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roundycat

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About roundycat

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  • Birthday 22/08/47

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    http://www.dens-astropics.org.uk/

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  1. I would have another go at this one. It seems your exposure is adequate but you have only used two channels? Use a mix of Ha/O3 to make a synthetic blue (or green) channel. Try stretching more gently using Curves. All the tools in PS can be used with great sensitivity. Sorry about your other thread on flats being closed down by the police. There is no need for this behaviour, if you want, contact me privately as dozens of others do. Dennis
  2. I have never found it necessary to use two exposures on a galaxy, or cluster come to that. M42 is the real exception because of its brightness range. The real secret is to get to grips with contrast stretching so you can do it without shifting the white point. Dennis
  3. The simple answer to your question is no. Read what Olly said above. Regardless of the filters used (bandpass, colour, parfocality, make, price) they still pick up dirt and your camera chip will still exhibit fixed pattern noise. If you want good pictures there is no substitute for exposure or good flats. You might wonder why, when bad technical advice is given it is not jumped on by the moderators. Dennis
  4. Do a test exposure. Look for the longest time without star bloat or saturation. Dennis
  5. here is a quick guide as to what bit of 7000 you have, rotated to North up. Dennis
  6. Don't know if this is any use with your mount but it works like a charm with my AP. I also seem to remember doing this with my G11 when I used to set up each night. Make sure your handset is correctly set up in respect of Lat/Long and time. First, I never Park the mount in the accepted sense. I simply switch off, slacken the clutches and then lower the scope so I can shut the roof. I then put the scope in a 'comfortable' position and lock up. So, first thing is to open the roof and I have to lower the scope to do that. Polar alignment is not lost as the mount is on a pier. Second job; point the scope at a known star, ideally near my centre of interest for that night. Set focus mode on the camera and centre the star (or use an eyepiece). Tell the handset what star the scope is pointing at, ie; Synchronise the scope to the sky. That's it. If I move to a star a long way from the first star the mount might lose synch slightly. I don't care as a re-cal, once centred on the new star, takes about four seconds. I have never fully understood the need for multi star alignment as your mount handset knows how many ticks of the encoder it takes to go from A to B. Therefore your alignment should be accurate no matter how many stars you use. Just use one star, close to your object of choice. Synchronise on it. GoTo your object of choice. Re-Cal (not really necessary) Take pictures. Dennis
  7. I use MaxIm and set x2 binning on my guide camera pretty well all the time. Centroiding is not a problem and binning helps to keep the rapid fire corrections under control without going to a longer exposure. My guiding RMS is normally well under 0.1. Dennis
  8. Can't answer that. I believe the relevant SBIG s/w is CCD Ops which I never use being a MaxIm man. Setting any order you want in MaxIm is as easy as falling off a log and then you can change it again in the auto exposure sequence. Dennis
  9. Many short subs will never equal one long one. In the first place read noise will become a real problem with lots of short subs (find out what the read noise of your camera is) and there is the added problem of short exposures, by definition, never being deep enough to 'see' the low level detail you are doubtless after. Lots of exposures (at least eight) help no end if you can stack using a sigma reject algorithm. Nigh on all of the bother from sat and con trails, intermittent dodgy guiding, a lot of the hot pixels and so on can be automatically rejected leaving you with the inescapable conclusion that throwing subs away is daft. One of the tests I did some while back was to take sets of different exposure length. These were combined in the normal way (MaxIm, manual two star alignment, SD Mask) and the resultant masters were studied carefully. Although the masters were arranged to have the same total exposure the one with the longest subs was clearly superior to the others. Almost certainly down to read noise. And that using an ST10 with double co-related sampling. Dennis
  10. As an aside, I would dig into the Windows Display settings and choose a much darker grey for your application background. No point in being blinded by it. Dennnis
  11. Tom, your image was a bit on the dim side inasmuch as none of the stars had reached level 255 or peak white. You don't always want that but you also don't want them stuck at 195 or whatever as it just looks dim. Always maximise your dynamic range but preferably without saturating everything in sight. So, Curves to brighten, High Pass filter under a star mask to accentuate the galaxy detail and Neat Image to reduce the noise present because of the shortness of the exposure. A final touch of Curves to smarten up the contrast/brightness. None of this works very well on a jpeg. Dennis
  12. SBIG filter wheels are usually marked but the order is unimportant. You just need to know the wheel and its s/w are singing from the same hymn sheet. Dennis
  13. your M51 will clean up quite a bit and the posted version is miniature. There must be plenty of scope for getting the original to look a bit better. I would go for more time spent on polar aligning. Although you cannot align on the pole star you can go through the motions in daylight. Then use the longest exposure you can trust and lots of them. Make sure you use good alignment software. Dennis
  14. Another thought just ocurred to me; why not use a Macbeth Colour Checker. OK, they cost the earth but you can get good figures for all colours. I scanned mine years ago, back in the days of film and we were all getting used to Photoshop 4. It comes with the correct RGB values for each swatch written on the back. Or somewhere. Dennis
  15. Rob, that much I understand. You can vary the output levels using Curves, just move the ends up or down, it does the same thing as Levels. The thing is, with Curves, you can see what it is doing to the graph. If you drop the output the contrast goes down as the output is dropped pro rata from 0 to 255. Are the two things really the same, ie, MaxIm's colour ratio and PS's Levels? Dennis