What ttl flash metering mode do you prefer?

What ttl flash metering mode do you prefer?

Spot, Evaluative, Center Weighted average, Partial, etc…?

Photo Example:

Element 1: Blue water in the back, good exposure on manual mode (f4, 1/90sec, iso 400) no flash needed.

Element 2: Turtle in the front that needs a little flash.

I would personaly prefer the spot mode (on the turtle) with a ttl flash, but it’s very difficult to use the finder underwater aiming at a precise point.

I'm fairly new to all this myself (ignore post count - I yap way more than I shoot) but if you can't put the 'spot' on the turtle to meter during the shot, then how can you frame it? The zone shouldn't be THAT small....

I'd say you're fine with spot or center-weighted type modes. I found I had a harder time getting AF to focus where I wanted than getting the TTL metering to expose right, until I turned off the left and right AF zones for center-only (I'm on an older Olympus E-system DSLR with only 3 autofocus areas). Then if I wanted to intentionally offcenter a subject for framing I'd center, half-press for focus and metering, and then reframe before depressing all the way. Otherwise close-backgrounds like an eel peeking out of a nook in the coral would be nicely focused on the coral to one side or the other of the nicely blurry eel. Don't know how many wonderfully composed shots I wasted that way....

Even with the blue-water background example, you're probably still using some sort of weighted average or spot mode, especially if you're after that nice blue background. Again, YMMV since I'm on an older E-system with the 4:3 sensor and can't really shoot up at ISO400 or higher without unacceptable noise, but I found I did better keeping the ISO lower (100 - 125), and could still lower the aperture (f5 or higher) with short exposures (1/125th or less) - at the worst the background goes to black vs. blue, but with TTL the subject was still quite well lit.

You are mixing your metering. There are potentially two types of metering going on. The first is your ambient light metering. This is your spot, center, evaluative (matrix in Nikonese). In your example, this would be your background exposure, i.e. whatever your meter says when you point it at something. It isn't clear in your example what setting was on your camera when you got the f4, 1/90 at ISO400. Did you spot the water or is it center weighted?

Now, assuming you are using TTL flash. There is a second metering going on that tells the flash how long to flash. How your camera does this is a big dark proprietary secret, but it is different and not necessarily related at all to your ambient light metering choice.

I am willing to guess that in your example, with TTL flash, you will overexpose the turtle, regardless of your metering choice. The flash doesn't know that only the turtle needs a "little" flash. It doesn't know it can lighten anything past about 5 ft. away, but it doesn't mind trying.

Here's the old film technique:

1) Set meter to spot. Camera on manual mode. Aim at blue water that I want to be neutral luminosity. Set exposure.

2) Strobes set to manual. Set strobe power based on Guide number/estimated distance to foreground subject. Bracket.

3) Pray on the way to the lab to pick up slides.

New digital technigue:

1) Set meter to matrix. Camera on manual mode. Set exposure at roughly what the meter says, maybe underexpose.

2) Set strobes to half power.

3) Shoot. Look at image/histogram.

4) Change f/stop for background exposure adjustment. Change strobe power for foreground exposure adjustment.

TTL Flash (I don't want to mess with 'nuttin)

1) Set to matrix meter.

2) Set exposure comp to between -.5 and -2.0

3) Fire away.

4) Adjust exposure comp if using digital.

New digital technigue:

1) Set meter to matrix. Camera on manual mode. Set exposure at roughly what the meter says, maybe underexpose.

2) Set strobes to half power.

3) Shoot. Look at image/histogram.

4) Change f/stop for background exposure adjustment. Change strobe power for foreground exposure adjustment.

I am trying to figure out how to use a strobe and struggling a bit. I have been looking on here and reading a few books, (eg Martin Edge) I was under the impression that the shutter speed adjusted the backgroung exposure and the f/stop would adjust the flash exposure and the background.... the strobe I have at the moment only has full and half power so I cant make too many adjustments on the strobe alone....

New digital technigue:

 

1) Set meter to matrix. Camera on manual mode. Set exposure at roughly what the meter says, maybe underexpose.

2) Set strobes to half power.

3) Shoot. Look at image/histogram.

4) Change f/stop for background exposure adjustment. Change strobe power for foreground exposure adjustment.

 

 

I am trying to figure out how to use a strobe and struggling a bit. I have been looking on here and reading a few books, (eg Martin Edge) I was under the impression that the shutter speed adjusted the backgroung exposure and the f/stop would adjust the flash exposure and the background.... the strobe I have at the moment only has full and half power so I cant make too many adjustments on the strobe alone....

In TTL (thru the lens), the flash actually will turn off early (the formal term is 'quenching') when the camera reports a certain level of 'exposure' was seen through the lens. As scorpio correctly corrected me, this can't happen fast enough for really close subjects, nor is it always related to the metering chosen to set the 'right' level of desired exposure in the first place - but I do still think they're related. Set to evaluative and shooting one bright object on a mostly dark background might not prompt the TTL to start the quench as quickly as if you were set to spot...

...or do I still have my head up my <beep>?

In your case, sounds like you don't have a TTL but a manual flash. TTL requires some sort of multipin electrical sync cable right now (optical TTL is possible, but right now to my knowledge optical cabling is only used as a trigger, not also as a TTL data channel, for underwater setups).

... the strobe I have at the moment only has full and half power...

In that case you need a strobe arm that will let you effectively bracket the strobe power by pulling back, increasing the strobe-to-subject distance, and reducing the apparent brightness of the strobe. OR use a manual strobe setting and bracket the f-stop (you may have to use a relatievly slow shutter speed to give you a high enough f-stop).

I use Inon strobes and optically linked sTTL, but often limit the strobe power to 1/2, 1/4 or even 1/8, so that the sTTL puts a limit on the maximum exposure, but the variable power actually does the work of getting the lighting right; I guess that this is a sort of hybrid "manual TTL".

Tim

I was under the impression that the shutter speed adjusted the backgroung exposure and the f/stop would adjust the flash exposure and the background.... the strobe I have at the moment only has full and half power so I cant make too many adjustments on the strobe alone....

If, by background exposure, you mean that part of the frame that is not lit by strobe, then both shutter speed and aperture can be used to adjust exposure.

If you have limited or no control over strobe power, then you must adjust aperture to get the foreground exposure correct and shutter speed to get the background exposure correct. This is not easy. As Tim mentioned, if your background exposure is OK and your foreground exposure is a little off, just shove your strobe closer or farther away.

If, by background exposure, you mean that part of the frame that is not lit by strobe, then both shutter speed and aperture can be used to adjust exposure.

 

If you have limited or no control over strobe power, then you must adjust aperture to get the foreground exposure correct and shutter speed to get the background exposure correct. This is not easy. As Tim mentioned, if your background exposure is OK and your foreground exposure is a little off, just shove your strobe closer or farther away.

Tim, Scorpio_fish,

Thanks for the input. I will go and play in the bay and see what happens........everything used to be so easy on the compact, it like starting all over again!!!!!

Thanks again

Duncan