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Thread: Night Driving

  1. #11
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Re: Night Driving

    OK, its been a while since my last post, so here is the latest update.

    I went ahead and permanently fitted the 4-stop neutral density film, and while I was in the camera housing I removed the IR LED board. I also took the opportunity to replace the camera board screws with longer items, because the increased focal length of my narrow FOV lens and standoffs for clearance meant the original screws could barely bite. I've been driving the car like this for the whole of this season and there has been some improvement in the night driving, but in high contrast conditions (e.g. unlit sections of motorway with several lanes of traffic behind) it is still very difficult to distinguish individual headlights and judge distance and approach speeds... meaning that often as not I remain confined to the inside lane behind a lorry

    You can see how much glare continues to be generated by the monitor in Nova Night Drive II, ironically also captured on the return trip from Exeter. However, please note that the Mini-DVR has much better low-light sensitivity, so what looks like a searchlight in the dash is actually not that bright

    http://www.youtube.com/watch?v=9qvLt_5GbKA

    Much of the glare is just generated by the camera with no ambient light in the FOV, indicating that I need to stop down the iris even more.

    Unfortunately I did not have any more neutral density filter film, but I have got a roll of deep smoke window tint film, so I decided to experiment with that. Amazingly, I now have the neutral density film, plus two layers of window tint film over the camera lens, and the auto-iris is completely unaffected in daytime driving. I have not used this set-up in anger for night driving yet, but completely covering the camera lens now results in a deep grey screen instead of a snowy white one, so I am hoping that I have stopped the iris down enough this time.

    Frankly, its quite amazing - I can barely distinguish any detail looking though the cover glass with my own eyes - its not far short of the tint in my welding mask!

    I will post further observations (possibly some more video) once I've been on a few more night drives. I'm fast closing in on the optimum CCD configuration now

    Lauren
    only Pythagoras can save me now!

  2. #12

    Re: Night Driving

    I have looked at the comparisons with CCD reversing cameras, the bumf that is on most web sites including actual film and screen shots does show a vast improvment. As I have fried my camera which was a cmos, I will on my return invest in a ccd camera and list my results.
    http://jimsnova.page.tl/
    Club Nova / avante membership 031

  3. #13
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Re: Night Driving

    There's certainly no disputing CCD produces a sharper image than CMOS, but I believe that CCD also has better low-light capability, which might be a hindrance rather than a help if, like me, you use the telecam all the time for rear vision.

    The other interesting observation I have made running with the neutral density filter is that with less of the visible light spectrum entering the camera, the daytime image is shifting into the infra-red, so that (in my B&W monitor) grass appears to be as bright as fresh snow! It doesn't seem to have got any worse after putting the smoke tint film in, so it should be OK for me, but I'm not sure what it would look like in a colour monitor! Could be quite strange!!

    Lauren
    only Pythagoras can save me now!

  4. #14
    ***Euro-Nova Supporter*** Spacenut's Avatar
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    Re: Night Driving

    OK, a quick update. New filters in place and I was out in the dark on Friday. The new set-up makes very little difference to the night driving experience, and now I know why - the neutral density filters stop down the visible light spectrum, but make virtually no difference in the IR region of the spectrum, which is where the majority of car headlamps are working. Hence the glare. Yesterday I set up an inspection lamp on my bicycle, parked behind the car and facing the camera. Extra layers of neutral density film over the lens (to go with the three layers already in the camera), made no difference; the CCD merely winds up the gain to compensate, and the glare is as bad as ever.

    In an attempt to reduce the energy at the red end of the spectrum (around 750 nm) I tried some blue tinted film over the lens, and this did seem to make more of a difference than the neutral density film, although not really enough to warrant taking the camera apart again.

    Doing some searching on the Interweb I find that most DSLR cameras (which use a CCD imager with the same IR sensitivity) use a dichroic filter, a so-called "hot mirror" to reflect the IR portion of the spectrum before it reaches the CCD imager. Otherwise the resulting pictures would look very strange indeed!

    So ideally I need one of these dichroic elements over my CCD to allow just the visible light spectrum through, which I can then control with neutral density filters. Unfortunately, hot mirrors are precision optical devices, are usually around 52mm in diameter and made of glass - and cost a fortune. A possible cheaper solution may be the solar control film applied to domestic glazing to reduce heating due to IR transmission, but I don't know how effective it is when used with CCD imagers, and a roll of the stuff is probably as expensive as a dichroic lens

    So I will probably have to live with the headlamp glare for a while longer yet!

    Lauren
    only Pythagoras can save me now!

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