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The times they are a chang'n, for sure. There have been so many amazing images created using OSC cameras lately. It sort of makes me regret going the mono route--though 4-5 years ago when I started it was a different game. Still, I am seriously considering the OSC route for my next camera (if there is a next camera), as there are some amazing full frame, super sensitive, cooled, 16 bit, back illuminated CMOS sensors that didn't exist a few years ago. The one aspect of OSC imaging that I had not considered before - and for me it very well could be the most significant reason to go with a OSC camera - is all data is collected under the same conditions (other than a variability due to changing conditions that is pervasive across all data). With a mono camera, due to my sky, I am forced to collect data over weeks, sometimes months (most times actually). So invariably, different filters are used in wildly variable conditions. This can really throw a monkey wrench (left handed or not) into image processing. Halos, gradients, signal imbalances between colors, major differences in star profiles, etc. So, with this in mind, I would be appreciative of opinions regarding OSC cameras. Keep in mind that if you image from a dark sky site that has stable seeing, the benefit I describe is largely nullified. So this thread considers the benefit of using a OSC camera in Bortle 6-8 zones that are dominated by temperamental weather. Since I know nothing about OSC imaging, I may be overstating the benefit, or not seeing a downside connected to the very "plus" to which I refer. |
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Hi Rodd My 2 cents....... I use both mono and OSC cameras under my Bortle 6 skies. Both work well and both have pros and cons. The OSC cameras like the one I have, ZWO ASI2600MC Pro, is excellent. I use either a LP filter for galaxies or a duo NB filter for nebulae. It also works well with no filters under certain conditions and DSOs. The only con with the newer OSC cameras is that you still need to gather more subs vs. the mono camera to get a "great" image. With that said, the OSC cameras have definitely closed the gap with the mono cameras using color filters but will never equal or surpass them given the Bayer matrix. Bruce |
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Bruce Donzanti: Not even with the the fact that all data is the same quality? Combining mono data of wildly variable quality really hurts an image. If the OSC data is collected during good conditions, that must make a big difference compared to a mono where a couple of filters, and/or portions of filters were collected during really bad conditions |
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Rodd Dryfoos:Bruce Donzanti: There is also the possibility if OSC with wildly different conditions. Chances are you will still need several hours of data and that can be equally hard to collect and imoossible to keep uniform. If you image over many nights, or focus shifts due to temperature, or seeing varies, or your target moves sonewhere with a different gradient... And this is actually harder to fix because pixels are convolved in debayering. Which is why OSC are actually recomnended for clear, dark sites. OSC is very convenient and the thing with the new sensors is their very high sensitivity, very low noise and very deep full well. They are so good they beat many a mono sensor, especially if you factor in practicalities such as having to refocus (and not necessarily getting it right). But they would not beat an identical mono sensor without the bayer matrix. It would still have cleaner resolution and 2-4 times the light grasp. |
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Hi Rodd, I use both types of cameras, but unfortunately my opinion is not so clear. I’m a relatively beginner in astrophotography, but I have quite a bit of experience in photography and image processing. Which one I use, can be affected by many things. On the other hand the combination of them, results in many good experiences. For example, OSC gives the colors and the mono camera gives the luminance layer. You can find a lot of examples on astrobin for this combination. Usually I use them in parallel, one of my telescope (mainly the SW ED120) is running with OSC and the other (mainly the Esprit100) with the mono camera. One of the main problem for OSC is that you do not have possibility for NB imagining. Some special filters like Optolong L-extreme gives nice results, but it is not like the possibilities what you have with a set of HSO filters. Some nice comparisions you can find on below link: https://www.cloudynights.com/topic/684715-osc-vs-mono-cameras-comparison-cases/ Hope, it can help you in your decision. Clear sky - Álmos |
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| I totally agree and I can only confirm dkamen’s and Bruce Donzanti's opinion. |
