optical lightning detector

Cydrome Leader wrote:

 
> this might be ok out in the country, but 20s exposures are going to pick
> up too might stray light in a major city.
> 
> It may be possible to set a super low ISO in the camera and use a super
> dark ND filter to attentuate the garbage light, but for the hell of it, I
> want an electronic solution vs. brute force. I've not found a screen cap
> from an oscilliscope of the light intensity of a lightning flash as
> measured by a photodiots. This would be interesting to see.

Note that for most cameras, video mode is not the same resolution as when it 
shoots stills. I mean, you could shoot lightning with a gopro, but the still 
frame wouldn't be epic.

Stray light may not be the problem you think it is. I've done star trail 
photos in the high desert with no moon. There isn't enough stray light to 
illuminate the object that you want to combine with the star trails. 

But you will need ND in the city. The other thing to consider is lens flare. 
If you stop the lens too much, you see the iris in the flare. That is why ND 
are important. You can learn a lot about the flare of the lens by shooting 
the full moon in various locations in the frame and at different f stops. 
Stating the obvious here, you want a prime lens.

miso <miso@sushi.com> wrote:
> Cydrome Leader wrote:
> 
> 
>> 
>> the camera has shutter lag of 40ms or less, so it won't be too slow.
>> Lightning really isn't all that fast, I just want an electronic trigger
>> system that only triggers the camera when a flash of light of the correct
>> speed and intensity appears. It's fairly bright in Chicago so long
>> exposures when you're inside a storm mostly pickup reflected light from
>> the city itself, which is an ugly orange color. Yeah one could use blue
>> filter and all that, but it's still very bright.
> 
> 
> Are you sure that 40ms isnt that "trigger button halfway down" mode? Most 
> cameras are in a sleep mode when just sitting there in manual. The link on 
> this Mk III shows this (model specific of course). 

It's a nikon d3s, so it's the league of fastest cameras out there.

> The stepped leader has a number of 1us pulses. That is what you would want 
> to trigger on. There is a very high frame rate video of a lighting strike on 
> the internet, but I can't find it at the moment. Too many false hits on 
> google. The stepped leader is not as bright, but the very short duration 
> steps would make for a good trigger, giving you some advance notice before 
> the return strike hits. The video wasn't on youtube, but hosted on the 
> authors website. I snagged a copy of it with a little hacking, but I need to 
> locate the file.

I'm under the impression the return strike or whatever it's called is the 
brightest one, so there is no loss having a small amount of lag.

miso <miso@sushi.com> wrote:
> Cydrome Leader wrote:
> 
> 
>> this might be ok out in the country, but 20s exposures are going to pick
>> up too might stray light in a major city.
>> 
>> It may be possible to set a super low ISO in the camera and use a super
>> dark ND filter to attentuate the garbage light, but for the hell of it, I
>> want an electronic solution vs. brute force. I've not found a screen cap
>> from an oscilliscope of the light intensity of a lightning flash as
>> measured by a photodiots. This would be interesting to see.
> 
> Note that for most cameras, video mode is not the same resolution as when it 
> shoots stills. I mean, you could shoot lightning with a gopro, but the still 
> frame wouldn't be epic.
> 
> Stray light may not be the problem you think it is. I've done star trail 
> photos in the high desert with no moon. There isn't enough stray light to 
> illuminate the object that you want to combine with the star trails. 
> 
> But you will need ND in the city. The other thing to consider is lens flare. 
> If you stop the lens too much, you see the iris in the flare. That is why ND 
> are important. You can learn a lot about the flare of the lens by shooting 
> the full moon in various locations in the frame and at different f stops. 
> Stating the obvious here, you want a prime lens.

I never though about using the moon for a flare test, but streets lights 
are for me the the "test".

Wide angle lense seem to suffer from more flare where you see weird 
artifacts because of internal reflections from what I've seen, and a 
filter, even a good clear super ultra multi coated whatever ones compounds 
this on the WA lenses. Bright daylight from clouds tends to make telephoto 
lenses lose contrast as they seem to pick up a "glow" or sorts with no 
defined shape- it's just that the shadows seem too bright.

Anyway, for the lightning project the lense choice would be a manual focus 
prime.

This all started when I finally came across a breakout type cable that 
let's you control a nikon SLR (film or digital) with 3 banana plugs that 
essentially give you access to the shutter button, but electronically.

