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narrowbandpaul

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Everything posted by narrowbandpaul

  1. You should be able to grab an image of say the moon and Jupiter with a phone with just a bit of perseverance. As for the forecast up here, it has been dreadful for weeks. Shame we are not cloud gazers!
  2. Probably not the news you were wanting, but it's best to have good advice rather than bad. If you really want to image, then perhaps go along to your local Astro club and maybe see how the imagers take their images. Perhaps you can learn on an apprentice type basis, absorbing practical knowledge from those in the know. Maybe you will get a flavour of what you want to image...planets or Deep sky. With your new knowledge you will know what works and what you need. By this time you may have saved money to get a setup that will work for you. Deep sky on a very tight budget is very tricky. Maybe your local Astro club has so,e kit you can borrow. Worth a shot Paul
  3. Hi Tim, I think the one on the right looks better, but that's very subjective. The only real way would be to try to estimate the SNR of the same area in each image. I would expect/hope that the PI would win, based on cost and sophisticated algorithms. Paul
  4. Hi Tim, Are people not allowed an opinion on something that potentially they are looking at purchasing? Have you had chance to use one? If so, what did you make of it? I dont doubt that Skywatcher will fix the issue, but I really don't think it's unreasonable to say that a mount shouldn't be shipped if it's not up to the job...at least in some cases. There are some good EQ8s but there should be only good EQ8s. Having a mix of both gives consumers no confidence, and when spending 3k, people are going to want confidence. I grant you that I don't have one, but it was under consideration as a remote mount. Recent reports have shed some doubts on its suitability, which I'm sure will be fixed in the coming months, but I think it's fair to have an opinion about the situation. It's human nature to form an opinion, and at this stage there is some doubt. Obviously the only reports you read are the bad ones. Those with fully working EQ8s won't make a big song and dance. This effect will skew the average to the negative side. Cheers Paul
  5. No worries. Happy to have cleared up confusion. The astronomy lark is lifelong learning! Paul
  6. I checked APOD, was it the M33 image you are referring to? They used the term HII region, which is an area of ionised hydrogen that emits Ha, Hb, Hgamma, Hdelta and so on. That's those pink regions. We have them too in our galaxy, areas like the heart nebula, North American and so on... So HII regions are types of objects and Ha, Hb are particular emission lines. The emission lines are useful for highlighting these areas, Ha being the most useful (as it brightest). Hope that helps Paul
  7. HII isn't the correct term. It's H_beta. HII is a term that describes areas of ionised hydrogen. It's a general term. Ha and Hb describe transitions of ionised hydrogen. In Ha it's the n=3 to n=2 transition at 656nm (red) and Hb is n=4 to n=2 at 486nm. Ha is the stronger emission by roughly a factor of 3. Your camera though is more sensitive at Hb than Ha. This is certainly true for a DSLR. With a CCD the difference usually isn't as pronounced. The question is whether the efficiency of your camera is 3x higher or more at Hb than Ha. Might be true for a DSLR, especially I modded, but I can't see it ever being true for a CCD that normally peaks around the 550nm mark. I suppose Hb is the second transition in the Balmer series though, maybe that's where the term HII came from, though I have never heard HII being used for Hb. Hope that was informative Paul
