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D300 & SB-900 - TTL Failure?

Rafi Epand , May 22, 2010; 04:47 p.m.

I shot a wedding recently with a new SB-900. Most of the time I shoot at ASA 1600 with the camera set to shutter priority. Flash was on camera in the standard position. I do switch to from Matrix metering to center weighted depending upon the lighting effect I want … I set the camera to JPEG, High Resolution. I am using Nikkor AF-S 16-85G-ED DX lens.

I am puzzled by what I regard as failure to the TTL system to provide enough light in certain situations:

a) Small Group of 5-8 people in the side of the hall with a gold drape background about a meter behind the group. (Center-Weighted metering)

b) Large group of about 30 shot in the hall with cream colored wall divider about 2 meters behind group. The first was the groom’s family and the second the brides. (Both Center-Weighted)

In these last shots I noticed the flash was not putting out enough power. For the second group I set the flash to +2 or +3 EV to get more power out and that solved the problem. (For the underexposed shots I compensated in post processing by adding fill light. But naturally I would have preferred to get it right the first time.) I noticed that if I left the flash set +1 or +2 EV… then close ups would be burned out so this is not an option.

My question is WHY? Why didn’t the camera / flash sense this an automatically compensate??? How can my settings be improved?

Responses


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Matt Laur , May 22, 2010; 04:56 p.m.

This was direct, on-camera, flash-straight-at-their-faces lighting ... or were you bouncing?

And since you were in shutter priority mode, what shutter speed were you using? Was the flash having to fast sync?

Nadine Ohara - SF Bay Area/CA , May 22, 2010; 10:26 p.m.

Why? Because TTL is an automated process, and as such cannot think. It only does what it is programmed to do. I don't shoot Nikon, so I can't give you detailed explanations of what i-TTL does in the various modes and metering modes. However, I don't have to know this to know that it isn't going to be perfect every time. This is why you have compensation control. With Canons, they are separate, with Nikons, there are certain times when they are integrated. Do your research, but know that you aren't going to get perfect exposure all the time. That much I can say with certainty.

Most pros familiarize themselves with the various exposure modes and do a lot of testing, to be able to predict how the systems react to various lighting conditions. Then, in the field, they compensate accordingly. This gets you close most of the time, and you just need to ride the compensation dial basically, "all the time". It is a fact of wedding photography life.

Frank Skomial , May 23, 2010; 01:05 a.m.

Most likely you exceeded the maximun number of flashes allowed in short period of time, and did not give enough time for the flash to cool down. When this happens the flash should shut down, unless you disabled that flash protection. If is overheated, it could misbehave producing less power and eventually end up with the tube destruction.

Flash tubes have a number of pops life span, and when that is exceeded, and the life of tube is near the end, the flash will produce diminished light output. The tube output gets reduced at higher temperatures.

I assume that you were waiting for the flash ready confirmation light and/or sound signal? If you did not let the flash fully recharge ? then the flash had no chance to output required energy, even if it was cool.

See if your flash tube quality was already compromised, by completely cooling it down, and testing at full power.

In one of my jobs, ages ago, while designing and prototyping flashes, I managed to blow, and deteriorate many various flash tubes on purpose to evaluate optimal parameters and life expectancy of the tube, or pushing tubes to the limit, mosty by applying parametrers well exceeding nominal, e.g. voltage, energy, trigger level, and tube operating temperature.

You have only tube temperature at your disposal that could possibly deteriorate the flash tube temporarily, until the tubes cools down, or permanently cripple the tube output.

Rafi Epand , May 23, 2010; 04:29 a.m.

1) Matt: Shutter speeds … I vary depending on the action. 80 for slow… or sometimes at 250. (250 is the normal Nikon sync speed.) But my failures were at 80th.

2) Flash was straight on… no bouncing. The TTL generally allows me to shoot a ‘natural’ photo that looks like available light. (This is the effect I like.)

