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Depth of field preview

Discussion in 'Help Team' started by oddjob, Apr 2, 2002.

  1. oddjob

    oddjob Active Member

    Hi All

    This may be a dumb question but here goes!

    When I use the depth of field preview, how do I actually interpret what I see through the viewfinder?

    As with all previews, my viewfinder goes darker when used, but what is it that I am actually looking for that gives me the dof for the particular scene?

    Looking through the manual,all it tells me is that there is a dof preview and the viewfinder will go darker, not much help really!

    Am I being thick?! (please be kind when you answer that!)

  2. Brian

    Brian Venerable Elder


    A depth of field facility is very useful but interpreting the results needs some experience. For instance if you are going to use f22 the operation of the depth of field lever will make the screen go very dark., and for most purposes useless. A little tip is to select a few stops up from the minimum aperture, say if you are going to use f22 then select f8. now operating the D of F lever should enable you to see how much D of F you have gained, after that it becomes more and more difficult. But persevere, with time you will find that you can sense or feel what is going to be sharp and what is not.

    Its a matter of using your judgement on what looks sharp in the ground glass area of the viewfinder. Remember practice makes perfect.

  3. oddjob

    oddjob Active Member


    That's why it doesn't explain more in the manual!

    Thanks for the tip, I think maybe thats where my problem is, stopping down to f22 or whatever then trying to make sense of a pitch black viewfinder!

    I'll stick at it and hopefully one day I'll get the hang of it


  4. RonM

    RonM Alpha Napper


    As Slimey has already said it takes a bit of time and practice to get used to, but, you will be able to distinguish the areas of the image in your viewfinder that are 'sharp' and those that are not the 'sharp' bit is your DoF

    /img/wwwthreads/smile.gif<font color=blue>RonM FRIPN</font color=blue>
    Everyone has a photographic memory. Some just don't have film.

    PS Hope you got my reply to your insurance query in the 'Lounge'
  5. Lounge_Lizard

    Lounge_Lizard Well-Known Member

    It's easier to work out the DoF on Brian's camera AND his viewfinder stays bright all the time. His lenses have a little scale on them. Nothing that a drop of Viakil won't shift. Mind you, his body's also got red spots on it.

  6. Canonball

    Canonball Well-Known Member

    Well I heard Brian's red spots were clearing up nicely since he took some of Smiffy's Bob Martins by mistake.

    Poor old Smiffy isn't keen on that Gordon's stuff though. /img/wwwthreads/smile.gif

  7. Brian

    Brian Venerable Elder

    In truth David three of my bodies haven't got a spot between them. The one that has got a spot, the blemish is black. Do you think I should consult Clive and get his opinion.

    But yes, with all of them the viewfinder stays bright and crystal clear. But every lens in 35mm format I have ever owned has had a dinky little DoF scale on it.

  8. Mick

    Mick Well-Known Member

    The DoF preview button is often most useful for telling what is not in focus and how much out of focus it is than accurately seeing what is sharp: for example,to get an idea of what backgrounds in close-ups or portraits will look like.
  9. Lounge_Lizard

    Lounge_Lizard Well-Known Member

    I suppose I use DoF preview to ensure that the aperture I've chosen DOESN'T make the background too sharp. For portraits outdoors, I'm usually erring on the side of almost wide open.

  10. Benchista

    Benchista Which Tyler

    That's one of my favourite uses. Also for macro work. I don't need it much for landscapes, though.

    Nick BSRIPN
  11. dogbyte

    dogbyte In the Stop Bath

    Your timing in asking this question is perfect - you're looking at a man who's just spent a few hours making up DOF tables as I've found the dof preview button on my original EOS600 a complete waste of time. I always thought it must be faulty but when I bought a second body I found its dof button was a complete waste of time as well.
    To make a table first you need to find a calculator on the net - unless you fancy working it all out longhand. Try Forum member Glenn Harpers website.
    You can input the film format (35mm probably), lens length, f number, and distance of subject. The result gives you near and far and total dof, and hyperfocal distance.
    I've made up miniature tables printed on photo paper for durability. Then when I'm out at Marwell Zoo for example I can see that at 300mm at 10 metres and f16 I'll get near 9.5 and far 10.6 and total dof 1.1 metres - good for a face shot. Or if I'm cycling along the Kennet Canal I can see that at 28mm at 5 metres at f5.6 I'll get near 2.3 metres to infinity dof; great for capturing near detail like lock gates and berries on bushes and a landscape as well.
    I'm hoping that with practice the dof scales will sink in like driving a car, but to reinterate, the dof previews on my camera bodies are a non-starter.
  12. RonM

    RonM Alpha Napper

    Or you can download f-calc (free software for windows and mac) from http://tangentsoft.net/fcalc/
    which will give you all the DoF tabular data you need plus many other calculations as well. This site was publicised in AP the other week.

    /img/wwwthreads/smile.gif<font color=blue>RonM FRIPN</font color=blue>
    Everyone has a photographic memory. Some just don't have film.
  13. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    Stopping down to f/22 on a 35mm lens isn't usually the best idea anyway (macros excepted) as diffraction sets in beyond f/11 or so. I find that f/8 usually does the trick for good DoF.

    You work your life away and what do they give?
    You're only killing yourself to live.
  14. Brian

    Brian Venerable Elder

    It might as you say have been an interesting question Pete, so why didn't you answer it. The 'poster' wanted to know how to use a depth of field preview facility, not how to download a depth of field table. You might think that a preview facility is a waste of time, on the other hand I would not consider a single lens camera which didn't have one.

    Mind you, as a happy snapper who delights in simplicity perhaps I should not get involved in these highly technical discussions.

  15. dogbyte

    dogbyte In the Stop Bath

    Thought I had answered it - not a lot of use really, too rough and ready, so if its important use tables until the basic data sinks into your brain.
    I expect I'll always carry little tables from now on and refer to them where its critical. They fit in my back pocket.
    My cameras have that fancy feature as well where you can focus on two objects, near and far, and they'll calculate what aperture is needed to obtain dof across that range - but who can be bothered?
  16. Burgy

    Burgy In the Stop Bath

    Strangely enough I used tto use the EOS5's DEP setting occassionally, an found it quite useful especially for portraits, (1st focus point on the tip of the nose, second on the ear, ensuring a that the absolute minimum required DOF was set.)

    The 5 also had a a quirky way of accessing the DOF Preview, you had to look at a little square in the top left of the screen and the lens then stopped down.

    Its not what you've got, its who you do it to. [/url]www.pressfotos.co.uk[/url]
  17. Brian

    Brian Venerable Elder

    But David, lots of M series have two depth of field indicators IN THE VIEWFINDER ( thats not shouting I don't know how to do italics)

  18. Reading

    Reading Well-Known Member

    Trouble with using tables and/or lens markings is that the distance scale on the lens will almost never be 100% perfect. Even if meticulously calibrated (unlikely as it is only really an indicator), I am sure I have read that infinity for example moves with temperature variations etc. Isnt that why most lenses go a little bit past infinity?
  19. Lounge_Lizard

    Lounge_Lizard Well-Known Member

    Neither is peering into a viewfinder screen with a DoF preview a 100% certain method of determining whether you have critical sharpness by the time the image is blown up to 12x15 inches!

  20. Benchista

    Benchista Which Tyler

    Who can be bothered? Well, me for one! I wouldn't buy an SLR without DOF preview, and I wouldn't buy an AF SLR without DOF mode. Granted, neither is perfect, but the zone of acceptable focus is, to me, one of the most impostant decisions a photographer has to make in composing each shot.

    Nick BSRIPN

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