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CCD Camera design
Hi Leonard, Stu,
With all due respect, narrow band imaging can be done with color detectors. There is an interpolative process to yield the final image, but the results are not as bad as one might think, especially for imagers with small pixels. If you get a chance, here are links to my only 2 H-alpha images with a one-shot. http://www.heavenlyview.com/b33halphasxvh9c.htm http://www.heavenlyview.com/ic405sxvh9c.htm I don't have an OIII filter, but there's no reason to suspect this would be much different. Depending on the filter cross-over, this could generate signal in the blue or green filtered pixels, or both. Maybe these are "less than desired" to some, but I'm quite happy with the outcome. Judge for yourself. Best regards, Alan http://www.heavenlyview.com/ "Leonard" wrote in message ... There is another big drawback to using a "color" detector. You are stuck with the filters the manufacturer placed on the front of the chip. While fine for the daytime snapshot they do not have the high efficiency of or color balance available in astronomical filters. You could not do a Ha or OIII shot very well (yes you could put one of those filters in front of a color detector but I believe the results would be less than desired. Of course if you have already selected a specific chip there may not be a color filter option for it. You can only buy / get what they make. In general CMOS sensors do not offer as low as noise as CCDs. Howerver the new Canon digital SLR cameras have CMOS sensors and dark noise far below what my CCD based camera would produce (at the same sensor temperature). I wish you the best of luck on your endeavors. Please publish the design if you get it to go. Leonard On Fri, 06 Feb 2004 09:09:18 GMT, "David Nakamoto" wrote: Color CCDs achieve their results by placing a matrix of color filters ove r the sensor array. This cuts down on the sensitivity of the array, increasing exposure times 2 to 3 times or more. It also reduces the resolution, since every three to four pixels are used to recreate a single color one. CMOS does have higher noise, and less low light sensitivity. The best color results are still from using a black and white CCD with a color filters, taking one exposure per filter. "Alain J" wrote in message ... Hi I want to build my own astronomical camera. I don't have decided which I'll use. I want to put a color CMOS sensor but many web sites relates that CMOS sensors are not very good (high dark level) I've seen a color CMOS sensor with 1,3 Mpixel (1280x1024) at a very low price (about $140). For best performance, do I use a color sensor or B&W sensor ? In term of sensitivy, dark noise which is the best (colour or B&W)? Cordially Alain |
#12
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CCD Camera design
They are nice shots.
I didn't say you could not. But assuming a RGBG Bayer color filter on the front of the chip, it throws away 3/4 of the light / signal. Same depth in 1/4 the time or 4x the resolution sounds really good in comparison. I notice you mention Sigma reject. I know Russell Crowman. He really is a nice guy. Here is his shot. It is less than 10% longer in exposure time on a 4" f5 scope. Granted it is a different camera (Kodak CCD) but it is deeper and higher resolution (click on image to see the full resolution details). http://www.rc-astro.com/nebulae/ic434_region_ha.htm It is quite a bit better than my shot. Mine was shot unfiltered line of site to 3 streetlights. CB245, 27 x 15s (6.75 minutes), cooling off, ambient ~ +35 deg F, with darks, no flats, no defect map, 8" f5.3 Newtonian http://photos.yahoo.com/z_leonardh Leonard On Fri, 13 Feb 2004 00:49:48 GMT, "Alan Chen" wrote: Hi Leonard, Stu, With all due respect, narrow band imaging can be done with color detectors. There is an interpolative process to yield the final image, but the results are not as bad as one might think, especially for imagers with small pixels. If you get a chance, here are links to my only 2 H-alpha images with a one-shot. http://www.heavenlyview.com/b33halphasxvh9c.htm http://www.heavenlyview.com/ic405sxvh9c.htm I don't have an OIII filter, but there's no reason to suspect this would be much different. Depending on the filter cross-over, this could generate signal in the blue or green filtered pixels, or both. Maybe these are "less than desired" to some, but I'm quite happy with the outcome. Judge for yourself. Best regards, Alan http://www.heavenlyview.com/ "Leonard" wrote in message .. . There is another big drawback to using a "color" detector. You are stuck with the filters the manufacturer placed on the front of the chip. While fine for the daytime snapshot they do not have the high efficiency of or color balance available in astronomical filters. You could not do a Ha or OIII shot very well (yes you could put one of those filters in front of a color detector but I believe the results would be less than desired. Of course if you have already selected a specific chip there may not be a color filter option for it. You can only buy / get what they make. In general CMOS sensors do not offer as low as noise as CCDs. Howerver the new Canon digital SLR cameras have CMOS sensors and dark noise far below what my CCD based camera would produce (at the same sensor temperature). I wish you the best of luck on your endeavors. Please publish the design if you get it to go. Leonard On Fri, 06 Feb 2004 09:09:18 GMT, "David Nakamoto" wrote: Color CCDs achieve their results by placing a matrix of color filters ove r the sensor array. This cuts down on the sensitivity of the array, increasing exposure times 2 to 3 times or more. It also reduces the resolution, since every three to four pixels are used to recreate a single color one. CMOS does have higher noise, and less low light sensitivity. The best color results are still from using a black and white CCD with a color filters, taking one exposure per filter. "Alain J" wrote in message ... Hi I want to build my own astronomical camera. I don't have decided which I'll use. I want to put a color CMOS sensor but many web sites relates that CMOS sensors are not very good (high dark level) I've seen a color CMOS sensor with 1,3 Mpixel (1280x1024) at a very low price (about $140). For best performance, do I use a color sensor or B&W sensor ? In term of sensitivy, dark noise which is the best (colour or B&W)? Cordially Alain |
