Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx> Just a few comments although Terry seems to have it all covered.My camera can run to ISO 1600 and has noise reduction for long shots of up to 30 seconds. Aperture is 3.5 - 32. Shutter speed to 1/8000 sec but this is not needed. It really is chalk and cheese compared to my Ricoh Digicam in terms of low light capability, distant focus and manual controls. The advantage of a digicam is that the image from a small mirror will encompass the full field of view. I didn't use a UV filter on most recent shots. The photos I take show the mirror as only part of the image so a lot of resolution and light catching ability is lost due to the small mirror compared to the size of the 180mm lens. A bigger mirror would be next improvement to capture sparks across the full frame of the photo. Auto-focus would work fine then. Exposure is not critical. The first image shown has an exposure of 1/5 sec at F3.5. To increase the likelihood of catching a spark just increase the time delay. If you don't catch anything just try again. Too long an exposure will just overlap sparks. With my current guesses about 50% of photos are OK. All my pics are taken with an infrared remote trigger, but camera shake is not an issue with these type of events. Colour balance can be done automatically by the camera or software later but auto colour balance of a purple spark will give a green background. Manual balance is easy enough and twiddling is needed to bring ou the really faint events like the "second harmonic" line between the main ringdown channels. My motor speed is slower but my camera is better. A bigger mirror might really help. Time is an issue with me and due to work, I can rarely do anything during the working week. Last week though I was off sick with the flu - but not so sick I couldn't work in the shed.
And flash lamp info? This site is helpful. I am looking forward to Terrys "first light". Peter
Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx> Hi Gary,
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The bright arc is burning a "lot" of power. Perhaps if the camera were more sensitive (higher ISO) then the arcs would look much more constant. This picture does show smearing.http://tesladownunder.com/HVRotMirrorTeslabigSparkElectrodeglowDelay.jpgA flash lamp, like the super high speed ones, just use a power arc. So the "flash" can be very fast. Scientific American had an amateur scientist article on flash lamps once.... I should try and find it...Peter is running the coil normally and taking many pictures hoping a few will catch the arc at just the right time. I am not sure what his ratio of successful pictures is but it is low. I have four mirrors for my setup and a wider field of view so I am hopping to get a high yield of cool pictures as opposed to the floor ceiling etc...
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I know he has been trying all kinds of camera settings so I am not sure if it has found the "good" ones yet. Here are my "guesses" for my setup but I have never done it yet so don't believe me ;-)Aperture - How big that iris thing is. I think it should be kept as wide open as possible to catch as much light as possible. It is really the only light control we have. Mine goes from 2.7 to 11.0.Focus - Have to set it up. There is nothing for the camera to focus on when the mess is running. Peter said it was hard getting the focus just right.ISO - As high as possible. For digital cameras, ISO or film speed is fixed and the ISO settings are software tricks. If one hits a limit for aperture setting this might be another way to adjust the light further.Shutter speed. Not sure... Mine goes to 1/800 second. It could probably be far slower based on the BPS of the coil. It would be very hard to accidently superimpose two bangs...Color balance - Manual probably daylight. The auto setting does not work in the dark and can't adjust to a fast arc. Peter was having trouble with odd colors at first due to this I think.Mirror speed - Mine goes from very slow to 24000 RPM so I have it covered ;-)) Peter's is 3000 RPM sync motor (50Hz) I think.Zoom - I figure you can zoom close to the arc and loose the frame a lot, or go wide angle and catch more arcs...I looked hard at "cheap cam" (Olympus D-395) and it does not have many (hardly any) of the mentioned settings as "manual". My old Olympus C-3000 can do everything manually if you read the instructions enough ;-)
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The block is machined to about +- 0.002 inch and it runs smooth even at like 25000 RPM!! .......I also made the calibrator today. Just a LMC555 CMOS timer in the 50% mode calibrated to flash a high brightness red LED at 100.00KHz.http://drsstc.com/~piranha/PIRANHA/Cal-01.JPG http://drsstc.com/~piranha/PIRANHA/Cal-02.JPGIt uses the same timer cap from my TCT. Don't by one since I have 75 here on my desk for free ;-)) The LED is 20mA but I run it at 30mA with a 220 ohm resistor to the +9V and ground to pin 3 for +50mA capable drive. 30mA at 50% duty is about the same power as 20mA DC. It is very bright!!So I am just waiting on the four front surface mirrors now to be glues to the block....Cheers, Terry At 05:53 PM 9/13/2006, you wrote:Hi Terry, Peter: I'm not "getting" something. For Peter's image ... Is there some other opto-mechanical chopper in addition to the sweeping mirror? Also, Peter - what film speed and lens aperture did you use? I'm wondering if a garden-variety digicam is fast enough. I assume the coil operated in single shot mode? Thanks, Gary