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Rodd Dryfoos:Bruce Donzanti: Yes but ALL data will be consistent because you collect all the colors at the same time. There might be inferior data, but it will be in all channels equally. This is what I meant by "changing conditions that are pervasive across all data. The proper way to do mono imaging is not to collect all red subs, then all green subs, then all blue subs, etc. It is to alternate filters after each sub, which tends to smooth out varying conditions and sky position. A OSC camera does this automatically. |
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Hi Rodd, can you point me to any great images taken with a colour cam from a bortle 6 location? Richard. |
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Hi Rodd, can you point me to any great images taken with a colour cam from a bortle 6 location? Not off hand, but there were some recent TPs and other really good images I have seen. I commented on one image about it being taken with a OSC in Bortle 8 and that I have been "wasting my time", or some such words to that effect. I may have called the gentleman a wizard. And the question really is not only Bortle--its transparency, seeing, fog, sky position, etc, etc. Also--the real comparison is not between other imagers--but between my own images. If I want to collect data so that all my filters have similar FWHM, median values, etc, etc, it will take me months to collect one data set. My images invariably are a combination of data ranging from occasionally good to OK through really, really bad. If I used a OSC camera--there would be more data homogeneity. Gradients would be more consistent. True--I might need more data. But I already need 25+ hours, so I'm thinking this would not be very noticeable. |
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I see where you're coming from and obviously I'm a big fan of colour cameras but conventional wisdom on this subject is that mono is far superior in all but dark sky. You could end up with gradients that are much more difficult to handle, I know I do when I image in certain directions due to street lamps. I suppose there's only one way to find out if it works for you at your location and that's to try one. Might I suggest waiting a couple of months until the mono imx571 is released and then I can almost guarantee you'll pick up the colour version on the used market. Try it out, if it doesn't work you probably won't lose much. I think you might end up losing quite a bit if you bought a new full frame colour and then had sell on the used market. |
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I can speak to my strategy. I currently image with an ASI 1600MM. When I do LRGB imaging, I consistently find that luminance frames taken with the L filter are just vastly superior to the synthetic luminance derived from RGB filters with the same overall imaging time (i.e., L=R+G+B). It isn't close. Not only does the L filter admit more light, the dichroic filters we use for RGB have better transmissivities than the filters used for the Bayer array in OSCs. The physics is hugely biased in favor of mono. I agree that OSC cameras have their place for convenience, but to get meaningful images that you'd want to pair them with fast scopes that collect a lot of light in a short time. I do plan to add an OSC to my arsenal, but that will be paired with two fast Newtonians (f/3.3 and f/4.5) and used when I travel to my local dark sky site. The mono camera will go with my f/6 Stellarvue, predominantly for narrow band. |
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I see where you're coming from and obviously I'm a big fan of colour cameras but conventional wisdom on this subject is that mono is far superior in all but dark sky. You could end up with gradients that are much more difficult to handle, I know I do when I image in certain directions due to street lamps. Well--actually buying one is another story . One thing is for sure...trial and error has cost me a lot! Maybe my hypothesis , while perhaps true, is not nearly significant enough to make a OSC better than my current mono cameras. Not only would it have to be better to justify the expense, it would have to be significantly better. Not likely. |
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Rodd Dryfoos:Rodd Dryfoos:Bruce Donzanti: It saves you time and there is internal consistency within each frame. These are all good things. Personally, I am an OSC person. Primarily DSLR but also 178MC. I have bought the 178MM since last spring but I'm using it in a "detail-only" role: L or Ha. The color comes from the OSC devices. I can't be changing filters, let alone in every sub. I have two kids and a wife  But we are discussing the general impact of OSC (vs an identical mono sensor) in quality and there is a very clear drawback because of the fundamental way OSC works: The pixels have little filters in front of them, arranged usually as RGGB. Only half of the pixels capture G and only a quarter capture each of R and B. Your B pixels are 100% blind to G and R. So you have 25% light gathering ability in R,B and 50% light gathering ability in