#13
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CCD Camera design
Thanks Leonard,
I was just questioning the phrase "less than desired", since I'm quite happy with this result. As it turns out, when I increased the contrast and resampled down to match sizes, the 2 images are not all that dissimilar. If you are interested, I can send my resampled shot for you to compare. It really doesn't give much away at all at such a small scale. In fact, mine is deeper in stars (due to use of a wider 13nm H-a bandwidth), but Russell's has better contrasts of detail, due to the small 3nm bandwidth. The passband has much to do with the outcome of H-alpha images. I do agree that the resolution cannot be equal all else constant, due to the interpolative routines required to fill in the data, but the depth is similar for the given times. Russell's SigmaReject is a great tool. I only recently started to use that. I've also enjoyed his work over the past year and he is one of the premier imagers. Your shot only needs more time, but it's tough to overcome light pollution unfiltered. I'm thinking of going to a 10" f/4.5 Newt, since the optics on my SCT really aren't all that good along with the mirror shift. I think you have the right idea with the 8" Newt! Take care, Alan http://www.heavenlyview.com/ "Leonard" wrote in message ... They are nice shots. I didn't say you could not. But assuming a RGBG Bayer color filter on the front of the chip, it throws away 3/4 of the light / signal. Same depth in 1/4 the time or 4x the resolution sounds really good in comparison. I notice you mention Sigma reject. I know Russell Crowman. He really is a nice guy. Here is his shot. It is less than 10% longer in exposure time on a 4" f5 scope. Granted it is a different camera (Kodak CCD) but it is deeper and higher resolution (click on image to see the full resolution details). http://www.rc-astro.com/nebulae/ic434_region_ha.htm It is quite a bit better than my shot. Mine was shot unfiltered line of site to 3 streetlights. CB245, 27 x 15s (6.75 minutes), cooling off, ambient ~ +35 deg F, with darks, no flats, no defect map, 8" f5.3 Newtonian http://photos.yahoo.com/z_leonardh Leonard On Fri, 13 Feb 2004 00:49:48 GMT, "Alan Chen" wrote: Hi Leonard, Stu, With all due respect, narrow band imaging can be done with color detectors. There is an interpolative process to yield the final image, but the results are not as bad as one might think, especially for imagers with small pixels. If you get a chance, here are links to my only 2 H-alpha images with a one-shot. http://www.heavenlyview.com/b33halphasxvh9c.htm http://www.heavenlyview.com/ic405sxvh9c.htm I don't have an OIII filter, but there's no reason to suspect this would be much different. Depending on the filter cross-over, this could generate signal in the blue or green filtered pixels, or both. Maybe these are "less than desired" to some, but I'm quite happy with the outcome. Judge for yourself. Best regards, Alan http://www.heavenlyview.com/ "Leonard" wrote in message .. . There is another big drawback to using a "color" detector. You are stuck with the filters the manufacturer placed on the front of the chip. While fine for the daytime snapshot they do not have the high efficiency of or color balance available in astronomical filters. You could not do a Ha or OIII shot very well (yes you could put one of those filters in front of a color detector but I believe the results would be less than desired. Of course if you have already selected a specific chip there may not be a color filter option for it. You can only buy / get what they make. In general CMOS sensors do not offer as low as noise as CCDs. Howerver the new Canon digital SLR cameras have CMOS sensors and dark noise far below what my CCD based camera would produce (at the same sensor temperature). I wish you the best of luck on your endeavors. Please publish the design if you get it to go. Leonard On Fri, 06 Feb 2004 09:09:18 GMT, "David Nakamoto" wrote: Color CCDs achieve their results by placing a matrix of color filters ove r the sensor array. This cuts down on the sensitivity of the array, increasing exposure times 2 to 3 times or more. It also reduces the resolution, since every three to four pixels are used to recreate a single color one. CMOS does have higher noise, and less low light sensitivity. The best color results are still from using a black and white CCD with a color filters, taking one exposure per filter. "Alain J" wrote in message ... Hi I want to build my own astronomical camera. I don't have decided which I'll use. I want to put a color CMOS sensor but many web sites relates that CMOS sensors are not very good (high dark level) I've seen a color CMOS sensor with 1,3 Mpixel (1280x1024) at a very low price (about $140). For best performance, do I use a color sensor or B&W sensor ? In term of sensitivy, dark noise which is the best (colour or B&W)? Cordially Alain |
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