Re: High speed Tesla spark photographs

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Peter,

At 06:00 AM 9/14/2006, you wrote:
> 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.

I can see how the noise floor could be a problem.  At F2.7 ISO 800 
3sec exposure The camera and the despeckling software are right at 
the limit.  Here is a test shot with just the camera there (1.3MB):

http://drsstc.com/~piranha/PIRANHA/pictures/P9150024.JPG

> 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.

Modern video cameras can see in far darker light than we can.  A 
video camera might do very well aside from the fact that converting 
it to the computer (at least in my case) is rather messy.

> 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.

Yes!  Of course!!  So one does not need super high shutter speeds and 
all.  I can see some advantage too in covering the other area the 
mirror scans areas with black painted surfaces just to cut down on 
stray light.  The SISG can fire in single shot mode more or less just 
by using big 200K charging resistors.  I am thinking of increasing 
the light sensitivity as much as possible.

> 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.

I figure once it is set up and going, I just click the remote until 
the camera memory fills up.

> 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 out the really faint events like the "second harmonic" line 
> between the main ringdown channels.

I think "daylight" does fine.  Everything looks "right" there for me.

> My motor speed is slower but my camera is better.  A bigger mirror 
> might really help.

I am thinking about adding another fixed flat mirror just to give a 
better angle advantage.  But I will have to get something to work 
first before I go "fixing" anything ;-)


> 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.

Just quit the day job like I did :-))

> I am looking forward to Terrys "first light".

Still waiting on the mirrors.....

Cheers,

        Terry


> Peter
......