Anyone experimented with a ND filter for a GoPro? Maybe a small piece of window tint or something? It could be useful since we all use them outside...

you can get them at eyeofmine.com

,,,as well as a killer underwater flat port adapter to sharpen up the submerged video.

yeah I tried some underwater stuff with the normal housing and it looked awful..so after I was thru freaking out I read about the flat port housing and got one, makes all the diff..

The GoPro really cries out for ND when used in sunlight. To avoid diffraction the iris stops closing at about f/5.6 and from that point on the shutter speed increases. Increases to such an extent that frames taken from a cross-country trip on my bike are all pin sharp, and the wheel spokes show only the tiniest amount of image blur. The jello effect also means the spokes are all shown bent, but that's another story.

Of course this very high shutter speed (I estimate it at 1/750th sec, something like that) gives the footage an incredibly staccato look - which, when added to the non stabilised image - does look a bit crazy. Mercalli helps on the stabilisation timeline though.

tom.

There is no iris, the exposure is controlled by shutter and gain.

Take some stills with the GoPro Ian, pull them into Photoshop or Picasa and look at the detailed info. You'll see the camera uses all sorts of different apertures. Or are you saying these are extrapolated from internal (and undocumented) ND filters?

tom.

If you pull the GoPro apart Tom, you'll find there is no physical aperture in the lens. Video exposure is controlled by shutter and sensor gain. The Gopro aperture is fixed at f/2.8, that why it has an almost infinite depth of field. Everything is in focus in any light.

The EXIF data is usually reported incorrectly, most programs interpret it as f3.61 regardless of lighting conditions.

See this sample photo, the aperture is being reported as f/492.2 ......... yep f/492.2

Exif | GoPro Flight by GoPro Photos | Flickr - Photo Sharing! (http://www.flickr.com/photos/gopro_photos/5475023464/meta/)

If you add an ND filter, all it will do is slow down the shutter speed and then if the GoPro senses it requires more light. it wall crank up gain. It reaches a point eventually where the shutter is too slow and then the noise makes the video unusable.

If you know otherwise please educate me, but even GoPro resellers like the above quoted "Eye of Mine" reseller GoPro HD Hero for Professionals - EyeOfMine Multimedia (http://www.eyeofmine.com/gopro/hd/prof/index.html) on this page under EXPOSURE, quotes ""It is fully-automatic. The lens aperture is fixed - you get one big T-stop:) Because the lens is fixed, the only other variable is shutter speed which obviously can cause issues in bright daylight with stuttering because of fast shutter speeds. ""

This is why we have been nagging GoPro for a firmware upgrade to enable Exposure or Shutter Lock and it is coming in the next model.

Cheers Ian
BTW run this GoPro user forum, heaps of info there about everything to do with GoPro and projects.You're welcome to join us.
GoProUser.freeforums.org (http://goprouser.freeforums.org)

'fixed at f/2.8, that why it has an almost infinite depth of field' you say, but considering the small chip size and the very short focal length used, then once the hyperfocal has been set up the aperture makes very little difference to the dof in reality, just allowing (should you have the option to stop down some) for slightly closer focusing.

tom.

Focus from about 12inches to infinity regardless of light, pretty much fool proof focus wise.

, but considering the small chip size
tom.

1/2" sensor is not really small considering the size of the GoPro.

I haven't played with the ND much but I did add a polarizer and it makes a lot of difference.

From another forum:
'The idea was to mount a threaded upsize ring to a case permanently, without vignetting.

I used a method that I found on the board and took a 40.5 to 58mm Fotodiox ring and tried it with a 58mm circular polarizer and just held it in place. Worked fine with no vignetting but the shutter surround was in the way. I milled a tad off of the surround so the ring cleared and epoxied the upsize ring to the bezel.

Perfect fit except the bubble was higher than the top of the ring so I ordered a spacer ring from Fotodiox today as well as a 58 to 77mm ring. It looks like the spacer will just clear the top of the shutter button and that will let me add the 77 mm ring.

All my better filters are 77 mm so it would be nice if I cane use them with the go pro too. The big question will be if the added ring height will vignette.

I'll have the spacer and ring in a couple of days and will post the results."

http://i198.photobucket.com/albums/aa57/peternap/c1-2.jpg?t=1301879828

http://i198.photobucket.com/albums/aa57/peternap/c2-3.jpg?t=1301880361

http://i198.photobucket.com/albums/aa57/peternap/c3-2.jpg?t=1301880600

I did this test about 12 months ago, there is a slight increase in contrast with a polarizer and it does reduce highlights a bit, but a variable ND just introduces too much noise once you approach the point where the shutter speed is low enough to allow a nice motion blur.

I used a lineal polarizer in the example below, so i had to rotate it to get the effect, a circular polarizer won't need as much rotation.

Gopro with Polarizer on Vimeo

Hi Ian,
the CMOS chip (complete with masses of jello-wobble) is listed as a 1/2.5'', so exactly mid way between the 1/3'' (say Sony Z5) and ½'' (say EX1-R) chips. Small for any camera, but huge in a body the size of a GoPro.

Interesting your thoughts on the vari-ND introducing noise as the gain-up point is reached, a point we'll never be told about presumably. But the very high shutter speeds in sunlight sure spoil motion footage in my view, and motion blur (as shown in your MB3 video) definitely helps the impression of speed.

Next point - a polarisor shouldn't reduce highlights. It is after all simply an ND for wavelengths in one direction only.

tom.

