Optolong 3nm narrowband filters SHO
M42, the Orion Nebula, captured through Optolong 3nm narrowband filters and processed in a SHO (Hubble) palette.

This is my first image of 2022 and also first image taken using the new Optolong 3nm filters.

I haven’t had much in the way of opportunity to image with them. The past 2 months or more, we’ve had mostly cloud and snow. There were only 2 clear nights and I tried to accomplish a little bit of everything (like also testing the new L-Ultimate filter). 

I’ve used Optolong filters for the past 5 years now. They have performed well and are reasonably priced for the majority of backyard astrophotographers. Optolong sent me a set (Ha, OIII, SII) of their new 3nm filters and wanted me to try them out.

The advantage of 3nm filters vs the more common 7nm (or 6.5nm), is the bandpass is much narrower. This is good, especially for those backyard astro imagers dealing with light pollution. The 3nm filter will make sure that the data collected by the sensor is far more of the pure signal being emitted from the depths of space; and not unwanted photons such as light pollution from that street light or outside house light your neighbour likes to leave on while inside for the night.

For my first test images (below) and the image above, I used an Explore Scientific 127CF triplet refractor at F5.2, a QHY268M cool cmos camera and of course the Optolong 3nm filters.

One of the biggest issues facing backyard astrophotographers when it comes to filters is halos around bright stars. So I wanted to really test the Optolong 3nm filters performance with this in mind. I chose the star Alnitak in Orion which is associated with the infamous Horsehead and Flame Nebulae – a popular imaging target for astrophotographers. Alnitak is famous in the astrophotography community for having a severe halo around it in images taken of this region of space. Perhaps phrasing it, Alnitak exposes halo problems with filters very easily, is better. 

These are the test images I took. Click for larger view:

Optolong 3nm filter test H-alpha
2min exposure through the Optolong 3nm Ha filter.
Optolong 3nm filter test OIII
2min exposure through the Optolong 3nm OIII filter.
2min exposure through the Optolong 3nm SII filter.

And these are cropped images highlighting the star Alnitak:

Optolong 3nm filters test
Closeup of Alnitak (Ha)
Optolong 3nm filters test
Closeup of Alnitak (OIII)
Closeup of Alnitak (SII)
Closeup of Alnitak (SII)

So as I mentioned my main interest for these test shots of Alnitak were to see if there was any kind of halo appearing. Especially with the OIII filter which are notorious for halos. I was pleasantly surprised to see no halo at all with the Ha and SII filters and only a very slight hint of a halo in the OIII image. Really it was virtually halo free. That’s exactly what we want!

I plan to do more narrowband imaging with the Optolong 3nm filters, so stay tuned! Sign up for my newsletter and subscribe to my Youtube channel.

Are using or planning to purchase 3nm narrowband filters? Let me know your thoughts below in the comments!

Image Technical:

Explore Scientific 127CF Triplet Refractor (at F5.2) https://bit.ly/3FhnZ5k
QHY268M CMOS Camera (https://bit.ly/3Aj23FE), 26mp, 3.76um @ -10C
QHY CFW3-L 7 position https://bit.ly/3jAp9Sb
Optolong Ha-OIII-SII 3nm filters https://bit.ly/3GekTk7
Skywatcher EQ6 mount / Skyshed Pier (Skyshedpod.com)
Pegasus Astro Focus Cube https://bit.ly/3dzagfr
NINA 1.11 (beta nightly build) for acquisition
Processed in PixInsight
Seeing and transparency: average to good
Location: Kitchener, Ontario, Canada

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