optical lightning detector

In article <locdql$iqh$1@reader1.panix.com>, Cydrome Leader
<presence@MUNGEpanix.com> wrote:

> I want to concoct a trigger to fire my camera when there's lightning in 
> the area of where the camera is pointed. I do not want one of the RF burst 
> detectors, as I don't care about lightning that's not in front of the 
> camera itself. I'm thinking about some sort of photodiode mounted in a 
> housing peeping through the viewfinder for actual flash detection.
> 
> Past that, I'm not too sure of what's next.
> 
> Has anbody build something like that before? I'd like to somehow be able 
> to tune the detector's sensitivity to the flash or light as well as the 
> risetime of whatever it's detecting.
> 
> I've not yet tested if photographic slave modules actually pick up on 
> ligtning. Has anybody ever tested this?

It strikes me that there are lots of flashes that are not lightning,
and lots of radio impulses that are not lightning either, but the
coincidence of optical and radio may be pretty reliable.  Others had
mentioned that the leaders are dimmer than the return stroke, and I'd
guess that a coincidence detector tuned to microsecond pulses may work,
and one can set the thresholds lower without being swamped with false
alarms.

Joe Gwinn

haiticare2011@gmail.com wrote:
> 
> And the Devil in the Dishwasher here is that thing Dr. Hobbs calls "photon
> budget." No matter what your electronics do, you have to deliver a certain
> amount of photons into the front end. A lens magnifies the photons by the
> ratio of its area to the area of the PD - ideally. BUT - The lightning
> occupies a small part of the sky image that the detector (and the camera)
> "sees." So yes, the lens will magnify the photons from the lightning, but
> the lightning photons are a small part of the "sky image" brought to a
> focus by your lens. And the more you want to narrow the field of view
> down, the less surveillance you can do of the overall sky.
> 

But the point is you don't want to detect lightning in the overall sky. 
Rather, you want to detect lighting in a manner that replicates the field of 
view of the DSLR. That is why I suggest using an old C-mount surveillance 
type camera body and hack it to mount the photodiode in the focal plane. 
Based on the dimensions of the photodiode, you can pick a lens such that it 
sees what the camera sees.

On Sun, 29 Jun 2014 14:34:17 -0700, miso <miso@sushi.com> wrote:

>haiticare2011@gmail.com wrote:
>> 
>> And the Devil in the Dishwasher here is that thing Dr. Hobbs calls "photon
>> budget." No matter what your electronics do, you have to deliver a certain
>> amount of photons into the front end. A lens magnifies the photons by the
>> ratio of its area to the area of the PD - ideally. BUT - The lightning
>> occupies a small part of the sky image that the detector (and the camera)
>> "sees." So yes, the lens will magnify the photons from the lightning, but
>> the lightning photons are a small part of the "sky image" brought to a
>> focus by your lens. And the more you want to narrow the field of view
>> down, the less surveillance you can do of the overall sky.
>> 
>
>But the point is you don't want to detect lightning in the overall sky. 
>Rather, you want to detect lighting in a manner that replicates the field of 
>view of the DSLR. That is why I suggest using an old C-mount surveillance 
>type camera body and hack it to mount the photodiode in the focal plane. 
>Based on the dimensions of the photodiode, you can pick a lens such that it 
>sees what the camera sees.

Allow for multiple exposures.  The strike will be far brighter than
the surrounding landscape anyway.

Den s=F8ndag den 29. juni 2014 23.34.17 UTC+2 skrev miso:
> haiticare2011@gmail.com wrote:
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> > And the Devil in the Dishwasher here is that thing Dr. Hobbs calls "pho=
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> > ratio of its area to the area of the PD - ideally. BUT - The lightning
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> sees what the camera sees.

how about a photo diode mounted on the viewfinder ?

-Lasse

On Tue, 24 Jun 2014 17:51:17 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

>I want to concoct a trigger to fire my camera when there's lightning in 
>the area of where the camera is pointed. I do not want one of the RF burst 
>detectors, as I don't care about lightning that's not in front of the 
>camera itself. I'm thinking about some sort of photodiode mounted in a 
>housing peeping through the viewfinder for actual flash detection.

I suggest you rethink the RF detection method.  Although most of the
energy is in the 10-100KHz range, some detectors run at much higher
frequencies to prevent long range RF falsing.

LIGHTNING DETECTION METHODS AND METEOROLOGICAL APPLICATIONS 
<http://www.atmo.arizona.edu/students/courselinks/spring07/atmo589/articles/Cummins_Poland2000.pdf>

Lightning detector schematics:
<https://www.google.com/search?q=lightning+detector+schematic&tbm=isch>

Lightning detector chip (500 KHz):
<http://www.ams.com/eng/Products/Lightning-Sensor>
<http://www.ams.com/eng/Products/Lightning-Sensor/Franklin-Lightning-Sensor/AS3935>
<http://www.ams.com/eng/Support/Demoboards/Lightning-Sensor/Franklin-Lightning-Sensor/AS3935-Ref-Design>
<http://www.ams.com/eng/Support/Demoboards/Lightning-Sensor/Franklin-Lightning-Sensor/AS3935-Demo-Kit>
<http://www.digikey.com/en/articles/techzone/2013/mar/incoming-storm-a-lightning-detector-from-ams>

Lightning Radar:
<http://members.home.nl/fkooiman/lightning/index.htm>

Wikipedia article on Lightning Detection:
<http://en.wikipedia.org/wiki/Lightning_detection>

Lightning detectors:
<http://www.ambientweather.com/lightning.html>

-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

On Sun, 29 Jun 2014 14:34:17 -0700, miso <miso@sushi.com> wrote:

>But the point is you don't want to detect lightning in the overall sky. 
>Rather, you want to detect lighting in a manner that replicates the field of 
>view of the DSLR. 
>That is why I suggest using an old C-mount surveillance 
>type camera body and hack it to mount the photodiode in the focal plane. 
>Based on the dimensions of the photodiode, you can pick a lens such that it 
>sees what the camera sees.

