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Thread: Back / Forward focusing

  1. #1

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    Back / Forward focusing

    Im curious to know if back / forward focusing is an issue which only pertains to autofocus?

    I've recently branched out into the world of macro photography which has given me the challenge of becoming better at manual focusing. Im noticing that on quite alot of occasions the plain of perfect focus seems to be slightly beyond the eyes of my insect subjects, despite the fact that I have tried very hard to achieve focus on their eyes.

    I have heard people mention back focusing before but assumed it was purely an af issue. Is it possible that my viewfinder is displaying perfect focus on my subjects eyes, but actually focus is slightly beyond???

    Of course the other much stronger possibility is that im just being a bad workman and blaming my tools!

    Thanks in advance, Tom

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    Re: Back / Forward focusing

    do you have the eye-correction slider on your viewfinder set correctly? (which by the way is a bit fiddly due to your eye's ability to automatically adjust to incorrect settings)

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    Re: Back / Forward focusing

    Quote Originally Posted by Hero View Post
    do you have the eye-correction slider on your viewfinder set correctly? (which by the way is a bit fiddly due to your eye's ability to automatically adjust to incorrect settings)
    Out of interest, I find it easier to adjust the view finder focus by looking at the status indicators, not looking at an image.

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    Moderator Dave Humphries's Avatar
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    Re: Back / Forward focusing

    Hi Tom,

    As Colin suggests, I would suggest using any electronic rangefinder function your camera (?) might have, if it will work well enough on the small area an insect's eye probably represents within a macro shot.

    Hero's idea is worth looking at.

    Are these handheld or tripod shots? (If not tripod, is it possible you may be leaning forward slightly as you take the exposure?)

    Is the focusing through the traditional eye level DSLR viewfinder?


    At first, I too would have thought it just an AF issue, but I guess it must also be possible (in fact likely) that there are be even larger manufacturing differences between the lens to viewfinder vs lens to sensor distances than affects the AF sensor.

    Can you try manual focusing using Live View and a magnified image on the LCD screen? - now that really ought to be infallible because it uses the same sensor the image is taken with.

    Cheers,

  5. #5

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    Re: Back / Forward focusing

    Thanks guys

    @ Hero, Yes, im sure my viewfinder correction is set correctly. One notch in either direction and everything is complete fuzz.

    @ Colin. I do try when I can to use my status indicator dot but I have tended to trust what I see more than the dot. Maybe that's part of my problem. Ill keep trying.

    @ Dave. Your suggestion of using the rangefinder function interests me. I use a D5000 same as you, and it does have a rangefinder function hidden in the menus somewhere. I'm not totally clear on how to read the display (it looks the same as the meter display but behaves differently) so if you have any knowledge which you can share I would really appreciate it.
    As for using the liveview, I still struggle with that quite alot. In low light situations it seems pretty useless and when shooting bugs it greatly reduces the speed at which I can shoot. I'm not sure if this is because I lack experience with it or just because its rubbish! Maybe you can shed a little light on that one aswell?


    Thanks very much for your responses guys.
    Tom

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    Moderator Dave Humphries's Avatar
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    Re: Back / Forward focusing

    Hi Tom,

    Quote Originally Posted by MrGladstone View Post
    Your suggestion of using the rangefinder function interests me. I use a D5000 same as you, and it does have a rangefinder function hidden in the menus somewhere. I'm not totally clear on how to read the display (it looks the same as the meter display but behaves differently) so if you have any knowledge which you can share I would really appreciate it.
    It is in Custom Settings (Pencil icon) Auto Focus (a) and the fourth (= a4) called "Rangefinder", has two options; OFF and ON, I leave mine ON.

    It works on contrast detection, a sharp image has the highest contrast, so it lights the dot when that is the case. Now, the problem may be the area it is measuring contrast in, if you have single point, that's fine, but if you have a wider area mode selected, what's maximum contrast for the entire image probably doesn't correspond to what absolutely best for an insect's eye. When using; do keep the camera still, or it can be fooled by varying contrast, e.g. by waving the camera around a scene, it will flicker it on thinking you're going through focus. I don't believe it is connected in any way to the lens, so it doesn't know whether or not you're turning the focus ring, it just looks at the scene and comes on when it sees a higher contrast than it did a few seconds earlier.

    Quote Originally Posted by MrGladstone View Post
    As for using the liveview, I still struggle with that quite alot. In low light situations it seems pretty useless and when shooting bugs it greatly reduces the speed at which I can shoot. I'm not sure if this is because I lack experience with it or just because its rubbish! Maybe you can shed a little light on that one aswell?
    Yes, Live view is a much slower method of working. It just suits some occasions, but not that many for what I (or you) shoot

    Just position (with the pad surrounding "OK" button), the focus box on the area you want sharp and then use the "+" magnifying button to zoom in, then manually focus if AF won't work, mine does in low light, but it takes seconds on high contrast edges and may not work at all on 'flat', low contrast surface.

    Cheers,
    Last edited by Dave Humphries; 2nd November 2011 at 11:53 PM.

  7. #7

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    Re: Back / Forward focusing

    Dave your a star! Thanks very much.

    Unfortunately rain means I wont be able to test this on a live subject today, but ill let you know how I get on.

    Cheers, Tom

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    Re: Back / Forward focusing

    Quote Originally Posted by Colin Southern View Post
    Out of interest, I find it easier to adjust the view finder focus by looking at the status indicators, not looking at an image.
    The indicator usually works quite well, but there are a few expections. One of them is a +2D close-up on a 300mm f5.6. Dof is so awfully thin that most of the image is always out of focus. (Don't even try AF. the tiny spec of sharpness in the center is not large enough to fill the af-sensor. It'll waddle up and down between front- and back-focus)

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