preflash and exposure lock

[ali_baba2]

When I press the exposure lock button on my Canon the camera flashes the preflash, its actually using it to catch

the right exposure and lock it, or I misunderstood the way it works?

 

The reason for the question is that I have 3 strobes, one sigma EF530 and two old maxxum 2800. I intend to use all

of them offcamera with optical slaves and use the camera flash to trigger them (I do set the AF flashes as

"off"so its only the single preflash going before the actual flash).

Im making the optical eyes for the maxxum strobes myself, have enough junk electronic components to put them

together quickly and at zero cost, the point is that I could as easily add a small delay so that the eye will

ignore the preflash shot. Since the Sigma can be set as simple "dumb" optical slave, to be triggered by the onboard flash and DOESNT ignore the preflash Im wondering if I should make the other two "dumb" as well, no delay, so all of 3 strobes will work exactly the same, if I build them to ignore the preflash then I will have to make a smart eye even for the Sigma

strobe.

Am I wrong in thinking that if i keep the optical slave "dumb", triggered by the preflash also, then I have the

benefit that when i press the exposure lock button, the preflash will trigger all the other flashes and the

camera would then expose correctly taking in account even all the other strobes, so from then i can shoot away as soon as the strobes recycle keeping the exposure locked?

[mukul_dube]

<p>I do not know if it is possible to set your camera not to do the pre-flash. When I had a Canon A80, that is how I set it. It then became possible to use an ordinary optical slave with an ordinary manual flash-gun, with the camera on manual. Your proposed technique may work; but the handicap of having to wait for all the flash-guns to recharge will probably limit you to still life work.</p>

[William Michael]

<blockquote>

<p>I have the benefit that when i press the exposure lock button, the preflash will trigger all the other flashes <em>and the camera <strong>would then expose correctly</strong> taking in account even all the other strobes,</em> so from then i can shoot away as soon as the strobes recycle keeping the exposure locked?</p>

</blockquote>

<p>I don't think that you will get the "correct" exposure.<br>

<br /> Are you referring to Flash Exposure Lock? (FEL). That function works with the Canon E-TTL Flash Units. That is to say the Flash Unit "talks" to the camera. This is what we term a "dedicated" Flash Unit.<br /> <br /> I expect that the Flash units that you are using would need to be used as MANUAL flash units and you would manually calculate the exposure by setting the Flash Units POWER and/or setting the DISTANCE from the Subject - OR - by using a Flash Exposure Meter.</p>

<p>WW</p>

[Bill C]

<p>To the best of my knowledge, "flash exposure compensation" ONLY limits the power of the flash, and it must use the camera's TTL communication system to do so.</p>

<p>So unless you are using Canon's ETTL-capable flash units, either in the hot shoe or with the special hot-shoe-attached flash cable (or any special radio units with TTL capability), I don't believe your flash exposure lock will have any effect. (Except for the camera's built-in flash, which IS affected by flash expsoure lock.)</p>

[cabbiinc]

<p>Actually it is possible, but you'll likely find that it's not worth the trouble. Why not just buy optical slave triggers for the Maxxums and use the Sigma on camera to trigger them? http://www.flashzebra.com/products/0129/index.shtml</p>

<p>You can use FEC to trigger the preflash, then when you trigger the actual exposure it will only be one burst of light. You can time this yourself to trigger after your other flashes have recycled from the preflash. You however will have to be diligent to make sure that all slaves have recycled and that you still have FEC set (it auto disables after a time and also after each exposure). What the FEC would do is lock the onboard flash to whatever it saw was a proper exposure. It will not adjust anything in the camera to compensate for any external flash, you'll need to ensure that those three flashes are set properly for the settings on the camera.</p>

<p>On a side note, creating something from the Sigma flash to ignore the preflashes would likely be a wild goose chase. To use anything through the hotshoe the flash will require TTL communications, even if you set the flash to M mode. So you'd have to dig into the electronics of the flash itself. Frankly it's not worth it. I eventually gave my EF 530 Super away as I couldn't even sell it for $5 on my local Craigslist. Also depending on the mode and camera used there are sometimes more than one preflash coming from the camera, sometimes one. So trying to ignore them can be hit or miss.</p>

[ali_baba2]

Thanks guys, TTL communication wouldnt be an issue, all the offcamera strobes would be used as simple "dumb" strobes. I wasnt trying to have all the strobe communicating to compensate, they would all be on manual. I just thought that, since they would be also fired by the preflash, then the camera should be seeing the scene while its illuminated also by the other strobes while it is metering and expose accordingly, i.e. the camera would see a room illuminated by strobes rather than thinking its just a dark room... I guess ill set everything completely manually like i used to with my Yashica...

 

Dan, yes the optical eyes Im going to put together are like the Sonia ones at your link, basically I'd be replicating them using electronic components I already have sitting there gathering dust. the Sigma always did what i needed it to do without glitches up to now, but havent used it for anything too fancy yet so... crossing my fingers... I used it off camera few times, in slave setting the hotshoe triggers it normally.

[cabbiinc]

<p>In my previous post I kept saying FEC, when I should say FEL. Flash Exposure Lock. Just in case someone reads this in the future and is scratching their head.</p>