High Voltage Forum

Science photography => DSLR => Topic started by: TMaxElectronics on June 26, 2020, 06:31:08 PM

Title: Tips for taking arc shots of Tesla coils
Post by: TMaxElectronics on June 26, 2020, 06:31:08 PM
Now that I have a working Tesla coil, I took some pictures and thought I'd share some of the things I learned along the way. Some of these things are personal preference though ;D

First thing I see when people are talking about their pictures is the fairly long exposure time of >1sec. I found that that is not always necessary. If you can get the arcs bright enough (large enough aperture & ISO), you might try some shorter exposure times:
This image had one 6th exposure time and f5.6 with iso 400.
Also this was a ground strike, so a little brighter a usual arc.

This one is with 10th instead of 6th, but zoomed in and not a ground strike (also i think higher interrupter frequency)

The issue that I have with longer exposures is that the arcs start to look extremely branched, because too many individual arcs are within one exposure time. Even at 50Hz interrupter frequency, quite a few arcs will be in one 10th second exposure.

Secondly I have seen many images, where the arcs look completely white, even if they aren't a ground strike. This is likely to be because the arcs were over exposed (just like the top image here in some places).
I always try to under-expose an image, as over exposure leads to loss of color information, but under exposure (only to a point of course) does not. The pixels can always be brightened in post.

I can't tell you how exactly to set those parameters in your camera, but mode M is (usually) full manual (shutter, aperture and iso).
I would recommend that mode, because the cameras auto modes might be confused by the rapidly changing brightness.
Start by setting your ISO (the sensor gain), probably to 400.
Then set the aperture as wide open as possible and your exposure to around 1/10th second and take a picture. This will probably look bad, so you will have to tune your parameters from there.
Since all of the parameters change multiple things, there isn't just a list to follow for tuning the image, but here's what the settings do:

Manual focus is also suggested by many, but I never manage to get that on point. My camera (Nikon D5100) quite happily focused on the arcs though. And for those situations where it does not, I tend to light up an object at the distance, that the arcs will be at, let the autofocus do its thing, and then lock it (though this only works on a tripod). This way, you can be sure that the focus is good.

I also think a tripod is only necessary, when taking fixed focus shots, or ones with longer exposures.
The images above were made without one and even if I take 1/2s ones are not shaky (my lens has active stabilization though).

But the most important thing in my mind is the post processing of the images, exposure, contrast, sharpness, etc... That is where ALL images really start to look impressive, not just those of arcs.
Make sure to save the images in the RAW format and not just JPEGed if your camera supports it, because that will allow for much more freedom in edit (sometimes you can get a good looking image, even if a large part of it looks completely black).
I use an ancient version of adobe lightroom for this, but there are probably some free / open source alternatives.

And if you want to go all in, you can of course set up a scene with foreground and background. Just a few things that come to mind here would be the coil left side, half out of shot and the target, maybe a colored fluorescent lamp, in the top right 1/3 1/3 point, or the entire thing in reverse, shooting with the target in the front and the coil as the background. Maybe also experiment with different targets for the arc, different colored lamps or something else that lights up, maybe even yourself, if you have a remote trigger for your camera and the required safety equipment (!).

EDIT: i have more arc shots, at full quality on my website now if you want to download them: https://tmax-electronics.de/projects/tesla-coil/ (https://tmax-electronics.de/projects/tesla-coil/)
just scroll down to the sliding gallery at the end of the post and click on the image you want.

Hope this helps somebody :)
Title: Re: Tips for taking arc shots of Tesla coils
Post by: davekni on June 26, 2020, 07:41:31 PM
Do you have a UV-blocking filter on your camera?  I've found that UV tends to show up as pink-purple.  That's presumably the red sensor filter passes more UV than the green filter does.

Nice photos!  I'm surprised how fine the individual arc traces are.
Title: Re: Tips for taking arc shots of Tesla coils
Post by: TMaxElectronics on June 26, 2020, 09:51:10 PM
Do you have a UV-blocking filter on your camera?
Yes, but more as a general lens protector. Haven't even though about removing it ;)
But some filters might make the shots more interesting. For longer exposures a ND filter would be useful, so the Image is a little darker without decreasing shutter time/aperture.
Maybe even using a B&W camera with some very wavelength specific ones. But finding a B&W camera with adequate quality would be very hard I think...

One funny thing I found was that when the arc is lit from the side, the hot air streaks (? I'd call it schlieren but that's the google translate result...) are easily visible. Quite a cool effect actually.

Nice photos!  I'm surprised how fine the individual arc traces are.
Thank you, I think that is because of the short shutter speed, so each arc can't "move" around too much or get washed out by another one in a similar location.
I have got a few more aswell. I'll stick them up on my website, so people can get high quality versions of them (I believe imgur compresses them quite heavily). (edited the main post and added the link to them)
Title: Re: Tips for taking arc shots of Tesla coils
Post by: Max on June 26, 2020, 11:11:02 PM
Getting the focus perfect by hand is sonething I never managed either. So what I do is I use the autofocus to get perfect focus at the point/depth I want (holding some paper at that place if needed). Then I switch to manual focus and produce some crispy sharp arc pics ;)

Kind regards,
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