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... or with an OSC you could just spend the 3 hours for a different object. However, I agree that if you are in the comfortable situation to be able to use such short time periods due to access to a (garden) observatory there may be no reason to use an OSC. I need at least 5h of clear skies to get 3h of integration time with my portable rig. Have fun and clear skies Wolfgang |
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| Good point Wolfgang. For needing to travel the OSC plus L-extreme is a more practical option. Clear (and preferably moonless) skies! Tim |
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| I might understand the point although I do not subscribe to it with NB and very LP skies. But if you're going to a dark site why would you use tight NB at all? |
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andrea tasselli:Lynn K: Are you saying that a 1 pixel sensor is equivqlent to a 4,000x4,000 pixel sensor? Or that software extrapolating signal from real signal into other pixels is the same as real signal being picked up by those pixels? No way. Lynn has it right, for the same reason that one can't improve resolution by upsampling a dataset. Becuase the new pixles are not being filled with new information--just extrapolations--copied signal. |
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Rodd Dryfoos: I'm saying that what matters is the sky area "covered" by each pixel, not how many you have. Sure, you cover more sky area with a larger sensor than with a smaller one, all other things being equal but that is where the difference ends. I have from good sources that while the interpolated signal isn't as good as the non-interpolated one the difference would be hard to spot for the untrained eye, if your oversample the OSC sensor and make use of the drizzling algorithm (without changing the image scale, obviously). So in effect you DO NOT gain something for nothing, as you'll have to to pay the price in terms of additional filtering losses, increased exposure time because of the oversampling and additional CPU resources/time because of an additional post-processing step. |
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This may be a really stupid (relative "newbie") comment, but doesn't the mono/OSC question relate to the target we are trying to photograph and the light polution/seeing conditions from where we are shooting? I live in a suburban area and I could not really dream of shooting faint nebulas with a OSC. I would, however, probably use a OSC for galaxies if they are bright enough. I guess what I am saying is that there are times to use both. |
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Andy Wray: It's more a question of cost. Everything else being equal, mono is gonna beat OSC in terms of SNR gathering and detail every time. Mono setups are more expensive, especially the more efficient you want them to get; such as introducing a filter wheel, or an automatic focuser. Of course not everything is equal. You will spend more time processing mono stuff just by virtue of having to stack them separately and processing each channel individually in the beginning. Not to mention you will have to take flats for all the filters. Is it worth it? Yes, yes it is. There is no way I would of gotten the results on the North American Nebula that I did with an OSC / L-Extreme combo. Having used both that combo and mono, the mono setup is waaaaaaaaaaaaaaaaaaaaaaaaaaay more time efficient and creates a way better result. You couldn't pay me to use the L-extreme anymore. It's that much of a difference. OSC is often given a blanket advantage in light polluted areas because people reason you can slap a light pollution filter on it and call it a day, while mono is forced to use their RGB filters without any light pollution adjustment. Well, even here mono can do great work. You just use the light pollution filter as the luminescence filter. As with any light pollution situation, ya better be ready to put in the hours though (Something I routinely fail at!). See here: https://www.astrobin.com/314175/C/ What it all boils down to is how much you are willing to spend on this hobby in terms of cameras. It's a question of cost vs. quality with the OSC/mono debate. You pay for the extra quality in a monetary cost because the equipment costs more, and a time cost in learning how to use it in the field and how to process it back home. Not everyone can afford or want to pay the costs and that is okay. I mean I still use an OSC. As far as broadband is concerned I don't think enough people give them the credit they deserve. They have come a long way! |
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Andy Wray: Have you tried hard enough? I bet my bottom farthing that my situation is no better than yours if not even worse. |
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| IMO, cost is a major consideration in the choice of OSC vs MM, particularly for someone new to the obsession. A good set of 3nm filters plus LRGB filters, filter wheel etc. will cost as much as a reasonable camera compared to an L-Pro plus Antlia ALP-T dual filter. The arguments about whether OSC is quicker or slower than mono are moot IMO as I find I need a LOT of time with OSC to attempt to obtain the resolution I want, particularly on faint targets, and when I want to capture Sii too then it adds even more (I use an IDAS NB3 filter to capture Sii + Oii, but it is quite a wide bandwidth). I will switch to mono fairly soon and expect to be able to achieve equivalent quality in less time or better quality in the same time. |
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Signal is intensive not extensive. Claiming otherwise would be ridiculous. Each pixel "sees" a fraction of sky and that's that. How many are there is pointless and as long as you satisfy the Nyquist sampling criterion you are in, the original signal can be reconstructed. If I am in a scenario where signal can effectively be fully reconstructed by sampling 1/4 the number of pixels, then I would simply cut the exposure time of a mono camera by a factor of 4, construct 4 different subs from each gathered exposure and interpolation, thus reducing my collection time by a factor of 4. |
