[OldChE]

I expected my AF200T flash to work correctly on "auto" mode with my K-70, and it does - but it also seems to work in TTL mode, when it should not. The flash is an analog TTL + auto (red, green ranges) + manual (full, 1/2, 1/4, 1/8) flash that works TTL with my older film cameras that have TTL sensors (Super Program, ZX-L, MZ-S). The K-70 talks to the flash correctly with the flash on auto mode and the camera in P mode, setting shutter speed to 1/80 and aperture correctly as I change ISO on the camera or switch from red to green mode on the flash, and exposures are correct, all of which I expected. However, I also tried putting the flash on TTL mode just to see what happens, expecting it not to give proper exposure at all, since the K-70 being a DSLR does digital P-TTL but doesn't have an analog TTL sensor. What I found was that it seemed to give the right exposure as long as I was about 7 ft. away or farther, with the camera on P mode. As I changed the ISO on the camera across the ISO 100 to 800 range, the camera adjusted the aperture to the proper default setting for the flash's TTL mode at that ISO, and gave correct exposure at a variety of distances and ISO levels as I changed them, within a range of about 7 ft to 25 ft. The flash manual says that TTL exposure range (for the F-stops selected by the camera) would be about 16 ft max and a minimum of about 1/3 that value (~5.3 ft) when using the default apertures for TTL operation. I found the pictures overexposed in the 5 to 7 ft range, but they looked pretty good at longer ranges. These were the ISO and F-stop combinations selected by the camera in TTL mode (all at 1/80s shutter): ISO 100, F4.5; ISO 200, F5.6; ISO 400, F8; ISO 800, F11. Those are the same values that would be selected when using the AF200T in TTL mode on my Super Program at those ISOs. With flash on auto mode, and the K-70 on P mode at ISO 800, the camera selected 1/80s and F8 for the red range and F16 for the green range, which is correct. On all of the shots, it didn't matter what ISO I set on the flash itself (I think that ISO switch on the flash just moves the scales around, no electrical connection to the flash circuits themselves). I was using only the 18-135 WR zoom. I've not tested using the flash in TTL mode at user-selected apertures in Av mode on the K-70.

Has anyone tried something like this and can comment? Perhaps this is not really TTL exposure, but the camera is just selecting the right aperture to get about the right exposure for the flash at 100% full manual output? However, if that were the case I wouldn't get proper exposure both at 25 ft and 10 ft, which with my limited testing seemed to be the case.

Thanks --> Richard.

[shardulm]

Haven't tried. But TTL is through the lens metering/exposure calculation (P-TTL, I-TTL or whatever TTL is the same principle I think). I don't see why TTL should work differently than P-TTL. I have a feeling that TTL mode is for the flah to be used on other cameras with a compatible hot shoe (I have a feeling that Nikon shares the same hot shoe pattern). So if this flash used on a nikon body in TTL should work as well as that is the generic TTL and not Pentax-TTL.
But I am may be wrong.

[OldChE]

Haven't tried. But TTL is through the lens metering/exposure calculation (P-TTL, I-TTL or whatever TTL is the same principle I think). I don't see why TTL should work differently than P-TTL. I have a feeling that TTL mode is for the flah to be used on other cameras with a compatible hot shoe (I have a feeling that Nikon shares the same hot shoe pattern). So if this flash used on a nikon body in TTL should work as well as that is the generic TTL and not Pentax-TTL.
But I am may be wrong.

TTL is different than P-TTL. On older Pentax film cameras, they had a meter sensor inside the camera that read the light reflected off the film itself during the flash exposure to control the TTL flash. When enough light had been reflected for proper exposure, it would cut off the flash. On the last couple film cameras (ZX-L, MZ-S, iST) and for all of the DSLRs they switched to P-TTL which didn't involve a sensor reading reflection off the film. Instead a pulse was sent out by the flash, the exposure measured by the camera based on that pulse, instructions sent to the flash for duration of the main flash for proper exposure, then the main flash would go.

I don't think either method would work with Nikon cameras.

--> Richard.

[pschlute]

Richard is correct. Current Pentax DSLRs cannot perform TTL flash at all.

The early digital models *istD and *istDS did however still use TTL, the DS being the last model to do so.

[stevebrot]

Why am I getting TTL exposure with a AF200T and the K-70 DSLR?

As noted above, your camera lacks the sensor for TTL support and your flash does not support P-TTL.

These were the ISO and F-stop combinations selected by the camera in TTL mode (all at 1/80s shutter): ISO 100, F4.5; ISO 200, F5.6; ISO 400, F8; ISO 800, F11.

