Auto-focus when lightpainting?

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Auto-focus when lightpainting?

Postby GroundquestMSA » Jul 28, 2013 6:47 pm

I'm using a Lumix DMC-TS4. What focus mode should I use? There are a few options that allow for single or multiple points of focus. When lightpainting a large passage, what mode is best and what should I focus on in order to get good overall clarity?
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Re: Auto-focus when lightpainting?

Postby Chris V » Jan 19, 2014 7:21 pm

I would think you'd want to pick one point of focus, and close you f-stop down as tightly as your flashes will allow to get the best possible depth of field. If you're painting with the shutter on bulb or some other long-ish exposure setting, you wouldn't want the focus moving while the lense was open - not that it would do that I don't think, but you'll just have to bracket - try picking a few different single points of focus & see what works best.
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Re: Auto-focus when lightpainting?

Postby DannyW » Mar 29, 2014 8:41 am

I am new to cave photography but what I use above ground is a small torch with a focused beam for distance and light up the area I want it to focus on then once it is in focus I take the shot (if you are using single servo focus, continuous servo is a pain to use in the dark) or switch it straight to manual focus and take the shot when you are ready
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Re: Auto-focus when lightpainting?

Postby GroundquestMSA » Apr 1, 2014 1:02 pm

I played with this a little more, but no matter which focus mode I use, the results are crap. I suppose those are the results you get with a waterproof p&s. I'm still hoping that I'm doing something wrong, and that there's a possibility of getting better photos with a less than ideal camera...
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Re: Auto-focus when lightpainting?

Postby Phil Winkler » Apr 1, 2014 6:42 pm

Be aware when light painting that it is the flash to subject distance that determines the f-stop. Jim Jasek, in Texas, is a great expert in all of this.
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Re: Auto-focus when lightpainting?

Postby GroundquestMSA » Apr 1, 2014 7:15 pm

Phil Winkler wrote:Be aware when light painting that it is the flash to subject distance that determines the f-stop. Jim Jasek, in Texas, is a great expert in all of this.


The camera only has two aperture options, F3.3 and F10. I have used the F3.3 with a longer exposure, and F10 with a shorter exposure, and the results have been nearly indistinguishable. I've also played with various ISO and EV settings, but I don't really know what I'm doing. Nothing is crisp, no matter what I try.

I may give this Jasek character a shout, meanwhile I'm trying to get a handle on the bare basics of photography.
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Re: Auto-focus when lightpainting?

Postby Extremeophile » Apr 2, 2014 10:03 am

GroundquestMSA wrote:The camera only has two aperture options, F3.3 and F10. I have used the F3.3 with a longer exposure, and F10 with a shorter exposure, and the results have been nearly indistinguishable.

I have the Lumix TS3 rather than the TS4, but I don't believe my camera has any sort of aperture control. The combinations you mention don't make sense since the combination of open aperture (F3.3) with long exposure admits more light, and the other combination admits less light, so the overall exposures with these two combinations would be quite different. If you do have the ability to control aperture, then a larger f-stop will give you greater depth of field, and make the image less sensitive to focus problems, but you should figure out what the problems are with focus rather than trying to compensate with aperture. With P&S cameras you generally need to put enough light on the subject to get the autofocus to work properly. You are probably also aware that the shutter button has to be half-way depressed to get the autofocus to work, and in caves this can take several seconds. If your photos are fuzzy, and you're doing a long exposure, you also need to ensure that the camera isn't moving. I always use the timer to ensure that the pressing and releasing of the shutter doesn't cause camera movement.

The cover photo of the February, 2012 NSS News was taken with a Lumix TS3 and a 30 sec exposure using a headlamp for light-painting.
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Re: Auto-focus when lightpainting?

Postby GroundquestMSA » Apr 2, 2014 10:18 pm

Extremeophile wrote:combinations you mention don't make sense since the combination of open aperture (F3.3) with long exposure admits more light, and the other combination admits less light, so the overall exposures with these two combinations would be quite different.


You're right, I reversed them. For example, I tried a F3.3 for 4 seconds, or a F10 for 8 seconds... similar results.

I usually set the 2 sec. timer, put the camera on a tripod or a rock or something, then blast whatever I want to be the focal point with as much light as I can while I half-press the shutter. Then after the auto-focus does it's job I press the rest of the way and light the entire shot.

I've never tried an exposure of longer than 10 seconds. That has always been enough to light everything. What effect would less light and longer exposure have on the photo?
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Re: Auto-focus when lightpainting?

Postby LukeM » Apr 3, 2014 7:58 am

If everything in the photo is still, and the camera's on a tripod/rock then less light with a longer exposure shouldn't make much difference. Once you start getting toward 30s-1min of exposure you might start worrying about additional noise from having the sensor heat up.

If you have ISO adjustment make sure that's low. It'll make the camera less sensitive (more light/more exposure), but decrease image noise.

As far as focusing goes, it's tough without the ability to do it manually so you will want a small aperture/high f-stop (f10 in your case) to increase your depth of field. Once again, this will require more like or exposure time. Your method of making the subject as bright as possible to auto-focus sounds good. The focusing algorithm will be looking for edges and areas of high contrast so keep that in mind when placing the focus point.

If you want defined shadows keep your light in one place the whole time. If you want to reduce shadows move the light around a bit.
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Re: Auto-focus when lightpainting?

Postby Chads93GT » Apr 3, 2014 8:17 am

post an example. I do the same thing only with an Olympus stylus and they come out great every time.
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