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narrowbandpaul

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Everything posted by narrowbandpaul

  1. Thanks for all the feedback. Invaluable as ever.
  2. Hi All What is the best way to run EQ8 in SkyX. The mount will operated remotely and autonomously using SkyX and ACP. Am I right in thinking that it is the EQDIR cable plus the EQMOD ascom driver? are there better ways to operate the EQ8? Thanks in advance! Paul
  3. I'm most of the way down the line to a remote setup at IK's site in Spain. Its shared with two friends which makes things bearable cost wise. We are all friends so deciding targets should be a gentlemanly affair. Several factors encouraged us to go down the remote route. The obvious one is weather. There are lots of nice imaging setups in the UK that cost lots of money and only see stars a couple times a month, maybe less is Scotland. With the promise of approx. 250 clear nights, 2500hrs of clear dark skies, running remote suddenly doesn't look so expensive. So far I have really enjoyed the process of getting stuff together. It began at astrofest last year. All great plans are hatched at astrofest. From looking at mounts, spacing the rights adapters, reading manuals, testing under the few clear nights we have its been a good way to keep the mind active and focused on a goal. What I've learned is that you need to very sure what setup you are going for, get it all configured before you actually buy things. Changing your mind half way through can lead to tears. You need to know that all the bits you want will work together and will fit in the back focus available. There seems to be an opinion that in order to do astroimaging properly you need to sit and watch every photon enter the tube and set up from scratch each time, like doing otherwise is dishonest. This is of course nonsense. you don't need to sit there watching it collect data. You can sleep and let it collect data. There is far more involved in setting up a remote telescope with internet connections, and remote power switches and so and getting it to run reliably from 1000s of miles away. It is in fact quite an achievement, unlikely to be mastered at the first or maybe even second attempt. For me, messing about in evenings that aren't quite ideal trying to grab one hour of data before the tree gets in the way, moon rises and clouds come in is just a waste. It takes a while to get everything going and these nights only bring frustration. If you want to get lots of data to make nice pictures or do science then remote is the only choice from the UK. Otherwise an object will take a season to do well. Its not fair that we live at 50N, the worst place on the planet for stable weather but you have to play the hand you're dealt. Yeah its not cheap, you need to spend the cash to get a reliable system, an unreliable system will cost lots more long term. That's my take on it. I'm obviously very for it. Sending it all out in a few months. Maybe it will be a nightmare. Who knows.
  4. and for RBI info, as Olly points out Richard Crisp is the guy for it.
  5. here is the cloudy nights thread about the ambient temp dependent bias frames for the QSI683. Cant help but think this should never have been an issue http://www.cloudynights.com/topic/498053-qsi-683-vertical-banding-issues-solutions/
  6. Regarding RBI, it is not an issue for interline sensors as pointed out. Only full frame KAF type sensors. In a nutshell, there are mini-potential wells at the epi-bulk interface which are handily placed to trap NIR photoelectrons (electrons generated by absorbing NIR light) during integration. Over time these trapped electrons will detrap just like dark current (as a result of their thermal energy). Point a KAF sensors (particulary the 16803 and 09000) at a bright star, then take a long dark....you'll see the star in your darks. This detrapping causes havoc for precise calibration of images, so the only way to deal with it is to fill all these traps prior to every exposure. Then all images start from the same condition and things calibrate nicely. The dark current is increased considerably as a result and deep cooling is essential. I have been testing a PL16803 that I have a share of and the rbi is significant, but its the only way. Some will say that a good work round is to run the sensor warmer than normal so that the traps empty faster, then continue imaging. How anyone thinks that is a hallmark of a good camera is beyond me. Its not solving the problem, its a work round that the manufacturer suggest because they cant be bothered to fix the problem. And these aren't small companies either..... Anyway, i've mentioned a wandering bias level as a possible cause of inaccuracy in the flat process. This has been observed with the QSI683 where the offset changed with ambient (not ccd) temp. I can only suppose that the electronics are to blame, maybe a lot of use has taken its toll. Maybe send it to terry. He turned round a camera for Uni of Glasgow pretty fast. Until the results are repeatable its impossible to say what is the cause
  7. Hi Glappkaeft Yes, f ratio only isn't enough. The problem is that everything is intertwined. Changing one whilst varying the other will affect the third. The etendue argument seems good and I remember from my days as an undergrad. I suppose 2 set ups are identical if the deliver the same etendue per pixel. I will check the derivation myself as every scientist should do! Cheers Paul
  8. Longer exposure with an uncooled sensor will significantly increase the noise in the image. It means an accurate calibration is much more essential which is hard to achieve when temp is unregulated. It's possible but it ain't easy!
