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Jupiter 01/08/2014 from DEC
¿ªÔÆÌåÓýWell done Dan! You get more out of an all color camera than anybody I know! I actually bought a color flea because I admit to getting tired of getting good seeing for my red channel data, only to be stymied with much poorer seeing for the green and blue! That seems to happen to me constantly. I will make a report on the camera when and if I get around to using it! ? Brian ? From: C14_EdgeHD@... [mailto:C14_EdgeHD@...] On Behalf Of maadscientist@...
Sent: Friday, January 10, 2014 9:53 PM To: C14_EdgeHD@... Subject: [C14_EdgeHD] Jupiter 01/08/2014 from DEC ? ? Conditions pretty soft, not turbulent. Got more detail than expected. |
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"good seeing for my red channel data, only to be stymied with much poorer seeing for the green and blue" That may be what is actually happening because longer wavelengths are less affected by seeing.? Also, SCTs are not immune to chromatic aberrations (e.g. chromo-spherical).?Many users find?lunar SCT imaging?is often sharpest/best with a red filter. So a Bayer ("color") camera will probably not?improve?resolution but?rather reduce it to the lower seeing that you normally experience in green.? Bayer strongly emphasize the green?signal because there are 2x more green pixels than red or blue and those green pixels?have?wider bandwidth and usually have higher QE (esp for IR blocked cameras like DSLR).? Also, Bayer sampling is problematic so the sensor has less potential for hi-res than a mono sensor at identical sample rate. The ?advantage of Bayer is simultaneous color (e.g. no worry about the planet rotating between color exps), which is?questionable but occasional value.?The primary argument for Bayer is convenience.? But there are?significant disadvantages to Bayer and few (none?) of the master imagers bother with it. Stan |
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Hey Stan,
Although SCTs corrector plate can contribute to CA because technically it is a lens, the prescription is weak and is zero in a good chunk of the glass. "So a Bayer ("color") camera will probably not?improve?resolution but?rather reduce it " The camera does not reduce resolution, It is what it is. "Bayer strongly emphasize the green?signal because there are 2x more green pixels" Correct and rightly so, Human vision is way more sensitive in green. When you image mono, you get 4x green pixels. "Bayer sampling is problematic so the sensor has less potential for hi-res than a mono sensor at identical sample rate." Potential is the key word. I have never seen the potential higher resolution actualized in my rig from my location.. "But there are?significant disadvantages to Bayer and few (none?) of the master imagers bother with it." Hey, what am I, chopped liver?? :) Dan L |
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" SCTs corrector plate can contribute to CA because technically it is a lens, the prescription is weak and is zero" The primary aberration is not the usual chromatic where colors focus at different points but rather?convoluted spherical aberrations.?This is not unexpected because the job of the glass is to remove spherical.? The effect is small but does manifest in very high res imaging.??The usual SCT "sweet spot" for minimal spherical is in green light but that can change depending on the mirror spacing (which in turn is?determined by backfocus distance).? So an SCT can be tuned (wittingly or otherwise) to optimize red. "...Human vision is way more sensitive in green..." In?a case where the best resolution is red (for whatever reason) then neglecting the red signal and doubling (or more)?an inferior green signal (for whatever reason) will?result in lower overall resolution.? This is especially true for Bayer because the effective red pixel size is double the actual pixel sizes (because there is a?blank space between every red pixel). "When you image mono, you get 4x green pixels" The correct multiplier is 1x.? Every pixel in a mono camera participates in whatever filter is used.? So for every red pixel in a combined 3-filter/color?image there is?1 green pixel and 1 blue pixel. "I have never seen the potential higher resolution actualized in my rig" Have you really looked?? That would require using a mono and Bayer camera on the same night (preferably within minutes of each other) and/or extensive use of mono and Bayer over long periods. "Hey, what am I, chopped liver?? :)" You are obviously the exception that proves the rule! <g> Though I have to wonder what you might be capable of?using a ZWO ASI120MM. Stan |
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Hey Stan,
