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I have read all of the posts and as usual here I am confused by the technical data. Bottom line, if I have 8 hours to image a target in Bortle 7, will I get a better image with a 2600mc with an expensive Radian triad filter or a 2600mm with expensive mono filters? I have the 2600mc and would get a 2600mm if there is a real difference. I do not get many clear nights. |
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Arun H:Roman Pearah: I'll get to my response to you. I want to read your links first. I just wanted to clarify quickly for Tim. Thanks for your patience. |
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Dan Kearl: I've been imaging for almost 3 years now, mainly with the IDAS NBZ (Ha/Oiii) and occasionally the NB3 (Sii/Oiii). Recently I've switched to the Askar 6nm D1 and D2 filters and have been very happy with their performance. Having the second dual band filter for Sii/Oiii makes my 2600mc into a fantastic SHO narrowband camera. I try to get more Sii than Ha since it's much less abundant up there, but even with equal exposure time, I love the results. I made the switch because the bands are very close to the same, and the filter thicknesses are the same, so I don't have to mess with focus much when switching filters. To address your triad filter, to me it's nothing more than an extremely overpriced light pollution filter. It does not give you the ability to make SHO pallete images since there's no way to separate the Ha and Sii, because they're both in the red channel. It also passes more than just Ha and Oiii, so you can't even really do much with that. The only way to do it is with two different filters, so you get the two red bands separate from each other. You can do this with either two dual narrow bands filters like the Askars, or one dual band and one single band, which just feels like a waste of time since you could be getting two bands at the same time with a color camera. Edit: so to answer your question, I would stick with your 2600mc, avoid the triad, and look into something like the Askar D1/D2 if you want to go for SHO, or one of the 3nm dual Ha/Oiii filters if you aren't worried about getting Sii data. |
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Sascha Wyss:Joe Linington: I never said the NB3 or IDAS were superior to the Askar. |
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We can use Pixinsight SPCC filters characterisation to see another problem with the OSC + Dualband approach The Bayer filters in you sensor will allow other wavelengths, so you will get some [O III] light on the Red and some Ha light on the blue and green channels. You will not be able to get the same chromatic contrast that you get using MONO and NB filters of the same width. Yes, I know, the crosstalk is minimal, but it's here.
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| Generally speaking, color cameras are much more appealing when you start out in this hobby. If people understood the difference... Optolong and their L-extreme would probably be out of business. In my opinion it's an absolute HORRIBLE filter, and the rest aren't much better. It's easy as pie to pick a 'dual NB' image out of a lineup. It's not just the lack of efficiency shooting through a bayer matrix, it also comes down to filter quality. L-extreme leaves fat stars/halos that stand out like a sore thumb. I started this hobby with color... owned an L-extreme for not even a month, realized my mistakes. Sold it all, went mono. The difference is beyond night and day. I could never shoot OSC again, save for planetary. |
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ptolong and their L-extreme would probably be out of business. In my opinion it's an absolute HORRIBLE filter, and the rest aren't much better. Yes - and no..... The L-Extreme is a horrible filter and I can't get my head around why anyone would buy it. It is practically the only one who leaves these halos.... But as soon as someone asked what filter to buy everyone seems L-Extreme.... WHYYY??????? Anyway, but no, not all are bad. I have an Antlia ALP-T and it is absolutely great. |
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Sascha Wyss:ptolong and their L-extreme would probably be out of business. In my opinion it's an absolute HORRIBLE filter, and the rest aren't much better. ALP-T is definitely the best of the bunch, I won't argue that one. |
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Roman Pearah: Thanks for the clarification. Your original post all makes sense to me now |
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Arun H: Thanks very much for the link to the CN thread - It looks an interesting read. A clear list of starting assumptions and then the numbers that follow . |
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Sascha Wyss:ptolong and their L-extreme would probably be out of business. In my opinion it's an absolute HORRIBLE filter, and the rest aren't much better. I have it, I use it (a lot) and I can't find an halo for all the world's gold. |
