$10 optical only back up lens

[andrewwynn]

I added a backup lens. I bought a wide angle fresnel lens meant for a back window of an old school van (with vertical windows). Turns out as was was useless for X5 but after a few hours of trial and error I came across a winning combination.

I cut off the bottom 2-3 inches, and the top 2-3 inches and flipped the top 180° and doubled them up. There was a horrible ghosting effect like looking down a white tunnel until I discovered that ➀ pitching the bottom edge toward me and ➁ curling the sides toward me nearly eliminated the haze.

At first I just taped the lens to my back window. The curl made it ridged and it worked well until heat of course released the adhesive. Also the 3rd stoplight lit up the inside making it useless at night until I fabricated a shade which also helps greatly during the day.

It works a lot better during the day (nearly flawless). I can see the front edge of a car behind me at about 20". Not 4" away like some backup cameras can do but for a simple $6 lens and some creative application its a winner. Onto the photos.


I bent some aluminum "T" track to hold the parts.


I cut some dimpled plastic to be the sun/brake lamp shade, curled up the edge to make it fit into the track.


Drilled holes in the track and punched matching holes in the fresnel lens pieces. I assembled with 3mm screws and nuts. (I hate using non mechanical fasteners in a car opting for screws into metal or solid plastic any time it's possible ) Take note how you can see the scissors in the lens.


Example of how it works: notice the red thermometer in the lens is WAY below on the stool. I didn't measure the deflection angle yet but it's very strong. Maybe 50-60°


Attached to the frame around the window by drill and tap 3mm screws.


Another angle


Trim re-attached. I made notches about 1/8 inch deep and 1" wide to clear the metal of the T channel rather than have the trim flex around it.


Another angle.


Looking out the back. In the lens you can see two yellow spots in the bottom. Those are flags I attached to the corners of my backpack rack. They are barely above my bumper height.


A close up showing the view in the lens and that I can see the corner marker flags.


Finally: this was when I first had it taped on but parking in front of a car. You can barely see the bottom of the windshield of the car behind me but can see the grill of the car in the backup lens. Quite a difference!

I will do some new pics during the day and even a movie I'll also include a link to the fresnel lens I bought off amazon as I will buy a new one to swap in to improve the clarity. I manhandled the ones I have now 100s of times and have scratched them enough to cause some clarity issues.

I love the way it 'just works'; it is right where you need it to be; you can be looking over your shoulder or in the rear view mirror and you see what you need to see. When i back up until i no longer can see the grill of the car behind me I'm about 20" away from the car, a perfect amount of space to comfortably walk behind, open the tailgate etc. An added bonus is that it's extremely wide angle and when backing or driving forward past the sidewalk access you can clearly see when you've cleared it. In addition, the angle is so steep that you see nothing but lane stripes when driving so there is no distraction from following cars (well maybe in chicago or new york you'll have a driver so ludicrously close you might see their grill or front tag).

with the right high-temp tape you can simply curl the piece of lens and tape to the window; the angle of the window works perfectly, and if you are ok with the 'near distance' of about 40" vs 20" you don't have to double-up and you'll get a much clearer (perfectly clear in fact) view.

I want / need to see where my back pack rack is lest i bump into somebody with the thing, and occasionally have to parallel park in chicago, so need a better view of what's back there.

I almost went electronic; for about $50-70 I could put in a 720p camera and 7" monitor; i would put it in the same place i have the lens for the same reasons; power it with the backup light and it comes on in reverse only, but this is so elegant; it's hard to beat 'always works', no power needed and $10.