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symmetal

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Everything posted by symmetal

  1. I've uploaded the Excel spreadsheet to my MediaFire Cloud Storage account. I've uploaded two versions. The .xlsx is for the latest versions of Excel which I used, while the .xls version should work with older versions of Excel that don't recognise the newer format. The free Open Office suite of programs should read the .xls file without problems if you don't have Microsoft Office. I don't know if it recognises the newer format. ASI1600 Sky background ADU chart (.xlsx) ASI1600 Sky background ADU chart (.xls) If you want to enter your own values for gain and offset in columns one and two, you also need to enter the Read Noise in electrons (e-) in column three, and Gain in electrons/ADU (e-/ADU) in column four as read from the ASI1600 graphs in the manual which correspond to the column one gain. The values you've entered in columns three and four will be plotted on the graphs in the spreadsheet so you can see if the values are good as the curves should still retain their overall shape. I've posted the Zwo graphs below if you've misplaced the manual. I included a graph for the offset as originally I used the Zwo gain and offset values where the offset varied with the gain and the graph shape indicated if the values you entered followed the Zwo curve. If you use a fixed offset value then the offset graph doesn't tell you anything useful. Hope Mark and Doug and anyone else finds this useful. Alan
  2. Yes, that's right. It's more convenient to use the same exposure time for RGB so choose an exposure value which is close to the 'optimum' ADU value for all three colours. Astro dark isn't a fixed darkness but is a threshold value so images taken in the middle of the astro dark period will have a darker sky background than ones taken at the beginning or end of the period so wait until an hour or so after astro dark begins before doing the tests to get an 'average' astro dark sky background level and use this exposure setting for all your images. These are really only useful for LRGB imaging as doing narrowband the required exposures to swamp the read noise would probably be longer than 30mins unless you're in a badly light polluted site. Take a sample narrowband image at your usual exposure duration and see how the sky background compares to the 'optimum' ADU value. If it does exceed it then you should use a shorter duration but at most sites you will probably be well below it. A very useful tool for examining image statistics is Fits Liberator. This displays the mean and median values among others and gives a useful histogram of the image. Taking a very short dark frame (effectively a bias frame) the histogram will indicate whether the image is black clipped and is useful to find out your optimum offset value to avoid clipping at the gain used. The higher the gain used the higher the offset needed but it's simpler to find the offset needed at gain 300 (or the highest gain you'll use) and use this for all gain settings. I found offset 56 just avoided clipping at gain 300. If I was only going to use unity gain I could use a lower offset and avoid clipping but the loss in dynamic range of using a higher offset than needed is very small. Yes, I can upload the spreadsheet file so you can fill in your own gain/offset values if you wish. I'll do that later today. I can also put it in a new thread if there is enough interest. Alan
  3. Hi Doug, Here's a CN post describing the read noise swamping by sky background calculations. Look for the Jon Rista entries. I made an Excel chart calculating these values for various gain/offset values for the ASI1600. Initially I used the varying offset values recommended by Zwo but changed to a fixed offset for all gain settings (for simplicity) which avoided black clipping as the Zwo offsets were too low. The Read Noise and Gain graphs are plotted from the column entries and mimic the Zwo graphs from the ASI1600 manual. During astro dark, take an image of a star field which doesn't contain large areas of bright nebulosity. The image sky background ADU can be read as the median value of the image statistics panel which your capture program should display. The mean value should be pretty much the same value as the median. There are different opinions as to which calculation method (I've shown four) should be used for the 'swamping the read noise ADU value' and I use 10 x RN^2 which is the last column. The calculation for the 1386 ADU value in box J12 is shown in the equation at the top. If you use offset 50 just subtract 96 from these ADU values, ie. (56-50) * 16 Adjust your exposure duration until the sky background ADU is around the value in the table and that is the maximum exposure you need to use for that filter. The RG and B exposures should be fairly similar while the L should be about 1/3 that value. During astro dark, use these same exposures for your targets and you should be close to optimum. If you move to darker or lighter site you need to re-evaluate these exposure times. As currently there is no astro dark in the UK, exposures don't need to be as long to reach these ADU values. If you're in a light polluted site the exposure duration values will be a lot lower than than at a dark site. Hope this helps Doug and hasn't left you more confused. Alan
