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Anyone tried a GoPro with Rectilinear Lens?

Discussion in 'General Discussion' started by el cuajinais, Mar 9, 2016.

  1. el cuajinais

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    Has anyone used a GoPro with a rectilinear lens installed? What happens as you go from narrow, to medium, to wide? I would think to use the entire sensor one would chose wide, and that in wide mode you would get no fisheye correct? So I can shoot ProTune at 2.7k, 30fps (I have a Hero 3+), with no lens distortion correct? Because currently the only way for me to not get distortion is to shoot narrow which does not use the entire sensor, and you get only 1080p. Am I correct in assuming I can get a 2.7K resolution with no distortion if I install this lens? Anyone tried one of these?

    5.4mm Flat Lens No Fish Eye For Hero3+Black-White-Silver bokeh focus DJI Phantom | HD Wearable Video Custom Mods By RageCams
     
  2. Air Ontario

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    How do you have Protune on a 3+? Never mind, mine is 3+ silver.
    Wouldn't you get less fish eye the less wide you video?
    Some editors fix fisheye in post I think.
     
  3. PrecisionAeroworks

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    I have a Hero4 Silver with a 5.4mm flat lens. It works great. If it's a properly designed and installed lens, it still fills the whole sensor just like the stock lens. And yes, the image is still geometrically flat in wide mode (as it is a flat perspective lens). Of course the trade off is FOV.
     
  4. el cuajinais

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    So I take it you always shoot in wide mode to maximize the resolution and usage of the sensor right?
     
  5. PrecisionAeroworks

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    Yes. Unless I want to take advantage of a faster frame rate only available at a lower resolution.

    EDIT: And to clarify, available resolutions and frame rates are intimately tied to wide/medium/narrow settings in the complicated pixel binning schemes inside the GOPRO.
     
  6. el cuajinais

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    Yes that is understood. So let's take the 24fps which is the lowest "acceptable" frame rate:

    If you shoot wide at 24fps with the highest resolution available and compare it to narrow at 24fps at the highest resolution available...
    Neither video would show fisheye, but the wide one should look substantially better because it is at a higher resolution and uses more of the sensor. Have you tried this and verified that this is the case?
     
  7. PrecisionAeroworks

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    Well, like I said, the pixel binning schemes in the GOPRO are complicated. And to be completely clear, I'm speaking of a Hero4 Silver. A Hero4 Black is going to be different. A Hero3+ Black is very similar to the Hero4 Silver, but I don't know if it has all the same modes enabled or not.

    The Hero4 Silver has a "4K" sensor (and does have a 4K/15fps mode and a 4K video timelapse mode). So while 2.7K isn't the highest resolution, it is the highest resolution with, as you put it, an "acceptable" frame rate. What's implied in there is that in WIDE mode, your are binning pixels together on the fully illuminated 4K sensor to get a 2.7K frame.

    Switch to MEDIUM mode on the camera, and you have the same options, 2.7K at 24 or 30fps, but a narrower FOV (effectively zoomed in). In this case, it is cropping the 2.7K frame out of the full 4K frame, instead of binning the full 4K frame down to 2.7K. But in both cases, the ouput is a full 2.7k frame at 24fps. Narrow mode doesn't exist if resolution is set to 2.7K (but at 1080p resolution, narrow mode exists and includes some faster frame rates).

    With something like 10 different possible resolutions and half a dozen possible frame rates, plus the 3 different FOV modes (I left the useless "Superwide" mode out of the discussion), it gets complicated pretty quick.

    To discuss the quality differences between WIDE and MEDIUM modes at 2.7K, gets into things like chroma downsampling during binning and other things beyond the scope of this discussion. But the bigger issue when using the MEDIUM FOV setting with a 5.4mm flat lens on a drone is stability and rolling shutter. The effective zoom really exacerbates the vibration induced jello effect. A pretty dark ND filter may be required for acceptable results.

    TLDR; 2.7K at 24 or 30 fps in WIDE mode is probably the best mode to use for most situations when using a GOPRO Hero4 Silver modified with a 5.4mm rectilinear (flat) lens from a multirotor.
    (IMO) :)
     
    #7 PrecisionAeroworks, Mar 9, 2016
    Last edited: Mar 9, 2016