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andrea tasselli:Sascha Wyss:ptolong and their L-extreme would probably be out of business. In my opinion it's an absolute HORRIBLE filter, and the rest aren't much better. You had luck - that us all! Cuiv mentions in his videos multiple times, that the specs of the L-Extreme are all over - and that might also affect the tendency to produce halos. But the issue of the halos is well documented - be it by individuals in forums reporting it but also by filter tests - e.g. Nico Carver |
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Actually the combination of the ALP-T and the Askar D2 is quite nice, gives you twice the Oiii when capturing HSO with an OSC as already mentioned by others. This is very helpful with targets like California Nebula where Oiii is weak, it does not hurt to have twice the integration time in Oiii. Also when Oiii is strong it helps to have twice the Oiii, you can throw away more Oiii frames that were affected by the moon and end up with an overall cleaner image. The quality of the Askar D2 is very OK, it does not deliver the same contrast/SNR in Sii as for example the Antlia 4.5nm Sii filter but the difference is small. Also the Oiii that comes from the ALP-T 5nm has a little more contrast/SNR than the Oiii that comes from the 6nm Askar D2 but also here the difference is small, but more visible than the difference in Sii. (See attached screenshot of 1:40 hrs Oiii from each filter, the data was shot interleaved and on a night without moon) I combined 60% of the Antlia Oiii with 40% of the Askar Oiii and starting with SNR of 38.4dB / 36.2dB I ended up with an SNR of 40.3db  The stars in Oiii have similar size with both filters and the shift in focus point when switching filters is small, close enough so that autofocussing in Nina does take only 2-3 extra points to find focus after switching filters. Michael |
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Sascha Wyss: There are over 1800 photos with the L-Extreme in AB. I browsed a few good ones and I failed to see such noxious halos. We must have been all lucky... |
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Tim Hawkes: Always nice to see the math - generally hard to argue against numbers! On the whole mono versus dual NB debate - from the transmission numbers I am seeing, the mono should, on average, have about a 20% imaging time advantage over dual NB. This is because the transmissions of the Bayer array RGB filters peak at wavelengths different from the emission lines of S, H, and O, whereas true narrow band filters+mono does not have that problem. If/when I have time, I will do a more formal calculation and share it, but you can look up the transmission numbers for yourself from the PI SPCC curve explorer. This, plus the ability to shoot luminance, plus the ability to tune imaging time per channel to the subject, gives mono an advantage (to me) if starting from scratch and if money was not an object, |
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andrea tasselli:Sascha Wyss: Well, I was also one of the loosers of the l-extreme filter lottery, glad I sold it when the ALP-T came out and never looked back. A friend of mine still has his l-extreme and he also is on the looser side, so count yourself lucky but rest ashured that those poor guys with halo issues exist.... |
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andrea tasselli:Sascha Wyss: Probably because people don't like posting pictures with unsightly halos. Here's a couple of my images with l-extreme halos, I would say it was just my processing, but once I switched to the NBZ, I never saw another halo.   |
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The simple answer is the best argument for OSC is cost. The next best argument is simplicity. Given enough time and skill you can create the same (similar/close enough) result using OSC and modern filters but usually at a cost of time. But to show my point, I shoot with a full frame mirrorless camera that cost me $400 cdn. I also have an APS-C camera that cost the same. A mono IMX 571 APS-C setup with 7 mid grade filters and a filter wheel will cost around $4000 cdn. That’s more than I paid for my entire rig which includes an entry level goto eq mount, camera, filters, and a decent triplet. It’s not peanuts to switch. Simplicity, I choose a filter (or not), point my scope at the sky and take pictures. The stacking is done in one step. No filter switches, no missing data or channels, no mis aligned stars, no focus issues between channels etc. This is very important for the hobby. If everyone had to start with top tier gear and the best techniques, there would be far fewer of us and prices for everything would be even more out of reach. I enjoy the debate because I always learn something new from the guys defending OSC (get to spend more for one of those Askar filters now) but as hard as we poor OSC guys try, it’s not there yet. The top tier gear at a remote dark site that I occasionally « rent » always does better than my gear. |