  9. You need to be very careful with lasers obviously. I'm sure it goes without saying to never point them at aircraft. It's illegal in the UK not sure about the states. 5mW ought to do it. There are different classes of laser based on power and overall danger. There will be a limit to what you can obtain. My friend once had a 50mW and that was very bright! Green is best as it's near the peak response of the eye. They are frowned upon at star parties I believe. Paul
  10. Understanding how all these things work I find very beneficial in imaging. Doing something without understanding what it does is a no no for me. I'm not advocating becoming a scientist or anything but a little understanding will go a long way. Learning a little about how stellar spectra differ from nebula spectra will tell you why NB filters are good for nebulae but of less use for galaxies, except in the star forming regions. Understanding a little about how light becomes an image in your camera and what kinda of noise there is and how it's dealt with will improve your imaging. Fact. These concepts aren't too difficult to understand. The answers already exist on google and SGL so a simple search will answer the questions. Having a basic understanding of the imaging process, from polar alignment to telescope optics, from filters to camera, from image calibration to processing and from stars to nebula is, in my opinion, essential. Some say that it's not required. That you don't need to understand any of it, even at a basic level. That doesn't wash with me. It's nonsense. Look at the big guns. I don't know of many top imagers how don't have a reasonable understanding of what's going on either in space or in their telescope or camera. That's not to say that they know it all. Some imagers, including the top ones don't have a grasp on things that they probably should. I'm not saying that I do. I'm not as arrogant as that. In fact I know what I don't know. Some people don't know what they don't know. They are the dangerous ones. They say things that are unjustified and people swallow it up because if "he" said then they must be right. My original point is that most of the top guys know what's going on to some level. This is the common factor. Having the right tools for the job is not guarantee for success. A good set of golf clubs doesn't make you Tiger Woods. You need to know how to use the equipment to get the most out of it. So my advice is to keep asking questions and read up in things. The more you know the better your images will be. Fact. I'm not sure if I went off topic here, I lost track..... Cheers Paul
  11. You will often find excellent transparency associated with low pressure and especially with cold fronts. The lifting of the lower layers removes a lot of the pollutants and disperses them high far and wide. In summer during high pressure the descending air collects and traps pollutants in the lower levels making for very hazy days. A good test for transparency is to look at a distant object during the day. If it has high clarity the transparency will be good. If you can't see it it's bad. Seeing is caused by temp and pressure fluctuations in the atmosphere. This causes the refractive index of air to change on timescales of 10s of milliseconds up to a few seconds over patches a few cm across. Local affects count for much. Avoid looking over houses as others have mentioned. The heat given off will change the refractive index and disturb the path the photons travel. Concrete after a hot day is bad too as it retains heat for a while and then radiated it at night. Even your scope will have a residual heat if recently taken from indoors. You have control over a few things. In terms of the atmosphere, ideally you want little change in wind speed with altitude. Look at aviation forecasts for the winds aloft. The met office have a free subscription for general Aviation weather forecasting. They have a spot wind chart from surface to 24000 for the UK and Europe. To have such little change in wind speed you need high pressure where the isobars are widely spaced. This high pressure may trap pollutants though. Local conditions will determine the transparency. It depends in how high you are and how much crud is present in your local area. Low pressure is associated with tightly spaced isobars and generally high wind speeds. This doesn't lend itself to good seeing. Position of the "jet stream" also would be something to avoid. A jet stream is any wind over 60kts and it is generated BY the polar front depressions that hit the UK every couple of days. The weatherman never explains this correctly. The met office also forecast the jet stream position. So good seeing is normally encountered with high pressure and good transparency normally with low pressure or cold fronts. As with anything with so many variables only looking at the twinkling will tell you. Paul
  12. Hi Astroblagger I'm guessing you must be near auchterarder. I'm in the Stirling area. You will have some fairly dark skies up there. As for exact locations I can't help too much. Perhaps use google street view to get an idea of the horizon. The darkest skies would be to the N or NW, towards Muthill or Crieff. There is a road that goes from just north of Braco to Comrie. It's quite a good driving road but it feels pretty remote. Skies should be reasonable from there. Hope that helps Paul
  13. It's only the focal ratio that matters for determining the speed. Proven by both theory and experiment. Signal received per pixel depends only on the focal ratio. Aperture plays no part. The experiment is proved by DSOs requiring very long exposures at f10 and much shorter at f3. Time to reach a given SNR is shorter with the f3 scope. Perhaps it's counter intuitive but you shouldn't apply any prejudice you may have acquired from visual astronomy. The experiment and theory are in agreement. There is a reason people to mad for the latest ultra fast scope. If aperture was king, fast refractors and the Ricardi Honders would be overlooked in favour of an SCT or large newt. Aperture sets resolution, focal length sets image scale and focal ratio sets time to a given SNR. I don't suppose a large aperture and a fast f ratio will hurt things. Apart from your wallet. Paul
  14. You need high QE and low read noise. The KAF3200ME or the sony 674/694 fit the bill. Smaller pixels would allow for higher positional accuracy if that's what you are in to.
