Jump to content

Narrowband

ollypenrice

Members
  • Posts

    37,848
  • Joined

  • Last visited

  • Days Won

    302

Everything posted by ollypenrice

  1. OK, thanks for the encouragement! I tried again to exploit the TEC data in the inner galaxy and came up with the image below. To my surprise it was easy to upsample the RASA image to the scale needed for the TEC resolution to show. Full size is here: https://ollypenrice.smugmug.com/Other/Galaxies/i-psSP6gB/A Olly
  2. This is just what tried to do and have done many times before, but I haven't yet managed to make it work this time. In fact, scaled to fit the RASA image, there is not all that much more resolution in the TEC than the RASA. If I were to rescale in the other direction, making the RASA image larger, I'd be lifting the noise in the RASA and it's already on the ragged edge of the possible stretch. It doesn't help that the TEC field of view stops short of the upper spiral arm. If I can come up with any new ways of making the composite I'll give them a try. The obvious solution would be a RASA 14.... If the people would like to give Olly one, he'd be most willing to accept it! 👌 Olly Edit: there is another problem, too. The TEC's resolution requires dynamic range, ie contrasts within the central spiral arms. In the ultra-deep RASA image a lot of the lower dynamic range has been used by the faint outer streams so the dark stuff in the central spiral is brighter and can't be as contrasty. I'd be in danger of having the tidal streams brighter than the dark regions between the bright spiral and, in reality, they are not.
  3. You should be able to get far more of the long tidal tail to show, though it will run out of the frame on this crop, I think. It will be there in the data. If you have Photoshop, just go to Image-Adjustments-Equalize and it should leap out. You can't just use that as a processing technique but it will show what you have in the data. Olly
  4. You wouldn't go far wrong with this, on the astrophotography side. https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html Like most things in life, DSLR photography is best approached by thinking things through from the basics. There are really not so many of those and this is, for me, the big one: Understanding F stops and light cones. https://www.dpreview.com/forums/post/63155522 When a lens is wide open it lets in more light and therefore shortens exposure time, freezing fast action, but the steep light cone has a shallow depth of field meaning only selected parts of the image can be in focus. This can be good or bad, depending on the photographer's intentions. A stopped down lens has a greater depth of field but lets in less light and, therefore, needs longer exposure - which can introduce motion blur. If you were to go out with a basic DSLR and experiment with this single set of related parameters, and really get the feel for them and how they play out, you'd be self-educating very effectively, I think, and would have a grounding for further learning. For land and sky photography, check out the free Sequator software. https://www.startools.org/links--tutorials/free-image-stacking-solutions/sequator On image processing and U-tube tutorials, the instant you hear the presenter say, 'I just play with the sliders till I like what I see,' turn them off and never go back to them! Most astrophotographers are autodidacts and the best ones are the best because they seek to understand before they act. Olly
  5. Just for info, an all-new RASA 8 image has gone much deeper than this. Olly
  6. A deep dive with Paul Kummer (capture and pre-processing.) This had 9 hours in the RASA 8, equivalent to about 40 hours in a fast refractor of comparable focal length. After 3 hours we were going well but 9 hours brought out more structure and, of particular interest, the uppermost spiral arm winding anticlockwise in this orientation. This arm is a new one to me and was an exciting find in the processing. Edit: please scroll down for a version using TEC140 data to enhance the core. This is a close crop and is presented at one-to-one here: https://ollypenrice.smugmug.com/Other/Galaxies/i-sgC3bGn/A Olly
  7. The spring is a lean time for short focal lengths but mosaics in the Coma-Virgo cluster can be fun. Sooo many galaxies! Once the southern Milky Way starts to come up in early summer you can't go wrong. We're at Lat 44 and you'll be south of that but, even here, we get four hours of darkness in June. You can work through the year. I'd look at the Eagle and Swan, Sagittarius triplet, The Great Sagittarius Star Cloud, Rho Ophiuchus... Olly
  8. I denoise in a Photoshop top layer with the original underneath. This lets me erase, wholly or partially, any areas adversely affected by the NR. Often it's only needed on the faint stuff so it's easy to select and erase the bright stuff or just erase it by eye. I sharpen in the same way, though I sharpen the bottom layer and selectively erase the unsharpened top layer. Olly
  9. My small object imaging was initially done with an ODK 14 (2.6M FL) and then with a TEC 140 (1M FL.) Image scales were about 0.6"PP for the ODK and 0.9"PP for the TEC. I'm pretty satisfied that both were, in truth, oversampled, the ODK massively so. Alas, the ODK's camera would not bin satisfactorily so we were stuck with the oversampling. On the whole, I preferred the TEC. https://www.astrobin.com/335042/?nc=&nce= https://www.astrobin.com/full/tak87a/0/ I would say this: don't expect any kind of radical transformation in your high res imaging over what you can do with the Esprit 100 and a modern, small pixel CMOS camera. There will be more detail to come, but it may be a lot less than you think and your guide RMS will need to be no more than half of your image scale in arcsecs per pixel. Presumably you already know your guide RMS or can easily find out what it is. Olly
  10. Very stylish! They instantly reminded me of the beautiful Snow Hill Lane Bridge over the motorway, near Lancaster, UK. I have 10x25 by Leica and find them super-useful - but I'd rather have 8x, for sure. Light binoculars can be quite jittery, lacking much anvil effect. Olly
  11. A small amount of matt black paint fully covering the scratch and of a soft, rounded shape, will entirely eliminate it as a cause. No, the guide camera might be following the star perfectly but the imaging scope (or just its mirror) might be moving relative to the guidescope. An off axis guider removes this possibility by guiding on the imaging light cone itself. So called 'Mirror flop' has essentially the same consequences as flexure. However, I'd put money on tilt, in your case. (Not a lot of money but a bit... ) From what I can see, the elongations all go the same way, meaning they are parallel with each other. Optical defects rarely produce this effect but tilt does. Since you see the same thing in two cameras, it is unlikely to be a tilted chip. (These are not uncommon and some cameras have chip tilt adjustment built in.) I would look for sag or slack in the focuser. Are all your attachments screw-fit rather than push fit? Screw fit is best. Are you placing your camera in this orientation, parallel with the counterweight bar? It's the best. Tilt can spring up suddenly because some mechanical component becomes loose or a bearing breaks. Olly
