Help needed with on camera flash please?

Started 6 months ago | Discussions thread
Michael Fryd
Michael Fryd Veteran Member • Posts: 8,436
Re: Help needed with on camera flash please?

simonharris wrote:

hi all,

would some kind souls please give me a bit of their experience with regard to flash use please?

i normally shoot with ambient light only and studio strobes but I have occasion to do something which involves using my rarely used 580ex 11 on camera flash. Perhaps it would be best to describe if I describe what I am trying to do?

i would like to shoot this scenario and have no control over it really other than how I set my gear up.

i am going to shoot a cyclist moving at walking pace against a background of very bright inner city lights. The background will be very well illuminated but the foreground, my cyclists will be very under lit. Last time I shot this I had my iOS maxed out with a 1.8 aperture and the shots were passable but very noisy.

this time I would like to use my flash to illuminate the cyclist. I will use the focus assist in the flash to help with focus. The background just needs to be roughly in focus .

i don't have any time to test this at night so will ask for your advice. I imagine I will still have my iOS raamped up but would like to have the cyclist come out relatively sharp....

is this possibley? From what I have read so far it sounds as if it is. I imagine my shutter speed to be around 1/30 or so. The background will be important as it consists of lots of bright color.

i am shooting with a 5 d mark 2. I am not experienced at on camera flash but will probably shoot with the flash on manual as I feel I can understand its output better.

could some kind souls please chime in with an opinion, hopefully based on experience?

kind regards to all,


If it was me, I would have the camera and flash both in manual mode.

I am assuming you will know ahead of time about how far you will be from the cyclists.

Determine what aperture you will need for the required depth of field at that distance (an online depth of field calculator will help you here).

Estimate how much noise you can tolerate in the final image, an choose the ISO that corresponds to that exposure.

Run some tests in a darkened room to see what flash power you need to light up the cyclists.

When you get to the location, run some tests to see what exposure time you need to properly expose the background.

If you have enough light, decide whether to use a short exposure, smaller aperture, or higher exposure (less noise).

Make sure you have enough batteries for your flash.  As the batteries start to deplete, the flash will take longer to recycle.

Also be wary of shooting too fast.  If the flash gets hot, it will start recycling slowly.

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