  8. Managed the flame but not the HH with a 12" lightbridge from dark skies unfiltered. I imagine a filter helps.
  9. With the over and under sampling the theory is, and it's just theory, that your seeing should span 2 pixels. Typically in the UK this could be from 2-4" and can vary over the course of a night. A few places on earth have sub arcsecond seeing. So with this in mind a good scale would be from 1-2"/pix. With this movie mode you describe you are effectively binning the sensor. Not throwing it in the trash, but grouping a 2x2 or 3x3 matrix of pixels together and calling it a single pixel. This can also be done in software. The movie mode will feature short integration times so will be very limiting. Shoot long subs at high res and then bin them in software if you think it's appropriate. The reason the camera bins in movie mode is to reduce the file size so it can capture at 30fps. From the specs you quote the 30D has a better image scale with your scope and typical British skies. Hope that helps Paul
  10. Hi Olly, I wasn't implying you were having a rant, merely agreeing that this situation shouldn't have happened. You certainly weren't stereotyping anyone. I think eq8 owners whose mounts are playing up have the right to feel let down. I hope synta fix the issue because they could be on to a winner. Paul
  11. Well for £3k you would expect a bit of QC to ensure that the mount was fit for purpose. In Olly's and a few other cases anyway this hasn't happened. For the money they charge it should have been. Paul
  12. Welcome from Central Scotland, Dobs are a good way to start off, generally the biggest bang for your buck, and an 8" don will show you quite a lot especially from a dark sky. In terms of imaging though they aren't quite so good. It's due to the fact that the base doesn't rotate to follow the stars across the sky. You'll notice once you look through it that the objects in the eyepiece are continually moving. To capture really good images of deep sky objects need to be perfectly tracked for minutes on end. However you certainly can use a phone or off the shelf digital camera held up against the eyepiece to grab an image of the moon and planets (Jupiter is largest and well placed just now). I have held my phone against the eyepiece and it worked just fine. It's a bit fiddly but it is more than possible Hope that helps Paul
  13. Hi all, Have been trying out astrometry.net plate solving and it's quite good. However, I want to save the plate solved image with the WCS info added to the fits file. I believe this is the new-image.fits option. However when I click I just get an error type message. I can download the WCS info itself, but this is just the addition to the fits header. What I really want is the full image with the WCS info. Has anyone else come across this, or managed to save the new-fits output? Cheers Paul
  14. In fact I worked with a sensor that did just that. It had a region that could read out much faster. The technology clearly exists for this, but it needs to be CMOS for a "non-destructive readout"
  15. It's really not a daft question. If your sensor were CCD then the answer is a definite no. These typically have just one output, so it's either integrating or reading out. Not both. With CMOS each pixel should have its own output amplifier (active pixel) and so can be read out whilst other pixels integrate charge. I have often thought this would be a great feature, but CMOS sensors are not being applied to astroimaging as the CCD is still well and truly king. So in theory yes, a CMOS sensor could guide and integrate at the same time, but for your Canon it would depend on the architecture of the pixel and you would have to write your own timing signals. I think that's a far bigger issue than saving for an Orion Starshoot or equivalent. Hope that helps Paul
  16. Like Olly and Stuart have said, it's the total integration time that quoted because that is how long you have exposed for. In simple terms, ignoring read noise, if you double the exposure time or use 2 subs frames then the SNR is the same. Again, it's the ideal world. This will never be realised due to read noise and dark current. However the point is that for one, let's say you take 5min subs, then if you take 9 subs you have the same SNR as a 45 min sub. Clearly then you can relate the sub length and number of subs to the total integration time. Further the total integration time relates to the SNR . So when folk say that they used 22 hours worth of 10min subs or whatever, it is equivalent (only in the ideal case that does not exist) to a SNR of one single 22hr sub. The reality is that they are not equivalent but to work out the actual single sub integration time would be utterly tedious and quite pointless and tricky what with variable like read noise and dark current to account for. So using multiple subs and increasing the exposure time are the same only for the special case of no dark current and read noise. I point to this write up I did for the many short subs vs a few long ones debate. It may shed some more light. http://stargazerslounge.com/topic/200397-many-short-exposures-or-a-few-long-ones/ Paul
  17. I think the use of something like a G2-K0 provides a fairly good colour balance. The A0 was interesting but it made things look a bit red. The good thing is that in ex calibrator you can set the range of b-v to use, so you can experiment a bit to find what looks right. The more worrying question is what IS right? There must be someway of calibrating the image so that the colours are correct.doing it by eye is fine but it lacks precision. I like being precise. I like saying this is the answer. Olly, are these images using a convention colour calibration with no tweaks to make the image look right? There is certainly going to be blue stuff out there, the Ha will have Hb emission as well as OIII in hotter regions. You combine the blue and the red you get magenta. As example if you do a HaOIIIOIII image of the rosette, which as loads of Oxygen then the image comes out with a magenta core. Quite possibly in HII regions the colour might actually be magenta. After all if the gas is fully ionised then the Hb is about 1/3 of Ha and that surely gives the nebula a magenta tinge. Cheers for the discussion, all very interesting Paul
  18. You do raise a good point about the eye. I have compared some images with different stars used for colour balance. An A1 star gave a more red appearance to things and it didn't look quite right. A K0V or there abouts gave a much more usual appearance. All three have some merit it seems, with G2 -K0 giving standard results. I tried to take an average of B-V for K0V from the All Sky catalogue of some 2.5million stars to try to get a accurate B-V to aim for. The average was about 0.82 with a spread of about 0.17. Really quite noisy results. I think a b-v of 0.7-0.8 won't go far wrong. A boost of saturation helps too. Cheers Paul
  19. I know it's middle of the road,. It's a very average star. It is not a white star. A white star is defined in astronomy to be A0V. I know this is quite blue, but that's the definition. If it's middle of the road you want then you could ditch the G2V as the sun has peak emission at 500nm, which is bluey green. If you go for halfway in the visible spectrum (400nm-700nm) then you want a star with peak emission at 550nm. This equates to a temp of about 5300K and a K0V star with a B-V of about 0.8 So there are some stars that make sense for calibration A0V is by definition white G2V is a common star, but does not lie in the middle of the vis spectrum K0V has peak emission in the middle of the vis spectrum. Of those three, I would argue that only two have any real merit. The G2V seems to be a rather arbitrary convention don't you think? Paul
  20. What wasn't encouraging? I just presented some of the considerations, realities and background to the topic. I said any scope can be used for the job. It would be wrong not to point out the critical aspects especially when money is being spent. Thankfully the OP has done their research and as such can make better choices. Was just trying to spread some knowledge. Paul
