2 strobes with y-ttl and brightness questions

[rameus]

hello everyone!

just got back from a trip to the Maldives and it was fantastic! a lot of reef sharks, some mantas, dolphins the whole day (on the surface or diving) and a lot of fun on an excellent boat!

after one dive i apparently forgot to switch of one of my Ikelite DS-160 substrobes so the battery was dead for the next dive. Unfortunately I just figured that out after jumping and getting my camera ready to take some closeup shots of a nice wreck we visited. since one of the strobes was dead (not the master-strobe!) I figured I could just switch it off and the one which still had battery would work but IT DIDN'T! Could anyone tell me why? I tried wo switch both of them on or just one, nothing worked. therefore there was no underwater photography on that dive with my camera... ;-)

something else I found out: generally my photos are too bright when I shoot underwater. my settings are for the flash: normal ttl and for the camera shutterspeed 1/60.

if you have comments to one or both of the topics, feel free to comment.

thom

 

[Ardy]

The only thing I can think is that the second flash was slaving off the master. If it was done with a cable/fibre-optic link to both then I haven't a clue.

If your flashes are over exposing then the TTL is not working properly. Does this happen all the time? or just on odd shots? TTL can over expose if the subject gives it a reading that will OE due to TTL trying to get to standard grey. You might want to try spot focusing to reduce over exposure on TTL.

 

[terson]

Thom,
More info please?
Camera, housing and sync cords???
Bruce

 

[diveanytime]

Why your 2nd strobe did not fire?
Maybe your camera did not see the strobe ready light signal? Your dual sync cords may be designed to see only the ready light signal from the primary strobe, so even with good battery power on the secondary strobe your camera will not see a strobe ready signal. You should try this out on land to see how the dual sync cord works or doesn't.

On your 2nd question on why your strobes are too bright/hot?
Are you shooting with exposure mode of manual? or auto or TV or AV?

 

[smoore]

I cannot comment on why one of the strobes did not work. The TTL question is one I may be able to provide more help with. Some strobes allow you to to adjust the flash duration (power) even in TTL mode. It may be that you had the strobe set to an increased duration setting, that is positive exposure compensation. It is also possible that you have set the camera to overexpose images using one of the compensation settings on the camera. For example if you are shooting in shutter priority mode, which it appears you may be given a shutter speed of 1/60th, then you should check that you do not have any positive compensation set. With the Olympus Pen cameras, for example, you can actually set both the camera flash and the camera to both provide positive compensation. This means that there are 3 different settings (two in the camera and one for the external strobe) which can be adjusted. It is very easy to have one of these positive compensation settings on and not even realize it.

I find the TTL almost always over exposes silver fish and when I shoot them, I deliberately undercompensate them by about a full f stop. The comment about overexposing the image because of a dark background by Ardy also makes sense. To address this issue you may wish to change the metering to centre weighted (my preference) or spot so that the flash attempts to properly expose the foreground portion of the image.

Finally, if images are significantly overexposed you can usually tell this when you review the pictures underwater and then you can reshoot the image with some negative compensationin with the flash or the camera. This, of course, means that you are adjusting the the camera or flash to correct TTL errors. You may eventually decide that it makes more sense to get used to shooting in full manual. The other advantage of full manual is that there is no pre-flash from the camera's strobe so there is much less delay in getting your picture. This can make a big difference with subjects that are in motion. You are much less likely to expose the image after the fish has turned away from you.

Good luck figuring out what happened with the two strobes.