Why not hss?

Started Jan 2, 2013 | Discussions thread
tom Senior Member • Posts: 2,724
Re: Why not hss?

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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