Those are the same values that would be selected when using the AF200T in TTL mode on my Super Program at those ISOs.

What you are seeing is the aperture defaults for when a dedicated flash is detected. The flash is firing at full-power in TTL mode on your K-70 with the effective range being the same for each aperture/ISO combination. I think you will find the same behavior in the "red" auto mode with finger over the sensor.

I suspect the AF200T's flash dedication behavior is similar to my AF280T as detailed in my review of that flash.

PENTAX AF 280T reviews - Pentax Camera Accessory Review Database

On the last couple film cameras (ZX-L, MZ-S, iST) and for all of the DSLRs they switched to P-TTL which didn't involve a sensor reading reflection off the film.

The flash automation support matrix is sort of mixed in the early days of P-TTL. All three models you listed above support both TTL and P-TTL. The same was true for the *istD series with the exception of the *ist DL/DL2, both of which were P-TTL only.


Steve

[OldChE]

As noted above, your camera lacks the sensor for TTL support and your flash does not support P-TTL.



What you are seeing is the aperture defaults for when a dedicated flash is detected. The flash is firing at full-power in TTL mode on your K-70 with the effective range being the same for each aperture/ISO combination. I think you will find the same behavior in the "red" auto mode with finger over the sensor.

I suspect the AF200T's flash dedication behavior is similar to my AF280T as detailed in my review of that flash.

PENTAX AF 280T reviews - Pentax Camera Accessory Review Database




The flash automation support matrix is sort of mixed in the early days of P-TTL. All three models you listed above support both TTL and P-TTL. The same was true for the *istD series with the exception of the *ist DL/DL2, both of which were P-TTL only.


Steve

Steve - yes, I know. However, any idea as to why I was getting properly exposed pictures under the conditions I described (i.e., flash on TTL mode, camera on P, lens automatically set to the TTL default opening corresponding to my chosen ISO setting, and proper exposure at a variety of camera to subject distances in the range of about 7 feet to 25 feet)? I thought that I should not have been doing so.

---------- Post added 12-28-2017 at 10:10 PM ----------

What would be great is if any of you have a K-70 (or perhaps similar recent model) and an AF200T and can try a few test shots to see if you get the same behavior.

[stevebrot]

I thought that I should not have been doing so.

Re-read my note. To be explicit:

• Your flash is firing at full strength when in TTL mode on a non-TTL camera. This is easily assessed by a number of approaches.
• The camera's legacy dedication support sets the aperture based on a value passed as an encoded frequency through the hot shoe "mode" pin. The details for your flash are about halfway down the page under "Program Flash" on the Flash Systems Evolution article on the KMP (LINK). The same frequencies are used for both "auto" and TTL modes and vary by flash model guide number.
• The set aperture is appropriate for full strength* with your flash which should yield proper exposure from about 5' based on the guide number of 20 (ft)

Again...there is no magic at work here, just great backward compatibility of your K-70 to your legacy dedicated flash and graceful fail-over for an inappropriate flash mode. Before I wrote my response, I duplicated the behavior on my K-3 with the AF280T. I also double-checked on my Super Program. The AF280T has a different guide number (28 (ft)), but uses the same encoding scheme as your flash and gives correct exposure at 7' for f/4 in TTL mode. Your camera DOES NOT have an undocumented TTL sensor and your flash most assuredly does not support P-TTL.**

Addendum: I should have added that the flash always signals its strength regardless of body capabilities. A supporting body knows the encoding and will set aperture to follow (per protocol) when in P mode.


Steve

* What you get when no shut-off signal is received.

** You can demonstrate lack of pre-flash by setting the 2s self-timer. A P-TTL flash will do the pre-flash at the beginning of the timer count-down followed by the main flash.

---

Last edited by stevebrot; 12-28-2017 at 11:20 PM.

[OldChE]

[/COLOR]

Re-read my note. To be explicit:

• Your flash is firing at full strength when in TTL mode on a non-TTL camera. This is easily assessed by a number of approaches.
• The camera's legacy dedication support sets the aperture based on a value passed as an encoded frequency through the hot shoe "mode" pin. The details for your flash are about halfway down the page under "Program Flash" on the Flash Systems Evolution article on the KMP (LINK). The same frequencies are used for both "auto" and TTL modes and vary by flash model guide number.
• The set aperture is appropriate for full strength* with your flash which should yield proper exposure from about 5' based on the guide number of 20 (ft)

Again...there is no magic at work here, just great backward compatibility of your K-70 to your legacy dedicated flash and graceful fail-over for an inappropriate flash mode. Before I wrote my response, I duplicated the behavior on my K-3 with the AF280T. I also double-checked on my Super Program. The AF280T has a different guide number (28 (ft)), but uses the same encoding scheme as your flash and gives correct exposure at 7' for f/4 in TTL mode. Your camera DOES NOT have an undocumented TTL sensor and your flash most assuredly does not support P-TTL.**

Addendum: I should have added that the flash always signals its strength regardless of body capabilities. A supporting body knows the encoding and will set aperture to follow (per protocol) when in P mode.


