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02-18-2018, 05:02 PM   #31
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Certainly economical, considering that the Pentax cables cost more than the Yongnou speedlights. However, there are no P-TTL solutions applicable to 645N. Perhaps I find something nostalgic about using all-Pentax historical "stuff" with film. (This ignores the near impossibility short of accumulating enlarger equipment of staying purely historical. I have to have the film developed and Noritsu scanned before it can be digitally printed to photo paper. And if I want to mess with the image I need to use digital processing, even if not deliberately converting the image to something one could never see with real eyes, i.e., art.)

02-18-2018, 05:17 PM   #32
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QuoteOriginally posted by kaseki Quote
Certainly economical, considering that the Pentax cables cost more than the Yongnou speedlights. However, there are no P-TTL solutions applicable to 645N.
Well, that's the built-in cost of using vintage equipment, Kaseki.

You're going to have to do it old school.

Set up your five flashes or whatever, get out your light meter, and trigger them one by one and set their power ratings (one stop under for that fill one, one stop over for the rim, etc) until you're happy.
02-18-2018, 08:04 PM - 1 Like   #33
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Thanks for the encouragement.
02-18-2018, 08:16 PM   #34
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The satisfaction gained of using old skool TTL may well be worth the effort though !

The real limitations / hazards of using the extension cords in a studio situation is going to be the length of them (too short probably) plus the whole tripping over them / everything coming crashing down scenario .....we don’t want your next thread title to be something like “Help! Spare parts needed for multiple AF500FTZ flashes and 645N camera”

From the AF500FTZ manual I found online it looks like the Contrast Control Sync mode is limited to single slave plus pop-up flash setups ..... in that situation the pop-up will provide 1/2 the output than the slave does. Check the settings on your flashes when you activate the Contrast Contrast Sync mode, but it doesn’t look like there is a ratio setting for a split between slaves, like on the later P-TTL models.


It seems likely then that all of your flashes connected by cords in TTL mode will be emitting the same output, so it may be difficult to achieve very precise balancing. But as Clackers said, you can use Manual flash mode anyway. In that configuration you might find it more convenient to use a simple manual flash on the hot shoe as an optical trigger, at low power, and operate the AF500FTZs as “dumb” optical slaves.

And at least that way you’re not contaminating the purity of your legacy Pentax arsenal with some cheap plasticky radio devices!

02-19-2018, 01:24 AM   #35
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QuoteOriginally posted by kaseki Quote
Thanks for the encouragement.
(Laughs)

If you were someone already choosing to shoot film because it's the harder, more time consuming but ultimately more rewarding path, mission accomplished!
02-19-2018, 08:29 AM   #36
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QuoteOriginally posted by mcgregni Quote
The satisfaction gained of using old skool TTL may well be worth the effort though !

The real limitations / hazards of using the extension cords in a studio situation is going to be the length of them (too short probably) plus the whole tripping over them / everything coming crashing down scenario .....we don’t want your next thread title to be something like “Help! Spare parts needed for multiple AF500FTZ flashes and 645N camera”

From the AF500FTZ manual I found online it looks like the Contrast Control Sync mode is limited to single slave plus pop-up flash setups ..... in that situation the pop-up will provide 1/2 the output than the slave does. Check the settings on your flashes when you activate the Contrast Contrast Sync mode, but it doesn’t look like there is a ratio setting for a split between slaves, like on the later P-TTL models.


It seems likely then that all of your flashes connected by cords in TTL mode will be emitting the same output, so it may be difficult to achieve very precise balancing. But as Clackers said, you can use Manual flash mode anyway. In that configuration you might find it more convenient to use a simple manual flash on the hot shoe as an optical trigger, at low power, and operate the AF500FTZs as “dumb” optical slaves.

And at least that way you’re not contaminating the purity of your legacy Pentax arsenal with some cheap plasticky radio devices!
[LOL; here comes the historically authentic spaghetti studio]

With the AF-500FTZ in optical slave mode, the power output can be adjusted to 1/32. As might be expected, in TTL mode it cannot be adjusted. Beam width (zoom) seems to be adjustable in both modes. However, in either case one will likely be making choices of flash distance, flash diffusion technique, bounce vs. direct, spatial orientation, blocking, etc., measuring and modifying until the intended configuration is set and the power ratios measured at the object to be photographed (target) are as desired. These setup tests would all be done in slave mode at full power. At this point, an appropriate aperture setting could be established and an exposure taken.

