Proposal for a lens Test

Discussion in 'Digital Photography' started by jared_kipe, Sep 1, 2006.

  1. jared_kipe macrumors 68030

    jared_kipe

    Joined:
    Dec 8, 2003
    Location:
    Seattle
    #1
    So common wisdom says that under similar perspectives, a cropped DSLR has less background blur/more DOF than a non cropped DLSR. With the argument that you have to be farther away from the subject.

    I've been thinking about this for a while and have come to the conclusion (in my mind at least) that the only things that should matter for DOF and bokeh will be the distance to the subject, and the angle of view. My prediction is that something like a 50mm on a cropped DSLR (~80mm) with an identical framing of an 85mm lens on a non cropped DSLR will yield similar bokeh and DOF. (at the same f stops)

    I do not have the means for this test. So I'm asking for some help. Can someone with access to a 20D and a 5D, and 50mm f1.4 and 85mm f1.8 please set up a scene where you can monitor the bokeh behind an object to focus on. Its a pretty simple test, and if I had the means I would perform it.

    Thank you.
     
  2. jared_kipe thread starter macrumors 68030

    jared_kipe

    Joined:
    Dec 8, 2003
    Location:
    Seattle
  3. snap58 macrumors 6502

    snap58

    Joined:
    Jan 29, 2006
    Location:
    somewhere in kansas
    #4
    This is with a 85 mm on a 20D at F2 and a 135 mm on a 5D at F2. The FOV should be very close for both, looks like the blur is much better on the 5D.
     

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  4. jared_kipe thread starter macrumors 68030

    jared_kipe

    Joined:
    Dec 8, 2003
    Location:
    Seattle
    #5
    You are correct. Thank you. Makes me want a 5D now. ;)
     
  5. ChrisA macrumors G4

    Joined:
    Jan 5, 2006
    Location:
    Redondo Beach, California
    #6
    This issue is much older than digital

    People have have LOTS of experiance with this going back 100+ years. Long before there were digital cameras there was film and film comes in different sizes. At the small end we have 35mm which is 36x24mm and then medium formats ranging from 60x45mm to 90x60mm and then view camera in 4x5, 5x7 and 8x10 inch sizes.

    The difference between DSLR frame and a full 35mm frame is subtle compared the range of sizes avalable with film.

    With film we can choose the format based on the "look" we are after. But now that we are digital we select a format (sensor size) based on our budget. For years photographers used Medium format because to result looked different.

    The "look" has some to do with depth of field but more I think with camera to subject distance. It is this distance that controls perspective (the size ratio of forground to background objects) Using a short lens and getting close makes forgound objects look bigger while backing up and using a telephoto lens "flattens" the image. with the larger formats we tend to use relativly wider lenses.

    All that said. It is absolutly true that the larger formats have much reduced depth of field. Just try shooting products on a table top with medium format and will get to know f-stops between 16 to 32 well where as with a DSLR you can be at f/5.6 and using much less light. With an even larger format like 4x5 you will need to use tilts and swings to keep the subject in focus as there will never be enough DOF

    Bottom line. this is by no means a new subject. It's as old as photography

    If you read any of the video forums people there talk about how to capture the "film look" using video. Movie film is the same or our 35mm film but it moves vertically through the camera so the move frames are 24mm wide. high-end "pro-summer" video camera have CCD sensors that are between 8mm and 6mm So the "look of film" has a lot to do with DOF and perspective and is even more pronouced than what we see between film and digital SLRs. But they also have the issue of frame rates, dynamic range and color
     
  6. snap58 macrumors 6502

    snap58

    Joined:
    Jan 29, 2006
    Location:
    somewhere in kansas
    #7
     

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