PureNight Light Pollution Reduction Filter Comparison for Astrophotography

Man, that post title's a mouthful.

Anyway, back in May I received my PureNight filter by LonelySpeck (aka Ian Norman) and had a chance to test it out during a late night hike into the hills surrounding the bay. I was personally quite impressed but received the reasonable request from Reddit for a side-by-side comparison with and without the filter. This post is an attempt to provide side by side comparisons across various different light pollution levels (with provided raw files if you want to play with them) and will be updated as time goes on.

Bortel 5-6 (Natural Bridges State Beach)

In late June I made a trek down to Natural Bridges State Beach. Before jumping into details, let's take a look at the final result.

Milky Way over Natural Bridges. Cool, right!?

Alright. Why Natural Bridges? Well a) it's gorgeous and b) it's a 5-6 on the Bortle Scale looking out over the ocean and then back towards Monterey (another 5-6 zone). Which is to say that there was going to be some noticeable light pollution to deal with.

So, let's do some side by sides. Both photos are from a Sony a7Sii, 18mm f/2.8, 25s, ISO 6400, Daylight WB.

BTW, grab the raw files here and here to try your hand at editing both and let me know your results!

No filter. Only lens correction applied.

PureNight Filter used. Lens correction applied.

As expected the filter cut out a significant amount of the yellow and orange. Which is basically what it promises to do.

Now, time to adjust the white balance.

No filter. Lens correction applied. White balance adjusted.

PureNight. Lens correction. 0.7EV boost to exposure to bring the histogram in line with the one with no filter. White balance adjusted.

It looks like the PureNight did manage to pull out more contrast from the galactic core and more warmth. Not bad. However, I did find myself fighting to tone down the blue both in white balance and throughout the entire editing process.

Bortel 4.5-5.5 (Crystal Springs Reservoir)

After Santa Cruz I decided to try somewhere a bit more light polluted. Right on the boundary between red and orange. Crystal Springs. Honesty, back when I was first getting started in astrophotography, I wouldn't have even considered shooting somewhere this bright. It would have just been a washed out mess. But as I've gotten better at shooting and post-processing I decided to give it a go.

First, the final image.

I had some fun and posed in the shot. :)

This go-around I varied the ISO to compensate for the lost raw light so the histograms roughly peaked at the same spot for both photos.

Both are, once again, from a Sony a7Sii, 18mm f/2.8, 25s, Daylight WB. The one without the filter was at ISO 2500. The one with the filter was at ISO 4000. You can find the raw files here and here. For both photos I attempted to edit them as best I could while not touching any localized adjustments. In the end I managed to roughly bring the sky and light pollution to roughly the same intensity for a side by side comparison.

With filter. Edited.

Without filter. Edited.

Not bad. :)

As the light pollution increases the benefit of the filter becomes more apparent. I still need to work through how to tame the colors of the milky way when using the filter, but the extra detail in the core is pretty damn nice.

Things left to try

I'm going to leave this post as a <WORK IN PROGRESS> as I'd like to experiment with a few things in the future. Such as doing a comparison of stacking images with and without PureNight.

Anyway, if you have any other testing ideas, let me know. And I'll update this post as we go. In the meantime, I'll leave you with a higher res vertical pano from the Natural Bridges trip. :)