Quick question on controlling ambient light

ScarySquirrel

ScarySquirrel

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Hi all,

I understand that to control the ambient light when using a flash you should change the shutter speed. So if I wanted to darken a background I should use the fastest speed possible.

The fastest sync speed I can use is 1/200th second. If I am using this shutter speed and the ambient is still not as dark as I would wish, what else can I do to make it darker other than shooting when there is less ambient light (ie. when the sun has gone down).

I use a Canon 400D, with a 430EX and 'eBay triggers' (Cactus V2s).

Thanks in advance
 
Dal said:
Think the only other option would be to use an ND filter which is like sunglassess for your lens.
Click to expand...

this will reduce the effective power of the flash too and you will be left with the same flash - ambient ratio.
 
ruvor said:
increase flash power and dial down the aperture/ISO
Click to expand...

Ah yes, ok that makes sense.

So by dialing down the aperture you are 'darkening' both the flash and the ambient, so you correct the underexposed flash by upping the flash power?

Is that right? Makes sense now :)
 
You either need more flash power, or a faster sync, 200 seems low - what camera is it?
 
You're stuck at your max sync speed (200 in your case) unless your camera and flash set up supports FP* (focal plane flash). Far as I'm aware this only works on TTL set ups like Nikons CLS, so the manual radio set you have won't support it.
With FP flash you can go up to mad speeds like 8000 or more and get some really good effects but it sucks so much power and has a v limited range.
 
The eBay/Cactus triggers max out at 1/200 anyways :)

Here's what I'd do:

1) Set ISO to 100
2) Set Shutter speed to 1/200
3) Set Aperture to F/11
4) Take a shot. Background black enough for ya? If yes, goto #5, if not, set aperture to a bigger F-number (smaller aperture) and repeat #4
5) Turn on the flash, in manual off course as we are using radio triggers.
6) Set your flash power at 1/8th, point it at subject through whatever modifier you like.
7) Take a shot. Subject light enough for ya? If yes, goto #8, if No, repeat #6 at a higher power setting and goto #7. If subject is too light, repeat #6 at a lower power setting.
8) Rejoice. Dance around, high-five yourself or your assistant. Unless you are being paid to shoot, then you should try not to look too surprised.
 
dkspook said:
The eBay/Cactus triggers max out at 1/200 anyways :)

Here's what I'd do:

1) Set ISO to 100
2) Set Shutter speed to 1/200
3) Set Aperture to F/11
4) Take a shot. Background black enough for ya? If yes, goto #5, if not, set aperture to a bigger F-number (smaller aperture) and repeat #4
5) Turn on the flash, in manual off course as we are using radio triggers.
6) Set your flash power at 1/8th, point it at subject through whatever modifier you like.
7) Take a shot. Subject light enough for ya? If yes, goto #8, if No, repeat #6 at a higher power setting and goto #7. If subject is too light, repeat #6 at a lower power setting.
8) Rejoice. Dance around, high-five yourself or your assistant. Unless you are being paid to shoot, then you should try not to look too surprised.
Click to expand...

:clap:
 
dkspook said:
The eBay/Cactus triggers max out at 1/200 anyways :)

Here's what I'd do:

1) Set ISO to 100
2) Set Shutter speed to 1/200
3) Set Aperture to F/11
4) Take a shot. Background black enough for ya? If yes, goto #5, if not, set aperture to a bigger F-number (smaller aperture) and repeat #4
5) Turn on the flash, in manual off course as we are using radio triggers.
6) Set your flash power at 1/8th, point it at subject through whatever modifier you like.
7) Take a shot. Subject light enough for ya? If yes, goto #8, if No, repeat #6 at a higher power setting and goto #7. If subject is too light, repeat #6 at a lower power setting.
8) Rejoice. Dance around, high-five yourself or your assistant. Unless you are being paid to shoot, then you should try not to look too surprised.
Click to expand...

Thanks mate. I hadn't thought about taking a shot without the flash first to get the ambient light right first :bonk: :cuckoo:

THANKS :thumbs: :clap: :lol: :woot:
 
Happy to help! :)

Always do your strobist stuff one light at a time guys & gals - and remember to count the ambient ;)
 
Here the methods I can think of (some have been mentioned):

- Decrease ISO
- Increase f number
- Use ND filter or polarizer to reduce light
- Turn on HS mode on flash and use high speed shutter

All those will darken ambient light but flash will work harder to keep up the optimal flash exposure. In the last case flash will lose range as well.
 
Controlling ambient Vs flash has nothing to do with ISO, polarisers etc..