  4. Hopefully that's just the case. The stars at the bottom of the image are slightly larger than the stars on the rest of the image as they are a little out of focus. It's only very slight so not worth worrying about it too much. This is because the sensor isn't perfectly perpendicular to the telescope's optical axis. Working out what part of the optical train is the cause of the tilt can be time consuming, and you can waste a lot of imaging time trying to get it perfect. Alan
  5. Here's my WhiteCat edge crops with an APS-C sensor. It doesn't look much different and no worse than it did with the 4/3 ASI1600 above. The bottom left is the worst. I'm happy to live with it though. Click for full size Alan
  6. Hi JimmyDigital, That image looks very good and no obvious coma visible. It looks like the bottom of the image is a bit out of focus compared to the top so there is a bit of sensor tilt in the imaging train but the RedCat itself looks a good one. It's a 4/3 size sensor so there may be some coma with a larger sensor but you should be happy with what you have. Here's the CCD Inspector result showing the bottom just a little out of focus. Alan
  7. To avoid having a large collection of darks for different gains and exposures I just use unity gain all the time (as suggested by vlaiv ) and an offset of 56 to avoid black clipping. For exposure length I use a similar method to eshy76 where you expose until the ADU level of the sky background in your image is 10 times the square of the read noise. This makes the read noise insignificant. CN forums have the maths to calculate this ADU. At unity gain offset 56 this works out at 1386 ADU (16 bit). Very close to eshy76's value. With my bortle 3 skies this works out at around 60s for L and 180s for RGB. Currently with no astro dark these exposure values are around half that. With narrowband I won't reach this swamping background ADU unless I expose for an hour or more so I settle for 360-480s normally and accept that the read noise will have some effect. Exposing for longer than this swamping ADU value has no real benefits, and just causes more clipping of stars and a reduction in dynamic range, as the histogram just gets shifted to the right. Alan
  8. As you say it never seems to be mentioned, but in the diagram David posted at the top, the piece of flat glass will move the point of focus back by a set distance irrespective of the actual location of the glass as the incident angle of the light cone reaching the glass doesn't change, just the diameter of the cone. That's my interpretation but am willing to be proved wrong. 🤔 Alan
  9. Don't forget to add 1/3 the thickness of the sensor glass too. For the ASI1600 it's 2mm thick the same as the ZWO filters. Alan
  10. Hold the 'Shift' key down when you click the guide icon. Alan
  11. You do need to add the 2mm to your spacing making 12mm extra needed. The sensor glass as you say has an effect as well as the filters, though the filter thickness is the only one commonly mentioned as needing to be taken into account, with the sensor glass being overlooked.. Alan
  12. Got my WhiteCat back after Es' has had it on his workbench. It's certainly better than it was, though there is still a hint of coma in three of the corners with the bottom left being the worst. I've decided to keep it and see how it looks with real stacked images. Here's crops of the edges. Click for full resolution. Alan
  13. 0.2 for 5 secs. At low altitude I usually use 0.3 at 5 secs or it can take too long. I found at shorter times there is a good chance of it starting to image before it's fully recovered from a Dec dither. Alan
  14. Swoop1, I forgot to say the reason your initial MP4 to AVI conversion didn't work is because AVI is just a 'container' format for video which can hold a multitude of compression codecs including MP4, MPEG-2 and MJPEG. Autostakkert requires the AVI to contain an uncompressed RGB video file, so if your conversion program allowed you to select what format you wanted the AVI file to contain you would need to select 'Full Frame RGB uncompressed'. Many simple conversion programs don't give you this option, and yours may have just left it as an MP4 compressed format file, inside an AVI container file. For astro use all the AVI video files generally need to be uncompressed RGB (or Luminance if you have a mono camera). AVI can only work with 8-bit video files which is why the SER format is often used as that can work with 16-bit video files too (uncompressed as well). Alan
  15. Download PIPP (Planetary Imaging PreProcessor) This will import MP4 files, and others and output an AVI or SER file which Autostakkert can read. Alan