3) Frank: I was carrying lots of spare AA’s and changed every 100-110-120 shots to be sure. I heard about this overheating issue with the SB-900 so I was monitoring this. And the problems I had were actually in “slow” group shots where my flash had time to recycle.

4) Nadine: I am going take your advice to heart and “ride the compensation dial” the next time. However, weddings move very fast. It scares me that I will make a mistake and have the wrong setting at the wrong time. I will have to do testing, and compare this to my SB-800 but the question still remains:

Since i-TTL shoots out a pre-flash it should ‘notice’ that there is not enough light and increase the power of the flash on its own. This is still the heart of the mystery.

Jerry Litynski , May 23, 2010; 11:56 a.m.

"I am using Nikkor AF-S 16-85G-ED DX lens."

The lens is not helping with your indoor flash shots. Getting a f1.4 or f2 lens will give a better chance....should you require f4 with the speedlight working. Your zoom lens, nice as it is, is not going to give fine results wide open. A f1.4 lens stopped down to f3.5 or f4 will be sharper.

Another solution is use a tripod or monopod, so you can get into the 1/10th second shutter speeds with the camera in 'S' mode, so the flash output will blend in the with the room lighting.

Bob Sunley , May 23, 2010; 02:29 p.m.

Highly reflective backgrounds can easily give you under exposed flash shots. The metering is anything but perfect in all situations, if it was you wouldn't need a compensate function. :) If you had dark gray walls or curtain the odds are the exposure would have been quite different, maybe even overexposed.
Way back before the days of any automation, shooting with flashbulbs or early electronic flashes, they had one light output, full blast or maybe half power on the high end electronic units. You set the aperture manually for every shot. You still had to compensate for exposure as the guide numbers were somewhat optimistic and assumed some light bouncing from walls and ceilings.
Things are somewhat easier now(big understatement), but as Nadine pointed out you really need to know how the automated functions work and have to know when and how much to manually compensate.

Nadine Ohara - SF Bay Area/CA , May 23, 2010; 03:10 p.m.

Rafi--there is no mystery. The pre flash is still carrying out it's program. An automated system of exposure can never be perfect every time--far from it. As Bob points out, mostly white or light walls can throw the pre flash off to underexpose. So can metallic backgrounds. So can light or dark clothes. Plus, the program the flash metering system is basing its responses on can only have so many variables to play with. It cannot know what you have in mind, and you cannot assume it will. There is no part of the flash metering system that can read your mind, in other words.

Unless you have inadvertently set something like negative compensation on the SB-900. You also cannot expect that one model works the same way as another. If you are used to the SB-800, you will have to re-learn settings for the SB-900.

Kevin Delson , May 23, 2010; 09:01 p.m.

Rafi,

The TTL generally allows me to shoot a ‘natural’ photo that looks like available light. (This is the effect I like.)

While this (mode) along with (TTL-BL) attempts to accomplish this, it rarely does. To get the appearance you did NOT use flash, manual mode is far more predictable. This gentleman's website has a good explanation with examples. LINK
I don't think you've grasped how TTL works yet. It is not a matter of testing, it is a matter of understanding how your Nikon meters in two of the three focusing modes as well as how the flash receives this data depending on what the meter is looking at.

I hope you are not attempting focus and re-compose while in any of the flash auto modes.
I've seen no mention of FV lock yet. I strongly suggest you look into it.

Since i-TTL shoots out a pre-flash it should ‘notice’ that there is not enough light and increase the power of the flash on its own. This is still the heart of the mystery.

There is no mystery here. Read above.
The (pre-flash) only notices what YOU point at.

Kevin Delson , May 23, 2010; 09:13 p.m.

To get the appearance you did NOT use flash, manual mode is far more predictable

Finger jam. :) Sorry

I meant to say

"To get the appearance of natural light you should NOT use TTL flash mode, manual mode is far more predictable"

Personally, I find the TTL modes more difficult to use insofar as predictability is concerned.
I DO use them from time to time when either the light is changing rapidly or I am moving around my subject. If I have at least 6 secs to think about it, the flash goes into manual mode.


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