[Theory] Multi-Focus Distance Photography

Discussion in 'Digital Photography' started by Geniusdog254, Sep 12, 2009.

  1. Geniusdog254 macrumors regular

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    #1
    Ok, so I have what I think is a pretty good idea. Obviously on a camera you can only focus at one distance at a time. However, you can also only expose at one level at a time. This is based on the theory behind HDR photography.

    If you look at it like exposure bracketing, then you just set the middle focus point you want, & then the camera would snap shots with focus levels one step above & one step below. This isn't built into cameras (yet :D), but you could do it with manual focus.

    Then in post-processing on the PC you would use custom software (like Photomatrix Pro & the merge to HDR option in Photoshop, but these are for HDR) to merge the different focus levels.

    It all checks out in theory, and it would give a perfectly clear image that would look really good.

    I don't know how to write software to automate the whole process, but tomorrow if I get time I will make a patchwork shot in Photoshop by mixing different parts of several images in different focuses. I will see how it works & post the shots here. What do you guys think of this?
     
  2. SilentPanda Moderator emeritus

    SilentPanda

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    #2
  3. Geniusdog254 thread starter macrumors regular

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    #3
    Hmm thats very interesting. I've never seen that option in my CS4 or in any of the tutorials I've read. I'll definitely look and see if it's there.
     
  4. SilentPanda Moderator emeritus

    SilentPanda

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    #4
    In CS4 (in short):

    Load them in as layers.
    Select all the layers then choose "Edit, Auto-Align Layers".
    Then choose "Edit, Auto-Blend Layers".

    Of course then you need to do standard fixing much like with panoramic pictures.

    It doesn't take away from the fact that you thought it up on your own though...
     
  5. Geniusdog254 thread starter macrumors regular

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  6. toxic macrumors 68000

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    #6
    this is already done all the time, forgot what the technical term is. you can't do "focus bracketing" in-camera because the steps would be completely arbitrary depending on focal length, subject size, and distance.
     
  7. Naim135 macrumors member

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    #7
    I too have had similar thoughts. I thought of photographing a line of regular spaced objects such as fence pickets etc but shot from an acute angle. or in a similar vein how about a merging two different exposures of moving water one a slow exposure to give the misty effect with the other one fast to capture the movement.
     
  8. SayCheese macrumors 6502a

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    #8
    The correct term for what you are describing is 'Focus Stacking'. There is a Wikipedia article about it here.

    However as a previous poster stated this doesn't detract from the fact that you thought it up on your own. We need people to come up with these ideas and try them to progress photography forward. Also just because there is one way of doing things that is readily accepted doesn't mean that there isn't another better way yet to be found.
     
  9. Doylem macrumors 68040

    Doylem

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    #9
    Here's something I thought of recently. Though simple and elegant, it's hard to imagine any practical applications...

    [​IMG]

    ;);)
     
  10. Naim135 macrumors member

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    #10
    You're not a Teacher by any chance? Only they re-invent this on an annual basis:D
     
  11. Ruahrc macrumors 65816

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    #11
    This method of focus stacking is used a lot in Macro photography where the depth of field is often measured in fractions of a millimeter.

    I've thought about trying this out on landscapes however to kind of serve as a "poor man's tilt-shift lens", or "Software Sheimpflug"

    Ruahrc
     
  12. mickbab macrumors 65816

    mickbab

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    #12
    Was just randomly browsing through the Apple Downloads section, saw this and remembered this thread:

    Helicon Focus

    Is this kind of what you are looking for?
     
  13. Patriks7 macrumors 65816

    Patriks7

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    #13
    Well judging from the sharp edges, I bet you could cut your pizza with it, or maybe a cake...
     
  14. Edge100 macrumors 68000

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    #14
    This is the theoretical basis of 3D confocal microscopy, which is, more or less, my day job.

    Essentially, you take many (say, 60) stacked images of very thin focal planes (on the order of 250 nanometers), to give you a representation of a 3D object. You then collapse that 3D stack down to 2D using some kind of projection (sum, average, max. intensity, min. intensity, etc).

    This is typically combined with 3D deconvolution algorithms, which remove light scatter, which is inherent in any optical system (i.e. an illuminated point object is 'seen' as a 3D cone of light, with the cone being described by a point spread function, which is characteristic of the object and of the particular imaging system). 3D deconvolved confocal images look absolutely amazing.

    This could be applied to photography, I suppose. Take a 10-slice stack of a particular scene and then combine the focal planes later in PP. The only issue, I suppose, is that you'd have to have a good idea of precisely where your focal plane lies (i.e. how far from the lens) and you'd have to maintain some sort of consistency with respect to the actual distance between focal planes (i.e. every 50 meters, or whatever).

    It's not totally analogous to HDR, though. With HDR, Photomatix knows what is clipped and what is not, and can thus substitute the correctly exposed image in that particular region of the image. But with what you're describing, how does the software know what elements of each focal plane are in focus and which are not, in order to properly combine them later? This is where your idea will run into problems; in a photograph, the sun (or your flashgun) illuminates an entire scene, and your camera takes light in from the entire scene. In confocal microscopy, only a slice of the object is illuminated (or, more accurately, only a slice of the light is captured). So when I stack together confocal microscopy images and then deconvolve them, my software knows which elements are in focus because I have precisely spaced intervals. I don't see how you could overcome this obstacle in photography, where your focus intervals are not exact AND where the camera is capturing both in focus and out-of-focus light.

    What WOULD work is a (hypothetical) confocal camera, where you only capture multiple, precisely spaced optical slices of the illuminated field of view, and then combine them later.

    EDIT: After seeing the trsutedreviews.com link posted above, it looks like CS4 has some rudimentary tools to approximate this. Not sure what kind of math it's doing to get there (it can't be as simple as a back projection, since again the software has to guess at which regions are in focus and which are not), and the tool would likely get bogged down with more than three focal planes (which would likely be required for landscapes, for instance), but it's very cool that the feature exists at all.
     
  15. PeteB macrumors 6502a

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  16. ChrisA macrumors G4

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    #16
    Yes, you are right just like HDR. As it turns out "HDR" is a special case of "photo merge".

    The same process is used for HDR, Panoramas and multi-focus all have been done for many, many years. Another application of this technology is group shouts that made from a compose of several shots, so that you can add add people or select the best expressions from each person.

    It s hard to think of anything new in photography. most of the good ideas where though of 100 years ago. You can do this kind of shoot in-camera using film by taking multiple exposures and using a mask. Or in the darkroom by exposing the paper with multiple negatives. But now we have Photoshop that can merge multiple images.

    One thing you have to watch out for is that some times refocusing can change the image scale, that is "zoom" the image. then yu will need to corect for this effect
     

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