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Thread: Need help with back curtain night shots

  1. #1

    Join Date
    Nov 2011
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    Need help with back curtain night shots

    I could use some assistance in finding a starting point for some night shots using the back curtain mode. Iíll be trying to get some shots of runners on a trail carrying glow sticks. The only light available is the glow sticks and some will have little head lamps attached to the bill of their caps that put out a max of about 100 lumens. Iím attempting to freeze the runners with the glow sticks ghosting to the rear. Iíve never attempted any night photography so I donít know where to begin. I have the following equipment along with tripods and a variety of filters and gels for my flash units. Any suggestions would be much appreciated.
    Nikon D90 camera
    Nikon SB700 & SB900 flash units
    Sigma DG 50-500mm 1:4.5-6.3 APO HSM
    Nikon ED AF-S 70-300mm 1:4.5-5.6 G
    Nikon MICRO AF-S 105mm 1:2.8 G ED
    Nikon AF 85mm 1:1.8 D
    Nikon AF-S 18-105mm 1:3.5-5.6 G ED (DX)

  2. #2
    pnodrog's Avatar
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    Paul

    Re: Need help with back curtain night shots

    If you are in the country side well away from any lighting in the sky from the glow of city lights or moon at 3200 iso at f4 the exposure without flash will be over 15 seconds and up to several minutes. A couple of camping lanterns placed in strategic positions (hanging a tree - perched on a fence) near the track may be a huge help or ask them to run on a night with a full moon. Personally I would be trying to set up some sort of basic lighting that would give base exposure of less than 4 sec without flash so that with the back curtain flash the exposure could be between 1/2 sec to 2 sec in which time the runners may have travelled up to 5 meters or more if they are fast. After all you will need enough light to focus and compose the shots. You will need to adjust the flash level to be in balance with the basic lighting (70%flash 30% basic?) depending on the effect you are after. With the glow sticks etc exposing for a low key effect may look the best. I would certainly experiment in a dark spot in the garden with the house lights off before the event.

    For your sake I hope someone has already done something similar and may be a lot more helpful.
    For basic exposure information you could have a look at the following link - http://www.fredparker.com/ultexp1.ht...ensity%20Chart

    Good luck.
    Last edited by pnodrog; 27th November 2012 at 07:24 AM.

  3. #3

    Join Date
    May 2008
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    155

    Re: Need help with back curtain night shots

    This actually isn't too difficult.

    First of all, do these people know you're going to photograph them? They're going to be running along and then FLASH! right in their faces. Make sure they're okay with that.

    First you need to do some research, taking a cue from fireworks photography. With fireworks you set the aperture to f/8 or so and then open the shutter for two seconds when you see the fireworks go up. The fireworks burst and leave streaks on your sensor. You can control the brightness of the fireworks with the aperture. Opening the aperture brightens the fireworks and closing the aperture darkens them. You can also use ISO to control brightness. This works because fireworks act as a constant light source...as will your glow sticks.

    So this is the first thing you need to discover...what is the correct aperture and ISO necessary to capture the streaks of glow sticks? To figure this out you simply need to set up on your tripod and shoot some runners. Start with ISO 100, and your 85mm lens set to f/1.8. Try to find a very dark area of the trail, as you want to suppress ambient light as much as possible (your shutter will be open for a relatively long time.) Figure out how long a streak you want. So you'll probably determine a point A (just outside the frame) and a point B (where you want the flash to fire...but we're not using flash yet.) The time required to run from point A to point B...that's your shutter speed.

    So now you shoot some runners and adjust aperture (and ISO if necessary) to see how the glow turns out. You should now have a fairly good idea of an aperture and ISO that works. As I said, the glow sticks are constant light sources. Once you find the correct exposure, it won't change, even if your ambient light changes. Of course, if your ambient light is bright enough then it can overwhelm the glow sticks. In a case like this, where your shooting parameters are being dictated to you by your pictorial vision, the only way to control the ambient light is by moving yourself to brighter or darker locations. So if you want to completely suppress the scene, find an area with no light. Of if you want to scene to appear in the image, you'll have to scout around for an area with just the right light. That's no big deal...it's just part of the challenge of getting the shot you want!

    Once you have the ambient and glow stick exposures figured out, you can figure out the flash exposure...which is the easiest part. First, determine how you want your lights to be set up. Positioning them on either side of point B, about 45 degrees off the line between runner and camera, and 10 feet away, is a good place to start. You're shooting at night so the D90's Flash Commander should have no trouble communicating with the flash units.

    You can't take an i-TTL reading of the runner because that happens before the shutter opens...obviously no good because there's no runner at point B! So you must use manual flash. Now...I could write another 10,000 words on how to precisely set the flash power based on the Guide Number, subject distance, aperture, and so on and so forth. But as you have enough on your hands as it is, I'll say to simply zero in on your ideal settings via trial & error. For direct flash, start with 1/4 power and 35mm zoom. Set the timer on your D90, run to point B, and take a pic of yourself. Too bright or too dark...adjust the flash power using the Flash Commander (and take advantage of your two groups to control each light individually.) Is the light coverage too much or too little? Adjust the zoom of the flash units. It shouldn't take too long to figure out flash and zoom values that work. As with the glow sticks, once you figure out the flash power, it won't change just as long as you always set up the flash units in the same position relative to the subject (within reason...depending on ambient exposure, you may need another adjustment when you put everything together.)

    When you read it through, it sounds like a lot that you need to do...but is really isn't. It's just applying the basics of exposure in separate steps to accomplish separate goals. But if you do think it's a lot to go through, then take a look at this...
    http://www.dump.com/captureshot/

  4. #4

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    Re: Need help with back curtain night shots

    From my single photo of something similar I show that those headlights are powerful and do not need much exposure but the runners will need light added to balance their headlights ... not sure how bright glow sticks are ... they were used to mark the course and didn't seem very bright even for my eyes accustomed to the darkness.
    6400 ISO 1/30 f/6.3 [ my zoom is f/5.8 at the long end so I used f/6.3 and hoped I would hold the camera steady enough in this situation of inside a tent at 2am with just a work light to see/photograph by.] Manual -- Contrast detect AF.
    Need help with back curtain night shots
    I suspect you will need quite a small aperture to avoid burning out the headlights and the flash under exposing somewhat to not spoil the night effect ... at least where I would start from if trying to do it myself The aperture controls the brightness as well as the flash level of the unit and the combination will depend on the flash to subject distance when it goes off at the end of the exposure .. so it is a case of manual everything I think.
    First step is to determine the Guide Number of your flash so you can estimate the aperture required at the distance the people will be when the flash goes off [ GN/d=a ]
    That shaft of blue light is part of a projected image escaping off the edge of a screen left of frame.
    Last edited by jcuknz; 27th November 2012 at 10:22 PM.

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