On Friday, June 27, 2014 1:32:57 AM UTC-4, Cydrome Leader wrote:
> miso <miso@sushi.com> wrote:
> 
> > Cydrome Leader wrote:
> 
> > 
> 
> > 
> 
> >> this might be ok out in the country, but 20s exposures are going to pick
> 
> >> up too might stray light in a major city.
> 
> >> 
> 
> >> It may be possible to set a super low ISO in the camera and use a super
> 
> >> dark ND filter to attentuate the garbage light, but for the hell of it, I
> 
> >> want an electronic solution vs. brute force. I've not found a screen cap
> 
> >> from an oscilliscope of the light intensity of a lightning flash as
> 
> >> measured by a photodiots. This would be interesting to see.
> 
> > 
> 
> > Note that for most cameras, video mode is not the same resolution as when it 
> 
> > shoots stills. I mean, you could shoot lightning with a gopro, but the still 
> 
> > frame wouldn't be epic.
> 
> > 
> 
> > Stray light may not be the problem you think it is. I've done star trail 
> 
> > photos in the high desert with no moon. There isn't enough stray light to 
> 
> > illuminate the object that you want to combine with the star trails. 
> 
> > 
> 
> > But you will need ND in the city. The other thing to consider is lens flare. 
> 
> > If you stop the lens too much, you see the iris in the flare. That is why ND 
> 
> > are important. You can learn a lot about the flare of the lens by shooting 
> 
> > the full moon in various locations in the frame and at different f stops. 
> 
> > Stating the obvious here, you want a prime lens.
> 
> 
> 
> I never though about using the moon for a flare test, but streets lights 
> 
> are for me the the "test".
> 
> 
> 
> Wide angle lense seem to suffer from more flare where you see weird 
> 
> artifacts because of internal reflections from what I've seen, and a 
> 
> filter, even a good clear super ultra multi coated whatever ones compounds 
> 
> this on the WA lenses. Bright daylight from clouds tends to make telephoto 
> 
> lenses lose contrast as they seem to pick up a "glow" or sorts with no 
> 
> defined shape- it's just that the shadows seem too bright.
> 
> 
> 
> Anyway, for the lightning project the lense choice would be a manual focus 
> 
> prime.
> 
> 
> 
> This all started when I finally came across a breakout type cable that 
> 
> let's you control a nikon SLR (film or digital) with 3 banana plugs that 
> 
> essentially give you access to the shutter button, but electronically.

Hw many mpix does it have? I have the Nikon D700 and a 10-24 wide angle, if 
I remember. 

Are you ready to make this gizmo? I can give you product #'s for the 
Phtotodiode amplifier...You will have to be realistic about light gathering 
power of PD - What Phil Hobbs calls "photon budget." As I see it, the photon 
problem is to detect flashes on the horizon which don't really give much 
illumination. IE, if the lightning is a few miles away, is it giving you enough 
photons to detect?

I am skeptical - but as a crude test, I'd want to be able to hold up a sheet of 
paper and see the flash on it by eye. I think some close lightning will easily 
do that, but as you know, intensity falls off as inverse square. 

Detecting lightning say 5 miles away is a challenge. I'd consider a light-
gathering mirror or lens. Like a magnifying glass. Harbor Freight has 
magnifying desk lights with lenses about 5 inch dia. You can buy the lens from 
them as a replacement for $10. I would consider putting the photodiode in the 
focal point of that - probably about 12 inches. I believe that will give you 
light gathering increase, but the lightning is very narrow, so the PD may miss 
it completely. In other words, you may narrow your focus (field of view) onto a 
certain part of the sky, but then you may miss it completely. Or you may use a 
wide angle lens, but then the PD won't see the lightning because it is too 
small to cover the sky image.

I would consider the following modification of the lens: at the focal point, or 
just in front of it, put a reflective cone narrowing down to the size of the PD 
- about 4 mm dia. A flashlight reflector with PD at it's FP? The point is to 
throw away image quality and get into photon gathering mode...

Phil Hobbs may have some ingenious solution here. I'd suggest a imaging 
solution with SW pattern detection, but that would be too slow... I'm not
 having an "Aha!" moment over this. I'm pretty sure this is a problem where our 
eyes can do better than simple technology. What our eyes are doing is to 
parallel process all the pixels in the retina...The 192 core Nvidia chip that 
Google is using in it's tablet technology is the closest thing I know of...

