Why do I get a red haze along the top and right edge in 30-second dark frames on my Nikon D90?
Asked 11/9/2010
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When I make a test exposure with the lens cap on using a Nikon D90 in shutter-priority mode at 30 seconds, then let long-exposure noise reduction run, the resulting image is mostly black but shows a red haze/line along the right side and across the top. This seems to happen during long, high-ISO exposures (around ISO 2000 and up), which I notice most during astrophotography. I see it with both my 18-200mm and 85mm f/1.8G lenses.
Is this more likely to be normal long-exposure/high-ISO sensor behavior, or could it be a light leak or camera problem? What should I test to diagnose it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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I think it's quite normal -- especially if you are using a high ISO (sensitivity). It is something I experienced on my old D50.
I think that it is actually a sensor artefact caused by heat within the camera, rather than light leaking in somewhere, though that could also contribute.
Note that for long exposures you should cover up the viewfinder to prevent light entering from the rear of the camera.
Originally by user2019. Source · Licensed CC BY-SA 4.0
user2019
15y ago
0
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This is most likely normal for long, high-ISO exposures rather than a bad lens. Since it appears with multiple lenses and with the lens cap on, the lens itself is unlikely to be the cause.
Two likely causes were suggested:
- sensor/amp glow or heat-related sensor artifact during long exposures at high ISO
- stray light entering through the viewfinder during the actual exposure
A good first test is to cover the viewfinder and repeat the shot. On DSLRs, light can sometimes enter from the eyepiece during long exposures. Also compare results at lower ISO settings and shorter exposures to see whether the red haze decreases; if it does, that points toward normal long-exposure sensor behavior.
Long-exposure noise reduction may not remove viewfinder light leaks, because the second dark-frame exposure is made with the shutter closed. So if the artifact is caused by external light entering during the first exposure, it can remain after NR.
In short: probably not an urgent body/lens fault. Test with the viewfinder covered, and vary ISO/exposure time to confirm whether it’s a normal high-ISO long-exposure artifact.
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