Optolong LRGB Filter Testing and Comparison
with Baader LRGB Filters

By Terry Hancock

I was recently contacted by Optolong, a filter manufacture in China who asked me to test their filters. They sent me a set of 36mm un mounted LRGB and a set of 36mm Narrowband Filters, H-Alpha 7nm, OIII and SII 12nm. I was impressed when they arrived, nice packaging and presentation in a similar plastic case to the Baader. I limited my comparison for LRGB only which was carried out on the 15th and 16th August with similar average seeing conditions. The narrow band filters are not the final version that will be used for comparison. At the time they were only manufacturing them in 12nm pass band. The Baader equivalent is 7nm, which is more the industry standard. Sub sequentially they have started producing the narrow band filters in 7nm pass bands. They will have to wait for another day…

Optolong are not new to manufacturing Astro Filters. Established in 1999 they are a subsidiary of Yulong Optics Kunming City China. Their products include Astronomical Filters, Band pass Filters, Fluorescence Filters, Edge filters, Long pass & Short pass Filters, Beam spliters, Anti-reflective Coating and Optical Mirrors. They are Quality assurance certified ISO9001.

Optolong literature states:

LRGB Filters Optolong

• German Shott glass 2mm thick enabling parfocal performance
• Anti-reflection coating to eliminate halos
• Steep band pass filters to eliminate UV and IR interference

For the test the 36mm un mounted filters were fitted to a QHYCFW2-M-UltraSlim Filter Wheel. Camera used was a QHY23 Monochrome CCD, Telescope used was a Astro Tech AT130-EDT APO Refractor @ F5.6.

Optical spectrum diagram (optical curves) by Optolong

I first checked the Minimum and Maximum ADU to help determine if there is any difference in color transmission. Here is the result:

Baader August 15th	Optolong August 16th
LUM	LUM
Minimum 539-772	Minimum 745-751
Maximum 44405-46106	Maximum 45050-46088
RED	RED
Minimum 639-784	Minimum 733-748
Maximum 43749-45815	Maximum 44891-45787
GREEN	GREEN
Minimum 573-784	Minimum 733-753
Maximum 42253-44262	Maximum 42150-45189
BLUE	BLUE
Minimum 512-769	Minimum 742-754
Maximum 41932-43622	Maximum 41773-43586

Based on the above I find the color transmission to be very similar.

Next I checked for any halos using the bright star 52 Cygnus at the center of the image as reference and I found that the Baader Green and Blue Filters exhibited a much stronger halo than the Optolong.

Both the Baader and Optolong Luminance and Red filters showed only very faint halos.

I found no difference at all between the Baader and Optolong for either sharpness or contrast.

Neither Baader nor Optolong distribute reflections for this test target.

I found both the Baader and Optolong LRGB Filters are parfocal when used with this equipment.

One thing I find strange is that with the Baader Filters the bright star at about 8 o’clock to 52 Cygnus showed a spike in all filters except the blue filter. No such spike at all with any of the Optolong Filters.

Retail Price in US Price Comparison 36mm un mounted set of LRGB

Baader $477.00 per set

Optolong $299.00 per set

Conclusion

After taking identical images with the Optolong and Baader filters I was amazed at how similar the images were. The preceding images speak for themselves in large part. A closer observation of the images taken with Optolong filters, I found no noticeable reflections especially around the bright stars. Images showed excellent contrast with clear differentiation of colors.

The Optolong LRGB Filters offer similar to somewhat superior performance and quality to the Baader Filters at roughly 63% of the cost. This makes the Optolong filters a great value for the money. Optolong Filters can be purchased from the US Distributor www.astrofactors.com