Why not hss?

Started Jan 2, 2013 | Discussions thread
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Re: Why not hss?
In reply to howmanyds, Jan 3, 2013

Actually the Guide number does change between APS and 35mm format, but not apparently at the extreme focal lengths.

Look at the 1/1 for normal flash.  At a focal length of 70mm the GN for 35mm format is 35m.  The GN for APS-C is 41m.

Under HSS 1/250 shutter speed and 50mm focal length, the GN for 35mm format is 10.8 and for APS-C is 14.

These are about 1 stop differences.  That may or may not be an issue.  Iin auto it would affect max range, but for a person using a manual flash set-up they would probably adjust their settings (although 1-stop is usually easily correctable in post processing.).

The reason for the difference is that for the same lens FL, to cover the FOV of an APS-C lens the flash would not have to zoom to as wide a setting and spread the light out as much.


howmanyds wrote:

P.P.S. it looks like the GN doesn't change at all between APS-C and 35mm format. Also interesting. Not sure I get that.

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