Graduated ND filter hack for the mobius

Johannes

Johannes

New Member
Joined
Jan 12, 2015
Messages
6
Reaction score
13
Location
France
Country
France
Hi.
I am new on this forum. I own a Mobius cam and I wanted to share a small video I made to explain how to simulate a graduated ND filter for no cost. This can be very usefull for dashcam users because very often, when the car is facing the sun and the sky is cloudy, the camera will darken the image and you can't record what hapens on the road. This hack won't 100% fix the issue but will help.

 
Last edited:
Fun, very interesting idea there graduated filtering.

Nice computer voice by the way, what program did you use for the audio track?
 
I use the software TextAloud. But what makes the voice acceptable is the use of voices sets that I bought a few years ago.
This one is Ryan from Acapela http://www.nextup.com/acapela.html . They are not cheap but ... when I speak english myself with my french accent, most people don't understand half of what I am saying ;)
 
Will have to try this on the SJ4000, since a right sky messes up the exposure whe using it as an action cam
 
This trick should work on every dashcam but will not be as effective as the focal length is shorter, that means larger field fo view. The graduated effect is due to the blur of the black tape sticked on the lens. Short focal lenses have larger depth of field and the blur effect will be smaler. On the Mobius with lens A, the graduated effect covers about 1/4 of the image surface. With a shorter lens this may reduce to 10%.
 
I don't wish to sound like a spoil-sport, but I decided after reading this thread yesterday to post my thoughts about the idea so that anyone thinking of trying this goes into it with their eyes wide open. I think this is a clever idea and certainly a worthwhile experiment but I think it has some potential drawbacks.

The main issue is that masking off very nearly one half of the lens is literally preventing the lens from collecting the full amount of light it is capable of transmitting to the sensor. So, while it may be effective for balancing the exposure and dynamic range of the image in bright, high contrast settings, the laws of physics/optics suggest that in low light situations, such as at night, the compromised performance of the lens's ability to collect light will come into play and render poor or unacceptable image quality.

Another potential issue is the integrity of the lens itself. The electro-chemically applied anti-reflective multi-coatings on these lenses are quite delicate. (This is the purple/blue/greenish tint you see on the front surface of the lens, like in my avatar.) The longer you leave electrical tape on the lens, the more the adhesive on the surface of the lens is likely to damage the layers of multi-coating and the tape will also be more difficult to remove at some future date and this too will further risk damage from any attempt to clean the lens.
 
Last edited:
tried it on my gt680w ..

I was able to get the marked picture improvement as shown on the video in daylight... not tested it in motion in a car

remains to be seen what night vision is like.
 
The trick won't bring any improvement at night. As said by Dashmellow, the performance at night will be dramatically decreased. I also agree with the coating. I won't let the adhesive on the lens all the time.
I may try to 3d print a custom lenscap with this feature.
 
I accomplish a similar "neutral density filter" effect in a different manner. My vehicle has a dark tinted, approximately 5 inch wide strip along the top of my windscreen. By carefully mounting whatever dash cam I happen to be using at any given time so that a portion of the tinted strip is captured by the camera's FOV along the top of the image, it masks the sky in a similar fashion and provides for a more balanced exposure with a bright sky. The tint on the windscreen is blue, so it has the effect of making the sky look an unnaturally dark shade of blue, but I find this to be a worthwhile trade-off. Nighttime performance is unaffected and of course, I don't have to alter the camera in any way. The other benefit of this is that the mount for the camera is placed behind (on) the tinted strip and this completely prevents the mount from being seen from outside the vehicle and this also partially obscures the camera itself and makes it much more stealthy than it otherwise might be.

I wish I had a better example to post at the moment but this screenshot will demonstrate the effect I get.

tinted.jpg
 
Last edited:
~ 10-degree down angle right under the rearview mirror with WDR on ...

 
I think if someone will be willing to make it just "plug and play" similar to DSLR ND or CPL filters, lot of people would be very happy to pay real money to that person !!!
 
I would still prefer the polarized filter then ND, i am using Mobius as onboard camera, and if i will enter the woods, or bigger shadow, i'l l get dark image :(
 
ND filter will darken the whole picture and has no use for dashcams.
Polarized filter will remove dashboard reflection in the winshield but will not help to darken the sky.
 
An alternative would be to buy a replacement lens cap and cut out the bottom area. It won't have quite the same smooth effect, as you point out, but may be usable.
To avoid spoiling night performance just place the dividing line higher up. Look into the lens directly from the front. As long as you can still see the entire circle of the inner lens elements, you know forward performance will be OK.

Until now I've had my dash cam pointing down to prevent bad exposure caused by the sky. I briefly adjusted it back to horizontal because I got tired of seeing too much bonnet in the shots. But I quickly decided to point it down again as the exposure was bad too often.

I had been thinking of using a shield to block out the sky, even if it caused a black bar at the top (hey it might even free up some bitrate to be used for the more useful image areas!) But achieving a graduated ND effect is a better idea.
 
You must log in or register to reply here.
Back
Top