TTL Question?

[WOODMAN]

I have a C5050 and a D125 strobe and the ikelite housing, which I don't get to use nearly enough. I picked this setup partially due to the TTL availability, and I have used it for about a year now. I am wondering just how usefull the TTL really is. As I said, I haven't really used the setup that much yet, and hope to exercise it much more on my upcoming trip to the Bahamas in late April, and I thought I would ask you guys what you thought. I got some really nice shots recently in Cozumel, but it seemed like there were times when the TTL option on the strobe didn't really work well, and I had the manually power it down a ways to get better exposures. This particularly happened at night ( TTL overexposed crabs badly), and also it seemed to have trouble exposing a nurse shark that was tucked way back at the back of a deep underhang ( seemed to underexpose this one ). I just wonder what you folks thought. I have the Ikelite digital housing, but not the one with all the fancy strobe adjustment buttons on the back. Woody

 

[RonFrank]

You have a lack of understanding of how light meters work. This is NOT just in the case of flash, but in general. This is a photo 101 topic.

I'm NOT going to go into a detailed explaination. You really need to find some resources (and there are PLENTY) and then ask specific questions once you have some understanding of how reflective meters work, and how they control the exposure.

To give you some help, most meters are based on an 18% grey reflective overall evaluation. When the subject matter is highly reflective or white, or not reflective, or black, the meter continues to act as if the overall expose is based on an 18% grey mix. That will result in underexposure in the case of white, and overexposure in the case of black because the camera thinks that there is either more light than there really is (white) or less (black).

It would be nice to always get perfect exposures in all situations, however regardless of how easy it has become to take good photos without a clue of how things work, the reality is that if you don't understand the technology that your are using, you are going to have issues with some conditions. I'm always amazed that when people get good photo's they proudly take credit, and when they don't they blame the technology.

You indicate that the system did not really work well, however what I think you SHOULD be saying is that the photographer did not really work well. You are on your way to getting a better working photographer behind the lens by asking questions. There is nothing wrong with your setup, you just need to become a more knowledgable user.

 

[bobf]

Woodman,

I understand that you have the c5050, an Ikelite housing, and a DS 125. I have one question.

How is the strobe receiving its signals to fire and quench in the TTL mode?

Is the strobe hardwired to the housing with a sync cord and therefore relying on Olympus TTL? Or are you using the Ikelite gray TTL sensor to optically monitor the c5050 onboard flash?

If you are relying on the gray TTL sensor, that may not be as reliable in certain situations. If you are not hardwired with the correct sync cord directly to the housing for "true" Olympus TTL as controlled by the camera, then Ikelite now recommends the black manual controller with your rig.

For more information regarding your setup, Peter Schulz has compiled the most comprehensive collection of helpful and insightful knowledge on the Ikelte~Olympus c5050 system:

http://www.splashdowndivers.com/photo_gallery/underwater_photography/up_ikelite_olympus_ttl.htm


More useful links:

correct sync cord: http://www.ikelite.com/web_pages/sync_cords.html
settings guide: http://www.ikelite.com/web_pages/gide_o5050.html

I'd like to add:

Sometimes TTL metering can be confused if not enough surfaces of average reflectance are present within the photographic composition. In other words, say you have only a small crab in the lower left hand corner of your composition and the remainder of the image is of open water. Water itself is a poor reflector of light. Most of the light emitted from the strobe therefore will be lost "in space", not reflected off any object and returned to the TTL sensor. The TTL sensor then will continue to call for more light to help expose the space where open water is present, subsequently overexposing the area of the composition that does reflect the strobe light back to the sensor. Result: overexposed foreground.

hth,
b

 

[WOODMAN]

The strobe is hardwired to the camera through the appropriate Ikelite sync cord, which is connected to that special bulkhead which has the TTL circuitry to mate with the camera. I am sure that there is nothing wrong with the equipment, as it performs very well for most shots. There are situations which tend to fool the meter, as has been pointed out here, and that's what I am seeking to understand. The problem with the crabs has come up before, with a different camera which had no real control of the strobe, and they seem to overexpose even when they are filling most of the frame, and the background comes out okay. Strange. The nurse shark surprised me, but then it was hard to see that fellow at first, even when it was pointed out to me, and I suppose that the camera had trouble with this also? It was about 6-8 feet away, and I always hear that strobes are useless beyond 6 ft. Maybe that dark hole just overpowered the strobe? But the D125 has a pretty good light output, so I'm not sure about that. The shots seemed to be focused okay, just too dark. Maybe the darn thing was farther away than I thought. Distances can really be decieving underwater, as all of you know. Woody

 

[WOODMAN]

Oh, I forgot to mention-I am well aware of the superb work done by Peter at Splashdown Divers, and had set my camera with all of his recommended settings. I think I was using My Mode 1 for both of the situations described above. Woody