TTL External Flach - A tad confused!

Paul_Canning

Paul_Canning

Paul_Canning

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Ok, so I got an external flash (nissin di622) that supports E-TTL/TTL.

I have the TTL mode turned on on the flash (it ovvers manual and slave modes too) and I use Av mode on my camera (canon 7D)

In dark indoor environments, the shutter speed is quite low (which I fully expect without a flash) yet shouldn't it use a faster shutter speed as the flash will be providing tons of light?

Can TTL even be used with Av mode? Or should I be using Manual mode, setting my own aperture, ISO and shutter speed, and letting the flash throw out the correct amount of light needed to give a correct exposure with my manual settings?

tl;dr why doesn't TTL work for me and what modes can I use it in?
 
If you use TTL in Av mode, it meters for the background being correctly exposed. If you're in a dark place, it'll adjust the shutter speed so that the background is correctly exposed without the flash output. Why, I don't know.

When I use flash, I either stick it in P if I'm just doing rough TTL, or go fully manual.
 
I also agree it is a little odd/frustrating how canon flashes behave in AV mode. As growse said in AV mode it will use the flash as a fill flash on the subject, the slow shutter speed is to correctly expose the background. In low light without a tripod it is pretty much useless, not to mention the subject needs to be still. I do find it odd how they came to the conclusion that AV mode should be linked to fill flash.

I tend to always stick with manual when using the flash.
 
2StepSteve said:
I also agree it is a little odd/frustrating how canon flashes behave in AV mode. As growse said in AV mode it will use the flash as a fill flash on the subject, the slow shutter speed is to correctly expose the background. In low light without a tripod it is pretty much useless, not to mention the subject needs to be still. I do find it odd how they came to the conclusion that AV mode should be linked to fill flash.

I tend to always stick with manual when using the flash.
Click to expand...

Correct, though I would use the term "fill flash" to refer to a supplemental burst of flash to fill in the shadow, and I'm not sure how ETTL handles the exposure control on the subject in Good light ( i assume the same as it's metering an background average anyway)

When using Flash in Av mode the subject will be correctly exposed by the main light source; the flash. The Background metering will select shutter speed based onthe aperture selected for a "correct" exposure. ETTL will cut flash power when foreground subject is "correctly" exposed.

If you set the same aperture/shutter speed combination in Tv or M, the flash output from ETTL control would not be the same. I assume canon linked t like that as they thought people would like to use it.

For most Flash shots, I use Manual.
 
On the 7D you can set the flash sync to max, which I think is 1/250 from memory, if you're worried about shutter speed. (edit: or is that just with a speedlite?)
 
Av mode basically reads the BG as said. It's great for fill-flash but it's not designed for super low light. To do this you dial in you best ambient light setting (say ISO1250, 1/125, f/2.8) this might meter as 1 stop underexposed. Then when you fire the flash it's mixed with as much ambient light as possible and because yor cameras sensitivities and aperture are wider the flash will also reach further and recycle faster.
 
you should also be able to lock the shutter speed (its in custom settings on my 1000d) for flash sync to around 1/200s. the camera then seems to tell the flash how much power it needs, but IMO its just easier to stick it in ISO200 and use 1/16th power (manual setting on the nissin) as a starting point to see how it does.

you should just be able to adjust the power output to meet your needs then by checking the histogram.

I have exactly the same flash as you, and that's how i work with it in AV anywho
 
Paul_Canning said:
Ok, so I got an external flash (nissin di622) that supports E-TTL/TTL.

I have the TTL mode turned on on the flash (it ovvers manual and slave modes too) and I use Av mode on my camera (canon 7D)

In dark indoor environments, the shutter speed is quite low (which I fully expect without a flash) yet shouldn't it use a faster shutter speed as the flash will be providing tons of light?
Click to expand...


OH! ive found that using flash exposure lock helps here! if i use FEL, the camera will meter based on the exposure with the flash, giving you a faster shutter speed.

I still reckon the flash shutter sync lock method allows for more creativity though
 
I can confirm that the Sync speed on a 400D is indeed 200th, and I think the EOS 7D is 250th. I have a 7D and I have not read that part of the manual yet ! lol
Good luck with flash as they a re difficult area on DSLR to get to grips with !
 
2StepSteve said:
I also agree it is a little odd/frustrating how canon flashes behave in AV mode. As growse said in AV mode it will use the flash as a fill flash on the subject, the slow shutter speed is to correctly expose the background. In low light without a tripod it is pretty much useless, not to mention the subject needs to be still.
Click to expand...

The flash freezes the motion, though, since the flash duration is measured in the thousandths of a second. Doing it that way is the best way by far: you freeze motion in your subject, but you don't have the horrible look of a bright subject on a totally black background that you'd get if you tried to freeze subject motion with your shutter speed.
 
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