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roundycat

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Everything posted by roundycat

  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 th
  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 concl
  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
  16. Hi Rob, now that you mention the OSC camera the 100% thing makes a bit more sense. I am not sure how MaxIm does it and I'm also not sure how you can set those values using PS. Maybe by using layer opacity, colourising the layers and screening them. Is there another way to re-set colour balance in PS without 'bending' the curve? Dennis
  17. I have been doing it like this for years and often treat each channel separately although I always process the whole picture at once rather than in channels. Sometimes this can cause a dark halo which can be lifted by raising the LH end of the Curve to give what looks like a most un-natural shape but one which works. I still cannot make up my mind whether it is better to select in Quick Mask with a softish brush or use a hard brush and then feather normally. Either way, the size of the selection and the degree of feathering is critical. Dennis
  18. An interesting setup. You could probably use a Baader astro solar film as a neutral density filter, that would leave you at full aperture in case there are any odd effects from shooting at f200. Not sure I understand the bit about 100%. Does this mean full exposure as in 65,000 ADU or something else. Sounds like a good idea for all those DSLR users that pratt about with custom white balance when the proper white is there all the time. Do you think you would get the same sort of result under light cloud? Dennis
  19. I think you are trying to do the impossible. As you said, the full size version looks ok but when you reduce it the whole thing ends up looking dodgy. The reason is that you are effectively trying to shrink stars below the one pixel level. The software is interpolating as best it can but the task is simply not possible. There is a limit to the amount of reduction you can apply which in turn imposes a limit on the size of a workable mosaic. If you don't print it the size of your living room wall it will never work. Dennis
  20. Narrowband filters only really add detail when that detail is there in the first place. Although it might sound obvious if you spend ages on Ha or O3 and there is only a general splurge of colour as in many of the bigger nebula (and this one) it will not make much difference. If you do RGB on the Veil for instance and then add any of the NB colours there is a big difference to be had. Sometimes HaGB can be a benefit although you generally have to work on the cyan coloured stars. Dennis
  21. John, a thousand apologies; yesterday I posted a re-work of your M27 in the wrong thread. This kind of thing I do all the time although that is no excuse. It is now in the right place (I hope!!) and I have the notes I made to accompany the History palette if that is insufficient for your needs. If you need any clarification please ask. Dennis
  22. The message I posted here yesterday was attached to the wrong thread. It is now in the correct thread viz; http://stargazerslounge.com/imaging-deep-sky/150860-m27-7-hours-later.html My profound apologies to all. Dennis
  23. just had a look at the original. Or not. Do you have one that has not been stretched at all. The download I have here is half finished. Dennis
  24. I authored the Astrophotography link provided above. A couple of points. If you take flats and calibrate them, in theory you need to subtract darks that are the same exposure as the flats. These are called Flat Darks by the whole world, only the author of DSS calls them Dark Flats. An easier way to do this as the thermal contribution from a short exposure is not much is to just subtract Bias and forget about Flat Darks. As to the overall exposure for a flat this tends to tax people quite a lot. You hear about many different methods of assessing the 'workability' of your flats but in truth the
  25. Forget depth of field. The thing that should concern you is depth of focus, this is the amount by which you can move the film/chip without losing focus. It is very small, think microns. Dennis
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