Optolong L-eXtreme Filter Comparison
by Jim Thompson, P.Eng
Test Report – August 25th, 2020
The light pollution filter market continues to grow, with new offerings being released every couple of months. One of the latest filters to be released is the new L-eXtreme filter from the Chinese company Yulong Optics Co. Ltd. under their Optolong brand. I have a fair amount of experience with Optolong brand filters, all of which started in 2015 with a request directly from Optolong for me to test some of their filters for them*. I was impressed by Optolong’s filters then and I am still impressed today. Because of my history of testing Optolong filters I have a library of their products available to which I can compare any new offerings. This is exactly what I have summarized in this report: a comparison between the new L-eXtreme filter and Optolong’s other filter models. Figure 1 shows the spectral response of the new L-eXtreme filter that was released in North America just this past June. The filter is a refinement of their popular L-eNhance filter, having even narrower pass bands around O-III and Hα.
The data collected during this test confirms yet again that a filter with narrow pass bands produces an image with superior contrast on emission-type nebulae. Some other more specific conclusions drawn from this test are:
When compared to other available filters with the same %LT, the Optolong L-Pro filter provides inferior performance under light polluted skies. This observation is true for all filters of this type (i.e. Multi-band), regardless of brand.
In terms of cost per performance the Optolong UHC filter provides a very good value. The filter performs very similar to the Astronomik UHC but at a fraction of the cost.
There is a significant improvement in contrast on emission-type nebulae resulting from the use of the Optolong L-eNhance filter. There is however an issue with white balancing that was not encountered with the other filter models.
Of the six filter configurations tested, the Optolong L-eXtreme filter provided the largest increase in contrast. The increase in contrast relative to the L-eNhance filter was observed to be significant. The filter was also easier to use than the LeNhance due to it being easier to white balance.