noise reduction procedure

[cynott]

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Hi to every one!

somebody can help me explaining the procedure to avoid the reconstruction of the image  after very long exposure? I need it to take pictures of fallen stars. The long time to reconstruct images is long as the exposure time and prevents me to take shots very close each other.

thank you

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[jaapv]

Ah yes… LENR.  It is the only way to eliminate certain types of noise, so Leica has adopted it as standard procedure. A frequent subject on this forum. It is an obstacle to astrophotography as you note. 

[cynott]

LENR

does what it means?L....E...Noise Reduction?

[Ba Erv]

Long Exposure Noise Reduction 

[jaapv]

And a bone of contention because it cannot be switched off on most models. 

[cynott]

thank you

 

 

[Stuart Richardson]

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If you are not aware, what the camera is doing is taking another exposure with the shutter closed. So basically just turning on the sensor for the same amount of time as the exposure. When digital sensors are on for a long time, they tend to build up heat and false noise. Things like hot pixels get really much more apparent. So what the camera does in this context is make a long exposure photo of a scene, close the shutter and do the same exposure again. That second dark exposure captures all the sensor errors and hot pixels that occur because the sensor is not perfect. Then it maps out all those imperfections from the first exposure, and finally writes the dng or jpeg. While this takes twice as long, it cuts down on noise substantially, without otherwise harming the picture (using conventional noise reduction would get rid of lots of stars).

If you turn off long exposure noise correction, you can still make your own dark frame, and use that to subtract the noise (I have not done this exact procedure, so others would have to help with how to do it). People doing astronomy photos might prefer this if they are short for time, as they can make a single darkframe image for a given exposure time, and then just use that for all the photos. The Leica method tends to work very well, but it does double your time....as you saw.

I am not sure if it is possible to turn off LENR in the Q2. I believe it is in the SL2, so I imagine it might be...

Edited May 7, 2022 by Stuart Richardson

[cynott]

Thank you for your veri clear description of the procedure, but , substantially I cannot avoid it!.

Thank you again 

Stefano

 

 

 

 

 

 

[vedivv]

Other members explained the camera sensor long exposure/noise problem very well.

Stacking is really the way to go for really long exposure.  Have been using the technique for astrophotography for a while now.

Here is a link as how to do it:

https://digital-photography-school.com/how-to-improve-your-long-exposure-with-photo-stacking/