"The primary aberration is not the usual chromatic where colors focus at different points but rather?convoluted spherical aberrations" You are correct. Thisis why I image at 8 inches from the visual back where SA is supposed to be nulled. "In?a case where the best resolution is red (for whatever reason) then neglecting the red signal and doubling (or more)?an inferior green signal (for whatever reason) will?result in lower overall resolution.? This is especially true for Bayer because the effective red pixel size is double the actual pixel sizes (because there is a?blank space between every red pixel)." The goal of deep space and planetary imaging is to re-create the colors that the eye sees naturaly. Everything else is considered a false color image. We see green big time, so the final image will have around 50-60 percent green. Also the red resoution is NOT one quarter, even thought the pixel is one quarter the sample. This is a myth. "The correct multiplier is 1x" I was just saying the green is 2x in a 4x sampling bayer array. " Have you really looked?? That would require using a mono and Bayer camera on the same night (preferably within minutes of each other) and/or extensive use of mono and Bayer over long periods." Yes I have. I image with a Flea3 618 Bayer color camera, and? Flea 3 618 mono camera with filters on the same nights often. Same results with both cameras. I have done this for 2 years. I have an article on one shot color camera imaging coming out in the May 2014 Sky & Telescope. Hopefully it will debunk a few myths. " You are obviously the exception that proves the rule! <g>" Thanks Stan! But you see I am trying to adjust that rule a bit...... I have a color QHYL II with the same ZWO color senser and am testing it. |
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I imaged Jupiter recently (not good seeing) and was reminded how quickly it rotates; even the moons go whizzing by. I think you are?right to use a Bayer camera for color images of that planet. Stan ---In C14_EdgeHD@..., <maadscientist@...> wrote: Hey Stan, "The primary aberration is not the usual chromatic where colors focus at different points but rather?convoluted spherical aberrations" You are correct. Thisis why I image at 8 inches from the visual back where SA is supposed to be nulled. "In?a case where the best resolution is red (for whatever reason) then neglecting the red signal and doubling (or more)?an inferior green signal (for whatever reason) will?result in lower overall resolution.? This is especially true for Bayer because the effective red pixel size is double the actual pixel sizes (because there is a?blank space between every red pixel)." The goal of deep space and planetary imaging is to re-create the colors that the eye sees naturaly. Everything else is considered a false color image. We see green big time, so the final image will have around 50-60 percent green. Also the red resoution is NOT one quarter, even thought the pixel is one quarter the sample. This is a myth. "The correct multiplier is 1x" I was just saying the green is 2x in a 4x sampling bayer array. " Have you really looked?? That would require using a mono and Bayer camera on the same night (preferably within minutes of each other) and/or extensive use of mono and Bayer over long periods." Yes I have. I image with a Flea3 618 Bayer color camera, and? Flea 3 618 mono camera with filters on the same nights often. Same results with both cameras. I have done this for 2 years. I have an article on one shot color camera imaging coming out in the May 2014 Sky & Telescope. Hopefully it will debunk a few myths. " You are obviously the exception that proves the rule! <g>" Thanks Stan! But you see I am trying to adjust that rule a bit...... I have a color QHYL II with the same ZWO color senser and am testing it. |
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Hey Stan,
I agree with what you said. But, the monitors we use and the images we process in Photoshop (or whichever program) are set to display pictures in the human visual acuity, around 60% green, 30% red and 10% blue. So even if you do narrowband (and I do), the "narrow" nm spectrum is mapped to the wider visual spectrum. S2 to red, HAlpha to green, OIII to blue, (the hubble palatte) and displayed in those percentages. Deep sky imagers "try" and get the color correct by matching the color balance to a G2V star, like our sun. Hey, I agree, it is still not very accurate, and I goose stuff all the time, hence why my buddy calls me "Captain Crunch". However, I do believe that most people that do planetary and deep sky RGB and Bayer images are locked in to the human visual prsentation by the filters that are used, 400-700 nm, human vision, and the programs that process them, transmissive color, RGB for human visual. You can swap channels, insert narrowband, add Infrared, but essentially you are making a false color image that is mapped into the normal visual spectrum percentages. So for general color correctness, a red filter that captures photons in the red zone of the electromagnetic spectrum for human visual cone response is considered visually correct for a transmissive color device (your monitor). Same for green and blue. When you add an IR pass to the red channel, or substitute the IR for the red filter, you have created a false color image and it must be labeled in such a matter that the viewer knows he/she is seeing data outside the visual range. Dan L |
¿ªÔÆÌåÓýHi,
Have a look here for an in deep discussion of planetary color imaging : Best Christian Le 21/01/2014 02:01, maadscientist@... a ¨¦crit?: Hey Stan, |