I just got a ike 125 with a ttl controller. I plan on covering the flash on the pt-015 /5050 housing to reduce back scatter. This defeats the TTL quench for the strobe. The question I have is are there benefits on having 10 manual settings with the manual EV controller as opposed to the 4 used with the Ike? A half fstop seems miniscule especially when I can just change the compensation on the 5050. I plan on shooting only in manual and tweaking the shutter speed to get the correct exposure. The other school of thought is to utilize the TTL function and on board flash. I guess you can't have it all. Any comments or abuse will be greatly appreciated

I don't understand your comment regarding the defeat of the TTL quench. The Ike TTL sensor usually is aimed at the on board Oly flash from above, looking down, preferably aimed slightly backwards to avoid picking up any influence from the strobe it is controlling. The Oly onboard flash is usually only blocked from the front, to avoid illuminating particulate in the water. This leaves the top of the housing and the on board flash still visible from above, where the TTL sensor can monitor the onboard flash behavior.

The TTL controller will offer you the option of either TTL metering or if you prefer, four manual steps, full, 1/2, 1/4/, and 1/8 power (total of four stops of light).

To achieve a full dump in manual with the TTL sensor, be sure to set the c5050's strobe to slave setting. With the TTL sensor, you may vary your style, manual or TTL, while underwater. That's as close as you cat get to having it all, imho.

I prefer shooting strobe output with manual settings for daytime use, but switch to TTL during night dives. TTL metering works especially well with macro compositions and therefore is quite consistent at night in achieving acceptable results, imho. TTL metering will struggle though with tarpon or other shiny objects (day or night).

The EV controller offers you control of 4 1/2 stops in ten, half step increments. One advantage of the EV controller for manual adjustments is that the controller is closer to the camera than the strobe is. This is especially convenient if you have long strobe arms. Reaching out a distance to change settings on the strobe itself can be cumbersome.

You can also control strobe influence by varying strobe to subject distance. Generally, one foot underwater is equivalent to one f/stop of light. Therefore, if you move your strobe back 6", you'll lower it's effective influence by 1/2 a stop.

BTW shutter speed, combined with chosen aperture, influences background exposure and has little effect on foreground exposure, which is controlled by aperture, distance, and strobe output. Shutter speed will also control motion blur.

FWIW I own a TTL sensor and a manual controller.

Thanks Robert, What I have done is tape off the front of the housings diffuser. The Ike ttl controller still sees the onboard flash but since the camera "thinks" it is giving the proper flash, the strobe does not fire with enough power. If I remove the tape it works great. I was just trying to get rid of any backscatter. Oly flash seems to be pretty powerful by itself. Thanks!

Bob, one more thing. If the strobe is set to ttl and is supposed to mimic the onboard flash, why are all of my pics under exposed when I tape off the onboard flash?

"If the strobe is set to ttl and is supposed to mimic the onboard flash, why are all of my pics under exposed when I tape off the onboard flash?"

Bruce,

Many possibilities....

The DS 125 may not be aimed properly at your subject. Use of the built in modeling light or attach a mini Q40 to help in aiming.

The TTL sensor may not be aimed properly and is picking up light emitted from the DS 125, forcing it to send a quench signal prematurely. Make sure the sensor is aimed at the onboard strobe, but slightly backwards, towards you, when taking images.

The camera may not be in sync with the DS 125 strobe. For TTL strobe metering, the c5050 should be set to preflash (not slave) and forced flash ( IN+ ). The DS 125 is set to TTL.

The TTL sensor slider switch should be set to the right to denote preflash camera use. Following link discusses options:

http://www.ikelite.com/web_pages/dsenswitch.html

Sliding the switch to the left is another option that may solve your problem. I would recommend exhausting other possibilities first. And as a reminder, never switch sensor slider positions underwater. You will flood the sensor.

You may have chosen ( manually ) an aperture that is too small for the distance between the subject and the strobe.

If everything appears otherwise to be in order and your results are still consistently underexposed, then use the Oly's exposure compensation mode to modify the outcome. Try +1 EV. This will tell the Oly that you want twice as much light as Oly's brain thinks is necessary for an acceptable exposure. +2 EV will double the light again.

And remember that even with the strongest strobes available*, the furthest you will be able to illuminate a subject from the strobe head is only 4-5 feet. So when it comes to strobe use, I was taught that if you're not close enough to touch it, then don't shoot it.

*With preflash cameras, the maximum guide number for a DS 125 controlled by a TTL sensor at ISO 100 is 22, 16 with the diffuser installed.

Bob,Thanks for the help.