ehanes7612
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For sure, I always use dedicated power supplies for the electronics I use... Have burnt out my share of microprocessors
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CCD vs Canon 6D
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ehanes7612
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I just ordered an Halpha filter and a Oiii filter (my credit card is tapped out 
) , now I just have to wait until the sky clears
) , now I just have to wait until the sky clearsHaha! Well, you know, two big purchases in succession have most definitely invoked 'the curse', extra fluffy. It'll be cloudy for weeks now.I just ordered an Halpha filter and a Oiii filter (my credit card is tapped out
Joking aside, congrats. Any idea what your first target will be when the skies do clear?
ehanes7612
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The Rosette complex, hopefully larger FOV than just the Rosette Nebula.Haha! Well, you know, two big purchases in succession have most definitely invoked 'the curse', extra fluffy. It'll be cloudy for weeks now.I just ordered an Halpha filter and a Oiii filter (my credit card is tapped out
Joking aside, congrats. Any idea what your first target will be when the skies do clear?
ehanes7612
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curious as to what is the equivalent ISO on a CCD camera (something like Atik 314L)..trying to gauge what the exposure times will be if I am in a blue area using the filters and an 80 mm refractor.
sharkmelley
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I'd say that probably falls around ISO 2000-2500 for DSLR cameras with similar pixel sizes.
ehanes7612
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That should work well. Thanks
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sharkmelley
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It depends on what is meant by equivalent ISO.
For instance, the Atik won't saturate the sensor until the photosite well is full (i.e. reaches the full well capacity). So if the question is what "ISO gives equivalent non-saturated performance" then the answer would be to use the lowest camera ISO possible.
Mark
I was just going by what ISO would give you roughly the same signal per unit time at roughly the same read noise. However I forgot to account for the bit depth difference, 14-bit vs. 16-bit.
I am not sure it is as simple as saying use the lowest ISO. With an isoless camera that has a flat read noise curve, using the lowest ISO possible might work. With any camera that has increasing read noise as you drop ISO, which is all Canon's and even the A7s, I don't think one could just say use the lowest ISO. There are certainly differences in dynamic range...that is another one of the reasons to use a CCD, much better dynamic range even at higher gain.
Hi John
Thank you for your reasonable explanations. I have a 6D and also consider buying a new camera and am somewhere between CCD and DSLR. Your comments are helpful, but I still have some questions whether I have understood correctly.
To my understanding the readout noise of CCDs and DSLRs are about at the same level. The problem is the noise of the dark current, which is much worse for DSLRs. Is this correct? By design CCDs can collect light for a long period before the readout which makes them great for faint nebulas or when narrow filters are used. My experience with the 6D is, that it does not make sense to expose for more than about a minute. Which seems to fit to the numbers which I found in the marvelous analysis by Roger Clark (http://www.clarkvision.com/articles/evaluation-canon-6d/). Please correct me, if my considerations are correct.
Eos 6D @ ISO 6400:
Readout noise = 1.7e (very low). Dark noise at 6°C after 60 sec: Already 3.6e and thus dominating (I can neglect the 1.7e since noise adds quadratically). I always can increase the exposure time, but the dark noise increases with the square root of the exposure time. I can do 64 shots at 1 min or in theory one shot at 64 min and get the same noise result (but stars saturate). The signal to noise ratio will improve by a factor 8 (Square root of 64). After averaging and streched to the same Signal, then I get an noise equivalent of 3.6e * 64^0.5/64 = 0.45e.
Eos 7D Mark II @ ISO 3200 (ISO6400 does not make much sense here). Is a HUGE step forward compared to the 6D!
Readout noise = 1.9e. Dark noise at 4°C after 5 min = 1.6e (see http://www.clarkvision.com/reviews/evaluation-canon-7dii/index.html). So after 20 min (!) I expect about the same noise as with the 6D [1.6e * 4^0.5 = 3.2 and the total noise of (3.2e^2+1.9e^2)^0.5 = 3.7e]. So I had 20 times mor time to collect light and my signal to noise is 20 time better. My final numbers after 64 min are: 3.7e * (64/20)^0.5 / 64 = 0.10e. So MUCH better.
