EXPERTS: Help! How does Spot/Eval/Center affect FEL? (i only

[sprockett]

From what i know:
Pressing the FEL/AEL button during Av/Tv (fill flash) has 2 separate processes:
1. Calculates ambient light exposure.
2. E-TTL calculates Flash exposure.

***The question: ***
How do the different metering modes affect the 2 separate processes? I have heard that the metering modes ONLY affect AEL, and FEL always SPOT meters no matter what metering modeis chosen.

***Scenario illustrating my problem:***
1. Auditorium, with foreground target 2m away, and dark background (unlit stage)
2. Spot meter mode

Assuming i want BOTH foreground target AND
background to be properly exposed (all nicely lit up),
how is this possible?

If i FEL (spot meter) the Foreground target, the background will be underexposed, because EXPOSURE is calculated based on what is in the SPOT (which is the bright foreground).

If I FEL (spot meter) the background, E-TTL calculates flash output based on reflectance of the BACKGROUND, hence won't Foreground Target be OVEREXPOSED?

I know for higher end DSLRS, there is a separate FEL and AEL button. So one can LOCK exposure for the background, and LOCK FLASH exposure for the foreground target...Thus Background is nicely exposed, and enuff fill flash illuminates the FOREGROUND target w/o overexposing

However, D60s and below, only have a combined FEL/AEL button...

What do i do? I also still don't understand how FEL works in relation to SPOT/EVAL/CENTER metering...

[Stoneh]

Dunno about all that, I usually let the E-TLL do the work for subjects in front and a slow shutter speed for the background

[rdenney]

It seems to me you are giving the camera an impossible situation. The light from the flash is determined by distance. If the background is well behind the foreground, and if the aperture is open enough to allow the flash to properly expose the background, the foreground will be blown out. This would be true even without the spotlights.

That's why studios use background lights.

If the spotlights on the foreground subject are sufficiently bright, you might be able to expose the background enough to pull it up in Photoshop without blowing out the foreground. You'd have to rely on the ambient spotlights to light the foreground subject. Thus, I would meter using partial mode on the subject, and set the flash compensation to two stops underexposure. This should not add too much lighting to the subject but it may bring up the background just enough to be able to work with it. But from a camera-mounted flash, equally lighting a near and distant object with the same flash is impossible.

Rick "who thinks this is why the pros often use radio-slaved room-filling ceiling flashes" Denney

[sprockett]

i understand what ur trying to say,

but actually, what im trying to accomplish is the following:


1. Fill Flash for the fore ground AND
2. a Long enough shutter speed to expose the dark background.

(i hope u understand im not trying to illuminate EVERYTHING with my flash)

This way, BOTH foreground (illuminated by the fill flash) AND background (exposed properly via longer shutter speed) look properly lit.

Ideally, I would AEL the Background, so the camera selects a shutter speed long enough to expose the background,

and then i would FEL the foreground, so E-TTL calculates enough power to light up the foreground.

However, for 10D and lower cameras, By pressing the * button, BOTH FEL and AEL occur simultaneously at the metering point (be it EVAL,CENTRE,SPOT etc).

Im just wondering how i can over come this, and whether anyone knows exactly how FEL/AEL works in relation to the different metering modes...

[Pekka]

sprockett wrote:
Assuming i want BOTH foreground target AND
background to be properly exposed (all nicely lit up),
how is this possible?


Answer is Manual mode. Read camera metering (I use always center weighted), set exposure so that it slightly below normal ambient light exposure, and use flash as ETTL fill (FEL if needed). Or, better way IMHO is to put flash in manual mode and change exposure from camera: you can decide if it is speed, ISO or aperture which you change to control the light, and you'll never get any ETTL "surprises". In doubt do couple of quick tests and adjust based on that. Or just use experience - most situations can be either rehearsed, or it's been there done that kind of stuff.

Sounds like you're in process of going very deep into technical side of photography. Maybe you have forgotten how perfectly simple it basically is. Real difficulties come with framing, position, being there and seeing, but not from choosing speed, aperture, ISO or flash. :)

[sprockett]

thank u pekka.. in my quest to fully understand the electronics of my camera, i have forgotten what taking a picture really means.

[sprockett]

actually i was thinking , and have come up with a possible soln..

Scenario: Slightly lit foreground with dark background
Want to achieve: Fore/Background properly lit

Preparation:
1. Switch on flash to ensure capacitor is charged up.
2. Switch it back off.

The shot:
1.Spot meter BACKGROUND and AEL (pressing the * will only AEL because flash is off)
2. Switch flash back on, recompose, and fire. Preflash fires, but metering off the foreground target.


Seems to work well!

Tell me what u guys think