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andrea tasselli:Andy Wray: Your one-line answers are a little bit condescending if I'm honest. I'm a relative beginner at this and all you can say is "have you tried hard enough?" when I am actually trying my best. Despite your comments, I will strive to improve. |
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If I am in a scenario where signal can effectively be fully reconstructed by sampling 1/4 the number of pixels, then I would simply cut the exposure time of a mono camera by a factor of 4, construct 4 different subs from each gathered exposure and interpolation, thus reducing my collection time by a factor of 4. You are mis-associating spatial samplings with temporal ones. |
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Andy Wray: My apologies if my replay came across as condescending which wasn't meant to be. It is/was just a rather plain question. The only sure way to know if something does or does not work is to try it out and try as hard as you can to make it work. That's my experience anyway... |
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You are mis-associating spatial samplings with temporal ones No. The problem with applying Nyquist here is that you are not accounting for how signal to noise works. Even if I am spatially oversampled, with a mono camera, because adjacent pixels are capturing statistically independent incidences of photons, you are building signal to noise ratio faster than if you were only sampling a smaller number of pixels from the same sensor as you would with an OSC. That is, the SNR of an image made from a mono camera versus an OSC of the same resolution and equivalent integration times and assuming equivalent filter band passes will be higher. As I mentioned, were it not so, I could still retain an advantage by breaking down the mono signal from each sub as described. |
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OK, as an amateur I thought I'd give a less technical point of view. What's really nice right now for me about using a mono camera with filters is being able to see different aspects of an object in different wavelengths and being able to creatively process/combine them. I recognise that a OSC would probably get me to just as good a result in less time, but just having the insight into the different emmisions makes it a more interesting hobby for me. Also, computers are so fast right now that the whole calibration/registration and processing process takes next to no time compared to a few years ago, so having to combine all the separate channels and increased number of exposures is really a non-issue. Whilst i think about it: having a cheap autofocusser like the ZWO EAF 5V has made "autofocus on filter change" a bit of a doddle, so even if your filters are not parfocal then that is really a non-issue. One downside of the mono approach is that it adds extra optical elements into the train. For me, with cheap ZWO filters, that means I can't capture really bright stars due to the reflections between my filters and the camera sensor/cover glass. For captures like the horsehead I would either need to spend a fortune on new filters or buy a OSC which would probably be cheaper. |
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The OSC vs Mono debate has been done to death. OSCs are great at RGB imaging (and can actually be more eficient at it than monos) but lack the ability to capture luminance which is a very important advantage of monos. Rather than beat a long dead horse, here is the link to the math behind it: https://www.cloudynights.com/topic/682340-monochrome-vs-one-shot-color-%E2%80%93-by-the-numbers-please/ |
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Andres Salaverria:Guillermo de Miranda: I couldn’t agree more! I’m old school back in the day of hypersenitized film and what can be achieved with todays OSC and a good dual band filter (I use the IDAS NBZ) is in my opinion unbelievable. Dale |
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I think mono has greater scope for some targets but for the guys and girls with great acquisition/processing skills,they would produce great results with both mono or osc if we are honest.Im just trying to make the most with where i am currently at. They're just tools,with merits and disadvantages in different situations as far as i can tell. Im in the midst of two new-moon phase clear nights in the row.. i spent all of friday day trying to decide to shoot mono or osc.. I decided on osc because i cant be sure when my next new-moon, clear night of imaging ; session would come and i wanted to get something done. I own two fast setups which also lend themselves to osc. Everyones situation/skill set/equipment is so different. Such a personal hobby ,there are so many ways to get things done. Its great . |
