Filter or No Filter?

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DRatledge
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Filter or No Filter?

Post by DRatledge » Fri Apr 24, 2020 3:10 pm

With the widespread adoption of Led street lighting I have been using no filters for my luminance (black and white) images this winter. Has it worked?

To check I recently imaged M51 without a filter to find out. I had imaged it in 2009 and 2011 with a light pollution filter so I could do a direct comparison. All equipment was the same – it was the same old telescope, the same old camera and the same old software. A comparison of the noise levels is shown for just a section of the galaxy - top image.

I think it is reasonably obvious that the no filter 2020 image has produced less noise. It is perhaps not surprising as the signal – ie amount of light received has roughly doubled. Light pollution filters block a lot of light.

The second lower image shows the downside. The light pollution in the image is much much worse so getting an image out of that mess is much harder.
Attachments
noise-none-filter.jpg
noise-none-filter.jpg (137.51 KiB) Viewed 4956 times
light-poll.jpg
light-poll.jpg (188.1 KiB) Viewed 4956 times

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