remote control of exposition / TTL protocol?greenspun.com : LUSENET : Canon EOS FAQ forum : One Thread
I'm looking for ways to control an EOS body remotely (not only shutter trigger, but also exposure time).
Here is why: for solar eclipse (and other kind of events) I am used to take series of pictures with a lot of different exposures to record different details (very wide light range). To give you an idea last june I made picture of a solar eclipse with exposure time ranging from 1/2000 to 4 seconds by increment of half steps. I had to to this by hand on the camera body. This introduce vibrations (not good at 600mm focal length), it is slow, and I have less time to WATCH the event. For next time I want an automatized sort of thing (control with a little computer or dedicated MCU).
How to do (current thoughs): - use the mini jack remote trigger control in 'bulb' mode: it's ok for 'long exposures', more than 1/10 of a second and not very precise. it's not suitable for short time like 1/1000. - open the camera body and 'emulate' the turning button. It's a bit risky for the camera, isn't it?
So here is another idea, but I need your help: as far as i know, the camera body can communicate with an external flash using the 'TTL' protocol. I'm not sure of it, but it seems that the flash is the 'master' in this case. It can control the body and set exposure time. Is this right?
If it's that, are there any papers explaining this protocol so that I can emulate a flash and control the exposure time (the triggering can be done with the mini jack in this case)?
Thank you... any help is welcome !!!
-- sylvain chapeland (firstname.lastname@example.org), September 07, 2001
"as far as i know, the camera body can communicate with an external flash using the 'TTL' protocol. I'm not sure of it, but it seems that the flash is the 'master' in this case. It can control the body and set exposure time. Is this right?
There are two different kinds of TTL. In cameras, it means "through the lens", in other electronics, it means "transistor, transistor logic". There're not the same thing. It's too bad, because your idea is quite intriguing. In the case of TTL flash exposure, the light from the flash is measured off the film, as the exposure is being made, and when the camera decides it has enough light, it turns off the flash.
I think Canon EOS cameras can have firmware loaded through the hotshoe connection, but there would be a lot of work to reverse engineer Canon's protocols, and actually control exposure.
-- Geoff Doane (email@example.com), September 07, 2001.
The technical back E may have allowed such operations via a computer interface (I'm not 100% sure of this and I don't have a TBE manual around to look it up). The TBE only fits the 620/650/630 series of cameras with full functionality. It also fits the RT but some functions don't operate.
The TBE and 6xx series are no longer made but can be found used.
-- Bob Atkins (firstname.lastname@example.org), September 07, 2001.