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02-21-2021, 07:58 PM   #1
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Pentax 67II + AF500 FTZ

Reading the instruction manual for the Pentax 67II and relative flash instructions, I'm not sure why it is the camera automatically selects 'manual mode' in the Aperture Priority mode when using TTL Flash? It says the bar graph shows the exposure value for the background. Does the 67II with a TTL flash operate the same way as with the 645N where you select the aperture and flash duration is controlled by the camera?

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02-21-2021, 11:02 PM   #2
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There are only three components of control, ISO, exposure (or flash duration in this case) and aperture. TTL operates by quenching the flash when the camera detects there is enough light reflected off the film. It is only necessary that the shutter speed ensure the shutter is open when the flash is fired. No camera control of aperture can be made during the flash duration. So, in flash mode, the aperture is whatever the user has set (manually), the exposure is whatever goes with the flash timing (making it effectively manual) and the ISO is whatever is set into the camera (also manual).

In P-TTL (645D and Z) there are two flashes, and the camera uses the measured detection of the first to estimate target range and reflectivity allowing the camera to set flash total energy (power and quenching time).
02-22-2021, 12:09 PM   #3
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QuoteOriginally posted by Super645 Quote
I'm not sure why it is the camera automatically selects 'manual mode' in the Aperture Priority mode when using TTL Flash?
If I am reading the excerpt you posted correctly it seems to be saying that with a charged flash unit the camera will set 1/30s shutter speed and maintain your chosen aperture. The bar graph will show the exposure for the background. Your subject will be exposed by the flash operating in TTL mode. if the background is too dark you can slow the shutter speed or widen the aperture. If it is too light you can stop down or use a slower film.

The camera has a 1/30s sync speed. Not great for aperture priority fill flash.
02-23-2021, 09:41 AM   #4
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QuoteOriginally posted by Super645 Quote
Reading the instruction manual for the Pentax 67II and relative flash instructions, I'm not sure why it is the camera automatically selects 'manual mode' in the Aperture Priority mode when using TTL Flash? It says the bar graph shows the exposure value for the background. Does the 67II with a TTL flash operate the same way as with the 645N where you select the aperture and flash duration is controlled by the camera?
I use that combo as well and yes that 67II will control the flash duration depending on the set aperture. There is a table in one version of the AF500FTZ flash guide, that lists the apertures supported depending on the ISO and zoom setting you are using.

Check out this thread for more info:

https://www.pentaxforums.com/forums/48-pentax-medium-format/367096-pentax-67...oblem-ttl.html

Phil.


Last edited by gofour3; 02-23-2021 at 09:52 AM. Reason: Added link
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