85mm f/1.8 has pretty nice looking bokeh which makes it an ideal portrait lens. My Nikkor version is probably about as good overall image quality wise, but I have to be careful with it if there's a lot of light points in the background and possibly try to recompose the shot if I can. A lot of this is subjective though, so what looks good to one might look bad to somebody else. I specifically bought the Nikkor 18-135 for my setup because it was the only kit lens in Nikon's lineup that has nice bokeh rendering which is important for portraits. The 18-55, 18-70, and 18-200VR all have ugly bokeh, but the 18-135 is quite nice. Most people ditch this lens for bigger and better things, so it was easy to find dirt cheap used. :mrgreen:
     
  12. Mav

    Mav TPF Noob!

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    And while we're on the topic...

    Christmas lights with my 35mm f/2. This shows all three concepts: depth of field, bokeh, and diaphram shape. You can clearly make out the 7-bladed diaphram. This lens has pretty neutral bokeh and maintains fairly smooth edges on the light points with just a hint of darkened corners. Not bad, considering this is a pretty extreme example. I haven't tested it in more normal shooting but it's always looked pretty nice to me. :)


    @ f/2
    [​IMG]


    @ f/2.8
    [​IMG]


    @ f/4
    [​IMG]


    @ f/5.6
    [​IMG]


    I stopped at f/5.6 but should have done f/8 too. The fancier lenses with the 9-bladed diaphrams can maintain a much rounder aperture even when stopped down than one with fewer blades which can help with the bokeh too. But again, the optics have a big play in this also.
     

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