A99 w/studio strobes sync issues?

Started Nov 7, 2012 | Discussions thread
Gary Friedman Regular Member • Posts: 357
Re: A99 + Einstein test

OntarioJohn wrote:

I read most of the posts, but my eyes glazed over a lot like a piece of salmon under a broiler coated with maple syrup.

> I'd like to have someone write a synopsis of conclusions to this issue.

Okay, I'll give it a shot.  First of all, I tried this in my studio earlier today and came up with identical results as the OP: A small black band near the top when using a PC Sync cable, and a larger black band near the top when using a Cybersync (I'm using an Alien Bees B800 for testing.)  With Steadyshot on and off.  With e-front shutter curtain on and off.  My A77 works great in all these modes at 1/250th.

Before I summarize anything, let me point out something that was inferred by others but might have been missed while your eyes were glazed over: There are two completely different methods of triggering a flash on the A99.  The first is Ye Olde PC Sync connector and its cousin, the hot shoe  -- in the olden days it would short out the two contacts once the first shutter curtain opened all the way.  It was a mechanical switch tied to the shutter curtain.  Today (since you can shoot without a first shutter curtain enabled) it's done in software and the on-board computer activates a switching transistor which lowers the resistance across the contacts to something close to (but not equal to) zero ohms.

The second method triggers the Sony accessory flashes via a different mechanism.  With this method the camera "speaks" to the flash using a serial protocol (what used to be called RS-232, but you can think of it as a USB connection between the camera and the flash) where the camera controls the flash via a string of electrical ones and zeros.  THIS interface works just great at 1/250th (and above!).

CodySLC performed several excellent tests which demonstrated clearly that the problem is with the way the A99 handles the first method - the PC sync connector (or the center contact of the hot shoe) appears to be triggering late.  And if you have a radio trigger that will add to the delay (making the black band thicker near the top).

There are two things that I can think of that can cause this problem: the first is what most people suspect: somewhere in the firmware, the command to short the PC contacts (and/or the hot shoe contacts) together is happening a little late.  If this is the case, it would happen to everyone who tried it, regardless of the type of studio strobes being used.  This defect should be very easy to fix in firmware.

The other possible cause: Sony changed the type of switching transistor which drives the PC Sync connector and hot shoe, so the "closed" resistance is slightly greater (5 ohms instead of three, for example).  This would make triggering a slightly less absolute event and different brands of strobes would react to it differently (some would work fine, some wouldn't fire, and some would just trigger a tad bit late, all depending upon their internal circuitry.)  This would be impossible to fix in firmware.

No "solution" to the problem was proposed (only Sony can fix it), but as a work-around I would suggest putting a small accessory flash on your A99 set to manual output mode (no pre-flash) at its lowest setting, and enable the optical slaves on all of your studio strobes.  CodySLC's tests demonstrate that this should work just fine.

I think that's the essence of it.  Personally, I'm so happy that they fixed the flash exposure accuracy problem (which has gone unacknowledged and unaddressed in the A77, A65, and NEX-7) that this doesn't annoy me as much as it should.


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