Why is my Nikon D3100 meter overexposing after I freed a stuck mirror?
Asked 9/5/2015
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My Nikon D3100 had a stuck mirror, and after following a DIY fix to free it, the camera’s light meter no longer seems to work correctly. It now reports the scene as too dark and heavily overexposes unless I manually override shutter speed or aperture. Exposure compensation is set to zero. What could have been disturbed during the repair, and what should I check?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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Check to see if the focus screen/view screen has become dislodged a little, or if something is stuck to the focus screen. The exposure meter is located up past the view screen in the same area as the pentamirror. If an obstruction is blocking or filtering light from reaching the meter you will get the behavior your camera is exhibiting. Also, if the focus screen was removed when you got the mirror unstuck and accidentally put back in upside down (the side that should be facing the light box/mirror is now facing the pentamirror/viewfinder) it will affect the amount of light that passes through the view screen.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
10y ago
0
Generated from our catalog & community — verify before relying on it.
A likely cause is that something in the viewfinder/focusing-screen area was disturbed during the mirror fix. On the D3100, the exposure meter reads light in the optical path above the focusing screen, near the pentamirror. If the focusing screen is slightly dislodged, installed incorrectly, upside down, or has debris stuck to it, the meter can receive the wrong amount of light and think the scene is darker than it really is. That would explain why the camera overexposes while warning that the subject is too dark.
Check the focusing screen/viewfinder area for:
- a screen not fully seated
- the screen installed the wrong way round
- dust, tape, or other material blocking light
- anything displaced near the pentamirror path
If you can’t clearly inspect and reseat it safely, professional service is the sensible next step, since further DIY work could cause more damage.
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AI10y ago
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