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Joe Linington: This is very correct. For OSC to be better than mono, other than in some very specific use cases, you'd have to overcome some pretty stiff laws of physics and engineering. The base silicon and electronics are the same, so there is no edge in quantum efficiency or read noise. And the simple fact is that putting a filter on top of an array of filters, the array optimized for some completely different purpose, will never be as efficient as putting just a single optimized filter upstream of the sensor. You might claim that Bayer interpolation can make up for not capturing photons on every pixel as happens with OSC - but that argument falls apart when you realize that if that were physically possible, you could simply divide the mono signal into multiple frames, apply interpolation to each frame, and achieve the same result as the OSC in some fraction of the time. So if the questions is "What will give me the best result in most situations for given imaging time, money is no object?", the answer will be "mono". If you start adding constraints like sunk investment in equipment, money, etc., OSCs with various filters come into play. That they do as good a good as they do is a credit to the innovation of the companies that make them, the people that use them, and advances in semiconductor tech. But there is a reason that these observatories in remote sites are so heavily biased towards mono+filters. |
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| I mean, if anyone wants to compare single subs of Ha and Oiii I'm down to share. Some of us, including myself are visual learners. I do 10 and 20 minute subs. I do believe that in a single sub, 10-20 minutes, I'll get much more than any OSC/NB combo can with hours of integration. |
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Arun H: Arun, what you wrote doesn't make any sense to me. Are you suggesting that signal amplitude is an extensive quantity? |
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I mean, if anyone wants to compare single subs of Ha and Oiii I'm down to share. Some of us, including myself are visual learners. I do 10 and 20 minute subs. I do believe that in a single sub, 10-20 minutes, I'll get much more than any OSC/NB combo can with hours of integration. And you'll be wrong. |
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I mean, if anyone wants to compare single subs of Ha and Oiii I'm down to share. Some of us, including myself are visual learners. I do 10 and 20 minute subs. I do believe that in a single sub, 10-20 minutes, I'll get much more than any OSC/NB combo can with hours of integration. To many variables. A RASA 8 on a mountain in Hawaii with an OSC will destroy a mono rig attached to a f/5.6 scope in downtown Philly. The real ratio is somewhere near 2:1. There are exceptions and tricks to help but overall it’s between 2:1 and 3:1 if everything is identical. But everything never is identical. Even comparing a 1600mm to a 2600mc, the gap narrows because the 2600 has higher QE and larger pixels. |
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Joe Linington:I mean, if anyone wants to compare single subs of Ha and Oiii I'm down to share. Some of us, including myself are visual learners. I do 10 and 20 minute subs. I do believe that in a single sub, 10-20 minutes, I'll get much more than any OSC/NB combo can with hours of integration. You aren't wrong. Variables can be controlled however. For this, I kinda wish I still had my L-extreme. The obvious goal would be to control the variables as much as possible, same camera, bortle, etc. Realistically it's much easier to do it with math. A sensor QE curve, plus filter data is all I needed to understand the loss in efficiency. I wish I had the graphics to share, but I'm stuck at work right now. Basically I expect an OSC to be around 30% as efficient as mono per channel, the tradeoff is you ARE gathering data on both channels, but since bayer matrix, it's usually a 2-1, Oiii is much stronger than Ha, RGGB being the typical bayer. Beyond that, is above me. I'm still very new to all this, barely 5 months in. I went with the equipment recommendations of experienced individuals and have been 100% happy with my gear. |
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Joe Linington: A RASA 8/OSC on a mountaintop will certainly outperform a mono rig in Philly, but the reasons for that are known and can be quantified. 1. Aperture matters 2. Lack of light pollution matters - a LOT 3. Quantum efficiency and the amount of signal you actually collect on your sensor (through filter efficiency for example) matters All other things being equal, for equal integration time, you are, with a few exceptions, converting more meaningful photons (signal) gathered by your scope into electrons and ADU with a mono+filters than with OSC. There is just no getting around this. SNR is king in this hobby, and almost all the time, mono will get you there faster. |