I beg to differ (as usual).  Two problems.  

The lightning flash tends to be behind the buildings in the
foreground.  Then lightning hits at a distance, all the building are
backlit resulting in a black building.  You can see the effect on many
single frame lightning photos, where the photographer spent much time
with Photoshop trying to increase the contrast on the buildings.  This
is where HDR (high dynamic range) photography really works.  Instead
of a single image, a series of images is taken and added together.
Buildings being to look like buildings and small streamers in the
lightning strike begin to appear.  The trick is to trigger early, and
shoot as many frames as possible.  When to stop shooting is a problem.

Another problem is the field of view.  There is no way you can predict
where in the sky the bolt is going to hit.  It's highly unlikely to
start directly in front of the camera.  More commonly, as in cloud to
cloud strikes, the bolt starts to the side and move horizontally
across the viewing area.  If you trigger on the viewing area, you'll
miss some strikes or get a late start where a partial bolt appears on
the image.  RF detection will pickup bolts behind the camera, which
are rather wasted, digital storage is cheap, and easily accommodated
with the erase function.

Half full disclosure:  In about 1976, I helped a friend in Florida do
some lightning photography.  There's very little lightning in
California, so I had no easy way to test my trigger circuits.  So, I
fired up an old Tesla coil and immediately destroyed most everything
in range.  Hint:  Do not run tests indoors, near hi-fi's, TV's, or
other electro sensitive devices.  I later discovered that any small
spark will work.  Anyway, after 6 months, much fine tuning, and 3
major revisions, it mostly worked.  I ended up with two loops, tuned
to two different frequencies in the beacon band (about 300 KHz)
feeding an AND gates.  If there was noise on both inputs, it's a
lightning hit.  If there was noise on only one input, it's the Navy or
a local navigation beacon.  Separating the two loops as much as
possible reduced falsing from local sparking (auto ignition noise).

Oh-oh, not good:
"First impressions of the AS3935 lightning detector"
<http://fll-freak.com/blog/?cat=28>

-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

On Wed, 25 Jun 2014 04:16:04 +0000 (UTC), gregz <zekor@comcast.net>
wrote:

>I don't know how he does it here, but he seems to mostly take HDR
>photographs.
>http://davedicello.com/2014/06/pittsburgh-lightning-2/
>Greg

He gives a few clues how he does HDR under his "Helpful Hints"
section, but there's nothing there on triggering.  However, the
caption under the 3rd photo says:
   And then it happened.  My favorite picture that I&#4294967295;ve ever 
   taken of the Pittsburgh skyline (the first one in the post).
   I clicked my remote, the shutter opened and BOOM!  It hit.  
   A huge bolt straight down, spidering up.  I couldn&#4294967295;t have 
   asked for a more perfect view of it either. 
So, he's using a wired or wireless remote shutter trigger, and relying
on blind luck and his reaction time to obtain usable photos.

Incidentally, "a huge bolt straight down, spidering up" is not quite
correct.  Lightning bolts start on the ground, and go up.
<https://www.nssl.noaa.gov/education/svrwx101/lightning/faq/>
   Does lightning strike from the sky down, or the ground up?
   The answer is both. Cloud-to-ground lightning comes from the 
   sky down, but the part you see comes from the ground up...

Spoiler:  Average duration of a lightning bolt is about 50
microseconds.  
<http://home.earthlink.net/~jimlux/lfacts.htm>
The optical trigger will need to be fairly fast in order to catch that
image with a 1/1000 (1 msec) shutter speed.  About the only way to do
that is to anticipate the strike.  I couldn't find a design for a
negative time delay circuit, so that's unlikely.  What seemed to be
happening with my RF trigger was that the lightning was arriving in a
series of 2 to 5 strikes.  The camera would miss the first few
strikes, but pickup on the later ones.  I was scratching my cranium
for quite a while trying to determine why there were so many blank
photos.




-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Lasse Langwadt Christensen wrote:

> how about a photo diode mounted on the viewfinder ?
> 
> -Lasse

No viewfinder when you lock the mirror. You lock the mirror to reduce the 
lag.

Jeff Liebermann wrote:

> 

> Another problem is the field of view.  There is no way you can predict
> where in the sky the bolt is going to hit.  It's highly unlikely to
> start directly in front of the camera.  

Actually you frame the shot, then hope for lightning. That is, if you are 
trying to do serious photography rather than just lightning photography.

Can you predict where lightning will appear? Well probably not in Chicago, 
but no problem in the desert. If there is virga, that is where the lightning 
will happen.

> http://www.stormeyes.org/tornado/SkyPix/ftsumner.htm

Photos of virga don't do it justice. When you are in the desert, the virga 
is very easy to spot.

Jeff Liebermann wrote:
> 
> Spoiler:  Average duration of a lightning bolt is about 50
> microseconds.
> 
Go back and look at your link. That is text lifted from Uman's book. The 
full stroke will be 100ms on up.

Time duration of flash 	0.2 sec