The local weather has been uncooperative so I decided to run a few tests of the D70 digital noise and the built-in noise reduction (NR) capability. All of the images were taken at room temperature with the lens cap on. Original image size was 1504x1000 at the "fine" JPEG setting. Exposure duration was 5 minutes with no cool down between individual images at each NR setting. I did allow a 10 minute cooldown when I switched from NR OFF to NR ON. The tests were done on internal battery power.
In the first table below the images have been reduced from their original size and inverted (black becomes white) to better show the noise in the images. In the NR OFF images you see the green area in the upper left hand corner where the power supply for the camera generates heat.
|ISO||NR OFF||NR ON|
It is evident from the above that the noise induced from the heat source is more obvious at higher ISO settings but that enabling Noise Reduction is very effective at removing it.
The second table shows a central portion of the higher ISO setting exposures with the "levels" adjusted in GraphicConverter with the "white point" set to the start of the rightmost "shoulder" on each image. This brings out the noise that would be visible in a typical single frame exposure that has been edited.
|ISO||NR OFF||NR ON|
What surprised me was that enabling Noise Reduction actually increased the "noise" visible in edited images. I will do some actual astrophotography tests of this on my next trip to Oracle Observatory and report back on the results.
Here is a 10 minute ISO 1250 exposure unprocessed image of M45, the Pleiades, showing that having Noise Reduction OFF does not put significant noise in the central portion of the image. So unless you want a full field image without noise, consider using NR = OFF for long duration exposures where the object of interest is only in the center of the image.
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