a6000 Internal Flash and TTL Flash Metering

[foetusmachine]

Hi All,

I posted this question in an underwater photography forum, as that's my focus, but didn't have much success in getting responses. Maybe it's too technical a question, but I thought i'd try again in different forums.

I'm working to understand how my a6000 works in detail with the aim of (possibly) making my own LED TTL converter. At the moment I use the a6000 with its internal flash to trigger a set of underwater Sea & Sea YS-D2 strobes using my optical cables. I either use the strobes in manual or TTL mode. The TTL is reasonable, but not always perfect.

I wanted to understand how the a6000 TTL system works, so I connected a little oscilloscope to my hotshoe x-sync pin and used the other channel of the oscilloscope with a photodiode to monitor the flash.

See attached 2 screen grabs for two flash types - Fill Flash, Rear Sync. I also did a slow sync, but it's result was remarkably similar.

I wasn't able, in any case, either Manual, Aperture priority or full automatic, to witness any pre-flash whatsoever from the camera's internal flash.

Does the a6000 meter TTL during the exposure? Am I missing something here.

Welcome any insights, comments or suggestions to be able to run another oscilloscope test.

Cheers!

 

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[Username]

No digital camera can meter TTL during exposure. 

The sensor, which would serve as the metering cell, 

is occupied recording the exposure. The old "off the

film" type of TTL metered during exposure cuz the 

film was NOT the metering cell. Also, the film is a 

relatively matte surface where the filter pack on the 

digital sensor is a polished optical flat.   

   

Digital TTL metering actually makes a test exposure 

which is not recorded to the card, and is used by the 

flash to establish the appropriate power output to be 

delivered during the upcoming recording of the image.  

   

This uses a preflash, but the preflash can be very low 

power and still be useful for the purpose of metering. 

So, it really IS a TTL measurement, but NOT real time 

during the recording of the image.  

 

I'm uncertain whether the built-in flash is actually a 

TTL flash like the accessory flashes are. But if it is 

part of the TTL regime, perhaps you need to adjust 

something on your scope to pick up very weak test 

flashes emitted for metering purposes. 

 

Edited June 14, 2018 by Username

[Guest Jaf-Photo]

That's a question and a half. 

I haven't read any in-depth explanation of Sony's TTL system. I know a bit about the Minolta system which was carried over to Sony's A-mount cameras -- but it's different.

That said, coming from the more advanced "legacy" system I never warmed to TTL on E-mount cameras. Instead, In set the flashes manually to get the look I want. Whether it's practical when diving, I have no idea.