A flash is a really bright burst of light, for a minute fraction of a second. That is why changing the shutter speed from say 1/2 sec to 1/500 sec makes no difference to flash exposure, the burst of flash is still the same length, much much quicker than 1/500 sec.

Changing the shutter speed from say 1/2 sec to 1/500 sec, will only reduce the ambient light entering the camera

Putting a ND filter, or polariser, or closing the lens apeture down, will reduce ALL light entering the camera, including the flash. the balance between flash and ambinet will remain unchanged, the overall exposure will be the only thing that changes

The only answer to this question is to shoot at the fastest sync speed possible - if that isnt giving you a big enough differential between ambient and flash - get a camera with a faster sync speed and/or get a more powerful flashgun/head
 
packham said:
Here the methods I can think of (some have been mentioned):

- Decrease ISO
- Increase f number
- Use ND filter or polarizer to reduce light
- Turn on HS mode on flash and use high speed shutter

All those will darken ambient light but flash will work harder to keep up the optimal flash exposure. In the last case flash will lose range as well.
Click to expand...

The problem here is you are implying your camera knows how to do the maths. At the same time you are not understanding the relationships and formulas between ambient / flash / overall exposure / the cameas decision making process

Cameras cant make creative desisions about the split between ambient and flash - they need telling what split the photographer wants - and thats what the manual setting is for
 
Well, I was assuming we are using the flash in ETTL mode, not manual.

Richard King said:
Putting a ND filter, or polariser, or closing the lens apeture down, will reduce ALL light entering the camera, including the flash. the balance between flash and ambinet will remain unchanged, the overall exposure will be the only thing that changes
Click to expand...

Yes. That is true when you set the flash to manual. Reducing apeture/ISO or using ND filter will reduce overall exposure including the flash exposure if the flash power is fixed. So we have to increase flash power to obtain the same flash exposure as before. But if you set the flash to auto using E-TTL then the flash will try to get optimal flash exposure at that camera's settings, and so by increasing its power automatically. That's why I said the flash will work harder to keep up the optimal flash exposure. Please advise if I'm wrong.
 
Richard King said:
A flash is a really bright burst of light, for a minute fraction of a second. That is why changing the shutter speed from say 1/2 sec to 1/500 sec makes no difference to flash exposure, the burst of flash is still the same length, much much quicker than 1/500 sec.

Changing the shutter speed from say 1/2 sec to 1/500 sec, will only reduce the ambient light entering the camera
Click to expand...

Just to be an arsey pedant :wave: changing the shutter speed between 1/2 and 1/500 will probably make a huge difference because you'll go from getting the flash at the slow end, through perhaps a half exposed (black line) shot when the sync speed is hit at around 1/200, to the fast end where you miss the flash.

Although I know what you mean and quite agree with the argument. If you'd said 1/150 or 1/200 instead of 1/500....
 
dkspook said:
The eBay/Cactus triggers max out at 1/200 anyways :)

Here's what I'd do:

1) Set ISO to 100
2) Set Shutter speed to 1/200
3) Set Aperture to F/11
4) Take a shot. Background black enough for ya? If yes, goto #5, if not, set aperture to a bigger F-number (smaller aperture) and repeat #4
5) Turn on the flash, in manual off course as we are using radio triggers.
6) Set your flash power at 1/8th, point it at subject through whatever modifier you like.
7) Take a shot. Subject light enough for ya? If yes, goto #8, if No, repeat #6 at a higher power setting and goto #7. If subject is too light, repeat #6 at a lower power setting.
8) Rejoice. Dance around, high-five yourself or your assistant. Unless you are being paid to shoot, then you should try not to look too surprised.
Click to expand...

Good post dk v informative - and dam your sig makes me laugh
 
As I understand it the flash duration for a 430EX is approx 1/30000 ths sec. The range will be between approx. 1/1000th sec and 1/50000th sec The actual flash duration will vary with flash power

The limiting factor (with regards to the OP question) is the comparitivley slow speed the camera will actually sync to this flash. Canon do have a high speed sync mode, but it relies on reducing the flash power to match the shutter speed chosen (the flash power is determined by the flash duration)

This is why the only answer is to either use a more powerful flash, or get a camera that synch's faster to the flash power you do have available
 
Exactly.

I'm tight, so I have never looked at what sync speeds you can run with pocket-wizards etc, only the cheapy cheap cactus/pt-04's
 
you might be able to reliably push it to 1/250th but no amazing differences

supposedly the new clever ttl pocket wizards can get another stop at the expense of range (camera-flash not subject-flash)
 
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