• Photography basics: Depth of Field and composition

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    Depth of field is the range within which focusing is resolved in a photo.
    Aperture has a huge affect on to the depth of field.

     

     

    Changing the f-stops (f/#) of a lens will change aperture and as such the DOF.

    f-stops are a just certain number which is telling you the size of the aperture. That’s how f-stop is related to aperture (and DOF).

    If you increase f-stops, it will increase DOF, the area in focus (and decrease the aperture). On the other hand, decreasing the f-stop it will decrease DOF (and increase the aperture).

    The red cone in the figure is an angular representation of the resolution of the system. Versus the dotted lines, which indicate the aperture coverage. Where the lines of the two cones intersect defines the total range of the depth of field.

    This image explains why the longer the depth of field, the greater the range of clarity.

  • Embedding frame ranges into Quicktime movies with FFmpeg

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    QuickTime (.mov) files are fundamentally time-based, not frame-based, and so don’t have a built-in, uniform “first frame/last frame” field you can set as numeric frame IDs. Instead, tools like Shotgun Create rely on the timecode track and the movie’s duration to infer frame numbers. If you want Shotgun to pick up a non-default frame range (e.g. start at 1001, end at 1064), you must bake in an SMPTE timecode that corresponds to your desired start frame, and ensure the movie’s duration matches your clip length.

    How Shotgun Reads Frame Ranges

    • Default start frame is 1. If no timecode metadata is present, Shotgun assumes the movie begins at frame 1.
    • Timecode ⇒ frame number. Shotgun Create “honors the timecodes of media sources,” mapping the embedded TC to frame IDs. For example, a 24 fps QuickTime tagged with a start timecode of 00:00:41:17 will be interpreted as beginning on frame 1001 (1001 ÷ 24 fps ≈ 41.71 s).

    Embedding a Start Timecode

    QuickTime uses a tmcd (timecode) track. You can bake in an SMPTE track via FFmpeg’s -timecode flag or via Compressor/encoder settings:

    1. Compute your start TC.
      • Desired start frame = 1001
      • Frame 1001 at 24 fps ⇒ 1001 ÷ 24 ≈ 41.708 s ⇒ TC 00:00:41:17
    2. FFmpeg example:
    ffmpeg -i input.mov \
      -c copy \
      -timecode 00:00:41:17 \
      output.mov
    

    This adds a timecode track beginning at 00:00:41:17, which Shotgun maps to frame 1001.

    Ensuring the Correct End Frame

    Shotgun infers the last frame from the movie’s duration. To end on frame 1064:

    • Frame count = 1064 – 1001 + 1 = 64 frames
    • Duration = 64 ÷ 24 fps ≈ 2.667 s

    FFmpeg trim example:

    ffmpeg -i input.mov \
      -c copy \
      -timecode 00:00:41:17 \
      -t 00:00:02.667 \
      output_trimmed.mov
    

    This results in a 64-frame clip (1001→1064) at 24 fps.