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glappkaeft

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Everything posted by glappkaeft

  1. Firstly, when you say bits do you mean ADU ("Analog to Digital converter Unit" AKA pixel value)? Secondly, you are not calculating the signal, you're calculating the pixel values which is a thing we generally already know. Signal is simply the number of detected photons. So either 1000 for both cameras (if you mean that the photons where all detected) or 330 vs 220 (if the photons hit the pixel and we then take QE in account). Note that lower resolution of the 10D sensor will mean that its pixels are significantly larger so will be hit by almost exactly twice as many photons everything e
  2. Sorry I just noticed that I missed answering your main question. The four 12-bit equal to one 14 bit image is not technically true although it is trueish in many circumstances. It's one of those common but potentially dangerous mental models many people use for stacking. The right way to do this is to look at the actual signal and signal-to-noise-ratio (SNR) and it is not as scary as it sounds. In technical terms the signal is just the number of detected photons. The SNR is just like the name implies the ratio between just signal and the noise and it is the value that isn't good enough wh
  3. Not necessarily. When it comes to proper astro cameras that have RAW formats that are actually raw, the pixel value is simply a count of the electrons in the pixel electron well (1 electron per photon detected). If the electron well cannot hold more than 4096 (2^12) electrons then there is no difference between 12 and 14 bit data. When it comes to DSLRs the camera sensor specs, like the size of the electron well, are not public and the camera does a lot of processing even on RAW images that depends on the camera settings (iso settings, etc). In that case it is tricky without a good test setup
  4. Why waste time speculating when the info is only one quick search away? http://web.canon.jp/imaging/eosd/eos40d/specifications.html I think much of the online confusion stems from the 400D having a 12-bit raw format.
  5. That don't really mean much since your guide camera is limited by the pixel size and focal length to a pixel scale just above 4". Using the Nyquist theorem (which isn't 100% accurate in the case of digital sensors - pixels have an measurable area) any measurement below 8" would be questionable due to sampling errors. Fortunately sub-pixel guiding comes to the rescue when it comes to actual guide errors. The best I seen on a night of truly excellent atmospheric seeing in southern Sweden (should be reasonably similar to the UK) is 1.1-1.2" for 20 minute exposures using a well collimated 41c
  6. The main issue is nothing very theoretical at all. FWHM is a measure that has units of degrees, preferably in arc-seconds or similar, but most of the time it gets reported in pixels since that is what the software defaults to unless it has the proper data (pixel size and focal length used). If it doesn't offer the option to input this I would consider it to be faulty software. Since the FWHM value in pixels is proportional to the actual seeing and in the same range as proper arc-second values this looks resonable at first glance but is worthless for comparisons. When measurements using arc-se
  7. I believe that CTIOPI has the most recent data for TRAPPIST-1, here you go: http://iopscience.iop.org/article/10.1086/505706/pdf TRAPPIST-1 is referred to as 2MASS 2306-0502.
  8. https://en.wikipedia.org/wiki/Jupiter#/media/File:Jupiter_diagram.svg
  9. It is quite possible to script the processing and apply it to full sized RAW images if you need the additional information for your image processing. It might not be necessary most of the time but I tried it on some Milky way time laps I took on Tenerife and it did help bring it out additional color and contrast. I used the recipe function in Canons Digital Photo Professional to apply some pretty aggressive curves and then down scale the image but most serous programs should be able to something similar.
  10. I bought the 10 mm Samyang APC-C lens for my 600D and 7D since I wanted a faster and wider field than any of the other options provide. I only regret that I didn't buy it before the astronomy trip to Teneriffe we did where I was limited by my otherwise excellent 24-70 mm Sigma zoom. I believe that the 10 mm would have beaten the pants off both the Sigma and the slower Canon 10-22 one of my friends used, I have been very impressed with the stars the edges, even wide open.
  11. The general steps are: * Align the image twice, one time aligned on the stars and one time aligned on the comet. * Stack both images using methods that remove pixels that remove random pixls and moving objects (median, sigma clip etc.) . * Of the two images you get from this one will remove the stars (fixed comet, moving stars) and one will suppress the comet (fixed stars, moving comet). * Align an merge the images.
  12. Not quite comparable since we run long focal length scopes (2 and 3.6 meter) and we are located in Sweden (should have the same, i.e. poor, seeing as the UK though). Best long exposure 1.2-1.5", good seeing about 1.8-2", typical 2.5-3.5". We have found that to be able benefit from the good days means that everything else must perform up to spec, focus, tracking, guiding, local seeing, collimation, etc.
