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ND filters for Jello?

Discussion in 'General Discussion' started by JoeC, Jul 22, 2013.

  1. JoeC

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    I've seen some things online claiming that an ND filter helps eliminate Jello.
    I'm wondering if there's any truth to this, as it seems to go against the physics of what causes jello in the first place...

    The GoPro has a CMOS sensor - as a frame of video is recorded, that sensor doesn't grab a full image instantly - instead the sensor is read from top to bottom - then that info is stored as a frame of video. Of course, at 60fps, this happens very quickly - but any vibration that happens while the sensor is being read will result in Jello.

    People have been saying to use high frame rates with the GoPro because a higher frame rate forces the sensor to read faster - allowing less time for the vibrations to affect the image.

    The purpose of the ND filter is to trick the GoPro into thinking it needs more light - so the amount of time the shutter stays open is increased. I don't see how this trick will do anything to eliminate Jello - logically, it could seem to cause more jello because the shutter is open longer and more vibrations would happen during that exposure.

    The only benefit that would make sense is that sometimes when flying toward the sun, I get propeller shadows over the image and it looks similar to jello. An ND filter might help eliminate these shadows - but so would a lens hood.

    So what am I missing here? I've seen some extraordinary video samples from companies selling these ND mounts, but my feeling is they weren't honest in the examples.
     
  2. CameraGuy

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    http://www.youtube.com/watch?v=dLRwOeeHdlg

    I have found that the PolarPro NAKED filters can be positioned on the GoPro and it does make a hiuge difference in the jello factor.

    The video above, which talks about a flyaway, shows the new filter on the GoPro.

    I only fly with them on now.

    Hope this helps

    Darren
     
  3. martcerv

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    At first I thought this was counter productive too as faster shutter speeds should help reduce jello on a rolling shutter cmos camera. But the thing is that jello is caused by very high frequency vibrations that aren't a huge camera movement it may only be vibrating up and down one or 2 pixels but doing this so fast due to being caused by the props high rpm.

    Then even at the very fastest shutter speeds in the best light the image will move up or down a couple of lines as the screen is captured because these vibrations are such high frequency. If you had a global shutter or ccd camera it will also be effected by vibration but as the frame is captured all at once any movement will be a motion blur and not a warping jello effect of the rolling shutter cameras.

    By using a ND filter you slow down the shutter speed enough so that instead of getting jello this small movement will turn into some blur which looks much better then jello. All ccd cameras had this effect and all new global shutter cameras will and a high shutter cmos rolling shutter camera has always had this issue. If the jello is caused more by a low frequency vibration or simply by the camera moving up and down a little in motion then a higher frame rate and shutter speed will help more but in very high frequency vibrations blurring the motion will work better then jello.

    Easy way to test if you don't have any filters is go fly your phantom on a very bright day and then in low light, you should easily notice the reduced jello effect in the lower light footage. Also the advantage of ND filters is in very bright light you wont get that stroby effect in motion caused by very high shutter speeds on video. It will slow down the shutter giving some motion blur making the motion much smoother in your video. If the shutter speed is so high then at 30p or less playback you don't want perfectly crisp frames even if they were jello free as it doesn't flow so nicely and has the traditional action cam look to it. Most high end video cameras come with buikt in ND filters for this reason as you may want to shoot wide open aperture in good light but still slower shutter speeds. The gopro has no aperture settings its just a wide open lens controlled purely by shutter speeds for exposure so nd filters are a great tool to have.

    I have used the SRP adapters and filters with my gopro's for quite a while and the big advantage of this is you can use whatever filter's you want with or without the housing as they are regular threaded filter adapters. I use filters from clear uv just as a lens protector in very low light to ND8 on bright days and a few in between for conditions in between.
     
  4. Gizmo3000

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    I'm with ya man..

    I kind of asked the same thing a few months ago, and nobody could actually explain or provide a website explaining just HOW both fast frame rates AND slow frames can help reduce jello.

    my guess is that the slow framerate kind of blends or blurs the jello in a single image
    .and a high framerate sort of reduces the frequency/amplitude of the jello because it's drawing the frame out twice as fast. (if that makes sense)
    ti's kinda voodoo
     
  5. JoeC

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    Thank you martcerv,
    Your answer makes sense. Do you get vignetting with the SRP mounts and filters? I like to fly with the gopro in its housing, so that looks like a better solution than the one that slips over the lens. The SRP website seems to say that they were designed for underwater use and that vignetting goes away underwater.
     
  6. JoeC

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    I watched your video - Must be heartbreaking to watch one fly away. I wonder if there was some 2.4 ghz wifi interfering from that building... Maybe go back there and check with your cell phone and see if there are any strong wifi signals in the areas you had the problems.
     
