Optolong L-eXtreme First Impressions

Optolong L-eXtreme First Impressions

On Monday I took receipt of the new Optolong L-eXtreme Dual Narrowband Filter. This puppy lets through Hydrogen Alpha and Oxygen-III only. As luck would have it, Monday night was also clear. As was Wednesday and Thursday. So I screwed it onto my trusty Sky-Watcher Reducer Nosepiece and got ready for a night of astrophotography with this new Optolong filter.

L-eXtreme First Impressions


Like most gear, there’s a learning curve. Even a filter can take you a little bit to familiarise yourself with. As such, I chose a really easy target that absolutely lent itself to this L-eXtreme filter – NGC 6992 The Eastern Veil Nebula. This supernova remnenant primarily consists of Hydrogen Alpha and Oxygen-III. So it was the perfect candidate of low hanging fruit I wanted, in order toget used to a new filter.



Finding Focus

Focusing with the L-eXtreme
A bahtinov mask view using the L-eXtreme

As I always bang on about, focusing with a narrowband filter is a bit more tricky. Even if this dual narrowband filter technically lets more light through, it’s at 7nm anyway. So it’s not as easy. Either way because of the index markings on my focus tube I was able to get near focus straight away, and then fine tuned it from there. Afterwards, the bahtinov mask and the bright star Vega were all I needed. Once I had found focus, it was time to lock it down and slew to the Eastern Veil Nebula to start stretching this L-eXtreme filter out. (I’m having difficulty not writing L-eNhance!).


The Eastern Veil Nebula


The first port of call was general framing. Not a hard task with plate solving mind you. The real work was deciding on an exposure time. I tried 3, 5 and 10 minute exposure times with my modified Canon 600D DSLR camera. In the end I decided 3 and 5 didn’t show enough signal for me. The 7nm nature cut out too much light I think for my f/6 telescope system. In the end (yes, in the summer) I opted for 10 minute long exposures.


Were they noisy? Of course. But they weren’t too noisy. There’s a fine line in difference. I did see sensor banding but that’s a common ailment with the Canon sensors, as well as high temperatures and only a little data.


By the time it came to pack up on the Monday with the Eastern Veil Nebula, I had amassed just over 2 hours of data with the Optolong L-eXtreme filter. 13 exposures to be exact.


The images straight out of camera suffered quite a green cast to them. I was confident these would calibrate out.




The colour cast didn’t calibrate out too much. I could probably have changed a setting in DeepSkyStacker but ultimately I knew I could correct for it in Photoshop.


The Colour Cast With The L-eXtreme
As shown with the Histogram, there’s an excessive amount of green



Once I was in Photoshop and editing, the quality of data was okay. The heat had definitely took its toll and the fact that 2 hours really isn’t enough for 7nm narrowband data. But I had to work with what I had.


Plenty of noise reduction and colour balancing later, as well as some curves to boost the red and blues, I ended up with this image. I’m very happy with it considering the somewhat challenging circumstances that birthed this picture. But it was a good first test of the L-eXtreme, but I knew to see what it’s really worth I had to go to emission nebula.


That’s where Wednesday and Thursday came in.


The Pelican Nebula


On Wednesday I turned the telescope over to the Pelican Nebula within Cygnus. I was ready to test out the Optolong L-eXtreme filter on emission targets. To see what sort of detail it picks up, colour casting, colour balance and such. I remember the predecessor – the L-eNhance – had great colours in emission nebulae as well as a great ease of use. But the L-eXtreme is tighter than the other filter so I was fully expecting to see difference.


To be clear, I did shoot this target with a 7nm Baader Hydrogen Alpha filter as well. So I do have some sort of benchmark to compare it to. Though, it isn’t going to be an Apples to Apples comparison.


Granny Smith Apples vs Jazz Apples comparison, maybe.


Temperature DegradationPelican Nebula w Optolong L-eXtreme


Much like Monday, Wednesday was also hot. In fact a heatwave had struck Britain. That day had been 30-32’c with no clouds in the sky. A beautiful day so long as you don’t want to do DSLR narrowband deepsky Astrophotography. The night was somewhat cooler. But not much.


My sensor was reporting a toasty temp of 30’c on average during that imaging session. The raw images really shown the noise from the heat. It was discouraging most certainly. But that’s due to my sensor and camera (well more so the weather) than the filter. However last year I tried shooting with the Tri-Band filter and I lost all detail. This year the heat didn’t ruin it too much. If you want to see what damage the heat did then, you can see the video.




L-eXtreme DetailI found the details I were getting within the structure of the Pelican Nebula to be quite agreeable. On this occassion I wouldn’t go as far to say it was better than the Baader 7nm image. But the Baader image also had the benefit of not being in the middle of a heatwave at the height of summer.


Plenty of noise reduction had to be applied during my first editing pass. This still failed to hide the banding going through the image – a feat only more data can solve I suspect. But it certainly helped to make the image a bit more tolerable. However there are aspects and areas within the nebulosity with the Pelican Nebula where data is straight up missing. I blame heat.



Fine detail was lost due to the noise. I’ll have to try again when it’s cooler if stacking larger stacks won’t fix it.




I really enjoyed the colours coming through with the Pelican Nebula using the Optolong L-eXtreme. The reds were very deep but not deep to the point where it might as well have been a Ha filter. The inclusion of the O-III very clearly helped balance the colours and add some neutrality to the sky.


For comparison here is a raw Baader frame and here’s the L-eXtreme. I really think the Oxygen-III is responsible for the colour balance.


Top: L-eXtreme, Bottom: Baader 7nm Ha


Initial Summary


The filter is certainly exciting. I lament the fact I don’t have a cooled camera to test it out on properly. Else I’d really be doing those 10 minute exposures and such to get all that detail. But I have to run with what I’ve got.


I’m looking forwards to capturing more emission targets with this filter. As mentioned above the reds are deep and yet the image is generally colour balanced (to the point of having a dark sky with no obvious tint).


L-eNhance or L-eXtreme?


I’ve already received this question several times now, and I can understand why. On paper they’re directly comparable. But at this point I’m not ready nor happy to make a conclusion on the L-eXtreme so I can’t give both filters a fair fighting chance with one another. Keep watching this space as the L-eXtreme filter review will be dropping in the future, and there I’ll try to surmise these filters and help educate you in which filter might be right for you. In the meantime you can check out my Optolong L-eNhance review.


Until then, though. Clear skies everbody. Keep looking up and keep them cameras clicking.



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