When I fist saw the announcement of a new filter from Optolong, I really got excited and thought that they were making an alternative to the much more expensive Radian Ultra Quad Narrowband Filter, but to my surprise, I think they just used the word quad to add more punch to the filter name. The L-Quad Enhance Filter is being advertised as a quad bandpass light pollution suppression filter for colour cameras, but I would rather say it is a stronger version of their popular L-Pro filter. For me, a dualband, triband and quadbands have a much narrower transission window than this filter.
L-Quad Enhance Filter Spectrum
Spectrum from Optolongs advertisement
Its spectrum resembles alot of its predecessor and the main difference is that is now suppressing all light transmission between 575 to 625nm while the L-Pro let some light pass through in the 600nm range. Instead, the new L-Quad also lets in more UV-light and IR-light. How it really affects the image quality is for me yet unknown. It also have a much broader bandpass in the redder part of the spectrum.
My own measured spectrum of my two filters L-Pro and L-Quad Enhance
Comparison
This is the equipment I tested the filter with. The left is a TS-Optics 115/800 mounted on a Skywatcher EQR-6 Pro and ASI2600MC camera while the right one is a Sharpstar76EDPH on a Skywatcher GTI and a Sony A7III.
Backyard photography with a Bortle 5 sky and lots of lights surrounding my house.
Backyard photography with a Bortle 5 sky and lots of lights surrounding my house.
My plan was to test three different kind of objects that all had different characteristics: a bright galaxy, a faint dark nebula and last a strong emission nebula that had the three major elements, Oiii, Ha and Sii represented. Due to clouds coverage, I only managed to complete two of three tasks in the time given by Optolong to finish testing and present my results. Sadly, the last test was also the type of objects I think this filter would show its full potential.
First test was done on our nearest neighbor galaxy, the Andromeda Galaxay M31. It’s easy to shoot, even without a tracker from a very light polluted sky.
The image below shows the comparison in full view between L-Pro and L-Quad Enhance as a stack of 30*3min. I did a test without filters as well. But then I remembered that the camera that was used to test this was a full spectrum modded Sony A7III. So it was hard to use it as a reference. My plans was to reshoot the test, but as stated, weather gods prevented me from doing so. For your info, the full spectrum image was actually quite good. No star bloat or CA. But the colors couldn’t be matched properly within PixInisghts SPCC so I chose not to include it in this review.
If you look closely at the images, you might see a faint reddish signal around the galaxy, this signal is also present in the full spectrum version. I have not yet identified what it is, but I doubt it is Ha. It is not removed by any gradient nor light pollution removal in post editing. This is most prevalent in the L-Quad Enhance image, second is L-Pro and the faintest in the full spectrum version. I have not ever seen it in my other M31 images I have taken over the years.
The image below shows the comparison in full view between L-Pro and L-Quad Enhance as a stack of 30*3min. I did a test without filters as well. But then I remembered that the camera that was used to test this was a full spectrum modded Sony A7III. So it was hard to use it as a reference. My plans was to reshoot the test, but as stated, weather gods prevented me from doing so. For your info, the full spectrum image was actually quite good. No star bloat or CA. But the colors couldn’t be matched properly within PixInisghts SPCC so I chose not to include it in this review.
If you look closely at the images, you might see a faint reddish signal around the galaxy, this signal is also present in the full spectrum version. I have not yet identified what it is, but I doubt it is Ha. It is not removed by any gradient nor light pollution removal in post editing. This is most prevalent in the L-Quad Enhance image, second is L-Pro and the faintest in the full spectrum version. I have not ever seen it in my other M31 images I have taken over the years.
Andromeda Galaxy, full view
Left: L-Pro Right: L-Quad Enhance
Below is a cropped version of the comparison. There are minuscule differences in the images. The good part is that none of the filters show any star bloat or halos. Noise levels seems to be about the same. If I were to stack several hours with each filter, the differences might be more visible.
For the second test. I chose a faint target, the Dark Shark Nebula LDN1235.
Just like the test on the Andromeda Galaxy, the differences are miniscule after doing some gradient removal and color calibration. I did however notice differences in the gradient between the images in the original stacks. Since I can’t control the environment and the fact that its apparent position in the night sky is not fixed, I have chosen to use the calibrated versions.
Just like the test on the Andromeda Galaxy, the differences are miniscule after doing some gradient removal and color calibration. I did however notice differences in the gradient between the images in the original stacks. Since I can’t control the environment and the fact that its apparent position in the night sky is not fixed, I have chosen to use the calibrated versions.
Dark Shark Nebula, full view
Left: No Filter Center: L-Pro Right: L-Quad Enhance
Image below shows that details in the reflection nebula are more visible in the no filter version while the L-Pro and L-Quad enhance are about the same. It should also be mentioned that I have chosen a target that is close to zenith so that I can shoot through as little atmosphere as possible.
Dark Shark Nebula, crop
Left: No Filter Center: L-Pro Right: L-Quad Enhance
Cropped into the sharks eye, you’ll notice better contrast with no filter and least with L-Quad Enhance. Noise levels are about the same in a stack of only 90min.
Dark Shark Nebula, crop
Left: No Filter Center: L-Pro Right: L-Quad Enhance
Final images and thoughts
It is hard to make a definite conclusion of the performance of this filter tested in my type of skies with targets chosen high in the sky with so little time to test it. I also miss the final test on emission nebulas where I truly think this filter might help in light polluted skies. It’s called Quad Enhance for a reason and my two tests were not on emission nebulas at all. My personal thoughts however are whether light pollution filters really help me when choosing faint or very strong targets like the Dark Shark Nebula and the Andromeda Galaxy, especially when shooting them with least atmosphere as possible in Bortle 5 sky.
I need more time to test!
I need more time to test!