Steve

* What you get when no shut-off signal is received.

** You can demonstrate lack of pre-flash by setting the 2s self-timer. A P-TTL flash will do the pre-flash at the beginning of the timer count-down followed by the main flash.

Thanks Steve, and thanks for taking the time to give a longer explanation. I suspected it might be something like that, though I'm still curious on why it seemed to work over a range of distances. I never thought there was some undocumented TTL sensor nor it magically supported P-TTL, although it was amusing that you thought that I may have. Being an amateur photographer for over 50 years and an engineer for almost 40, I hope I can figure out what sensors are in the flash and camera to start with. So, you are saying that when I use the flash on TTL mode and the K-70 on P mode, the flash operates as if on manual at full output, and the camera selects the old "TTL" aperture appropriate for the current ISO for that flash. That makes sense, since in that case everything is working as it was originally designed, except that there is no TTL sensor in the camera to tell the flash to stop flashing, so it naturally goes to full output. If this is the case, I should be able to reproduce the same results by firing the flash on manual setting at 100% output, and setting the camera to the same fixed aperture setting (the default TTL aperture for that ISO). I'll try that for a range of distances and compare results to using the TTL setting.

[stevebrot]

I suspected it might be something like that, though I'm still curious on why it seemed to work over a range of distances. I never thought there was some undocumented TTL sensor nor it magically supported P-TTL, although it was amusing that you thought that I may have.

Yes, it is amusing, but not unknown in the realm of this site . The backward support for legacy flash dedication is a happy surprise that I discovered shortly after I bought my AF280T and is something worth exploring. It makes "auto" mode almost as seamless as P-TTL, but with the benefit of more predictable performance.

I should be able to reproduce the same results by firing the flash on manual setting at 100% output, and setting the camera to the same fixed aperture setting (the default TTL aperture for that ISO). I'll try that for a range of distances and compare results to using the TTL setting.

Let us know what you find.


Steve

[fwcetus]

Richard is correct. Current Pentax DSLRs cannot perform TTL flash at all.

The early digital models *istD and *istDS did however still use TTL, the DS being the last model to do so.

Actually, to be most correct, the *ist D, the *ist DS, and the *ist DS2 can all use TTL, so that the DS2 is the last model to do so. [Admittedly, of course, a DS2 is basically a DS with a larger LED screen -- are there any other differences? -- so I am guilty of quibbling, I guess.]

I have two DS2 bodies that do TTL flash with AF280T and AF080C flash units just fine.

[OldChE]

Actually, to be most correct, the *ist D, the *ist DS, and the *ist DS2 can all use TTL, so that the DS2 is the last model to do so. [Admittedly, of course, a DS2 is basically a DS with a larger LED screen -- are there any other differences? -- so I am guilty of quibbling, I guess.]

I have two DS2 bodies that do TTL flash with AF280T and AF080C flash units just fine.

Thanks, good to know. I've always been impressed that my AF360FGZ flash does both TTL and P-TTL, depending on which body it is attached to, and also does auto mode on the older bodies without TTL.

[fwcetus]

Thanks, good to know. I've always been impressed that my AF360FGZ flash does both TTL and P-TTL, depending on which body it is attached to, and also does auto mode on the older bodies without TTL.

Yes, the same with the AF540FGZ.

And the AF200T and the AF280T do a (perhaps surprisingly) very good job at good ol' "auto (thyrister) flash" on older bodies and even on the newer DSLR's.

[The AF080C ring flash that I mentioned, though, lacks the external thyristor sensor (which might be difficult to implement on a macro flash anyway), so it can't do "auto flash", but it does work nicely for TTL on film bodies and those first three Pentax DSLR's, and it also works well fror manual flash.]

Pentax, sometimes purposefully and sometimes accidentally (as in this original topic of this thread, I would say), usually seems to offer a lot of forward and backward compatibility, and it's always nice to have options.

[OldChE]

Thanks to all for the comments. Happy New Year!

[tromboads]

Thanks for those before me that discovered this. I was using the K5 and an AF200t the other day and getting weird things going on, until I noted that yes, it is passing the setting to the camera via the hot shoe.


Legacy code indeed!

You Tube

You Tube

Neato!