FE lock and alternative usage

[brian_donaldson1]

While at a gathing the other night, I was getting ready to take a

photo. My 20D was pointed down and I accidently hit the * button and

the flash went off. I was shocked.

 

When I got home I read up on what that button did (besides for viewing

playback). Well now the old brain is working overtime and I need some

professional guidance.

 

I now understand that the FE lock is used to maintain a flash exposure

setting in memormy, but for only 16 seconds (I believe). That would

have been perfect for this gathering, I did not move but my subject

did. If I want to maintain the same exposure setting with the flash

but for longer periods of time, can I not just get the meter settings

then set the camera to M and program those exposure settings? Would

that work or am I missing something?

 

Was this enough information? Thoughts?

[digitmstr]

>>can I not just get the meter settings then set the camera to M and program those exposure settings? Would that work or am I missing something?<<

 

FEL (Flash exposure lock) works on the FLASH output only, doesn't do anything to the camera's aperture and shutter settings. Therefore, if you set the camera to M you'll only change the AMBIENT light not, the flash output, which is ONLY controlled by the E-TTL (including FEC, FEL and EC).

 

Once the FEL expires you'll have to take another reading. The only other alternative would be to use the flash in MANUAL mode (E-TTL OFF) and use a flash meter to determine the exposure. In that case, you must use the camera in M mode and take a separate ambient light reading. That would be the best level of control one could achieve.

[brian_donaldson1]

Yep, I'd say that I was deffinitly missing something. Thanks!

[athinkle]

Doesn't FE lock also work on a sort of "flash spot metering" basis, taking only the value for a small part of the frame? That's what my 3 does, so I'd assume it's probably similar in the 20D. That would be important for something like a wedding where you may be running into extremes of contrast.

[mark u]

Some confusing responses...

 

If you hold the * button down after depressing it, the reading is maintained (see the manual). However, if your subject is moving (and therefore the flash-subject distance is changing), or the subject becomes lighter/darker than metered (e.g. turning to present different coloured clothing), the metered flash exposure will no longer be appropriate.

 

Flash metering on the 20D uses the E-TTL II algorithm, which depends on the setting of CF 14:

 

http://photonotes.org/articles/eos-flash/#ettlii

 

FEL operation is described here:

 

http://photonotes.org/articles/eos-flash/index3.html#fel

 

Setting a constant exposure in M mode only applies to the selected aperture and shutter speed, not the strength of the flash.

[eosdoc]

Beware that any automatic adjustments, such as <a href=

http://eosdoc.com/manuals?q=NEVEC

>NEVEC</a>, are applied when you push FEL.

<P>

And if you understand FEL, you <a href=

http://eosdoc.com/manuals?q=fakeFEC

>adapt</a> it can make full use of the system.

[digitmstr]

>>Some confusing responses...<<

 

How's my response confusing? He asked:

 

"can I not just get the meter settings then set the camera to M and program those exposure settings?"

 

which means he *thought* he could manually set the flash settings resulting from FEL, which of course it's not possible. And that's exactly what I answered. And he understood it very well, hence his reply.

 

What are you confused about my post?