G. Effectively, your resolution in B is only 25% the nominal resolution of the sensor. R too. G is better, at 50%. Of course, the final image is debayered, meaning the values of the RGGB pixels are convolved into extrapolated R,G,B values. So the final loss in resolution is no so tragic. I think it is around 10% or something like that. You definitely do not care about it with those sensors because they have crazy resolution to begin with, you can afford a 10% effective loss (you cannot do much about the loss in light gathering ability but read below). However, while repairing resolution, debayering introduces another problem: the RGB value of any given pixel (say pixel x=10,y=10) is a function of multiple source pixels, its neighboors in the original sensor data (x=9,y=10, x=11,y=10, x=10,y=11 and so on). The function is generally very complicated and irreversible and takes into account pixels quite far from the current one, which is why you cannot recreate a raw file from a debayered TIF even if the TIF is 32 bits and just came of the raw converter without any tampering whatsoever. In simple terms, green signal (recorded by a G pixel on the sensor) can, in fact almost certainly will "leak" into the R and B values of nearby pixels. Same for red and blue signal, of course. The debayering algorithms are very good at avoiding this but they are not perfect, especially in places where there is a sharp change such as stars situated against a dark background. Also, it is not helping that our kind of photography works with signal really really close to the natural noise of the electronics. So removing unwanted stuff is always more difficult with OSC devices because red unwanted stuff spills into the green and blue channel and does so in a manner that is not terribly easy to deal with. Chromatic aberration correction is more difficult: People can get very good results with achromats and filtered mono. This is downright impossible with OSC. Background extraction is more difficult (especially on Bortle 6+ and if your frames span more than an hour). Sharpening is more difficult. And there is always an insane amount of green in the picture which is quite difficult to tame without making things unnaturally purple. Coming from a mono background and at your level of expertise with your current gear, you will probably find those things quite frustrating (also, you will probably face a learning curve with CMOS sensors in general, they do not behave the same as CCDs). And now the big BUT: the sensors are really good. Most of those things make very little practical difference, especially if your optics are good. You have very low noise so things will not be half as bad as with a DSLR or an older, low-end OSC. You can bin 2x2 and have 7 micron pixels with 200 thousand electrons full well and maybe 10 electrons read noise, an insane dynamic range which the 16 bits (in ASI2600's case) will be perfectly capable of digitizing with zero quantization errors. Because of the high sensitivity you can not only do narrowband, but can also do duo-band which is pretty unique to this category of OSC sensors and a real time saver. Also, for the IMX533 at least, a mono equivalent does not exist. And for the 2600, the sensor is so large it probably pays not having to use color filters (because of vignetting) having the tiny filters on the sensor instead. So yeah, just because they are not as good as a theoretical identical mono sensor does not mean they are bad. Definitely worth a try. |
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Rodd Dryfoos:Rodd Dryfoos:Bruce Donzanti: Well--since I already have the filters and filter wheel, it makes more sense for me to get a really good mono senor (The asi 2600 would be perfect for my 36mm filters). The ASI 6200 would require 2" filters which would be almost as much as the camera for something decent. But that would be my #1 choice. But then comes the color version (or QHY 600C). I would not need new filters. That is how this all got started in my brain. Trying to find a way to get a full frame 1ASI 6200. Mono is too expensive--but OSC might be doable.......I don't mind frustration as long as the end result is good. I was thinking the super efficiency and ultra sensitivity of the OSC sensor, coupled with 16 bit and back illumination would compensate for the reduction in light gathering ability for each color. What is really better, a 60% efficient front illuminated mono sensor, or a 90% efficient, back illuminated OSC sensor? |
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| Modern OSC sensors are great way to go unless you're into, massively, narrow-band imaging. I find, after having had 20 years of experience of mono (CCD) sensors and LRGB-Ha-Hb-UHC-UV-IR-YouNameIt colour imagery, that going OSC with the likes of ZWO is great way to get what I call "General Purpose' imaging system, possibly associated with some background filtering (e.g. L-PRO). It is much bloody easier get a properly calibrated image that the nightmares I had with different flats with different filters at different times nearly always resulting a slightly different flat field than the one that should have been. Never mind difference in imaging the subject across few weeks. Try to do that across few years! With the kind of sky I have and the kind of weather I'm in I'm just grateful that I can run the whole thing as quickly and as easily as it does with an OSC camera. Just me tuppence. |
