----------------------------------- rbrtgmn 06 Mai 2020 13:22 gain/offset by bortle scale ----------------------------------- salutari aveti recomandari pentru setarile unei camere (gain and offset) dupa bortle scale? am bortle 4 unde locuiesc, nu a atat de poluat din ce inteleg de pe net, pentru dark sites, este bine sa folosesti valori scazute la gain si offset (contrast mai mare) am achizitionat un ASI294mc pro, dar vad ca pentru gain mic (sub 120) read noise(e-rms) este foarte mare fata de gain mai mare de 120 Dupa un calcul rapid( vezi tabel ) pentru a elimina read noise este nevoie de exponere time = 600secunde Am ales Electron Polution Rate [P] = 2.3e/pixel/s (bortle intre 4 si 5) care ar fi cel mai bun compromis? multumesc ----------------------------------- tudor 06 Mai 2020 13:50 ----------------------------------- Bortle 4 este un cer extrem de bun pentru Bucuresti :o dar cred ca stai mult in afara orasului ca altfel nu se explica! Poti vedea M33 cu vedere periferica cand e sus pe cer? Eu nu ma pricep la astfel de setari, dar colegii cu astrofoto te vor ajuta!!! ----------------------------------- rbrtgmn 06 Mai 2020 13:58 ----------------------------------- scuze pt dezinformare, tin telescopul la țara, de unde provin, mersi ----------------------------------- gabi 06 Mai 2020 15:39 ----------------------------------- Salut, Recomandare Stark Labs. 1. Take a bias frame and look for the minimum value in it. Is it at least, say 100 and less than a thousand or a few thousand? If so, your offset is fine. If it's too low, boost the offset. If it's high, drop it. Repeat until you have a bias frame with an offset in, roughly 100 - 1000. Don't worry about precision here as it won't matter at all in the end. You now know your offset. Set it and forget it. Never change it. 2. Aim the camera at something bright or just put it on your desk with no lens or lenscap on and take a picture of say 1s (the idea here is to ensure you’re saturating the CCD so the wells will be full). Look at the max value in the image. Is it well below 65k? If so, boost the gain. Is it at 65k? If so drop the gain. Now, if you're on a real target (daylight ones are great for this) you can look at the histogram and see the bunching up at the top end as the camera is hitting full-well. Having that bunch-up roughly at 65,535 plus or minus a bit is where you want to be. If you pull up just shy, you'll get the "most out of your chip" but you'll also have non-linearity up there. You've got more of a chance of having odd color casts on saturated areas, for example, as a result. If you let that just clip off, you've lost a touch but what you've lost is very non-linear data anyway (all this assumes, BTW, an ABG chip which all of these cams in question are). Record that gain and set it and forget it. Never change it. By doing this simple, daytime, two-step process you've set things up perfectly. You'll be sure to never hit the evil of zero and you'll be making your chip's dynamic range fit best into the 16-bits of your ADC. Again, all the cameras in question have full-well capacities below 65,535 so you are sure to have enough ADUs to fit every electron you record into its own intensity value. ----------------------------------- rbrtgmn 06 Mai 2020 15:46 ----------------------------------- awesome, thanks