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07-29-2022, 07:51 AM   #1
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Pentax 645 Leaf Flash Help


I'm considering purchasing one of the leaf shutter lenses for the 645, but I haven't been able to find much guidance on how to set it up with a flash outside of looking at the manuals.

Couple of questions:

1. Do the 645 leaf shutter lenses work with the AF-400T flash only? or will any third party flash with a PC sync cable be usable?
2. When using the flash, is it as simple as setting the ISO on the flash (in manual mode), then setting one of the shutter speeds on the leaf lens and then setting the appropriate aperture on the lens for the distance of the subject? Or is there more to it then this?

Any help on this would be welcome!


07-29-2022, 08:13 AM   #2
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Used mine with Metz & 645D + extension tubes for Macro.

07-29-2022, 11:48 AM   #3
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I've been wondering this myself. I think (or hope), since the 645 supports TTL, that any hotshoe connection to a Pentax TTL supported flash would work at any lens shutter/aperture combination... assuming you're within range. For non-TTL flash, I'm assuming you put the flash in an auto (or manual) setting and set the recommended aperture. Shutter speed won't matter other than helping to balance ambient light. Also this would be for hotshoe or PC socket on the body or lens. Again...I'm guessing.

07-29-2022, 05:05 PM   #4
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Lens Manual:
PENTAX SMC 645 LS 75MM F/2.8 OPERATING MANUAL Pdf Download | ManualsLib

There are two different operating modes when using these lenses,
One-Lock open the leaf shutter in the lens, and use the focal plane shutter in the camera. In this mode, you would use the Hotshot or PC contact on the camera body to fire a flash, and the body shutter would be set to X-synch (1/30th?, just guessing, not sure). You should be able to use the TTL flash with a capable flash with this set up.

Two-Leaf shutter, really only valuable for using with flash,
In this mode the body shutter is set to a slow speed (1/8-sec or slower), and the shutter in the lens is used. Set the shutter speed with the ring on the lens, and then the lens must be cocked separately, in addition to cocking and advancing film in the camera.
To Synch with the leaf shutter, Flash units must be connected to the PC outlet on the lens. If you connect the flash to the body they will not sync the flash to the leaf shutter.

Exposure with flash is determined the same way in either case. I don't believe that TTL flash control is possible through the Leaf shutter.
When using the Leaf shutter with flash, the Leaf shutter speed and aperture control the ambient light exposure, and the aperture and flash settings/distance control the flash exposure. You need to play around to balance them, given a common aperture; find a flash distance and shutter speed for the effect you want. When I've done it with leaf shutters in view cameras, I've usually used the ambient light as key, and the flash as fill, a stop or so under the key exposure. Mostly using the flash to lift shadows.
Especially with film cameras, a flash meter is very helpful.

Takes some messing to get it right, but very useful technique,

Sorry, got into the technique and did not answer the questions:

#1 Any flash you can synch with a PC cable should work. The hot shoe on the body is synched to the focal plane shutter, so you must have a PC cord to connect to the lens shutter. The PC cord is a "dumb" connection, it has no extra pins to control things. All it does is fire the flash at the right time.

#2 Pretty much, just remember that the shutter and aperture control ambient light exposure. The leaf shutter has essentially no effect on the flash exposure. The flash part of the exposure is controlled by aperture and flash distance.
You control the balance between them by varying shutter speed and/or flash distance. If you vary aperture (once you've determined the one you want to/can use), you change both parts of the equation.

Last edited by K-Three; 07-29-2022 at 05:25 PM. Reason: Never answered the questions
07-29-2022, 07:29 PM   #5
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QuoteOriginally posted by tomw95 Quote
Do the 645 leaf shutter lenses work with the AF-400T flash only? or will any third party flash with a PC sync cable be usable?
You will need to get one of these Leaf-Shutter flash accessories to use with most modern flashes with no sync socket/cable like the AF400T has: (4P to X-Sync cable)

Pentax Hot-Shoe Adapter LS reviews - Pentax Camera Accessory Review Database

Note TTL flash is not possible.

07-30-2022, 07:41 AM   #6
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Original Poster
Thanks for going through this @K-Three, my intention for this setup is to use the higher sync speed of the leaf lens (1/500s) to photograph crowds at sport scenes. So the high shutter speed would freeze crowds with lots of movement. Therefore the process would be what I described in the first question, as the ambient light isn't really as much of an issue as long as the people in the photo are lit by the flash.

Also thanks for pointing out that accessory @gofour3, I was looking at third party flashes that have a built in PC sync cord but now I'l be able to use any other Pentax clip on type flash which will widen the options.

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