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Hi, my 2 cents. An average could be a mono CMOS and its color equivalent. Like ASI 1600 MM and MC or the new ASI 294 MM and MC pro. No need for filter wheel. You could take the luminance on good nights with the mono one and can still make narrow band. When the seeing is worse you take color, which needs less definition. Then you mix them together. Cheers. JF |
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Great discussion! I'd like to respond to a couple of comments about the great OSC vs. mono debate. First, this discussion is exactly what's rolling around in my mind as I consider whether to buy a mono or just stick with my OSC so the timing is perfect. Great points by everyone and I appreciate the feedback as I mull over the decision myself. However, I would like to respond to a couple of comments concerning not being able to use NB filters with an OSC and another one about not getting meaningful pictures from an OSC if I understood the comments correctly. I'm a long time amateur and nature photographer but fairly new to AP (3 months). I live in Bortle 4 skies and started off using my Nikon D850 45 MP DSLR before recently buying a full frame QHY 367PRO-C. I have been able to take decent images with an IDAS NB-1 triband filter coupled with the 367. Are they the quality of a mono with filters? No, but I don't expect them to be although it seems that the NB-1 is entirely compatible with the 367 and will produce good images. As far as images straight from an OSC, the 367 is a wonderful camera and matches well with my Takahashi TSA120. It's produced some nice images. I think two of mine of M31 and M33 are pretty good examples. I'm at the beginning of the learning curve on astro processing so I'm looking forward to continued improvementas as I gain more experience with my rig and improve my processing skills. Meanwhile, my decision process continues....😄 |
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| Hi Rodd, I say go for the osc. You won't regret it! Like someone mentioned above, you can use your mono for the Luminance and osc for the rgb. Or just use the osc with a Triad or L-xtreme filter for targets with a high Ha signal. I know what all of you mono camera purists are going to say.... Mono is more efficient than osc, Undoubtedly, but, if you want to produce a descent image without the hassle of using four different filters get a osc. The whole reason I am in this wonderful hobby is to have fun, and if I can produce a descent image and get a top pick every now and then , even better! I use the Zwo 071 mcPro from my Bortle 7-8 backyard about 80% of the time. The other times I go out to my " Dark Site" Bortle 4. I say, go for it Rodd! |
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I agree that OSC cameras have their place for convenience, but to get meaningful images that you'd want to pair them with fast scopes The FSQ 106 at F3 fits the bill I suppose. But what really makes fast scopes superlative is aperture. A 10" F4 is way better than a 4" F3. The FSQ 106 at F3 is nice because it affords a much larger FOV than at native. But in my sky, I can't take 60 sec luminance often, as it blows the median of the image into gray. So the faster I go--teh shorter the subs have to be. I have collected 2,000 subs for an image and I am not partial to the CMOS approach, really. |
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Elmiko: The only problem is changing cameras is something I eshew. I hate changing anything as it takes away from imaging. When you get 1 or 2 days per month, every second counts. I purchased a ring set to tweak teh spacing of the FSQ and camera--a .3, .5 and 1 mm ring. I got it 2 weeks ago and haven't even opened it yet because I do not want to loose my camera orientation becuase then I will have to crop and I am working on a mosaic, so I have to be careful. I make changes VERY infrequently. I always say--wait until I am done with a particular image--but then I am always starting new images. Its the same reason I don't learn autofocus and plate solving. I am in awe of people who can set up the rig every day, and switch cameras and try different configurations. |
