Wednesday, April 21, 2010

TTL multi segment sucks (sometimes)

Just a small interlude to show you why modern "superduper" TTL can drive you sometimes crazy and a good reason to shoot Manual. The very sophisticated microchip driven TTL "I evaluate ambient and flash in 1000 segments" can sometimes lead to strange results.

If you follow my blog you have realised that today's flash automatic at its highest form has evolved with ever more layers of technology. In my Blog I try to show the steps in this technical development and show examples of the advantages and disadvantages each technology presented.

Today's top model flashes have ALL of the past layers in them and come with thickly handbooks. My first flash had literally a one page instruction the size of a postcard.

In this Blog I want to show a short coming of the most current technology. I will not explain how we ended up with it, that will become clear with the future installments of the Blog.

Take a good look at the picture above.

I wanted to have a picture of the car, with Burj Khalifa in the blue evening light after sun down and a reflection of the cars headlights in the puddle. I planned the shot long ago, because puddles are rare and are not around for long in Dubai. The evening after the rain I went to the spot I had scouted out in advance. The camera was quite low. To get the perspective right and because I wanted the car to look a bit more aggressive. (As far as possible with a long limousine.)

I started in P mode adjusted the aperture to my liking and played around with the ambient light setting by dialing in some negative adjustment until I had the right background light level. Switch on my 4 Speedlights all in remote i-TTL driven by a commander.

The picture on top was the result? You see very, very little flash if you look carefully. I dialed the flash up with the commander as far as I could with pretty much the same result.

At that point I started swearing. The light moves fast, fast, fast when you are near the Equator.
I thought I made some mistake with the set-up and checked camera and flash settings.
All OK, all flashes firing.

Then it hit me: %/*-@#$% i-TTL. Two problems in the scenario:

1) If you dial down ambient light by reducing the main exposure compensation that reduces the complete exposure (my setting was at -2) so if you dial up flash exposure it is relative to this base setting. The maximum the controller allows is plus 3. (so my overall flash exposure was only overall plus 1)

2) The headlights from the car were in the picture. Causing the i-TTL to "think" that there is already waaay too much light in the highlights and suppressing the flash down to next to nothing

OK Switch Camera to Manual and all flashes to Manual.

There you are!

The problem is, that the design approach for i-TTL comes from the fill flash world. You know, models in bright sunlight further brightened up. That is what it does perfectly. It struggels in some other situations and specifically when you do not want to smooth out contrast but rather increase it.

Next post we go back to a time when such problems did not yet exist.
Stay tuned

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