Atik 460ex b/w (http://www.cloudynights.com/topic/457191-atik-460-ex-results-of-testing-for-photometry/)
Read noise 3.8e. dark CURRENT= 0.001524 electrons per pixel s-1. So after 64 min I get 60*64*0.0015e = 5.7e. So the dark noise should be 5.7^0.5= 2.4e. Total noise after 64 min = (3.8e^2+2.4^2)^0.5=4.5e. Signal to noise is 4.5e/64 (assuming the same light Efficiency??) = 0.07e. For exposures with narrow filters it will win another factor 3 compared to the 7DII since it is b/w.
Did I understand this correctly? The EOS 7DII is a huge step and DSLRs catch up fast, but CCDs in the range of a Atik 460ex are still significantly better than a 7DII and much much better than a 6D for faint nebulas. CCDs also have a much higher dynamic range, but I can fix that with the combination of different exposure times in PixInsight (works pretty well). For bright objects DSLRs are at least not worse than CCDs and simpler to use.
Did I get this all right? So I have to get used to the thought that I have to spend a fortune for a CCD if I want to get realy good nebula and galaxy shots and take my 6D for normal family Pictures...
Moritz
Thank you for your reasonable explanations. I have a 6D and also consider buying a new camera and am somewhere between CCD and DSLR. Your comments are helpful, but I still have some questions whether I have understood correctly.
To my understanding the readout noise of CCDs and DSLRs are about at the same level. The problem is the noise of the dark current, which is much worse for DSLRs. Is this correct? By design CCDs can collect light for a long period before the readout which makes them great for faint nebulas or when narrow filters are used. My experience with the 6D is, that it does not make sense to expose for more than about a minute. Which seems to fit to the numbers which I found in the marvelous analysis by Roger Clark (http://www.clarkvision.com/articles/evaluation-canon-6d/). Please correct me, if my considerations are correct.
Eos 6D @ ISO 6400:
Readout noise = 1.7e (very low). Dark noise at 6°C after 60 sec: Already 3.6e and thus dominating (I can neglect the 1.7e since noise adds quadratically). I always can increase the exposure time, but the dark noise increases with the square root of the exposure time. I can do 64 shots at 1 min or in theory one shot at 64 min and get the same noise result (but stars saturate). The signal to noise ratio will improve by a factor 8 (Square root of 64). After averaging and streched to the same Signal, then I get an noise equivalent of 3.6e * 64^0.5/64 = 0.45e.
Eos 7D Mark II @ ISO 3200 (ISO6400 does not make much sense here). Is a HUGE step forward compared to the 6D!
Readout noise = 1.9e. Dark noise at 4°C after 5 min = 1.6e (see http://www.clarkvision.com/reviews/evaluation-canon-7dii/index.html). So after 20 min (!) I expect about the same noise as with the 6D [1.6e * 4^0.5 = 3.2 and the total noise of (3.2e^2+1.9e^2)^0.5 = 3.7e]. So I had 20 times mor time to collect light and my signal to noise is 20 time better. My final numbers after 64 min are: 3.7e * (64/20)^0.5 / 64 = 0.10e. So MUCH better.
Atik 460ex b/w (http://www.cloudynights.com/topic/457191-atik-460-ex-results-of-testing-for-photometry/)
Read noise 3.8e. dark CURRENT= 0.001524 electrons per pixel s-1. So after 64 min I get 60*64*0.0015e = 5.7e. So the dark noise should be 5.7^0.5= 2.4e. Total noise after 64 min = (3.8e^2+2.4^2)^0.5=4.5e. Signal to noise is 4.5e/64 (assuming the same light Efficiency??) = 0.07e. For exposures with narrow filters it will win another factor 3 compared to the 7DII since it is b/w.
Did I understand this correctly? The EOS 7DII is a huge step and DSLRs catch up fast, but CCDs in the range of a Atik 460ex are still significantly better than a 7DII and much much better than a 6D for faint nebulas. CCDs also have a much higher dynamic range, but I can fix that with the combination of different exposure times in PixInsight (works pretty well). For bright objects DSLRs are at least not worse than CCDs and simpler to use.
Did I get this all right? So I have to get used to the thought that I have to spend a fortune for a CCD if I want to get realy good nebula and galaxy shots and take my 6D for normal family Pictures...
Moritz
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