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About Seelive

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  1. As I understand it, the Sigma part is effectively how 'strong' the effect is, the Kappa is how many times it iterates. The smaller the Sigma and the larger the Kappa the greater the effect it has on the image. If you're not familar with the term sigma, search for Gaussian distribution on the net to see what it is (but probably avoid the maths!)
  2. Best of luck. To start with, try to get as many 'long' exposures as you can, the short exposures take no time at all. They don't need to be taken all on the same night and you can stack different combinations to get the best the final result. Just remember to set the DSS threshold level to a value so that it detects sufficient stars (>12?) on the shortest exposures so that they are included in the stack (you might get hundreds on the longest exposure but just a few on the shortest). Perhaps one other tip, if some of your long individual exposures have not got perfectly 'round' star images, try Kappa-Sigma stacking them with sigma set to around 2. As long as the star 'un-roundness' (I'm sure that's not a word) is not the same in every image (i.e. star trailing), it can help circularise them. Once I initially rejected several dozens of images taken during high winds because the stars were slightly elongated. Looking closely, they were generally 'elongated' in different directions and it turned out that stacking every image gave a better result (less noise but still circular stars) than just selecting the 'good' images.
  3. Assuming that you use DSS for stacking your images, put the different exposure lights and associated darks in separate groups, then just select the Entropy Weighted Average (High Dynamic Range) option in the stacking tab. This is a crop of M42 stacked using the Average option on the 20 x 180s exposures. The core and the brighter stars are all saturated. This is stacked using the Entropy Weighted Average option with the 20 x 180s exposures plus 20 exposure each of, 60s, 20s and 7s. The core and brighter stars are no longer saturated and the trapezium stars are now visible. Of course the nebulosity of M42 is significantly brighter than that of the Pleiades so the method may not be as effective on the Pleiades (I certainly haven't tried it). The 7s exposure was chosen so that the trapezium stars would just saturate the camera sensor and the 180s exposure was set to keep the level of sky background caused by my local light pollution at a reasonably level. The mid exposures were therefore chosen with a x3 factor.
  4. You could try using DSS Entropy Weighted Average (High Dynamic Range) stacking. I've used it successfully to image M42 so that I got the full faint detail of the nebula but was still able to see the Trapezium stars. I used 20 exposures each of 180 sec, 60 sec, 20 sec and 7 sec. However, for the Pleiades, I just stacked 20 x 180 sec to get the nebulosity (Canon 200D, 400mm telephoto at F5.6, ISO1600, EQM-35 mount). You can see the resulting image here https://britastro.org/sites/default/files/styles/xl_image/public/member_images/M45 400mm F5.6 ISO1600 20x180s HR.jpg?itok=mIFNHrCA
  5. Hi dd999, sorry, it didn't register that both were your images. I agree, I would also be happy with that image of Saturn. But the same argument applies, 1.3 sec is too long at that focal length on an undriven mount, and at F10, you can't expect to see much faint detail with such a short exposure.
  6. Given that Saturn is at a declination of about -20 degrees, then during your 1.3 sec exposure Saturn will have moved about 18 arcsec. Given that the SW130P has a focal length of 650mm and you are using a x2 barlow, then the movement of Saturn at the camera sensor will be 0.115mm. Assuming that the Canon 600D has a pixel size of 0.0043mm, then Saturn will appear to have trailed by about 27 pixels. Given that the rings major axis diameter is currently about 42 arcsec, then the rings will only have with a width of about 62 pixels. A driven equatorial mount will certainly help, but don't expect too much from a single exposure, and you will probably need to shorten the exposures rather than lengthen then.
  7. Yes, just using 1 dark frame will be worse than using none. You really need to stack several dark frames (I always try for at least 20 to 30) for them not to effect the noise in the final image. The more lights you stack, the lower the final image noise will be (in theory reduced by the square root of the number of lights) so just keep adding to them (up to a point anyway, the law of diminishing returns comes into play!). Is LENR the in-camera noise reduction? If so, you could test the results with and without using it but I think the general census of opinion is to turn it off, it can give more problems than it solves, and just use darks. The star images certainly look sharp but I think I would be tempted to open the lens up by a least a stop or two. With a F1.4 lens, I would try F2.8, you will get considerably much more detail in the images for the same exposure time at the expense of some distortion in the corners, but you could always crop the image.
  8. ... Bear in mind I just use a 'regular' tripod Well that will certainly provide the necessary movement between the images. Leaving a random interval between images and occasionally re-centring the target will give you the same effect.
  9. The idea of dithering is to ensure that when the stars are aligned during stacking they are located at different camera pixels in each image. Cropping the images edges will not achieve that since stacking will just realign all the stars and hence the camera pixels again. If your tracking is slightly off so that each of the images are slightly offset from each other prior to stacking (the usual case), then that effectively has the same effect as dithering, but since the offset between images is not random, it will be slightly less effective.
  10. Providing you have sufficient images in each nights stack for the sigma rejection to do its job, then the resulting set of stacks can just be average stacked. I have found that resulting noise of a sigma stacked image decreases as expected as the number of individual images increases BUT only up to a point, after that, the final image noise level flattens out or even increases. I tend to break a large number of images (even those taken in the same session) into separate stacks of no more than 20 to 30 images ( I try to keep each stack with about the same number of individual images), sigma stack those and then average stack the separate sigma stacks. That way I get a resulting image with a noise level the same as if I had just average stacked all the images in one go but without the satellite trails, hot pixels etc.
  11. Just a diode in the positive supply will provide reverse supply protection.
  12. So here's my stack of your lights + calibration frames (no processing, the TIF straight out of DSS). This is with the stacking method set to Auto, quite an abstract work of art!: And this is with the stacking set to Bilinear, still not good enough but a lot better. As previously pointed out by carastro, the lights stack perfectly without the calibration files, but I've not have the chance to try each possible combination. That's something I've also seen in the past but never got to the bottom of it - I'll leave that to you!
  13. Definitely DC to DC converters are the way to go at those power levels. Based upon your circuit diagram, your total output power requirement is 70 Watts with a maximum current draw of 7.5 Amps. The 24 Volt supply would therefore need to be rated for at least 180 Watts, and the linear regulators would need to capable of dissipating up to 110W. Even if the DC to DC converters only had an efficiency of 80%, then the 24V supply rating would be reduced to a minimum of 88 Watts, and the total power dissipation would only be 17.5 watts. Depending upon whether you go for off-the-shelf DC to DC convertors or decide to build your own, you may need to use a linear regulator to generate the 7.4 volt supply, but it you use a LDO type from say a 9 Volt output DC to DC converter, then any additional power dissipation will be minimal.
  14. I've had similar problems in the past, especially with Milky Way images. DSS has successfully stacked some of my images with the threshold set at 2% (more than 40000 stars detected!) but on other images, even with the threshold set at a much higher value, I've still ended up with 'swirls' (at worst, or just elongated stars in one particular area at best) in the stacked images. I've found that changing the alignment mode from 'Auto' to Bisquared or Bilinear cured the problem. If you look in the stackinfo.txt file, you will see the stacking coefficients used for each image. If you see any numbers (within the brackets next to the alignment method used for each image) much greater than 1 then the stacking is likely to have had a problem. Unfortunately, each number is to 20 decimal places and there are quite a few of them for each file!)
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