  7. Roadkilt

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  8. martcerv

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    There are quite a few options for stabilizing the mount and these are needed too as just a filter on its own wont do you much good. The ND filter will just smooth out the last bit of micro high frequency vibrations that show up mostly in bright conditions. Im quite happy with the grommet type anti jello mounts and have used a couple but I mod mine to stiffen them up a bit as being too soft causes camera shake at speed or in the wind. I think a wire method would be great in calm conditions and very slow flying but at speed or in any wind it would let the camera swing too much I think.

    Balancing props and a good isolation mount are needed for good results but even with those I found flying in bright conditions made me get some jello. With ND filters its also a balancing act to find the right one as you dont want to take away too much light to make the camera up its ISO but just enough to force shutter slow enough to get some motion blur to smooth out the last bit of jello. I mostly use ND4 or ND8 in the Marumi filters but have also tried the tiffen N.6 and .9 with fairly similar results. I tend to prefer the marumi a bit more but in very bright conditions the tiffen .9 is a bit darker then marumi nd8 so I use that.

    With the hero3 black SRP adapters and using low profile filters I get no vignetting with the 55mm over the housing adapter or the 52mm micro adapter with the frame in any mode. The Hero2 had more issues in terms of vignetting as even with the lowest profile filters some cameras would get a slight vignette using a 55mm filter outside the hero2 housing. The tolerances on the gopros isnt that great and the odd camera would be worse then others, its possible that even some hero3 blacks may get a slight vignette with a low profile filter in 1440, 960 or wide photo modes as these are the modes that use the most sensor area out of this camera but I havent heard of any. In the hero2 it would have been about 25% or so that would get a slight corner effected by the housing, originally they made these for UW filter use and how I came about them. UW there was no vignetting in any modes with all cameras and their filters. Im not sure about silver and white hero3's how they handle these as I dont have either of those cameras.

    Ive even used the micro 52mm with a 52 to 58mm adapter without issues and there are quite a few low profile filters around. If you use a deep filter then its likely that you will get some of the filter frame in shot but I dont use any of these.

    Here is a pic of the 2 hero3 options.

    This is the 55mm Blurfix3 SO for over the housing use, I use this underwater and with all my early phantom flights while crashing was more of a possibility.

    [​IMG]

    Here is the micro 52mm for the naked gopro camera and I use this mostly now.

    [​IMG]

    Those pics were borrowed from the SRP website here is a pic of my current phantom setup with the micro 52mm with ND filter

    [​IMG]

    Here you can also see my modified anti jello mount, its a carbon fiber grommet setup from helipal much like the VGE mount I had earlier but broke in a crash. I have added some foam and rubber bands to stiffen it up and this allows me to fly a bit faster without getting the terrible camera shakes these types of mounts tend to do when they are too soft.
     
  9. CameraGuy

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    That is the opinion that there was some sort of 2.4GHZ interference. DId you know a microwave oven with a faulty door can cause the problem? I remember a microwave oven and a wifi network I had in 2008. We would loose the internet every time we used the microwave. We just wrote it off to - Oh well...

    In truth, it could have been a serious issue I guess.

    The building has a lot of Seniors, so I'm guessing it was something like a bad wifi network, or perhaps even a bad microwave.

    What I decided to do was to replace the radios. Now I use a DX8, which has a superior radio transmitter and receiver. I am hopeful this prevents another flyaway.

    Darren
     
  10. CameraGuy

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    Here are some pictures of the Polar Pro product.

    I like them, and have not had any vignetting even when using the widest setting on the gopro.

    I think they make a difference. A significant difference in your picture quality.

    I have not used the polarize yet, but hope to try it soon

    Darren
     

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  11. martcerv

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    Regarding radio interference it can be so many weird things you just don't expect. The strangest I have ever seen is at my mums place she got a new LED light globe in the bathroom and if that is turned on her digital radio completely loses reception, not sure what frequency that particular station is on but as soon as the light is switched off it's fine again. The light is in the opposite side of the house to the radio so its very odd and I would never expect a light globe to cause such interference.

    Thats always the risk of flying just about anywhere but in denser populated areas with lots of people and electronic devices you never know what will cause issues. Upgrading the radio may help sending out a stronger signal but even that can be overpowered by many things you cant see. If the new radio also has telemetry giving info on signal strength it will greatly help avoid such issues so that would be a big help.

    What filters have you got with the polar pro stuff, I had some issues with them and their early uw stuff so I haven't used it but I may get a set of their filters, to compare against my SRP gear.
     
  12. CameraGuy

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    In the flyaway, one of the filters, the 3ND, broke and came out of the holder and had a crack in it. On the 4ND you see in the picture, you must be very careful about making sure the filter is on correctly, or you can get some back reflection. That happened, and Polar Pro admitted it was an issue.

    Over all, I like your solution, but mine is less expensive I think. I bought 3 for $60.00

    Darren
     
  13. careysb

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  14. martcerv

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