Review of Baader’s New UHC-L Filter: The Ultimate Weapon Against Light Pollution?

Wonderful, thats most appreciated 👌

Thanks for publishing these results and math. It's clear they are blocking too much of the spectrum. Ever since you first showed the led spectrum in your other video I have been searching for a led blocking filter. There is a company called stcoptics that has a multispectra filter however it looks like it may also pass too much blue. It would be nice if you could try tracking down other led specific blocking filters and perhaps review them - it would be a great service to the astrophotography community who live in badly light polluted area with led lights. Thanks for your work on this!

Really enjoyed your video and immediately subscribed to your channel ofcourse. I really appreciate the experimental exploration and validation you bring to the "filter graveyard of broken promises". I am somewhat confused by the problem statement; as both the galaxy and iris (reflection) nebula are broad band targets. Using a filter to suppress broad band spectra (like LED is broadband) would not be a typical application, but a rather obvious tradeoff. I assume your point was that this should have been clarified on the suppliers website. Now in the case of emission nebula - with only OIII and Halpha emissions; I wonder if you can show that a UHC filter does make sense as a better than nothing (ofcourse a dual narrow band 3nm being the best solution for OSC). My hypothesis is that as long as you pass the target wavelengths, surpressing anything else will help a bit in the right direction (given finite well depth). Because some UHC filters are much cheaper (50$ vs 300$) than dual narrow bands, a UHC could be attractive to beginners in AP shooting emission nebula only. Would you agree? I could not reconstruct your SNR calculation to support this hypothesis because I did not understand how you derived Lp in the Bader case (Python script)? I would expect that a UHC SNR with an smaller and smaller bandpass would eventually approximate a dual narrow band (emission nebula). Again, really enjoyed this excellent exploration, looking forward to your next video!

Bonjour Julien. Merci beaucoup pour cette video et ce test. La question que je me pose dans le cadre du protocole de test de deux filtres (ou plus) est : ne faudrait il pas comparer les deux résultats à SNR équivalent ? Je sais que communément on compare des temps de poses équivalents mais si l'on considère, comme vous le précisez, que le filtre Baader va nécessité plus de temps de pose pour un SNR équivalent (quasiment 2 fois plus si mes calculs sont bons), et que c'est le prix à payer, en retirons nous profit au final ?

Interesting! Can you have a look at Antlia filters? Both narrowband and LRGB?

Hello . I was hoping you might have scanned the Filter from both sides since you did mention that it has a Telescope-Lead-side Indicator . Would be interesting to see if they measured differently . Also , with real DSO objects , taking a few images again through both sides to see what the differences would be . Halos I imagine but still interesting . Thanks for your video ./SRK

Quelle probité ! Avec une démarche méthodique en plus. Admiratif. Finalement la seule méthode c'est une longue durée d'intégration avec filtre luminance ou rien ? J'en suis à mon 4ème filtre broadband.

Hi, Thanks for the very instructive video. I'm not sure I understand the SNR formula you use, I would expect 0 LP to produce a value of 1 (f.e. that would be the result with squared values under the root) When I add the squares I get that the filter would help only when the LP is about 2.5 time the Signal or more. The formula I used is SNR = S / SQRT( TS^2 + LP^2) where TS is the total signal and doesn't change when you put the filter. so f.e. when using the filter with LP = 0, leeds to an SNR of 40%; when S = LP = 100 then the SNR0 is of 71% without the filter and SNR = 39% with the filter; when S=100 and LP = 300 then the SNR0 is of 32% without the filter while the SNR is 34% with the filter. Please let me know if these numbers make any sense. It would be interesting to do this test with targets at different elevations and see if the SNR is better with the filter when looking at targets that are closer to horizon. I also don't think this is the intended use for this filter; what I understand from what they write in their website is that it is intended to replace the luminance filter in an LRGB setup, and I have no idea how that would affect the picture. All that been said I agree with you that this filter will not improve the results on a broadband targets (as you have proved) but maybe it can help in light polluted areas, by allowing you to take longer exposures without clipping the image. And this might have advantages depending on your setup / processing power.