Next, switching to photos with TTL, the lighting ratios should be retained within the consistency of the flashes' lamp discharge function. And with TTL, given sufficient flash power in all flashes, aperture selection is less restricted -- allowing lower f/nos for more bokeh, say.

In any case, I need the wiring connection parts before I can definitively comment on relative merit of alternative approaches.
02-21-2018, 03:00 PM - 1 Like   #37
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TTL propagates at least to two additional flashes.

Ref: Pentax 645N Operating Manual, page 64. "When discharging more [kas emphasis] than 2 Pentax dedicated flashes, make sure that they are of the same type, ... .

Test configuration. Camera is a 645N with Pentax A 150mm/3.5 lens. One AF-500FTZ was mounted on the 645N hot shoe. The camera was tripod mounted. The camera was facing south into an under-stairs closet where a test target was placed about 5-feet away.

A Pentax extension cord F5P(L) of about 2.9-m length was connected to the camera flash 5P connector and extended to a second AF-500FTZ flash attached to a Hot Shoe Adapter F where the 5P cable connected. This second flash was aimed westerly into a second room in a manner where its output would have negligible effect on the first flash target illumination. A second Pentax extension cord F5P(L) was connected to the second camera flash 5P connector and extended to a third AF-500FTZ flash, connecting at the third flash's 5P connector. This third flash was aimed northerly toward a Minolta Flashmeter IV set to non-cord flash detection to read the light level and compute a suitable F/no for the conditions (ISO 400 -- 1/60). This third flash was about 15 ft away from the first flash and directed away from it. The second flash's F adapter and the third flash's hot shoe were each mounted to a plastic hot-shoe flash stand on the floor.

All flashes were set to TTL mode and to their default 35-mm beam zoom. When the camera was actuated, all three flashes flashed. For this test, I did not try to measure the flash durations. However, TTL action seemed to be confirmed by the Flashmeter IV, as measured with its hemispherical diffuse window at about 33 inches in front of the third flash, about 5 inches below the flash beam centerline. Flashmeter IV readings at the third flash were as follows:

Test flash (full power): F/64.2
Normal TTL flash; camera lens set at F/3.5: F/5.62
Normal TTL flash; camera lens set at F/11: F/11.2
Normal TTL flash; camera lens set at F/32: F/22.8
(Higher Flashmeter values correspond to higher detected flash energy.)

Clearly the flash power required for normal TTL flash at F/3.5 was a lot less than the flash's full power capability, so some quenching was taking place at the third flash. Also, the reduction in lens aperture clearly led to the third flash increasing in output energy.

The actual effective lens aperture that occurred during these flashes may not be the value set on the lens and listed above. I was unable to reliably catch the brief aperture feedback in the viewfinder due to the awkward positioning of the camera, but my impression was that the reported aperture was not the value set on the lens. This would be consistent with the inconsistency in changes in measured stops and lens settings. So, while the measurement scheme was a poster child for crude, the results confirmed that at least wired TTL capability can be performed with multiple flashes.

Bottom line: A set of three AF-500FTZ flashes can operate in synchronized TTL mode.

I will need yet more cables to test with yet more flashes. I also need to review the flash-camera-lens interaction in this mode to understand the results in detail, as well as review the Flashmeter IV modes, as I believe the Flashmeter can be set to report a measure of illuminance instead of the indirect measure I used.
02-21-2018, 03:13 PM   #38
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Nice write up!

02-21-2018, 05:13 PM   #39
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Thanks. Probably worth the 9 Portra frames of the same closet interior view.

With respect to aperture variances: The lens I pulled to do this experiment happens to be the one, along with a zoom I don't have, specifically called out in the 645N Operating Manual (page 44) as having an aperture indication in the viewfinder that may not agree with the aperture set on the lens. While this comment isn't associated with flash specifically, one wonders whether the point is that the readout is in error and the setting canonically true, or vice versa. I suppose TTL wouldn't care as much as the experimenter might.
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