Why does nobody sell plug-in TTL control for strobes, or why don't strobe provide on/off signal capability?

I asked this question some years ago, but got no response...

 

With TTL flash having been around for 20+ years, I wonder why studio

lighting has no TTL compatibility, or why camera manufacturers don't

sell dedicated radio control TTL modules.

 

After all, the most sophisticated dedicated speedlight can be

functionally separated into two parts, 1) the power and light module

connected to a 2) TTL electronic module that signals when the light

goes on, and when it gets quenched.

 

It would be a simple matter for strobe manufacturers to offer an

input socket in their units that would allow for signals to turn the

light on, or off (they would have to provide additional circuitry to

dump the unused charge in the capacitors), that would take plug in

TTL units.

 

Or is studio strobe lighting such a considered exercise that TTL is

meaningless? Even so, I can see benefits in locational lighting,

such as weddings.

I think you�d spend all your time programming in light ratios for multiple light use. It�s a nice thought though, one big powerful flash. Just dial in your aperture of choice and pop away�

"programming in light ratios for multiple light use"

 

With multiple heads, don't you do that anyway?

 

Please forgive if the question and my response are totally ignorant; I'm only a very occasional user of a little on camera bounce fill...

The only time I've ever really found TTL flash necessary is for macro work with a 35mm camera (you can't easily measure extension like you can with a monorail). I think most of the people using studio strobes are accustomed to using handheld flash meters. The market for a TTL strobe system is pretty limited -- if someone were to produce one, I'm sure they'd sell a few of them, but most of the people that shell out for the capability to completely control all of the light striking their subject want to work manually.

"I wonder why studio lighting has no TTL compatibility"

 

My guess is serious studio shooters wouldn't trust it anyway. If the setting is static there's no need for it and if it's dynamic then even the most sophisticated reflected light metering system can get confused and that usually when you least expect it.

 

What I'd like to see is an industry standard for remote/computer controls for studio gear so mixing different products wasn't so complicated. The Pocket Wizard + Profoto + Dynalite alliance is a start but they still have far to go.

 

If the Profoto D4 is fully controllable with a USB cable and computer then it should be controllable via a 802x wireless link too.

Lumidyne and Quantum have plug-in modules that provide TTL capability with many cameras. Quantum also has radio-control devices that provide this capability. Nikon SB-80 and SB-800 flashes have built-in remote TTL; the remote flash shuts off to match the master flash.

 

The difficulty is that TTL (or auto-anything) doesn't work well in the studio, or with multiple lights. It's relatively easy to establish exposure and lighting ratios in manual mode using a flash meter.

 

In TTL mode, you would have to put in compensation settings in each flash and the camera, probably in many iterations. In the best case, TTL would simply match the manual settings. In the worst case, the exposure would change with every minor change in the setup, probably not in a desirable way.

 

Now remote, manual settings...!

It would be very difficult to design a system which handled

multiple lights in a way that maintained specific lighting ratios.

The total amount of light that a flash puts out during an exposure

isn't regulated by varying the brightness of the light--it's the

duration of the flash that provides control. To maintain ratios, a

TTL metering system would need to shut off certain lights earlier

in the exposure than others. With an incident meter and manual

control, it's not hard to measure the contribution of individual

lights to an overall exposure--having the camera's meter do that

same job in real time based only on the light that's bouncing off

the subject would be a very formidable, probably impossible,

task.

TTL flash metering is only functional when the light is reasonably close to the same axis as the camera lens. For instance, if you set a single light for dramatic side lighting, TTL won't give the proper exposure. You have to meter in the direction from which the light is comming from; TTL would cause the light side to be blown out. The other thing is the precision that light is used in a studio (small fractions of a stop), and TTL isn't precise enough for commercial use.