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andrea tasselli: I have had a pretty easy time of calibration (other than glitches with the camera/filter wheel that cause me to have to take flats more often than I would like). But I hear you on the OSC convenience....I think, I actually know nothing about them other than basic theory. So far, NO method, gear, approach has worked as advertised for me. There is always a fuzziness around everything that diverts from theory. often the fuzziness is extreme. A good example is someone using a guide scope to image with a cassagrain at 2,500 mm and getting great results, or creating amazing images in 5 hours total when I need over 20. These things seem impossible, yet there they are. I will say this, my goal is to create images that are as good as possible...and for me, every little bit is important. So the OSC has to do 2 things...it has to produce results at least as good as my mono setup, and it has to be easier, otherwise, what is the point. If it is harder but produces superior results, I would go with it--always choosing what yields superior results. What started me on this idea was seeing some amazing images taken with a DSLR or astronomy CMOS camera. What I have to remember is, even if I had the exact setup I would not be able to produce such images....due mostly, I think, to my sky and only OK processing skills. There is fuzziness around this too, for I have seen amazing images taken from a sky worse than mine. Sometime I feel my I have had a pretty easy time of calibration (other than glitches with the camera/filter wheel that cause me to have to take flats more often than I would like). But I hear you on the OSC convenience....I think, I actually know nothing about them other than basic theory. So far, NO method, gear, approach has worked as advertised for me. There is always a fuzziness around everything that diverts from theory. often the fuzziness is extreme. A good example is someone using a guide scope to image with a cassagrain at 2,500 mm and getting great results, or creating amazing images in 5 hours total when I need over 20. These things seem impossible, yet there they are. I will say this, my goal is to create images that are as good as possible...and for me, every little bit is important. So the OSC has to do 2 things...it has to produce results at least as good as my mono setup, and it has to be easier, otherwise, what is the point. If it is harder but produces superior results, I would go with it--always choosing what yields superior results. What started me on this idea was seeing some amazing images taken with a DSLR or astronomy CMOS camera. What I have to remember is, even if I had the exact setup I would not be able to produce such images....due mostly, I think, to my sky and only OK processing skills. There is fuzziness around this too, for I have seen amazing images taken from a sky worse than mine. Sometime I feel my [processing skills are working at a "light mode"--like PI light or PS light, where not all the tools are included for the user. I can't access all the tools, which makes me think I am missing something. I don't think OSC will change this....but who knows? |
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So the OSC has to do 2 things...it has to produce results at least as good as my mono setup, and it has to be easier, otherwise, what is the point. I can certainly see the OSC being easier But better? I don't think so; the physics isn't there. I've seen great images produced by using both OSCs and mono cameras. And you can certainly use Triad or other filters with OSCs. But think about what these filters do. They filter out light pollution, but they equally effectively filter out desirable color and detail from a DSO. This is basic physics - no filter can differentiate between these two. If you want a really deep image of a DSO that includes not just the emission components, but also dust and reflection components, you are going to have to put in the integration time. And you are going to have to do it without a light pollution filter. And this is by physics going to be much less with a mono than with an OSC. With both cameras, it is very desirable to shoot broadband with a dark sky site. You are going to get to your SNR faster and will have far fewer gradients to deal with. My deepest image was taken with an OSC - but that was paired with an Epislon-180ED, a 180mm f/2.8 scope, and taken from a Bortle 1 or 2 site. My deepest image of M42 was again taken with an OSC (an uncooled DSLR actually), but from a dark sky site. My deepest and most detailed M31 image was again taken from a dark sky site, but this time with a cooled mono camera. The detail I got from the L integration was far superior to anything my DSLR gave me. Look at Anis Abdul's absolutely spectacular IOTD today; look at the equipment he used, and where he shot it from. There is no way that IFN is going to reveal itself using a light pollution filter. The best thing you can do for broadband imaging is shoot from the darkest site you have access to. Within that, mono cameras with filters will give you the best results in the shortest time, but OSCs paired with fast scopes will also be very very effective. The thing about astrophotography that I have realized is - there are no short cuts. There is no magic solution. You look at your constraints, decide what you want to accomplish, and buy your equipment based on that. Then you put in the time and effort. |
