4 replies to this topic

[james]

I am reading through this month's issue of Ocean News (commercial dive/research mag) and I found an ad for the new Tetra5000 housing.

I just thought I'd pass along their description of the strobe exposure control options:

"The Tetra5000 includes the revolutionalr ROC (Remote Optical COntroller) strobe controller. ROC enables the user to shoot using Digital TTL, Manual bracketing based on TTL feedback and full Manual with the ability to adjust in 12 half stop increments with any TTL compatible strobe."

I had to laugh about this one: "Manual bracketing based on TTL feedback" Which I translate to: Shoot a picture in manual, look at in on the LCD, stop down a stop, shoot again... What Jim Watt is calling TTB or "through the brain" exposure feedback.

So it looks like the flash sensor will be "functional" with this housing. That is good news! To further confuse the reader though, LMI shows a photo of their Tetra3040 housing which has no port for the flash sensor. I guess they don't have a prototype yet that they can use for marketting photos. I hope they have one soon, I can't wait to have a look at it.

Cheers
James Wiseman

[herbko]

Oops. Forgot to sign in before the last post.

Herb

[scorpio_fish]

Digital TTL isn't really TTL. It just sends out a small flash impulse to get a measurement before firing. The sensor that reads the reflectance on the CP5000 is located between the flash and the lens.

One way to handle not obscuring this sensor is using a very wide port opening such that the sensor is not obscured. Another is to add an opening that allows the sensor to be seen (as would be done for LCD control panel).

I have a queasy feeling in my stomach that this is just another "sort-of", "kind-of", quasi TTL. With the added benefit of small manual adjustments.

As to when TTL is handy? All the time. I shoot film with strobes on TTL for macro. It's almost foolproof. Stopping to evaluate an image for its exposure after every shot seems ludicrous and time consuming. Such time is better spent on stalking and framing.

[james]

Actually, the Nikon cameras meter the flash during the shot - they don't use the preflash for metering. They do not use a preflash to meter the shot then fire another flash while the "shutter" is open.

To further confuse matters, the CP5000 DOES fire a preflash, but only sometimes...lol. When the camera's internal flash is disabled and no external flash is hooked up it does NOT fire a preflash. When an external flash is hooked up it DOES fire a preflash, but the preflash does absolultely nothing for the exposure. You can put black tape over the flash and take a few shots if you don't believe me. The preflash on the CP5000 is a firmware bug. I can provide proof upon request.

I sometimes don't understand why people think digital camera flash metering is inferior to "true" TTL. What is the difference between 1) the camera measuring light returning to the flash sensor right next to the lens and 2) the camera measuring light hitting the film plane? Honestly, can someone tell me what difference this is going to make to my exposure?

Of course TTL doesn't work in all situations. Simply put, flash energy has to come back to the flash lightmeter no matter where it is. If you're taking a wideangle shot of a whale shark, odds are that most of your flash is going to disappear "off into the abyss" of blue water. In that case, you should go for a manual flash or you'll get a full dump. Heck, maybe you want a full dump anyway! I think you get my point though.
TTL DOES work and it does work on consumer level digicams.

This is my honest opinion only.

I need to go diving. Well at least Seaspace is this weekend.

Cheers
James Wiseman

[davephdv]

See post I made under member galleries. I made several close n wide shots using ttl with a 5000 and 2 DS 125s that came out well exposed. Something you cannot do with a film camera as the TTl almost always seems to over expose the foreground subject. Look under member galleries to see the images.