Question about using ttl

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I have bought my first off camera flash which I use with my Nikon D5100. I have used it a few times and am happy with the results but I have a couple of questions which I hope some of you can help with.

What I want to know is if I am using my camera in manual mode with the flash set to ttl does changing the metering mode effect the way the ttl works on the flash or does ttl just set the flash power depending on all what's being framed.

Also when focusing do I just focus using focus point and half pressing shutter button then repositioning what I want in picture then press shutter fully down to take picture, which is the way I do it when not using a flash.

Advice would be appreciated.
 
ttl typically works by the flash firing a pre-flash as you press the shutter button to take a shot. This pre-flash is so fast you typically won't see it (some subjects can see it - eg some insects - and some are even fast enough to respond to it); but it is used by the flash to gauge the effect it has on the scene based on the light that is reflected back through the camera lens (information then passed up to the flash). The flash then sends out its primary light source based upon the data it got back.

So framing and recomposing won't affect it (though if you are doing that be careful as recomposing after setting the focus can mean that the plane of focus moves off the original point of focus and thus might cause you to get miss-focused shots).
 
I have bought my first off camera flash which I use with my Nikon D5100. I have used it a few times and am happy with the results but I have a couple of questions which I hope some of you can help with.

What I want to know is if I am using my camera in manual mode with the flash set to ttl does changing the metering mode effect the way the ttl works on the flash or does ttl just set the flash power depending on all what's being framed.

Yes, there is a detail or two, perhaps depending possibly on which flash you have. The main thing to know generally is that camera Matrix and Center Weighted metering probably does Nikon TTL BL balanced flash metering (unless you have one of the very few flashes with a menu that can specify TTL vs TTL mode). And Spot Metering will switch from TTL BL to be TTL mode (i.e., Not TTL BL balanced mode if Spot metering). And realize that Matrix, Center, or Spot are only about the ambient metering, the flash has its own central area metering system. So, Spot Metering switches ambient to Spot, and it does switch from TTL BL to be TTL mode.

What TTL BL or TTL mode is, is described at Flash pictures are Double Exposures- Outdoors (toward page bottom).

TTL is automatic flash exposure no matter what camera mode is selected. Including Camera manual mode, TTL is still automatic flash exposure. But it might be what is called TTL BL or TTL metering mode.

There are two exposures involved with flash, the ambient and the flash. The camera automation (camera A, S, P modes) sets up the settings for the ambient exposure. Then TTL works automatically into whatever settings it discovers are in effect. So it is good to give flash some consideration when selecting automation.

Flash Compensation is how you tweak TTL flash results, to be more what you want.

Also when focusing do I just focus using focus point and half pressing shutter button then repositioning what I want in picture then press shutter fully down to take picture, which is the way I do it when not using a flash.

Advice would be appreciated.

Focus works the same way, flash or not. Some flashes have a focus assist LED on them, to help illuminate the center spot of focus.
 

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