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I have a D200 and have been trying to take star trails but the photos are red on the corners of the photo. Do you have a simple answer that I am doing something wrong. I had it set for 2 hours.

enter image description here

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    What do you mean by ' the cars of the photo ' ? – Janardan S Oct 10 '16 at 9:59
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    Corners maybe ? – Henk Holterman Oct 10 '16 at 13:02
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Two possible explanations for the red blotches:

(1) Light leaking through the viewfinder. You should cover your viewfinder when doing long exposures, otherwise handling light sources (flashlights, mobile phones etc.) near the camera can result in unwanted exposure.

(2) Thermal noise. This seems more likely in your case because of the very long exposure time. Heating of the sensor and adjacent structure can result in non-uniform noise across the image.

Thermal noise (as well as other varieties of fixed-pattern noise) can be removed using dark-frame subtraction. This can also reduce the occurrence of hot pixels and is generally recommended when doing long exposures.

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Many Nikon cameras use a small near-infrared emitter inside the light box to confirm the correct operation of the shutter mechanism. If the IR filter in the sensor stack has been removed this near-IR light is allowed to be detected by the sensor. This isn't an issue at normal exposure times and lighting levels where the very dim near-infrared light does not significantly affect the resulting image. At very long exposure times in dim lighting, though, it can show up in the final result.

Due to the location of the light in your example, though, it looks more like some light is entering your camera via the viewfinder and leaking around the edges of the raised mirror which is held against the viewscreen during image exposure. You can reduce the influence of such light by covering the viewfinder during long exposures.

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