Yes you're right 1/2.5" that was a typo, still big for a GoPro as we agree.

In keep telling the guy's on my forum the Polarizer won't reduce the blown highlights in Snow and theoretically it shouldn't, but if you watch my test above carefully, the Polarizer when rotated does reduce the blown white clouds just above the horizon and the waveform monitor in Sony Vegas confirms it. It has me stumped, but hey if it works, it works. But it is hard to dial in for sports use where conditions are changing constantly as they do when you use a POV Cam.

Please suggest an ND filter density for the following: I need to blur the prop on an airplane. The prop is 72 inches in diameter and rotation speed varies from 1500-2600 RPM. I get rolling shutter artifacts with no ND filter on a sunny day. Camera is a GoPro Hero HD.

We have had success with as little as ND 1.2, i just depends on the amount of light on the day. But reducing the shutter below 1/250 should do the trick.

Thanks Ian.

Jim, your rolling shutter artifacts will be there regardless of the shutter speed the GoPro uses. ND will only reduce the shutter speed, and by introducing motion blur will reduce the staccato.effect of the GoPro's high shutter speeds in sunlight.

I don't think Jim is talking about jello wobble, he specifically mentions the effect rolling shutter has on the prop. However, if you are also suffering jello wobble, shoot in 50/60fps to reduce jello by about half of the 30/25fps modes.

This is a very interesting experiment one of our members did with regard to jello, we determined in the end the reduction/elimination was mostly due to the added mass/weight of the adapter and ND filter. However, the ND does seem to have some effect also.

GoPro Jello fix - R5 mode on Vimeo

How's this for an ND or filter solution as well as an antifog solution and a flat lens fix.

BlurFix GoPro Adapter Independant Review on Vimeo

Here's the full review i did.

This single Product fixes 3 common issues with the GoPro HD Camera
1. The underwater focus
2. Inability to attach filters
3. Fogging

http://img708.imageshack.us/img708/5324/blurfiximage.jpg

I found the adapter and filter very easy to install, taking no longer than 10mins, just follow the well written and pictorial instructions included. (See Video below)
I was very impressed with the build quality, the BlurFix is machined from a single piece of Aluminum billet and is Anodized to prevent reflections.
The two most popular modes R3 720 and R5 1080 show no signs of vignette, however if your GoPro camera is not perfectly aligned within the case you may see a small vignette on one side in R3 mode, simply ensure your camera is seated correctly. My one year old camera had a slot worn in it where it had vibrated against the case locating lugs at some point, so needed the wear slot fixed, my newer cameras had no issues. There is vignette in R4 960 mode, but it's not a mode most people use underwater. The high quality filter that came with the BlurFix has the outer threads machined off to make it low profile, so stacking filters is not possible, but you have the option of changing the filter to say a CY filter, polarized etc. If want to use your own filters, they must also be low profile. Or there is a range of quality low profile filters available from BlurFix.

The video below confirms underwater sharpness is now optimal and you have the option to remove the filter for above water shooing if required and leave the adapter in place. I tested the unit to 50ft over 1 hour with a line and anchor and it remained completely watertight. I have no reason the believe it won't go lower, the manufacturer has tested to 130ft.

I found the anti fogging beads worked perfectly, not once did i see any fogging and i assembled the GoPro and filter in midday 22 degree, 65% humidity conditions. For comparison i also had an unmodified GoPro accompany the test unit and it fogged. Be aware though, you must ensure the O ring, adapter and filter is free of any water/sweat inside the cavity for the beads to do their job of absorbing moisture in the air.

Pros and Cons

Pros

Easy to fit
Glass not Plastic
Precision made from solid billet (one piece)
The flat black anodizing eliminates reflections
Original case dome lens remains intact so does your main case waterproofing.
Can be fitted with most 55mm filters (polarized, ND, UV, Grad etc)
No Fogging - replaceable desiccant beads
Completely fixes the focus issue in 720 and 1080 modes (no vignette)
Does not interfere with camera operation - buttons etc.
Optimal focus in or out of the water
Can be used above water with no vignetting in all modes (including R4 960 and stills) when filter and o-ring are removed (adapter stays)


Cons

Requires assembly (application of silicon)
Will require maintenance to prevent filter threads from sticking (lube)
Overall Slightly more added weight.
Slight vignette in Stills mode and R4


Highly recommended for the following uses

Underwater Video and Stills
Canoes and Kayaks for the anti fogging attributes and water droplet repelling flat lens.
Airplanes or situations where an ND, polarizing filter or other filters are required.
Shutter speed control.
You could get very creative with Graduated ND filters, especially in Snow or Timelapse videos.


You could use it for motorsports as long as you're aware the filter glass may break if hit hard enough.

I have not been paid for this review, the supplier simply shipped me a single product unit to independently review.

I just tried one of the above mounts for 55mm lens, and used some Tiffen ND's. Was VERY disappointed in the image quality. It lost tons of sharpness without fixing much of the blowouts. Returning ND's now. It is nice to use underwater with a clear UV, but I had high hopes for the ND fixing a lot of issues. Jello is not a concern, so .... damn.

Yes the ND's on the GoPro do nothing to fix blown highlights, actualyl i've found they blow the highs even more. There is too much dark foreground in that image for yhe GoPro to handle bright sky. Grad ND's do work ok though but are expensive. Funny but a polarizer actually works better than an ND, but i suspect that may be due to the coloring more than the polarizing effect..