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Hi All


I have 2 150w flash heads, 1 is used with a soft box from the front (45 left) the other at the rear. Rear is on the floor 5" away pointing at white background and set to 100%, front is set to about 25% and the results (F8 125 ISO 100) are great.

However I can not keep the over-exposed white background if I go to F14/16 or increase shutter speed to anything like sync speed (250).

If I wanted to shoot at say F14 with a faster shutter speed I assume I would need more light at the back? Would using a 300w at the rear instead of the 150w do the job? I could then use the spare 150 at the front to give different lighting results. I can get a 300w at a good price:)

Cheers
 
Rule of thumb , to keep a white background,without it blowing out, it needs about 1 1/2 stops more exposure than your main light. Just check that you are not totally blowing out the background with lots of light. Try reducing the second units power down to 50% and see the difference. I suspect you may be putting more light onto the background than you actually need. If it looks OK at 50% try 25% and see how low you can go and still retain your white background.

You may need to check how the lighting looks with the reduced background light, as this may have had some effect on the subject.

The shutter speed is a irrelevant as you are using flash. The flash duration controls the exposure time. The only controls you have is the camera aperture and the flash power, so no need to worry about that

I reckon to get to F14/16 you'll need to wind the front flash's power up to 100%. See how things go with your existing set up before you splash out an a third flash head, unless that is you want to. ;)
 
I am new to this, so a few more questions. Will the lens used not effect the SS as well as the flash? If using 120mm to avoid shake would not the SS need to be above 120? Or an extreme 200mm need a SS approaching the sync of 250?
 
No - the duration of electronic flash is extremely brief, much shorter than the fastest shutter speed of your camera anyway.
 
Thanks for reply.


I am afraid I do not understand this so will have to have a search and a read on this.

Thanks
 
Well... let's say the shutter speed is 1/60sec. The shutter opens and the flash fires but it's very very brief and intense. The flash dies away, but the shutter is still open for the remainder of that 1/60thsec. It's highly unlikely though that the prevailing ambient light in a studio would be strong enough to produce secondary (blurry) images on the sensor at 1/60 sec.

Using longer shutter speeds (Your flash will actually sync all the way down to your longest shutter speeds) then the danger of those blurry secondary images increases if there's any subject or camera movement during the exposure.

Any help? :)
 
Thanks CT, that is a nice simple explanation:thumbs:

I have also read a bit on another website and am now starting to understand.

Thanks V much:)
 
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