On Wed, 25 Jun 2014 16:46:55 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

>haiticare2011@gmail.com wrote:
>> On Tuesday, June 24, 2014 6:46:25 PM UTC-4, the rain in spain. wrote:
>>> Buy one of the consumer digital cameras that has a SDK. Set it to =
record video for 20-30 seconds at a time, and wait for a input from your =
flash detector via serial or USB. If there was a flash, save or download =
the video. If not, start recording again.
>>>=20
>>>=20
>>>=20
>>> Steve
>>=20
>> Yes, that's clever. An even simpler way is to not use a detector. Do =
time lapse=20
>> photography every night, each 20 s. long, and if a thunderstorm =
happens, review=20
>> your photos. If not, erase the photos. (total chip erase.)
>>=20
>> simple. easy.
>
>this might be ok out in the country, but 20s exposures are going to pick=
=20
>up too might stray light in a major city.
>
>It may be possible to set a super low ISO in the camera and use a super=20
>dark ND filter to attentuate the garbage light, but for the hell of it, =
I=20
>want an electronic solution vs. brute force. I've not found a screen cap=
=20
>from an oscilliscope of the light intensity of a lightning flash as=20
>measured by a photodiots. This would be interesting to see.
>

It is really not all that hard to filter out the HPS street lighting. =
They
have filters specifically for that.  Do not confuse them with LPS filters
though.

?-)
=20

Cydrome Leader wrote:

> miso <miso@sushi.com> wrote:
>> Cydrome Leader wrote:
>> 
>> 
>>> 
>>> the camera has shutter lag of 40ms or less, so it won't be too slow.
>>> Lightning really isn't all that fast, I just want an electronic trigger
>>> system that only triggers the camera when a flash of light of the
>>> correct speed and intensity appears. It's fairly bright in Chicago so
>>> long exposures when you're inside a storm mostly pickup reflected light
>>> from the city itself, which is an ugly orange color. Yeah one could use
>>> blue filter and all that, but it's still very bright.
>> 
>> 
>> Are you sure that 40ms isnt that "trigger button halfway down" mode? Most
>> cameras are in a sleep mode when just sitting there in manual. The link
>> on this Mk III shows this (model specific of course).
> 
> It's a nikon d3s, so it's the league of fastest cameras out there.
> 
>> The stepped leader has a number of 1us pulses. That is what you would
>> want to trigger on. There is a very high frame rate video of a lighting
>> strike on the internet, but I can't find it at the moment. Too many false
>> hits on google. The stepped leader is not as bright, but the very short
>> duration steps would make for a good trigger, giving you some advance
>> notice before the return strike hits. The video wasn't on youtube, but
>> hosted on the authors website. I snagged a copy of it with a little
>> hacking, but I need to locate the file.
> 
> I'm under the impression the return strike or whatever it's called is the
> brightest one, so there is no loss having a small amount of lag.

The return strike is the big deal, but what you want to do is detect the 
stepped leader. The stepped leader can be flicking for 10 to 30ms before the 
return strike hits. Ideally you would open the shutter within 10ms of 
detecting the stepped leader. If you researching this a bit further, this 
has been done using external shutters in front of "stock" cameras in bulb 
mode.

There is much research on the stepped leader since disturbing the stepped 
leader is a means of preventing lightning.

This paper covers the spectrum of the stepped leader if you want to enhance 
your set up.
> http://onlinelibrary.wiley.com/doi/10.1029/2011JD015663/pdf

The paper you should really have is "Spectrum of the Lightning Stepped 
Leader" by Richard E. Orville. (Journal of Geophysical Research, Vol 73, No 
22, November 15, 1968.) 

If you read research papers on lightning, there are a small number of names 
that keep cropping up. Uman or course, but Orville is another.

There is a video by Tom A. Warner online that uses a high speed CCD camera. 
THe last Adobe flash update screwed up my linux desktop machine, and many of 
Tom Warner's videos don't play. When you find it, it will not be eye candy. 
It is scientific imaging. I have a still from it and it read "Fri Jul 10 
2009" on the lower third. You can watch the stepped leader build.

There is something odd about the shutter lag testing on the D3s. For 
instance, it is 47ms in the manual focus mode.
> http://www.imaging-resource.com/PRODS/D3/D3A6.HTM
The reason this looks odd is the time is nearly the same as the "button 
halfway down mode" of 43ms. 

I would think your first project would be to measure the lag time yourself. 
You want to measure the time with manual focus and the mirror locked. On the 
Canon remotes, you can make it look like the camera button is halfway down, 
so I assume Nikon can do the same thing. That gets around the wake up time. 
However Canon has a limit on how long you can sit with the mirror locked. It 
isn't much, like maybe a minute or two. There are hacks around that since 
the "Magic Lantern" crowd have reversed engineered EOS.
> http://www.magiclantern.fm/

For the shutter lag test, I'm guessing you would have two rows of LEDs that 
the camera would photograph. One row counts in a thermometer code. The other 
acts as an accumulator, also in thermometer mode. 