  16. Thanks Julian. I wasn't aware of that problem as I've only used them in full step mode on my focusers. Here's a useful article describing the problem when microstepping and using the diodes to 'cure' it. I only used the DRV8825 as they were described as an 'upgrade' to the A4988. Alan
  17. You set the microstep stepping mode by setting the relevant pins on the driver module high or low. For the commonly used DRV8825 stepper driver module there are three mode pins M0, M1 and M2 which set the microstep mode according to the table. Just connect the mode pins you want to use to a corresponding digital pin on the arduino and set those pins to be outputs. Writing high or low to those arduino digital pins will then change the stepping mode of the motor. If you don't want to have all 8 microstep modes you can just connect the unused pins to 5V or Gnd as necessary. For example if you only want Full, half, quarter and eighth, connect M0 and M1 to two arduino digital pins and connect M2 to Gnd. Each pulse to the step pin will then move the motor 1 microstep as set by the mode pins. If you are microstepping you normally need to have the stepper motor powered all the time (Enable pin kept low) so it will get warm. If you're using full steps you can often just power the motor (using the Enable pin) only when you want to step it, as the motor naturally wants to stay in a full step position (its detent torque) when un-powered. If this torque isn't enough to hold the mount still, you need to keep the stepper motors powered so they generate holding torque which is higher. When microstepping the motor needs to be held between full step positions, so power must be applied all the time to keep it in that position. If power is removed when microstepping the motor will jump to the nearest full step position. Different driver modules may only have 2 pins to set the stepping mode as they may have only 4 stepping modes and not 8 like the one above. Alan
  18. On Friday (longest daylight) with clear skies though no astro dark and half moon up, I tried the Eagle Nebula in Ha with my dual imaging rig. It was low in the sky so didn't expect great results and the guiding wasn't smooth, but star shapes were pretty good nevertheless. The SGP auto-focus performed as it should, with good v graphs for both scopes, and while the Atik had a best FWHM of 0.8, the Zwo best was 2.1. The Zwo images were noticeably out of focus and rerunning auto-focus produced the same result. While the Atik was imaging I tried some luminance test images on the Zwo with manually altering the focus and shifting it by 30 steps from the SGP 'optimum' the stars were much sharper although SGP reported a slightly worse FWHM on the image. Imaging other objects at higher altitudes the Atik manages about 0.7 FWHM while the Zwo manages about 1.0. With the Atik imaging at 1.52"/pixel and the Zwo at 2.18"/pixel I'd have thought the low altitude seeing would have had more affect on the Atik. At correct focus on the Zwo it may well have been, but I didn't have time to do any more Ha images on the Zwo as it was getting light at 3am. I know SGP autofocus fails on globular clusters but was surprised that M16 upset it too, though only it seems on the wide field Zwo image, and not the narrower view Atik. The whole fields were flat with no issues in that respect so it wasn't dodgy edge stars throwing the auto-focus off. Here's a centre crop of a single sub from each camera at the 'optimum' focus as determined by SGP and given a quick stretch to make them similar. It looks like I have to keep a more watchful eye on the auto-focus FWHM results and pan off to nearby 'cleaner' star fields for auto-focusing if they look suspicious. Alan
  19. Hi Nubian, For an APS-C sensor that looks pretty good. There is slight coma in the bottom corners but unless you're really fussy not enough to worry about. The CCDI plot makes it look worse than it is in reality and is an indication of where the problems are but the actual figures displayed don't mean much. It found 2918 stars which is good for the check. Hope you're happy. Alan
  20. Peter, The new unit sounds promising. Hope you get it to work without any problems. Alan
  21. Peter, Hope you manage to resolve it OK. The GL-MT300Nv2 looks like quite a useful little box and hopefully will give you more reliable WiFi. Good luck. See you in mid July. Alan
  22. That's an exceptional image with great detail. Alan
  23. Glad that fixed it. Does it need to be as high as that. What does it measure on the Eagle, as the Eagle manual suggests 12.8V at the input to the Eagle as the camera and any 12V equipment will get this same voltage. Alan
  24. Capturing an image of the Imperial Death Star lurking nearby is more impressive. Alan
  25. Hi R3tr0, Your replacement is certainly an improvement. There is still slight coma in the corners but whether that would bother you in real images where stacking would likely make it less noticeable only you can say. Alan
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