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| Concur wholeheartedly with everything said by Arun H in the last post. I'm VERY satisfied with my 183mcPro OSC as paired with a RASA 11, but that's under the constraints that it's used exclusively at Bortle 1-2 skies in the southwest US. I probably wouldn't be as happy if I was contending with LP in Bortle 7-8. However, in the best conditions, the OSC is VERY convenient to use, and produces good results quickly. See my gallery for examples. I acknowledge up front I could use more exposure time for all targets, but I'm really happy with the OSC. Cheers... |
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no filter can differentiate between these two. Well--some filters filter out sodium light pollution, and mercury light pollution, which is not part of most DSOs, correct? So it is possible to remove LP without impacting the target....if it actually works as advertised. Also--there is invariably a mix of frequencies in LP--so for the most part you are right. Here was the situation I was considering. Lets say I collect my green subs during really bad seeing and poor transparency, but I collect my red subs during good seeing and OK transparency, my blue subs during windy, poor seeing with the target below 45 degrees. Now, when those stacks are combined, there is likely to be frustration. Now, if I use a OSC, essentially all subs of each channel (once they are debayered) will have been collected during identical conditions. If I wait ti shoot when the seeing is good and the sky dark, all subs will be taken under good conditions. I may have to wait for that night, but I have to wait while I shoot all my filters anyway--which usually takes me 3-4 nights per filter. So we must compare the data from a OSC collected during good conditions to data collected with a mono camera collected at wildly different conditions--but none better than what is experienced with the OSC. The gap has to be reduced in this case. A word on luminance. I rarely see much of a difference between LRGB and RGB if I collect allot of RGB and conditions were decent. In fact, any difference I achieve can be attributed to processing. I shoot luminance because "we are supposed to", but quite frankly, in my sky, it just doesn'y really add much--other than gradients--maybe a little if I collect a lot. But its pretty subtle, and for brighter galaxies like M31 it results in blown cores where RGB does not. I did an M33 RGB and one LRGB. The RGB image got more likes (same RGB data), and the difference was mostly due to processing. So I am not really sold on teh benefits of lum. Quite often, my red and green channel has higher resolution than my lum (lower FWHM) |
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Well--some filters filter out sodium light pollution, and mercury light pollution, which is not part of most DSOs, correct? So it is possible to remove LP without impacting the target....if it actually works as advertised. Also--there is invariably a mix of frequencies in LP--so for the most part you are right. It is very important to distinguish between emission components (H-alpha, H-beta, OIII, SII) and reflection components, dust, and broadband stellar spectra. The former (i.e., emission) can very effectively be isolated using LP filters, and even more effectively using narrow band filters. The latter cannot. For example, look at the solar spectrum and compare it to the cutoffs of a light pollution filter of your choice to see how much is lost. Things like dust, IFN, etc. are very broad spectrum. Tons of light from them are eliminated when you use a light pollution filter. LP filters do an incredible job of capturing emission components but in the process, you lose a lot of broad spectrum starlight, reflection components, and dust. Compare any image of (say) the Lagoon Nebula from a dark sky site with that taken using a light pollution filter. To your second point - the way I think about it, you have a fixed set of what I'll call "good conditions". If you split your RGB time between the three filters under these conditions, you would get similar or better results using a mono setup as with an OSC. It is unfair to the mono to have data acquired under poor conditions be compared to data from an OSC under good conditions. A fairer comparison is to have the set of good conditions be divided between filters and compared to the OSC. Admittedly, this is where the convenience factor of OSC comes into play, a convenient solution being what Caspian Ray mentioned - shoot lum with a mono, and shoot RGB with an OSC. Many people do this. To your final point, I can only say that my experience differs from yours. In image after image, my true lum has more depth and detail than the synthetic lum from RGB. I would also again point to Anis's IOTD. Why did he take the lum data if he could get what he wanted from RGB alone? The reason is simple. You are collecting photons 3x faster when you use a lum filter and therefore building SNR that much faster. With faint detail like the IFN and the outer parts of galaxies, that is absolutely critical. |
