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01-04-2019, 01:56 AM   #1
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LS lens on 645N


I am trying to use the LS feature of my 135mm on 645n ...
Just wasting film for now ...

I use a synch cord, connected to an hot shoe adapter (this one, no contact with the camera : ), connected to a modern Sigma EF 610 GD which works perfecty well on my pentax film camera (Z70 & 645N in focale plane mode), but :
- The image is still viewable in the viewfinder even when the lens is not cocked

- no light at all when releasing the shutter

Any help would be usefull Thank you

01-04-2019, 02:17 PM   #2
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You have to set the camera shutter at 1/8 sec. and only use the sync plug on the lens to fire the flash. Be sure to remember to cock the shutter in the lens.
01-05-2019, 12:02 AM - 1 Like   #3
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QuoteOriginally posted by sad_punk Quote
... The image is still viewable in the viewfinder even when the lens is not cocked ...
That should not be the case. If you haven't cocked the lens shutter and you're using the lens in leaf shutter mode (that is you've selected a shutter speed on the lens barrel) you should have a blocked / black viewfinder until you cock the lens shutter.

It is not completely clear to my whether or not the Sigma flash fires. Your claim that is works in focal plane mode gives me the impression that it does not fire in leaf shutter mode.

Have a look at the section 'Using in Leaf Shutter Mode' of the LS lens manual. Using the lens on an original Pentax 645 I can vouch that the procedure how to use the lens is exactly as described. I also used this lens on a P645N and I am not sure if the camera switches to 1/8s shutter automatically. Have to check that.

I would recommend to check out the manual and make sure you'll notice the view finder blockage when you've tripped the leaf shutter. If you do not see the blockage, your lens in malfunctioning hence no flash output.

On a side note. You should be able to test drive this setup without film. Unlike the 645 the 645N fires when no film is loaded.

Good luck!

01-06-2019, 07:19 AM   #4
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Original Poster
Thank you for your answers, problem resolved at an old phography local shop : the sigma was too recent for the LS lens, even if compatible with the camera with focal plane shutter mode, as the technology for the 135mm LS is from a different génération.
The shop sold me an old agfatronic and everything is ok with it


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