… aperture / shutter speed / ISO

Those are the three controls we have over our exposure of ambient light.
But depending on whether we are using manual flash or TTL flash, our control over our flash (in relation to our ambient light), changes somewhat.

To recap quickly from the previous posting where I went over the differences between manual flash, and TTL flash.

With manual flash,  two (of the four) things that control our exposure:
 - aperture,
 - ISO.

With TTL flash,  we have only one control over our flash exposure:
 - flash exposure compensation.

The reason for this, as explained is that our two controls that affect manual flash, seemingly become transparent with TTL flash.  And therefore we have to control TTL flash exposure with flash exposure compensation.  The flip-side of this is … that we can now use aperture and ISO to affect our ambient exposure.  This we couldn’t do with manual flash, because it would’ve affected our flash exposure as well, and not just our ambient exposure.

The point of this posting? 
It’s just a correction to a lot of the mistaken advice I’ve seen on the photography forums,
where incorrect advice is given,  such as:

 - aperture doesn’t affect ambient exposure. 
Yikes!  Just because shutter speed is the only independent control you have over ambient exposure when using manual flash, doesn’t mean that aperture doesn’t affect ambient exposure.

- your choice of aperture affects flash exposure. 
Weeeell, it could be.   As we’ve seen, this depends on whether you’re using manual flash or TTL flash.  If you’re using TTL flash, you could use aperture to affect only your ambient exposure. ie .. you could affect your ambient-vs-flash ratio by controlling your aperture. (The same goes for your ISO setting.)

This and the previous posting have been very wordy, so perhaps it is time for some photos again …