For this scheme to work, you would need a lens in front of the photo diode. 
The effective field of view of the lens as it projects on the diode should 
match that of the camera. This is to say, the photo diode seems what the 
camera see.

But the optics don't have to be very good. You can use a cheesy C-mount zoom 
lens. A busted C-mount CCD surveillance camera will provide the body. That 
is, you just gut the surveillance camera electronics, just taking advantage 
of the light tight box and the mechanics to mount the lens. 

Note Nikon has a motion sensing mode. It may be possible that you just leave 
the camera in motion sensing mode and the lightning flash will trigger it. 
But you will be catching the later flashes since the live view isn't 
particularly fast.

If you do a patent search, there are lightning detection schemes using pulse 
transformers rather than AC coupling the photodiode. Remember, you need to 
reject all the ambient light and just catch the flash. 

An AM radio detuned to a open channel will do a nice job of detecting lightning. This is  basic the principal of the aircraft lighting warning systems such as "Stormscope".  Stormscope patents are worth looking at.

 If I had to detect this optically I'd use a small area, fast response photodiode and look for the AC coupled spike.

Google "personal lightning detector"
Steve 

On Saturday, June 28, 2014 4:34:51 AM UTC-4, miso wrote:
> For this scheme to work, you would need a lens in front of the photo diode. 
> 
> The effective field of view of the lens as it projects on the diode should 
> 
> match that of the camera. This is to say, the photo diode seems what the 
> 
> camera see.
> 
> 
> 
> But the optics don't have to be very good. You can use a cheesy C-mount zoom 
> 
> lens. A busted C-mount CCD surveillance camera will provide the body. That 
> 
> is, you just gut the surveillance camera electronics, just taking advantage 
> 
> of the light tight box and the mechanics to mount the lens. 
> 
> 
> 
> Note Nikon has a motion sensing mode. It may be possible that you just leave 
> 
> the camera in motion sensing mode and the lightning flash will trigger it. 
> 
> But you will be catching the later flashes since the live view isn't 
> 
> particularly fast.
> 
> 
> 
> If you do a patent search, there are lightning detection schemes using pulse 
> 
> transformers rather than AC coupling the photodiode. Remember, you need to 
> 
> reject all the ambient light and just catch the flash.

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. 

You see, we take for granted what our eye-brain easily does. Our system can 
zoom down onto a few retina pixels where we see a lightning flash in the midst 
of a large darker sky. 

I tried to help matters by putting a concentrator at the focal point. Another 
trick is to use an array of say 4 photodiodes and detect a differential between
them, in an effort to catch the sliver of light.

If you look at the engineering reality of a PD detector, what you get is 
simplicity and speed. The area of a bwp34 PD, is about 3x3 mm. Compare that to 
the pixel size of a CCD - say 5x5 microns. 10 mm2 / 25 microns2 abt= 
10exp6/25 = 40,000X. That 40K ratio is the rub. The PD wants its area lit up 
with photons, but a CCD pixel has an SNR 40,000X better right out of the gate. 

And I believe this approximate figuring becomes operational when the lightning 
is farther away than several miles. Just as you will have trouble detecting 
meteors with a PD, so you will have the same problem here. 

There are certain things that simple optics cannot do, and violating the 
limits of the photon budget is one of them. 

On Saturday, June 28, 2014 6:35:29 AM UTC-4, nO...@NOSPAM.COM wrote:
> An AM radio detuned to a open channel will do a nice job of detecting lightning. This is  basic the principal of the aircraft lighting warning systems such as "Stormscope".  Stormscope patents are worth looking at.
> 
> 
> 
>  If I had to detect this optically I'd use a small area, fast response photodiode and look for the AC coupled spike.
> 
> 
> 
> Google "personal lightning detector"
> 
> Steve

Probably a radio detector is inherently more sensitive than an optical
detector, due to its narrow band-width. I question whether it's fast enough to 
catch same-strike photography, but lightning does have recurring strikes.
The lightning detector can turn on the D3s time-lapse photography feature and 
start capturing. 

Here's the reality of professional digital photography: Out of 500 photos you 
take, you get maybe one good/great shot. Then you erase the 499 and call it a 
day. Why do the pros shoot like this? Because there are many factors for a good 
shot, many fleeting. My best photo I ever took was a child in the wreckage of 
Haiti. The photo was there only a few seconds, and, with the superior 
auto-focus and handling of the Nikon, I grabbed it. This would have been 
impossible with a Canon. 

With Cydrome and the D3s, I still think you have to take this philosophy - take 
massive numbers of photos and erase 99.9%. Set your camera up in a place that 
will be striking, such as the DC fountain area, etc.