changing lenses with the mirror locked

[sorry_no_photos]

<p>Live and learn, I guess. Just got some of my holiday pics developed and noticed some of the photos grossly overexposed (ie, nothing left). It took me a lot of head scratching. Initially, I thought maybe the lens contacts were dirty or that the lens shutter was dirty. Finally, it hit me like a ton of bricks. With the mirror locked up, there is nothing protecting the film from light when a lens gets changed. Just thought I'd share this. If it saves one other poor sucker from doing the same stupid thing, it will be worth it.</p>

[tim_ludwig2]

<p>Evan,</p>

<p>The mirror being locked up has no effect on exposing the film unless you also have the focal plane shutter open. The shutter totally blocks all light until and unless you release the shutter. It sounds like you may have possibly had the shutter on B or T setting while the mirror was up which could have done as you described, or, you could have simply grossly overexposed the film...possibly due to a faulty meter or even a program problem with the camera.</p>

<p>Locking the mirror up prior to exposure is a common practice in order to ensure that all possible sources of camera shake have been eliminated before making a long exposure on a tripod. Until the shutter is released, the mirror is out of the way, but NO light can arrive on the film.</p>

<p>What camera are you shooting?</p>

[Ed_Ingold]

<p>With an Hasselblad, you can't remove the lens if the mirror is pre-released. However, I don't think there's any safety to prevent pre-release if the lens is already removed, or you could press the shutter release. In that case the mirror is raised and the auxillary shutter (or focal plane shutter) is opened. Light will reach the film unabated. Keeping the darkslide engaged would protect the film and prevent accidental operation of the shutter release.</p>

[tim_ludwig2]

<p>Even, My apologies. I'm thinking 35mm and answering in your medium format post. If somehow, you could lock the mirror up and change the lens while the dark slide is out, that would indeed blow out the film in a camera that relies on exposure from an in-lens shutter.</p>