Combining strobist work with long exposures

bomberman

bomberman

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How can i combine a strobist portrait outside in the dark with a long exposure? The shot i'm thinking is of someone stood on the side of the road lit by a softbox with red tail light trails of passing cars next to them.

I guess my main question is if the shutter stays open for 10+ seconds and the flash goes off within that time frame, will my subject have to move out of the shot once the flash has gone to avoid a blurry portrait?

is this possible?
 
Use rear curtain sync, then the flash will go off at the end of the exposure not the beginning...
 
Thanks for that link.

With regards to rear curtain sync and TTL, i don't have a sync cable. i was thinking it might be possible to have a ttl enabled flash on camera, blinkered and pointing to a slave to one side?
 
a manual flash will work (ie any ttl gun set to manual) and if its blinkered makes no odds to the photo

It 'should' work but I don't have a body atm to test it on :(
 
a manual flash will work (ie any ttl gun set to manual) and if its blinkered makes no odds to the photo
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ok i was just thinking about getting the flash off cam and wouldn't want the preflash for the slave trigger causing any problems

Like this:

- ttl flash on camera hotshoe set to 2nd curtain, pointing at slave off cam in a softbox
- 2nd curtain fires on camera preflash to trigger off camera slave.
 
should work but might not because of the latency from the optical slave bit being maybe bigger than the time between pulse and shutter close
 
My first try would be:

1) Make sure that the distance between the person and the traffic is maximised so that you get as much light fall off is possible

2) Set up some test shots so that you know what the flash powers has to be for a given aperture (broadly speaking aperture control flash exposure, shutter controls ambient) that gives you the light trails you want with the shutter speed you want.

3) Set up the shot without the subject

4) Open the shutter for - say - 10 seconds with the subject in position

5) Shutter opens and flash goes off.

6) get the person to move ASAP after the flash has gone off.

That way the person will only be a feature in the photo for a max of a couple of seconds meaning that they are only there for 1/4 of the shutter time - you can almost think of this as them losing 2 stops of 'presence'.

I think that for a 10 second shutter time, the flash will almost totally define the person. Just make sure that the light balance is not too heavily biased towards the flash.

I'd love to see your results and the technique you used to achieve them.
 
The key to success will be to make sure there is no ambient light falling on the subject. Get them to stay still after the flash, as that will ensure no ambient in the background behind them burns through.

First or second curtain sync makes no difference with a static subject.
 
Thanks for the replies! there's some good things to think about there. If the road was close to the subject in the shot (ie next to them in frame) but waaaaay way off in the background then i could have the subject stand in near darkness. maybe on a quiet road bridge somewhere with a busy underpass?

Hoppy good point about "covering up" the ambient behind the subject

I think it would also help if they were to wear dark clothing?

This is going to be tough! I hope my photoshop skills are going to be good enough! :lol:
 
bomberman said:
Thanks for the replies! there's some good things to think about there. If the road was close to the subject in the shot (ie next to them in frame) but waaaaay way off in the background then i could have the subject stand in near darkness. maybe on a quiet road bridge somewhere with a busy underpass?

Hoppy good point about "covering up" the ambient behind the subject

I think it would also help if they were to wear dark clothing?

This is going to be tough! I hope my photoshop skills are going to be good enough! :lol:
Click to expand...

I think the key to success will be getting zero amount of ambient light on the subject. Colour of clothing won't matter. But bearing in mind how hard that is likely to be, you can minimise it with relative adjustment of exposure settings.

I would get the light trails right first which will depend entirely on shutter speed. Once that is decided, reduce ISO and increase f/number so that the ambient exposure is reduced as low as you can get it at that shutter speed. With light trails you can often vary the exposure quite a lot and still get a good result.

You could maybe cut that back a couple of stops and still get the effect you want, but that will make a huge difference to the ambient affecting the subject.

Then increase the flash output to match the f/number and ISO.
 
Hodders said:
1) Make sure that the distance between the person and the traffic is maximised so that you get as much light fall off is possible
Click to expand...

and, for your own safety, it might be advisable not to fire your flash straight at a driver's eyes. ;)
 
If yu are using a 10 sec exposure, the you have all the time in the world to press the shutter button, flash gun in your hot little hand, step to the side where you want the flash to fire from - point it at the person to be lit, (counting as you go) and when you get to 9 fire the flash by pressing the "test" button....then the shutter closes. Job done.

If you have a stand to put the flash on, then you don't need to hold it, just walk over (counting the exposure down) and fir it just before the end - on the count of 9. The last bit of ambient from the 10th second isn't going to cause any blur from your subject....not if you tell them to hold still and for them to count, in their head, to 3 after the flash fires before moving...shutter closes long before they think it has. No wires needed, no triggers, just a finger.
 
As said minimise the amount of ambient on the person, and place them against a dark background so that if they do move (or if you try taking them out of the frame after the flash) there is no/minimal light to 'burn through' them.

I would just use regular first curtain sync, then your model knows exactly when the flash is going to fire. If you fire it at the end exact posing, facial expression is going to be a lot more difficult.

Lensflare said:
.. and fir it just before the end - on the count of 9. The last bit of ambient from the 10th second isn't going to cause any blur from your subject....not if you tell them to hold still and for them to count, in their head, to 3 after the flash fires before moving...shutter closes long before they think it has. No wires needed, no triggers, just a finger.
Click to expand...

Yeah, but the 9 seconds of ambient light before the flash will..
 
Jayst - actually, no it won't, because the flash exposure will sharpen it up. Just like moving shots then sharpened with a burst of flash at the end. You might have a little bit of edge softening, if they are really moving, but if you explain the system before taking the shot, then you wont.

This was a long exposure with just a hint of flash to bring out the shadows:
airifle002.jpg


I can't remember the exact exposure now - it was done a month ago, but it must have been 5 or 6 seconds and he was kneeling, not leaning against anything, breathing and the rifle is not blurred, even though it will have been going up and down with his breathing (up on the exhale, down on the inhale). The tiniest bit of flash has covered it up.

I kept the flash deliberately knocked well back, otherwise it would not have looked like night shooting. If the chap had been properly lit it would have screamed - he's hit him with flash at night. This just looks like the loom from the ambient light, except where the bolt handle gives the game away and the little shine on his glove.
 
Lensflare said:
..
I can't remember the exact exposure now - it was done a month ago, but it must have been 5 or 6 seconds and he was kneeling...
Click to expand...

Your EXIF says 4 seconds.

It's worked alright there. But surely it would've worked just the same flashed at the start. Exposure is all the same to the sensor, doesn't matter whether it's at the start or at the end does it?
 
Jayst84 said:
Your EXIF says 4 seconds.

It's worked alright there. But surely it would've worked just the same flashed at the start. Exposure is all the same to the sensor, doesn't matter whether it's at the start or at the end does it?
Click to expand...


You're right Jay. Flash at the beginning or end, first or second curtain sync, makes no difference to the exposure - unless the subject is moving and the blurred ambient element needs to move in a certain direction, eg the common moving car/headlights example.

Using second curtain sync also makes the timing of the flash much more unpredictable, if you're trying to capture fleeting expressions or movements for example.
 
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