I thinks it's unreasonable to expect that a narrower filter will produce better results at the same exposure. One of the costs of living in a light polluted area is exposure time. A more reasonable test would be to increase the exposure for the LP filter by the ratio of the bandwidths. That may in fact produce superior results since the in-band S/N should be better. Excellent work none the less. I always enjoy your videos.

Hi Julien, do you have planned any test / comparisons of triband filters, for us novices using color cameras and on the hunt for good filters. Could be like Anitllas RGB Triband or Idas GNB filters.

The use case I would want to try with this filter is to use it as the L-channel for RGB imaging of emission nebula targets, especially those with reflection components. There, a clear filter for L would be too low-contrast, and narrowband/dual-narrowband as L might be too aggressive. Clearly, as your #s show, reflection nebula targets are not the use case for this filter, and I agree that it'll almost certainly be a good visual filter for emission nebula targets.

Would this be a suitable filter for broadband targets using a osc camera and a fast f2 Hyperstar setup? I use a pre bandpass shifted IDAS UHC NBZ for narrowband emission objects but looking for a filter for broadband targets but with a fast hyperstar setup. Thanks

I agree this filter should not be used as a broadband LP filter but it does work well for narrowband. I use this filter and it is great for bright and planetary nebulae.

This filter appears to be designed for narrow band targets, not broadband targets. You will need to integrate luminance data from a broad band light pollution filter, or an IR pass filter, to recover your stars. Keep in mind that refractors may not be apochromatic for IR light.

Isnt problem that UHC filters are not suitable for broadband targets like galaxies as it is blocking big part of its spectrum? If you try it on suitable targets like emission nebulas it should work much better.

If S = 100 and LP = 50 then the SNR = 8.165, so it is possible to get a better SNR with this filter--but you have to have more signal. So it seems the question is really whether you are willing to increase exposure time sufficiently to increase the SNR when using this filter. If the number of electrons captured is proportional to exposure time, then 2.5x exposure increases SNR by ~1. 5x longer exposure increases SNR to ~11.5, which is more significant. 7.5x longer exposure increases the SNR to ~14.1, doubling the SNR without the filter. I don't know if taking 8x subs and stacking them is equivalent to a single 8x exposure time increase, though, as I am not an experienced imager. However, I thought I should point out that this filter can be effective if exposure time is increased sufficiently, based on the math in your video. You do mention increasing exposure time in an offhand way, but it might have been helpful to give an example (or show a graph) of how increasing exposure time with a light pollution filter can achieve a better SNR. Whether this one is better than the other similar filters on the market is another issue--I don't know if your mathematical analysis is sufficient to compare different filters precisely. It might be better to just do imaging tests and look at the resulting photos, as other people do on YouTube. That said, I appreciate the spectral testing of this filter--it's nice to see if the bandpass graphs are accurate.

The problem isn't the filter, the problem is the LEDs continuous spectra

I cannot understand why manufacturers don’t include 750-800nm in such filters. This band is very effective for galaxies.

Vidéo très instructive comme d'accoutumé. Par contre, il me semble que les cibles choisies pour les tests photographiques ne sont pas pertinentes. Les filtres UHC sont généralement dédiés à l'observation de certains types de nébuleuses et plus particulièrement les planétaires. Même en visuel, ce type de filtre n'est pas conseillé pour les galaxies. Il faudrait donc faire un test photo sur M57 par exemple où la majorité de ses raies d'émission se trouvent dans la bande passante de ce filtre UHC-L. Le spectre d'une galaxie s'étendant sur l'ensemble du spectre de la lumière visible, il n'est pas surprenant que le filtre L3 s'en sorte mieux que le UHC sur ce genre de cible...