  21. No one able to shed more light on the issues involved in colour calibration?
  22. Good post Olly, Hope they fix the backlash issue, especially given the cost of the mount. Glad it is living up to the hype in other areas. Certainly a mount to keep an eye on. Paul
  23. Yeah you can sub pixel dither and drizzle to enhance resolution but that will only go so far. I maintain that capturing a high number of frames and only stack the best few will yield good results, though with short exposures that might limit you in the fainter stars. Aperture helps with this. Yep practical knowledge is good as there are quite a few variables, but you should know the basics of what you're doing to understand limitations and possible avenues for exploration and improvement.
  24. Don't worry it's not really. There is absolutely no requirement to really understand what's going on. Point your scope at a close double, with a webcam, pick the best few frames and see what you get. It's as simple as that. Same advice for planetary, lunar and solar. On the other hand, understanding in a little more depth can help achieve better images. For example the use of the NIR (if you camera is not IR blocked). It's really up to you (anyone) how much you want to dig down deeper to learn about things. Some, like me, like to know how it all works. It's interesting even if not always practical. Others just want a pretty picture. I suppose that's the good thing about astronomy, you can go as complex or as simple as you like.
  25. Resolving double stars relies on a couple of things... First there is diffraction from the aperture. To resolve a particular separation the aperture must be large enough. The resolution of a telescope is approx L/D where L is the wavelength and D is the diameter of the scope. Multiply by 206265 to convert to arc seconds. There are different definitions of resolution, Rayleigh, Sparrow and Dawes if memory serves. They all state that resolution is proportional to L/D with a factor of no higher than 1.22. The worst case I believe is that resolution =1.22L/D. Again multiply by 206265 to convert to arcseconds. That's all theory, roughly 5 inches will resolve an arcsecond. However unless you live in La Palma the atmosphere will try to stop you (unless the separation is sufficiently large). A long exposure (really anything more than a couple of seconds) and the star will not be an arcsecond point source, it will be made larger by the seeing. How do you beat the seeing? Lots of short of exposures. And hope you get lucky. It's the same way planetary imaging works. Take lots of short exposures and spastically you might get a few where the atmosphere didn't adultery the starlight as it passed through the atmosphere. Webcam type set ups are good for this. The probability of getting lucky depends on how much you try to cheat the atmosphere. If you try to obtain 0.5" in 3" resolution you will wait a while. Another thing which surely must be true is that the stars you are trying to split must appear over at least 2 pixel. If you image at a scale equal to the separation then the stars would fall in the same pixel, and so could never be resolved. So what do you need? An aperture big enough to theoretically resolve what you want to split Enough frames to catch a lucky good one when the atmosphere behaved An image scale such that the separation of the stars covers two pixels. Other things worth bearing in mind.... Telescope resolution depends on wavelength. Blue light offers the highest resolution where as red light offers the lowest and NIR is lower still. This is easily seen from the formula. However, the atmosphere is more stable at longer wavelengths. So as the resolution of the scope falls as the light gets redder, the atmosphere gets a bit friendlier. If you plan on using red light or NIR then make sure the scope has the aperture required. You can put the following facts in to a formula... The result is quite elegant, if the image scale is half the airy disc, then for green light... The focal ratio F=3p, where P is the pixel size in microns. So if your camera has 5um pixels, then an F15 scope can deliver the criteria for green light. If you want to resolve 1" then you need a 5inch aperture (using the eq for airy disc). This doesn't mean that no other option will work. Any scope can be used to resolve binaries. Typical SCTs are F10. If you use the above example then a 5inch aperture at F10 doesn't have an image scale to properly split an 1". To get sufficient focal length you would need to increase the aperture. In the example of 5um pixels you would need a 50% larger aperture....ie a 7.5" f10 scope. That allows for the imaging of 1" binaries, but the scope in theory is capable of resolving about 0.7" now as we increased the aperture. I hope this makes some kind of sense and gives an idea of some of the theory behind trying to resolve things. Main points are scope resolution set by wavelength and aperture, the atmosphere blurs stars so capturing many frames and picking the best few is required and the atmosphere is steadier at redder wavelengths. Paul
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