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but for the guys and girls with great acquisition/processing skills,they would produce great results with both mono or osc if we are honest.Im just trying to make the most with where i am currently at. In astrophotography more than in any other area of photography, equipment matters. Processing obviously does, but equipment and location matter more than in other areas. The signal we are trying to capture is often barely above the threshold of background noise. Cameras with higher QE, capturing all the light that's incident on your sensor as happens with luminance capture and with low band pass, high transmission, narrow band filters used with mono cameras, these are important tools and advantages. This is the reason the majority of the best images here are captured using mono cameras and filters from dark sky sites, and the reason why these imagers set up remote telescopes at places like Chile and New Mexico. And having done that, they use mono cameras with filters to get the best data they can - they don't use OSCs simply to test their processing skills. I don't mean to be negative about OSC, just realistic. I own both a mono and OSC. I use them for different things. I'll use the OSC when I am collecting RGB data from a dark site I travel to. It is better at that than the mono I own, and I know I have a complete set of RGB in the event my session is cut short. But I hold no illusion that it can compete with data to which luminance is added captured using the mono. Similarly, all my narrow band imaging is done with mono. These are simply to be viewed as different tools to be used depending on your constraints. But saying that processing skill can make up for short comings in data capture - well, you might get an image you're happy with, but not as good as one if you understood the strengths of each tool and used it effectively. The first and most important thing is to get the best data you can. |
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| Frankly this idea that AP is kinda race where the best equipped and endowed with the best environment (which is an alias for the ones with most money) WINS is objectionable and strongly so. There are no best image, just images that people like best, especially people that give those awards. Your best images ain't mine best images and vice-versa. |
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"Frankly this idea that AP is kinda race where the best equipped and endowed with the best environment (which is an alias for the ones with most money) WINS is objectionable and strongly so. " It is not a question of winning or losing. Those are your words not mine. And I didn't bring up awards, you did. What purpose is served by trying to attribute to me words I didn't use? I find that objectionable, and strongly so. But I will take responsibility for not defining what I mean by "best". Best means bringing out the faintest possible detail and making it stand out. That does require a dark sky and good equipment. Of course, processing. That's physics, not opinion. I admire a very deep image of M1/82 region with IFN. Even when I know I will likely never have the time or equipment to capture such an image myself. |
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| You brought it up. If there is a "best" image there must be a "worst" one and everything else in between. And the idea of a race is intrinisic in the idea that you should strive for this "best" image that can only be achieved by using top notch equipment from top locations around the world (usually very remote and very expensive to reach and set up shop). |
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| ...but let's agree to disagree about much of what is AP. Except that a dark sky is waaaaaaaaaaaay better than a LP'ed one. |
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"And the idea of a race is intrinisic in the idea that you should strive for this "best" image that can only be achieved by using top notch equipment from top locations around the world (usually very remote and very expensive to reach and set up shop)." Who said anything about striving for the best image in the world? But striving for the best image I can get given the constraints of budget , time, and location - that's what I strive for. I judge my personal success by whether I am making meaningful progress in my eyes versus last year or two years ago. By that metric, I am "winning". I also have no problem saying an image taken from Chile using a 20" scope is "better" than my image of the same object. It should be, or the people running the scope in Chile, or processing that data, are doing something wrong. But an award or contest where both images are given the same weight - that's not a very meaningful one and not one that I put much weight in. |
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Although I‘ld still consider myself a beginner I‘ve extensively thought about, calculated and tested the difference between OSC and Mono for my light polluted skies (Bortle 6) and my generally oversampled setup (0.4“/px). My results were: - Mono LRGB gets me the same SNR and resolution as OSC in about 2/3 to 1/2 the time. This is less effective than possible by theory because I need rather much RGB to make gradient reduction easier and have enough color signal to support the L for the highly-saturated images I like. - Dual-Narrowband is even less efficient, the factor is at least x3 compared to Mono even with the excellent IDAS NBZ. I do use 3nm filters. This doesn‘t even include the benefit of increasing O3 integration time selectively. Resampling both (after drizzling) to the same seeing-adapted resolution (say 0.8 or even 1.2“/px) is paramount to realizing these benefits, otherwise the mono data is much more oversampled than the OSC (which has been smoothed by Debayering or Bayer Drizzling) and so has an unfair disadvantage concerning SNR. I can not follow the „time efficiency“ argument: Of course, you will want a filterwheel for mono and also automatic focusing. Compared to the cost of good narrowband filters, the additional expense is low. With them, you can quickly rotate between the slots, so even when inclement weather cuts your session you should have data for all channels. Time lost is minimal: Voyager can do single-star focus with my rig in 60s, including slewing to/from the focus star. Using focus offsets will even eliminate that time. I do agree that if you‘re limited to 3h in light pollution per object due to time or weather constraints, the difference will be very hard to see and probably not worth the expense, even though numerically it is significant. I also find single-channel data much easier to process, so much so that I will split channels on OSC data anyway for e. g. gradient reduction. |
