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jimjam11

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About jimjam11

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  1. You can also use nina (free) which has a built in optimal exposure calculator.
  2. Another person attempting to build an all sky camera! I have already built the dew heater etc, but the bit I am stuck on is routing the usb cable into the sealed camera enclosure. My setup will consist of a typical weatherproof box containing the camera and a home made dew heater + controller. I will run a 12V cable approx 6m from my AAG weather station laptop to the camera. I can use an active usb cable for the camera connection which is tested and working without issue, but I am unsure how to get the cables into the enclosure? I think I have a few options: 1. Cut the connector off the usb extension cable and pass it through a standard cable gland before wiring it to the camera via a terminal block? 2. Buy some kind of fancy split cable gland which means I can leave the cable intact. These seem very expensive and hard to source? 3. Buy a much bigger cable gland capable of passing the intact usb connector? Not sure how I would then seal around the much smaller cable? 4. Something else? Any advice on the best approach to take? TIA,
  3. When I speak to normal people who don't have an interest in astrophotography I find they ask a number of common questions such as: Where is this object? How large is it? Are the colours real? And the most common; how much magnification is required to see it? I have therefore set about collating images into easily identifiable areas of the night sky, typically constellations. By presenting these against a widefield whole constellation image correctly rotated and scaled it is possible to provide context to the objects and hopefully help answer some of these common questions. Video seems like a a sensible way of presenting this data because it allows motion and the ability to see closer versions of the objects. So here are Ursa Major and Coma Bernices. Ursa Major is one of the most obvious constellations in the sky and it is littered with galaxies. It has taken me 18 months to amass the source images and there are many more to go...
  4. Excellent article. I dont have an sqm meter but measuring from my images from last night the sky ceased darkening at approx 1am and started getting brighter from about 02:10. A whopping 1 hour of nautical (ish) darkness.
  5. You would be expected to use this with the flattener (or reducer) which exposes the right thread. You would typically use some of the spacers to reach the correct back focus for a flat field. https://www.firstlightoptics.com/reducersflatteners/william-optics-adjustable-flattener-for-zs73.html
  6. As an experiment it would be worth using the wbpp script with your data and then trying abe/dbe again. I have always found manual preprocessing a nightmare so always use bpp/wbpp even if I run image integration manually afterwards (the main part where you want to tinker). If you get the same result it would prove your manual preprocessing steps were correct and probably indicate an issue with your calibration files? I use lightroom/ps as the last step in processing, normally adjusting levels down to get the background where i want it.
  7. I guess another approach would be to test it and measure the result? Something like: Focus on 1 filter and then take 10mins with each filter. Then focus each filter manually and repeat. You could then measure the median fwhm for each set and compare the difference? With my zs73 (f5.9) it makes little difference so I tend to manually focus with lum. With my 200pds (f4.5) it does so I focus electronically and use offsets between the filters. I will probably add another eaf to my zs73 in time to fully optimise for all filters/subs.
  8. The image looks superb by the way! Did you run through preprocessing manually or did you use BPP/WBPP?
  9. Abe (or dbe) would typically be done immediately after stacking and prior to decon, mlt etc? If edge stacking artefacts cause trouble you could crop prior to abe/dbe. Do you have the warren Keller book, it has some excellent processing workflows in it...
  10. 1156? How did you reach that value because I reckon that more closely matches where I end up with LRGB imaging! With LRGB I dont like going below 60s because the acquisition overhead starts to become troublesome (interframe delay). As a result I usually end up in the range of 1000DN above bias so very close to you. Do you adopt that DN above bias for all gains?
  11. I wouldn't want to misquote but i believe the model was based on a number of different methodologies for arriving at the optimum dn above bias. The post from 12/06/17 17:53 states: However, the "expected ADU above bias" results in the last columns are similar to those from the well established John Smith/Stan Moore formula (~10*RN*RN/gain)*16 and Jon Rista's approximation (20*RN/gain)*16. The exception seems to be that (as shown in the attached table) Jon's method tends to underestimate at low gain and overestimate at high gain, compared to the other methods. I guess its purpose is to find the minimum sub length where read noise is adequately swamped whilst preserving as much dynamic range as possible. This leads to much shorter subs than people expect. Beyond this swamping point snr gains by going longer per sub is minimal? Another good reference is the Dr Robin glover presentation on youtube:
  12. Assuming this is at offset 50 which is typically about 800DN your median background is 6384. This means your background skyfog is approx 5600DN above bias. Optimal at gain 139 (taken from the CN thread) is approx 450DN above bias. You are therefore overexposed to the tune of 5000DN, a lot. If you look at the unstretched sub you can see tons of stars, these are over-exposed and you lose colour in them. I ran the binarize PI process on your sub and converted all pixels > 0.95 (> 62000 DN) to white. These are all overexposed and will clip to white. You could easily use much shorter subs and as long as your total integration time is the same you will not get a noticeable drop in SNR. You will gain in terms of star clipping, lose less subs to clouds etc and probably see improved resolution. The downside is you end up with more subs which take longer to process! As per the CN thread an optimally exposed sub will look terrible but this doesnt matter once stacked. This is one of my unstretched subs, 60s L , gain 0 @ F4.5. Raw frame is top left, binarized is bottom right:
  13. I never use unity gain; 200 for narrowband, 0 for lum and 76 for rgb. 300s at unity gain is likely to be dramatically overexposed. I switch gain so I can use 60s subs for lrgb without massively over exposing. The tables linked (on cloudynights) are a brilliant resource. Make sure your calibration frames match exactly. If you have the newer Asi1600 it defaults to offset 50 for all gains. It can essentially be ignored unless you go fiddling!
  14. If you use something like nina (free) or sgpro ($99) the hfr calcs are based on the entire field so you don't need to worry about bright or dim stars. It also gets you best focus across your entire frame as opposed to a single star at a singe point of the frame.
  15. 1. Depends on the ota in my experience. The zwo lrgb and ha filters are pretty much parfocal but the sii and oiii are not. In an ideal world focus per filter (or even better calculate offsets) using electronic focus. 2. Not very, if you are somewhere close it should be fine. 3. I get mixed results with a b mask, i tend to use the hfr measurements and mimic an auto focus run by starting one side of focus, moving in small increments to the other side and then trying to equal the best measurement moving it back. This is easy to do on the zs73 because the focuser has the wo logo so you can use that as a reference for your movements.
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