  15. Hi Ivo. 1. Normally the green would be brightest as the QE is higher. You could quote the average or max values in each channel, thought I'm not sure if it required. 2. Good point. With short subs the chance of saturation would be low I think. It should still be valid though to use the max. If an exposure shows that a pixel is overexposed then there is no way you can get a sensible value to correct the flat. The best thing to do would be reduce the exp time so that the brightest pixel is at an appropriate level. Hope that made sense. Alternatively you could show a histogram and the user can visually see where the peak is. Or you could median filter to remove the hot pixels. I don't really have any software know how. Just some thoughts as to how it might be improved. Perhaps some these suggestions are easy to describe but difficult to implement. Cheers Paul
  16. Hi Zak, Interesting choice of camera. Why the choice of the RS version over the 683? Are you planning on doing any kind of science with it? As for cooling the lower the better. I stick with the cooler at about 80% ish. I have never had any issues with this. The QSI is a good camera and the 8300 a good sensor. You'll enjoy working with it. Paul
  17. Hi all. Thanks for the responses, Dave is right with regards to how flats work. Each pixel in the flat is divided by the average. This creates a correction factor that then normalises the response of all pixels in the raw image. A high signal flat doesn't lead to large numbers for the correction factor, it leads to a high accuracy correction factor. As I said before the quality of a flat is signal per flat x no of flats. The issue of low signals used in the SX cameras is interesting. There could be a link there, although correlation doesn't always imply causation. I think it's possible for camera manufacturers to influence the linearity. Only thing is I'm not entirely sure how. Perhaps the gain changes with amount of signal. That effect does happen with CMOS sensors so it's possible. Thinking about I suspect that the gain is changing with signal. I don't know why the higher signal flats over correct things. The theory says nothing about that. If the gain is changing then using lower signals still might improve things. Just use lots of flats though! Good find on the QSI site, I would agree with Kevin. I normally aim for 40000DN, which is about 2/3rds. Cheers Paul
  18. Hi Ivo, Thanks for your response. I will respond to your various points in order (replying in my post was a good idea, very easy to see what comment you were answering) 1. There might the odd user who doesn't know that the saturation ADU will be around 60-65000. They may only know that they want about 1/2 of max. Just a thought. Also what about DSLR users? They normally have 14bit raw files. Do you show these raw files on a 16bit scale, or on the native 14bit. If 14bit the camera will of course saturate near 16000. 2. Sounds good 3. Fair enough, although I do think there is some value in quoting the max value, even just to show the user. Also perhaps the min value as well. I am thinking that the difference from the average value indicates the amount of vignetting. I.e. Max-min/average x100 would give the %vignetting. Of course it's just for interest, but people may like to know how bad theirs is. Of course even a truly flat image will show a small variation due to random shot noise but you could get a good idea as to how vignetted your images are. 4. Thanks for clarifying 5. Excellent. Though as an idea rather than having to take your flats and then reprogramme APT to take the corresponding bias or flat darks why not add 2 checkboxes, one to take a certain number of bias, and one to take a certain number of flat darks. If no checkbox is used then only the flats are taken. Some people may already have the bias or darks and so don't need to take them again. It just saves the user the hassle of setting up the flats, waiting for them to be done, then having to remember about bias/darks and then set them up. Perhaps a reminder somewhere that flats need calibrated with bias or dark frames in case they forget, get uncorredted images, and blame the software. You might need a warning message after the flats are done and before the darks or bias are acquired. The message should tell the user to now cover the camera for the bias or darks. Might be OK with CCDs with mechanical shutters but for DSLRs any image will pop the mirror up, so it would need to be capped for the dark/bias acquisition. Hope that made sense. 6. Yeah it may not be easy but potentially useful for sky flats. Something like.... For each flat... 1. Measure average (or max or min, doesn't matter). 2. If value within range then no change to exp time. 3. If not, then multiply exp time by Target ADU/Current ADU. This should be the exposure of the next flat I think you need step 2 in there to stop the exp time changing for every exposure. You porentially add a save feature too. If Current ADU is within range then save If not, then don't save and multiply exp time by .... When the user is asked to specify how many flats they want it could be that you keep acquiring flats until there are that many saved flats. Ie only ones within the range specified are then saved. I don't write software so I'm not sure how hard this is to actually implement. These could be nice features though. Hope that was useful Paul
  19. Hi Ivo No worries. I would just say saturation ADU is about 60-65000 but I don't think there is much point in displaying it. What's important is the target ADU. