The AFxxxT flashes have a thyristor quench circuit that reads the light
returned from the subject directly with a sensor built into the flash,
(i.e. not using the TTL sensor in the camera body), as an option. There
may be a model that doesn't have the sensor, or one that doesn't
actually support TTL. but in general the AFxxxT flashes support both.
The quench method of automatic flash exposure is pretty old tech. The
thyristor only kept the flash from simply dumping the energy stored in
the main capacitor, conserving it for the next pop. It was available on
a large number of intermediate to advanced flashes from the 1970's
onward and eventually filtered down to some of the lower models as well.
Pentax left the quench method in that series of flashes so that they
would have a useful automatic mode with cameras like the MX as well as
using the advanced OTF TTL mode of the LX. (There were a few other
manual focus film bodies that used OFT TTL as well I think). I think
they also support OTF TTL flash in later AF bodies, but I've only owned
two AF film cameras and almost never used them with flash.
The FTZ series of flashes were designed to use the in body off the film
plane sensor, found in various the auto focus film bodies, and the
*ist-D digital, (which because of the difference in reflectivity between
a digital sensor, and film never worked properly). They didn't have
their own sensor and were totally dependent on the body's sensor. The
*ist D was the last camera that supported OTF TTL for that reason. The
*ist-D was the last camera to fully support both the analog and digital
communication between the camera and flash as well.
Later digital bodies aren't supposed to support the analog flash control
interface, but I've found that in P mode every Pentax DSLR I've owned
will set the shutter speed to 180/sec and the proper f stop for the auto
range set on the flash and ISO selected by the camera with an A lens.
In fact it will even select the shutter speed using the reciprocal rule
with an F or FA lens based on the selected focal length.
Even with the bells and whistles such as reading lens aperture, and
setting the correct shutter speed and aperture for the selected ISO, the
flashes using the OTF TTL were still pretty simple, the flash was just
counting the photons reflected from the film or collected by the flash's
built in sensor until the calculations showed enough light for a good
I'm pretty sure that the FTZ flash failsafe mode is to simply assume
that there's an in body sensor, but since that sensor doesn't exist,
you'll get a full strength pop in OTF TTL mode because the flash isn't
able to count any photons.
To get useful flash automation you either need to get a much earlier
flash than your FTZ, that uses a thyristor circuit with it's own sensor.
or an FGZ that can use the P-TTL protocol. There are a few third party
flashes that also support P-TTL, but except for those made by METZ, the
Yongnuo yn585 I'm not sure which ones are still available.
On 2/19/2018 12:53 PM, Alan C wrote:
P J, Please elaborate on this. Off list if you prefer.
"I was using the AF200T with my digital cameras, and been pretty happy
with the results. Sure it's not P-TTL, but as far as it goes, having
it's own sensor, the fact that it actually sets the recommended f stop
and shutter speed when the camera is in program mode with an A class
or later lens, was convenient."
My AF330FTZ can only be used as a manual flash.
This email has been checked for viruses by Avast antivirus software.
America wasn't founded so that we could all be better.
America was founded so we could all be anything we damn well please.
- P.J. O'Rourke
PDML Pentax-Discuss Mail List
to UNSUBSCRIBE from the PDML, please visit the link directly above and follow