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I'm shooting with a Nikon 810, and my night shots often have a strong moire when I export them from Lightroom at 640x640 (optimized for Instagram).
This photo was shot at f2.8, ISO 4000, 15 seconds with a Nikkor 17-35mm. Does anyone know why this is happening??
I solved the mystery! I shoot RAW, edit in Lightroom, and export to JPEG. In LR I normally check "Enable Profile Corrections" under Lens Corrections. When I unchecked this box, the photo exported without the moire. Not sure what's going on under the hood, but lesson learned.
While I don't have an answer that I like, I can share my technique for dealing with this problem.
I have the same setup. It's not Lightroom, it's that for what you are wanting to do, long exposures at high ISOs are not usable...except to calculate the proper exposure. So, get the exposure right at a high ISO, then make a longer exposure at a lower ISO and, poof, no ugly artifacts.
15 seconds at ISO 4000 = 960 seconds at 125 ISO, but you can recover 3 stops of the shadows at 64-125 ISO, so you might be avle to get away with 600 seconds. Of course, if it's getting lighter out due ot sunrise, it would be even shorter.
If you want, when the long exposure at low ISO is done, shoot some high ISO frames for blending purposes. IE, ripples on the lake etc. Best of both worlds. Here's an example...
Interesting. Remove any blanket you have on your sky (Just a joke).
There is a chance you are seeing the resampling of the noise pattern of your sensor.
But something peculiar is that I had noticed a more defined pattern on Canon than in Nikon.
Apply some noise removal before resampling.
You could try to export a bigger version in Lightroom and resample the resulting jpg with another aplication. Another thing to try is to play with the sharpening. Probably avoiding it totally.
I cannot be 100% sure but it looks this way because:
Change every thing mentioned and see how it works for you. Try strengthening the noise reduction.
I would start with checking the optical path, namely cleanliness of the sensor.
I suspect that crisp colorful landscape like the one in the example required some dramatic corrections with the contrast, sharpness, clarity and similar other sliders. Try moving them one by one back and forth to a more neutral setting to see if the pattern disappears.
Try exporting to larger color space with 16 bit and no lossy compression to see if that makes a difference. E.g. ProphotoRGB 16 bit TIFF with all other optimizations you otherwise apply to the image.
This camera spots a CMOS imaging chip. The surface of this chip is covered with millions of photosites. Each contain a photodiode that convers photon hits to an electrical charge. The charge induced during the exposure is too feeble to be photographically useful. The CMOS photosites each contain tiny amplifiers. The job of the amplifier is to strengthen the charge to a useful level. The amount of implication applied is intertwined with the ISO setting. Night shots likely require a high ISO setting that applies lots of amplification. When we turn up the amplification, in an audio system we induce some static. The same is true in a video system only we call it “noise”. The CMOS design with an amplifier at each site delivers what is called “fixed-pattern” noise. We want each amplifier to start working at the same level and amplify at the same rate. This is just a dream. What actually happens with current technology is each amplifier is somewhat independent, they each have a different threshold when the start plus they amplify at different rates. This results in fixed-pattern noise. Such imperfections are in every image but we only notice them in mundane backgrounds like your night shot. To see how your camera yields fixed-pattern noise, shoot a picture or two with the lens capped. You will see some pixels with be a little lighter than max black. A camera with a CCD imaging chip transfers the signal to another chip that contains a single amplifier. This adjacent chip supplies signal processing and amplification.
