Confused by lighting results

[norm982]

Let me start this by saying I know I used the strangest, and most ridiculous setup... I have fixed that problem, I just don't understand the results I got.

I was doing some table top photos using a studio style light tripped by an optical slave. So I used the aluminum foil over the pop up flash trick to trip the optical slave sensor without lighting the subject... that then fired the studio flash using direct light, no bounce, no softbox. I could not get a good exposure, everything was very under... I had to crank the ISO to 6400, open the fstop all the way (4 I believe) and slow the shutter down to 1/30 and it STILL was underexposed.

Then it hit me that I have a hotshoe to pc sync adapter and I plugged the camera directly into the flash.

Without changing anything else, I started shooting at 1/16th power on the flash unit, 1/200 shutter, ISO 100, and f8 or so.

So, like I said, I realize the optical slave was unnessary, I just don't understand why using the optical slave versus the pc cord would have had such drastic effects on the lighting.

Any ideas would be appreciated. I am using a Canon T2i.

Thank you,

Norman.

[OsmosisStudios]

Is your optical slave setup to ignore the TTL pre-flash from your pop-up? was the pop-up in TTL or manual?

If the pop-up flash is in TTL, it sends out 2 flashes: one before the exposure to judge the scene and another during exposure to light the scene. Most optical slaves don't know the difference and will trip the flash on the first, pre-flash, and therefore wont light the scene. To the eye, you might not be able to tell because the flashes are so close together.

[zona5101]

Originally Posted by OsmosisStudios

Is your optical slave setup to ignore the TTL pre-flash from your pop-up? was the pop-up in TTL or manual?

If the pop-up flash is in TTL, it sends out 2 flashes: one before the exposure to judge the scene and another during exposure to light the scene. Most optical slaves don't know the difference and will trip the flash on the first, pre-flash, and therefore wont light the scene. To the eye, you might not be able to tell because the flashes are so close together.

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plus characters to make 10...

[norm982]

Thank you for the responses... I did see the on board flash doing a preflash, I thought that was to assist with the auto focus, not thinking about the exposure.

I did allow enough time between the preflash and the flash for the studio light to recharge, and I did make sure it fired each time.

As for the slave unit, it is a very simple slave flash unit... looks like a very cheap flash, but it will trigger optically... there are no settings but high or low. And since I was really just using it as a trigger, I even taped over the flash to prevent any light from reaching the subject.

But it definitely sounds like it was a ttl issue for the exposure.

Once I put the synch cord adapter on I was very happy with the exposures I was getting, and I played with it again today.

Thanks for the feedback!

[zona5101]

They make optical slaves that can ignore the pre-flash. I have one made by speedotron - i think it was $25 bucks. However save your money and get radio triggers - better for lots of reasons.