  13. While Canon has been silent on this subject (and removed the function on later cameras) the evidence suggests the 3x HD Crop Mode is actually a ~2.7x crop mode with one-to-one pixels taken from the center of the sensor on the 600D.
  14. Sorry I should have been clearer, I meant the Celestron statement. The text has been carefully edited so that it is mostly void of any real information like most ad copy. If that text was actionable the Clapham man would be a very busy man (disclaimer: I'm not a lawyer and if I was I would be a Swedish lawyer but I have heard about the Clapham man on QI).
  15. Similarly (I will not start to spam the forum just to be allowed to edit my posts) without any specifics the statement from Celestron basically says that unguided plus PA correction should work better than unguided. My assumption also includes that the user didn't mess anything up too much when setting up PA correction or polar alignment.
  16. I'd venture as far as saying that depending on what you call a "long exposure", your pixel size and the focal length I can't say that the statement is untrue.
  17. There is really no "best" resolution in astrophotography, only different compromises, so don't worry about too much. The perfect fit depends on the target and what you are trying to accomplish.
  18. Your signal is probably to low which result in a bad signal to noise ratio (which looks noisy). How many exposures did you take, how long where they and at what ISO?
  19. I'm well aware that Ha and Hb have different colours. My point is that they are emitted from the same spectral series (the Balmer series). This means that Hb is going to be more or less identical to Ha except Hb will bearound 3 times fainter. For photographic use with a mono camera you'd be wasting a lot of time if you'd use Hb instead of or in addition to Ha.
  20. A quality zoom lens will also have a much better manual focus ring and will work fine for astrophotography (I use a quite nice Sigma IF EX DG HSM F/2.8 24-70 mm) but you will have to pay a premium for the added flexibility. In the focal length range of around 35-70mm a prime lenses can be both cheap, fast and good. If you want a good ultra wide lens or a long focal length lens you only get to choose two out of three... Yes, but if electrical power (or cost, a dew band, controller and battery is a non-trivial cost) is hard to find a chemical hand warmer or two (available at outdoors stor
  21. If you have a H-alpha filter I'd think twice about also using the H-beta. The images will be nearly identical although the hydrogen emissions of the H-beta will be weaker and the stars might be either weaker or stronger depending on colour of the star and the narrowness of the filters). You'd save a lot of time just assigning H-alpha to two colours. Another problem is that most H-beta filters are design for visual use in mind, not imaging.
  22. With a mono camera there is no upside (except possibly if you you don't have a H-alpha filter) with a H-beta since the H-alpha is stronger. Visually the H-beta beats the alpha since our eyes are much more sensitive to that wavelength. I have been thinking that a H-beta (or possibly H-gamma) filter could be useful for unmodded DSLRs since they are well clear of the IR filter and the Bayer matrix has 50% blue pixels but I have not had the time to run the numbers.
  23. The only visible problem in that image is bad focus. The focus could be masking other issues but there is no way to tell without better focus. You put you Canon camera in Av (aperture mode or M-mode (manual mode) using the big knob that has P, Tv. Av, M etc printed on it. Then the f/number is usually set by rolling one of the scroll wheels (there might be one or more wheels) possibly pressing the Av-button depending on the mode/camera. The exact details vary somewhat between camera models and the different camera modes so you need to look in the manual. Setting a higher f/number is called s
  24. Hi Carole. When people speak of fixed lenses they mean fixed focal length not fixed focus. While fixed lenses are generally much cheaper than an zoom lens of equal quality you still need to focus it. The kit lens that you have is actually pretty OK to start with. There are three main tricks: 1. The wider the FoW the longer you can shoot before you run into to much problems with star trailing. With a fixed tripod 18 mm should get 20-30 seconds minimum, at 55 around 7-10 sec. For a equatorial tracking mount it depends on the quality of the mount and the accuracy of the polar alignment. With a
  25. I think you are probably misunderstanding what signal and noise is. Signal is the number of electrons detected in the pixels; noise is the uncertainty of this electron count. The only thing you can know about the noise (in astrophotography where the noise is Poisson distributed) is that the expected magnitude of the noise is the square root of the signal. The main signals in an astrophoto is the bias (a constant level added to avoid zero-clipping the values in the A/D-converter), the dark current signal (electron leakage) and the photon signal (photons converted to electrons). These signals al
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