Thom Hogan Article - DTTL

http://www.bythom.com/wireless.htm

Quote from Thom:

The D-TTL pre-flash contains 18 discrete pulses arranged in a time pattern:

 

              ooo oooo oooo oooo ooo ...(camera calculates)... Flash!

HTH

James

My problem with DTTL is that Nikon could have done what Fuji did with the S2 and made their digicam's work with standard Nikon TTL guns. Which would have been a great benefit for users of third party underwater strobes.

I have found DTTL works very well (on land) so long as you keep it easy for the camera. And there is no reason that it won't do the same underwater.

My D10 is currently being modified to work with DTTL gun (because subal supplied mine with on 3 wires of the 5 connected!). I should get it back this week and will report on how it behaves in the pool.

If you want to see DTTL in operation then put your D100 or D1 on a slow exposure (in M) and shoot rear curtain synch. You then get the pre-flashes and the main flash seperated by the length of the exposure. Of course if the reflectivity of the subject changes during this time the exposure is wrong. Bad luck Nikon D100 users!

TTL is a nice feature to have and it sure comes in handy at times - but a camera is not useless without it.

I posted the article so that underwater shooters can see what strobe manufacturers are up against when trying to make a "D-TTL compatible" strobe. If/when a DTTL underwater strobe comes out it will be a major engineering feat.

Cheers

James

D-TTL uses distance in strobe exposure calculations (I think it gets the distance from the lens autofocus system). "Regular" TTL does not - it just uses the flash TTL meters while the shutter is open.

That's why Nikon doesn't recommend you use two D-TTL strobes hardwired to their DSLR's. It confuses the D-TTL system if the flashes are not in the plane of the camera.

Cheers

James