  12. I would rather say that OIII is faint, rather than noisy. Russel Croman's Noise Xterminator is an order of magnitude better on astrophotos than any other NR routine I've tried. Because our RASA 8 data invites extreme stretching, I do often lift it well above the noise floor but StarXt sorts it out in an invisible or, in extreme cases, almost invisible manner. Here's a close crop pushed beyond its limit. Before Noise Xt... After noise Xt... Had I wanted to erase the brighter parts of the noise reduced image, feeling that the NR had damaged them, this would have been a ten second operation in Photoshop Layers but, really, are they damaged? Here I had the 'Preserve details' option in StarXt set to minimum. Alternatively, the noise reduced image could now be further sharpened. Olly
  13. Ouch, and if you want to do this collision thing properly (!!!) do it with a RASA... Phew. Olly
  14. I have three automated sheds based here and have developed some Golden Rules, the first of which is to accept that, if a thing can go wrong, it will. For this reason we have a 'No Possible Collision' rule. No telescope can ever stop in a position in which the roof can collide with it. (A much more lavish remote hosting provider a few miles away has exactly the same rule and he is orders of magnitude ahead of me in IT savvy.) A design using 'rolling roof and upper sides' makes this rule easier to comply with. Another simple thing is to make as much of the gear inside as showerproof as possible. Despite the best efforts of the IT guys who are responsible for the sheds here, unwanted openings have happened several times. Simple shower protection of fixed items can save a lot of money. Good UPS backup is essential but not so easy to assure because office UPS machines don't like the temperature extremes of observatories and tend to have a shortish life. You probably won't have our upper temp extremes, though. Olly
  15. It would be a shame to see a thread about books turn into a thread about screens! Olly
  16. We're running a RASA 8 quite happily on an NEQ6. This will weigh about the same as other 8 inch catadioptric systems. I've also imaged with a TEC 140 on this mount. I don't think a 6 or 8 inch SCT or RC will overload it. However, that's not the problem. The problem in imaging at high resolution is guiding accuracy. Have a look at your guide RMS in arcseconds while using your refractor. Fifeskies, above, gets 0.5 arcsecs 'on a good night.' This is a good value for an EQ6 and represents the best you are likely to achieve, but not all examples of the mount manage this. Anyway, you probably know your RMS or can easily find it. Multiply it by two and this gives you a decent estimate of the best resolution in arcsecnds per pixel that your mount will support. If your RMS is 0.9" there is no point in building a system which is working at 1.0"PP. If your RMS is 0.5" then, yes, that would work. Your local seeing is likely to impose ts own limit, as well. Where are you based? How stable is your seeing? Olly
  17. The first guideline is simply 'Don't.' Even quite a significant amount of dust has no discernible effect whatever. When, eventually, it becomes necessary you can follow the FLO guidelines above. My one caveat would be to suggest a first use of cotton wool by dabbing once and discarding. I wouldn't use any wiping action till the mirror was already very clean and I would always wipe both gently and in curved strokes since straight scratches (god forbid) will show at the eyepiece when curved ones won't. Remove rings etc before starting, or use thin rubber gloves. The website I normally recommend is no longer active so I took a quick look at the first few U-tubers who popped up in Google. They were not at all good. Stick with the FLO advice. Olly
  18. As long as the same defects appear in the lights, these flats will fix them. There is really no way of knowing till you try them. If your flats were perfect, ie totally flat, you wouldn't need them. However, Adam's point is correct. Olly
  19. If they work, they're good. If they don't, they're bad. When you take an astrophoto and apply them, do you see the defects seen in the first two flats. (ie slight vignetting, severe dark dust bunnies on the left, smaller ones near the centre and dark spots most notably near the centre?) The small dark spots may not disappear because the source must be close to the sensor and little signal may be getting past them. What are we looking at in the third image? I don't know this software. Olly
  20. I don't do background levels by eye, I always use the Ps Colour Sampler (in the Eyedropper tools) to measure it. I feel 23 per channel is ideal but sometimes have to settle for less. Imaging with the RASA complicates this because there is far less background sky than with slower systems. The RASA reveals faint nebulosity just above the background and also dust-darkened regions which lie just below the broader background. The deeper you go, the more you will encounter this. Olly
  21. Your image doesn't look obviously clipped, to my eye. Sometimes it can happen at the conversion to JPEG. Maybe have a look at your last 16 or 32 bit image prior to JPEG conversion for the web? Olly Edit: I have tested, several times, a screen grab against its original JPEG to be sure that the screen grab itself doesn't introduce any clipping and I have never found that it did. I think the screen grab does represent the original JPEG, therefore.
  22. Certainly yes. The thing about the faint data is that, when its gone, it's gone. Once you get your eye in, you can see when an image is badly clipped. The sky is jet black and even, because the noise-brightened pixels and any faint genuine signal have been clipped out. For a proper grasp of the black point, though, you need to keep looking at the histo in levels. It is actually easier to remove LP gradients from an unclipped image because the software has a more genuine picture of where it is. Gradient removal should be the second operation on the stack, the first being the edge-cropping of any border artifacts. If you don't crop these out they will confuse the gradient tools and give a messy histogram which is hard to interpret. Olly
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.