Hi All,

I'm totally new to large format and would appreciate some help with a lens i recently acquired. It's a 135mm Schneider Symmar 5.6 mounted on a Synchro Compur shutter. This issue is that the lower speeds on the shutter (1/15th and below) do not function correctly. The timings are much longer then they should be and are very inconsistent. I'm aware that it's possible to open up the shutter and give it a blast with a can of air which i'm hoping may help. The rear lens element unscrews very easily however the front won't budge at all. Can anyone give any advice on what i'm doing wrong? Click image for larger version. 

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