Adding a strobe (or 2). How does the camera know?

[Storker]

When I am shooting WA (which is most of the time here in the Great Lakes) I always shoot a couple of "just water" shots to get the background dialed in the way I want it.

I guess that works well if you dive mostly square-ish profiles. A lot of my diving is shore diving, and also when I'm boat diving I tend to have more triangular than square profiles. Under those conditions, the lighting varies with quite a few EV from the deepest and up to the safety stop. So for me, aperture priority with operator control works better than manual.

I find that the aperture really determines the colour of the water (via degree of lightness) and once I have it set, I tend not to mess with it.

I'm surprised that you use aperture for primary control of the ambient. That's the parameter I try to keep as constant as possible since it also affects DOF and strobe reach. For controlling ambient I prefer adjusting shutter speed, secondarily ISO (although ISO of course also affects strobe reach).

@stuartv : As you can see, there's definitely more than one way to remove the epidermis of a domestic feline

 

[Stoo]

It certainly has a huge impact on DoF, but shooting from a distance with a 10mm lens, the DoF is pretty much a non issue.

 

[Storker]

Good point. Aperture still affects strobe exposure, though.

 

[stuartv]

Thanks, guys.

I guess it's time to stop asking so many questions and go get in the water and start playing with the camera!

 

[Cali_diver]

Thanks, guys.

I guess it's time to stop asking so many questions and go get in the water and start playing with the camera!

Sounds like a great idea. I was just recommending those sites to you based on your other Forum posts in addition to this one, so I apologize if they weren't helpful to you. I have been on quite a few photography trips and have watched people struggle to expose pictures properly. The professionals all handle these people the same way... by steering them away from AUTO. I don't think Jack was saying you have to be an expert, he was just trying to get you past the frustrations of shooting in AUTO. It sounds like you just need to get out and do it. Happy shooting and best of luck.

 

[smoore]

I too am shooting with Oly cameras and have found TTL to work quite well. I usually use it for macro or any static situation. If I am shooting fish that are swimming I prefer manual because the delay while the pre-flash fires almost always results in a shot that has the fish in a different position that I was attempting to capture.

 

[KeithG]

The camera doesn't know you have external flash.

When the internal flash fires, the external flash picks up the pre-flash that the camera fires.
The external flash then also fires a pre-flash...the camera uses the pre-flash to meter the shot.

Then the actual shot flash is fired, with the appropriate duration determined from the pre-flash.
The external flash then fires for that same duration as the internal flash.

Basically, internal and external flashes do pre-flash, and flash, at the same duration.
Camera only adjusts the duration of the internal flash...external flash in TTL mode mimics this same duration.

This only works if the camera does pre-flash..otherwise you are stuck with shooting manual flash settings on the external.

This is a great explanation of the theory behind using external strobes as optical slaves. In practise, YMMV depending upon the camera / strobe combination.

Some cameras emit more than 1 preflash. Some strobes can handle more than 1 pre-flash. Some combos are not compatible. This type of mismatch generally means total TTL failure. Your combo just will never work together.

More annoying is the issue of sporadic TTL failure under certain conditions. It may work perfectly in 1 situation, but fail totally in another. my first camera strobe combo ALWAYS failed when shooting against a sand bottom in shallow caribbean waters - it always significantly over exposed. The trick is to learn which situations TTL will work in.

I claim this is due to a mismatch in the light discharge curve between the strobe and what the camera expects. The preflash is a fast low power burst of light and is used to extrapolate the actual flash duration required. It allows the camera to guess ahead of time how long to leave the flash on for. If the external strobe discharges faster than expected, you will then get over exposure. If the external strobe discharges slower than expected, you will get under exposure.

Modern digital camera's query the flash attached to their hotshoe and so know what type of flash is attached and what it is capable of.

 

[Nemrod]

Strobes that support optical (simulated) s-TTL like the Inon D2000/S2000 and Z240 fool the camera. The camera, in Program or in Auto (with pre-flash selected in the camera flash menu) will fire a pre-flash which the camera uses to set the exposure prior to (before) the main flash and actual exposure. The Inon strobes (when set to s-TTL setting or to expect pre-flash) will also fire a pre-flash coordinated with the camera's pre-flash. Since the camera flash window is blocked the camera only sees the Inon strobe's pre-flash and sets the exposure accordingly.

And yes I know what I am talking about and fully understand how it all works.

The Inon Z and D strobes also have an Auto mode in addition to the s-TTL mode which uses an onboard optical sensor to control the flash output, in this case the camera flash is not used to do anything but to trigger the strobes. This method can be set with both pre-flash or without pre-flash selected in the camera flash menu and is best done to conserve camera battery power, de-select the pre-flash, set the Inon Z/D to no pre-flash (magnet switch on D and rotary select knob on the Z).

Hope that is clear as mud, it is really quite simple and by the way, both the s-TTL and the Auto mode exposure works wonderfully with most cameras. Manual is for thre birds and those who cannot figure out how to take advantage of technology available to them in those expensive strobes and highly developed cameras.

The YS strobes have similar modes and operating capabilities, depending upon the model.

N

 

[jzipfel]

Manual is for the birds and those who cannot figure out how to take advantage of technology available to them in those expensive strobes and highly developed cameras.

N

Yeah, Alex Mustard probably just needs to use technology to get better photos.
His old world manual style just doesn't cut it anymore.

 

[stuartv]

@Nemrod Thanks for all that!

It just so happens that I received 2 Z240 Type 3 strobes yesterday.

From what you are saying, it sounds like the best way to run them would be set to Auto and set my E-M10 to no pre-flash and minimum flash power, yes?

For setting the strobes to no pre-flash, though, I'm not following you. From interpreting the pictographs on the strobe, it looks like I should push the button on the lower right and twist it to lock it down. I don't get your statement to use a rotary select knob.