Olympus C-5050 slave mode

I've been playing around with various flash modes of the C-5050 and there's something I'd like to find out about the slave flash mode. I know that - at least some - underwater strobes handle different power settings (full, 1/2, 1/4 etc.) by changing the flash-on duration while keeping the actual light output same. When in slave mode, the C-5050 internal flash intensity can be set to a value from 1 to 10. Does this setting change the flash on duration while keeping the actual light output constant?

If that's the way the slave flash works, I'm thinking may be this feature can be used sort of like a manual slave controller. By changing the slave flash intensity on the C-5050, it could be possible to get 10 level output from a DS-125 set to TTL with the Ikelite TTL slave sensor.

Any thoughts?

I think that when you dial the flash down on the Oly 5050 in slave mode, it lowers the power output - the flash duration is unaffected.

HTH

James Wiseman

Lots of confusion here.....

I don't have a C5050 or a DS-125, but based on what I know about how strobes work, the only variable is time. You can't change the intensity without really messing up the color temperature, a very basic law of physics.

Since the slave mode on the C5050 may only be intended to be use as a trigger, it's possible they can just lower the power output. The way to test it is to take a few photos using the various output levels with a fixed white balance and adjust the f-stop to get the same exposure. Use the highest shutter setting to keep any background light from messing up the experiment. If the colors come out the same then it's the flash duration that's varied. This is what I expect.

If that is true then you can use it as a flash controller for the DS-125. Maybe Ike can jump in and tell me I'm all wet, but I think that has to work on timing: flash on -> DS-125 on; flash off -> DS-125 off. I can't see how such a thing can be built any other way.

On the other hand if the C5050 slave flash works by changing intensity, you are out of luck.

Did a quick experiment:

I put the DS125 in TTL mode and used slave level 1 and took a photo. Then put it to level 10 and took another photo.

The picture was brighter with the the slave set at 10 so I would imagine the C5050 varies the duration of the slave flash and not the intensity.

I'm not sure why you would want to use the DS125 in TTL mode with the flash set to slave though......

This way you can use the camera to get 10 levels of power adjustment on the output of the DS125. This is similar to the function of the new Ikelite slave sensor.

herbko is right, this is what I had in mind when I posted this query. I thought the slave mode could be used like a built-in manual slave controller. Of course, this is not going to be an easy task even if it works right, because every time you need to change slave flash intensity, you have to go through a succession of menu operations to do it. Now, if only the custom button could be programmed to set slave flash intensity....

Turquoise's post is what I meant when I asked "I'm not sure why you would want to use the DS125 in TTL mode with the flash set to slave". It's pretty hard changing the slave level settings....

I use a C5050 with PT-015. I bought a DS50 a few weeks ago with the TTL sensor and tried it out on a dive trip to Lembeh Strait last week. After a couple of dives I gave up on the strobe as the photos were always way underexposed.

After I got back I did a few test shots on the table at home, and a few results are at

uk.photos.yahoo.com/bc/d3m2m

(look at the "DS50 tests" folder; and BTW they are not in numerical order on the page so check the number).

The photos are all identical setup except with differences as follows:

1. Internal flash set to compensation -0.3 (no particular reason); DS50@off

2. Internal @-0.3; DS50@TTL

3. Internal @-0.3 but blocked; DS50@TTL

4. Flash off

5. Internal @Slave 1; DS50@off

6. Internal @Slave 5; DS50@off

7. Internal @Slave 1 but blocked; DS50@TTL

8. Internal @Slave 5 but blocked; DS50@TTL

9. Internal @Slave 5 but blocked; DS50@Manual

I expected the results of 1,2,3 to be substantially the same (ie TTL should produce the same exposure with any combination of internal strobe and DS50 on or off) but obviously that's not what happened.

I suspect what is happening is that the C5050 internal flash is varying intensity rather than duration of the flash to achieve the desired exposure, and the amount of light dumped by the DS50 in TTL mode depends only on the duration. I draw this conclusion partly by comparing photos 7&8 which appear to be identical; however it's possible that the operation in slave mode is based on intensity whereas the operation in slow sync mode is based on duration, in which case there must be another problem.

On the other hand maybe there's a problem with the particular TTL sensor unit or the strobe. I have sent an eMail to Ikelite asking about this, but since that was only a few minutes ago I'm not expecting a response yet ...

-David

After I got back I did a few test shots on the table at home

If you'll forgive me for stealing some of your test photos . . .

I recreated your test here on my living room floor, albeit with a DS-125, not a DS-50. I did mine with the camera at f8.0, 1/1000th to reduce any effect of ambient light. My results are very close to yours. I put both of our results together in a crude table at:

http://members.cox.net/moelrich/images/str...trobe_tests.htm

What I take away from this is:

1. the external strobe always quenches early.

2. The camera is definitely sensing the light from the external strobe.

3. The external strobe is stronger than the internal one.

Depending on how the camera is reacting to the external strobe's light on the preflash and how the sensor is actually mirroring the camera's operation, the combination of these factors could explain everything, .

After a couple of dives I gave up on the strobe as the photos were always way underexposed

Just out of curiosity, did you try the combination (everything in TTL mode) of the strobe and camera with positive flash compensation dialed into the camera. In my tests before my trip to Bonaire in October (with my old C-4040z), I found that the strobe was always underexposing. Since it was always underexposing, I always dialed around +1.0 (acutally +0.7 to +1.3 depending on how things were progressing) and got very good exposures.

Maybe Ike can explain why the external strobes are quenching early. For now, I have a system that works . . .

HTH,

Mike

Interesting to see that someone else's experience suggests I'm not just doing something completely silly. (When things don't work I always wonder!)

Just to clarify, except where specified, in my tests I did not block the internal flash excpet where specified, so in some of my shots it's a combination of internal and strobe.

On the trip, with flash compensation of +2.0 (the max) and sometimes I would get shots which were reasonably close to properly exposed. Usually they wouldn't be sufficiently exposed even at +2.0. It changed from shot to shot, until I reached a tentative conclusion that the time the strobe was firing was independent of the situation.

Maybe the shots could be rescued in Photoshop, but I don't have enough experience to know how much can be done there and I didn't want to risk have too many shots too far underexposed. For my purposes (Mainly: letting people knopw what I had seen), I'd prefer to accept the additional backscatter and just get sensible exposure at the time of shooting...

-David

If you're getting underexposures with +2.0 dialed in, then something is probabaly amiss. However, you're test shots don't look that bad at -0.3. How did you have the sensor pointed? Was it right next to the camera?

Mike