Optolong L-extreme
An image of the Elephant's Trunk nebula in IC1396 taken with the Optolong L-eXtreme filter.

The Optolong L-eXtreme filter for astrophotography is dual band, allowing one shot colour cameras (OSC) to capture H-alpha and Oxygen III wavelengths at the same time.

I was fortunate enough to have Optolong send me an L-eXtreme filter for testing. And it coincided with a run of clear nights all in a row, allowing me to image two targets and put this filter through its paces.

L-eXtreme spectrum chart
The L-eXtreme spectrum chart showing the allowed and blocked wavelengths.

The L-eXtreme filter does differ from the L-eNhance filter. First off the L-eNhance is a tri band filter isolating the H-alpha (Ha), H-beta (Hb) and Oxygen III (OIII) channels. Secondly it uses much broader wavelengths to capture these channels. The L-eNhance uses 10nm for Ha and 24nm for OIII passes. This varies from the new L-eXtreme filter which passes Ha at 7nm and OIII at 7nm. 

For those using a OSC camera and wanting to image in the Ha and OIII channels the L-eXtreme filter allows for convenience and cost effectiveness. You can image a rich selection of emission and planetary nebulae, even in bright, heavily light-polluted areas, gathering data in both wavelengths with one filter instead of having to switch out between two.

My first target using the Optolong L-eXtreme was IC5067, prominent ridge of emission in the Pelican Nebula. The ridge spans approximately 10 light years and is 2,000 light years from Earth. The tendril to the right of center displays the telltale twin jets of an embedded protostar. This gaseous region of space contains Ha and OIII emission lines so it made an ideal target.

IC5067 in the Pelican Nebula taken with a QHY268C and the Optolong L-eXtreme filter.
Optolong L-extreme filter
The new Optolong L-eXtreme filter captures Ha and OIII for one shot color cameras.

The image above of IC5067 was processed in Pixinsight as a quasi Hubble palette look. Quasi meaning, sort of, kind of, but not really. This is because the data is from a OSC camera and the colour channels split and remapped to Ha, OIII and SII. However there is no SII, the red channel is simply substituted for it. This is why although it looks like a Hubble palette image it isn’t exactly that.

Unless your deepsky object has a lot of OIII (blue) in it, the images taken with the L-eXtreme will be predominately red in colour. The image below is the uncropped version of IC5067 and in the standard colour appearance delivered by the L-eXtreme. In this case IC5067 doesn’t have a lot of OIII (blue) in it so most of the colour data is red. This is isn’t a bad, thing, more just the nature of the beast depending on your deep sky object of choice. You can do what I did though and create a quasi Hubble palette look from the data if you want a different colour appearance. 

Unaltered colour from the L-eXtreme filter data will tend to be more redish unless there is a lot of OIII contained within the deepsky object. Image of IC5067 (uncropped)

With IC5067 being predominately red in colour I wanted to see how the Optolong L-eXtreme filter performed on an object with more OIII (blue) in it. I was able to take 15min of test data on the Dumbbell Nebula (M27) and also the Witch’s Broom (NGC 6960). Both of these deep sky objects contain a lot of OIII. This data consists of 3 x 5min exposures with flat and dark frames. Calibrated, aligned and stacked in Pixinsight, with some stretching applied.

With the L-eXtreme filter having much narrower OIII bandwidth of 7nm, than the L-eNhance’s 24nm, it should pick up more of that OIII wavelength and it should really pop in the image. My test results are below.

Optolong L-extreme test M27 Dumbbell Nebula 15 minutes
15 minutes of test data taken with the L-eXtreme filter and QHY268C. M27, the Dumbbell Nebula.

As you can see the OIII (blue) was picked up quite well by the L-eXtreme filter. There is even a hint of the outer shell surrounding the planetary nebula, with this minimal amount of data. Imagine what 2 hours or 10 hours of data would look like!

The Witch’s Broom NGC 6960 was another 15 minute test I performed using the L-eXtreme filter. This was the result…

L-extreme NGC 6960
15 minutes of Ha and OIII test data, taken with the Optolong L-eXtreme filter.

Not bad for just 15 minutes, wouldn’t you say?


The new L-eXtreme filter from Optolong is very capable and is proving to be a game changer, especially for those backyard astrophotographers using one shot color (OSC) cameras, be it DSLR or cooled cmos. It’s new design and more narrow Ha and OIII emission lines, isolates these channels well for extremely vivid images of deep sky objects. It’s an ideal choice for a variety of telescopes and cameras. As an added bonus for OSC users, the Optolong L-eXtreme also helps block a lot of light pollution which can ruin your astro images.

Are you planning to get an L-eXtreme filter for your setup? Comment below and let me know!

Clear skies.

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