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Flash and ISO??? (1 Viewer)

arjacee

Well-known member
Hi everyone. I was out practising today using my 430 flash and a better beamer along with my Canon 7D and 300 F.4 L. I am a novice when it comes to using the flash. I think I saw some improvement in a few shots I took (it was sunny ). Anyway I am really not sure what ISO to use and whether increasing the ISO increases the power / range of the flash? Sorry for what is a probably stupid question. If anyone could give me some pointers I would really appreciated it. Thanks alot. Bye

p.s the flash said 13 m and then said 3 m under the 50 mm which I think is the zoom setting. Does the 13 m signify 13 metres in reach?? Thanks again!
 
What settings on your camera are you using?
Flash is used as fill flash or main light source?
Do you use the flash in TTL mode?
Are camera and flash set to high speed sync, i.e. do you use faster shutter speeds than the regular sync speed in the 1/250s range?

Here are some answers:

1) By increasing ISO the ambient light will have more impact on the exposure, thus the flash when used in eTTL mode will have to use less output at a given distance to get the same result, or seen the other way have more reach with the same output. Same applies to aperture settings, i.e with the lens stopped down (e.g. f16) or wide open (e.g. f4).

2) The Better Beamer expands the working range of the flash by focussing the beam to a smaller spot. This will allow a flash under TTL control to use less power to light a target with the Better Beamer attachment than without it (i.e. flash zoom set to 50mm + Better Beamer vs flash zoom at 50mm and even its max setting). However, the flash (and your camera) don't "know" about the Better Beamer so the numbers shown by the flash(reflecting the max. usable range of the flash at the given setting) assume the "naked" flash. With "knowing" about the Better Beamer this number would be higher.
And the number assumes that the flash is the main light source (dark room, little other light), i.e. when using the flash as fill light its reach is longer than the number.

3) Point 1) applies also to point 2), i.e. pushing the ISO up with the Better Beamer will further increase the useful range of the flash.

4) If camera/flash are in high speed sync mode one can use much faster shutter speeds, but the working range of the flash will drop dramatically with faster shutter speeds. Still one can use a flash for fill light with 1/800s or a bit faster over ~20 -40 m (lens wide open) with the Better Beamer.

5) When using fill flash I set the camera that the shot would be 1 F stop underexposed, let the camera control flash output vie TTL, and dial in -1.3 - -1.7 flash exposure compensation. Depending on the subject and general lighting conditions (dark or light background) flash exposure compensation settings can vary widely (-2 - +1). This results most of the time in an image that doesn't look flashed. Fill flash acts mainly on the dark spots in the subject, so its effects can be very subtle.

6) If flash is the main light source the general procedure is the same, just that one should avoid shutter speeds to far above the native sync speed (best 1/250-1/320 depending on camera model). If the flash power/range under those circumstances is insufficient the only fix is to open aperture wider and/or crank up the ISO. However, results will most likely look like a flash was used.

Hope that helps

Ulli

P.S. Note that light does not decrease linear with distance. Each time you double the distance you loose 3/4 of the light.
 
Thanks for the reply. I don't know if I was using as main or fill flash...I was just experimenting. I was using aperture priority ( F8 ) at ISO 400 and 640. I was also using Shutter priority at 1/400 with the high speed sync on. Here are a couple of shots I took.....not sure if the flash has made a difference or not? Thanks
 

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In the first image I see some evidence for effective flash use.
Note the nice catch light in the eye. The underside of the right wing that shows structure and detail that without fill flash would likely just be in deep shadow. Similar results on the tip of the lower mandible.
Other than the shadow from the twig on the undertail hardly any tell tale evidence that a flash was used, that's what you want.

In the second one I see no indication that a flash was used, a good thing, but also nothing that would likely be much different without.

Ulli
 
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