On Mon, 30 Jun 2014 00:12 -0700, miso <miso@sushi.com> wrote:>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 secYep. The duration of the electrical discharge is in microseconds. The light produced by the ionized air lasts much longer. If triggering on RF, we're dealing with short microsecond bursts. If optically triggering, we have a much longer flash to work with. -- 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
optical lightning detector
Started by ●June 24, 2014
Reply by ●June 30, 20142014-06-30
Reply by ●June 30, 20142014-06-30
On Sun, 29 Jun 2014 22:42:55 -0700, miso <miso@sushi.com> wrote:>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.Use a mirrorless SLR. Nothing here says it even has to be an SLR. A DLR or even a rangefinder will work. <sheesh!>
Reply by ●July 1, 20142014-07-01
miso <miso@sushi.com> 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.we just had a lovely lightning storm here last night. I wans't able to locate slave strobe to see if they pick up lightning, but I was able to make some observations. the amount of lightning up inside the clouds was spectacular, with nonstop flashing of around 3 to 10Hz for at least 20 minutes. This is the noise I want to eliminate, and due to the fact it's cloudy during a huge storm, long exposures will be blown out by all this extra light. Giant flashes in view of the camera which are hopfully visible bolts of lightning is what I want to catch, automatically. "motion sensing" is not a feature of series of SLR I'd use, so that's not an option. I need to find a few photodiodes to play with next.
Reply by ●July 1, 20142014-07-01
haiticare2011@gmail.com wrote:> 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.I'm going to guess they burst detectors are just way too sensitive. Again, last night the amount of flashing in the sky I could see was going on at about 3-10Hz for 20 minutes. most of this wasn't visible and distinct lightning, of if it was, it was behind me and would not have been photograhable anyways. The visible lightning was much brighter than anything else going on in the clouds, which makes me keep thinking I want detect it optically. I did note some of the visible cloud to cloud lightning was rather "slow" to form and involved multiple discharges. So it's possible I'd want to trigger 1/4 or 1/2 second exposures, which is doable.> 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.I can't stand spray and pray methods, plus I want to be able to go back inside and make some tea while the camera+detector and does it's job all by itself, and then not have to delete 27,000 junk photos.
Reply by ●July 1, 20142014-07-01
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.the viewfinder window port of the camera is the best place to toss a sensor as far as I can tell. It will only pickup what the lense itself can see so there's nothing to adjust.
Reply by ●July 1, 20142014-07-01
miso <miso@sushi.com> wrote:> 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.I'm not so sure about this being necessary. the d3s is mind blowing fast, and really exciting lightning strikes last for a long time. there's some other funky behavior the camera has in mirror up mode when you want to take multiple shots, but I can't recall exactly what this is at the moment.
Reply by ●July 1, 20142014-07-01
miso <miso@sushi.com> wrote:> 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 secEven if the pulses in the timeline are super short, the total duration is long enough to be visible to the eye, even if you blink. Some of the cloud to cloud lightning visibly grows "streamers" as they say in tesla coil talk.
