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I have continued testing the two filters in an area of the sky with less light pollution. The results are somewhat different and I am finding it difficult to decide between the two filters. Please share your opinion!
I photograped NGC6384. I chose a dim object so that I could use longer exposures and compare core ADU. I was able to match core ADU with exposures of 330 sec with the CLS filter and 210 sec for the IDAS, a 2 minute difference in exposure.
I also took equal exposures of 6 minutes with both filters.
Comparing photos with equal core ADU it seems there is little difference between the two filters, except that the exposure for the CLS is 2 minutes longer. Subtracting the background from the core adu is 7000 for the CLS and 6,800 for the IDAS, however CCDStack measures rather a large difference in S/N. The IDAS = 2.07, the CLS = 4.81
Comparing the 2 6 minute exposures the difference between the background and core ADU is CLS = 8,200 and IDAS 12,700. CCDStack measures the S/N CLS = 4.83, IDAS = 6.86.
It appears that the IDAS is ca 30% faster, but pays a price in S/N when exposures are equalized in terms of core ADU. The difference in background brightness is striking between the two filters, especially in heavy light pollution, and less striking (though there) in lower light pollution.
In conclusion I cannot say exactly which filter would do a better job. I think it depends on the severity of light pollution. The IDAS is certainly faster so would minimize guiding errors through the ability to collect light faster and still do a reasonable job with LP gradients. Nontheless, there is something vicerally attractive about seeing such beautifully dark backgrounds in raw frames that make it hard to reject the CLS.
Peter
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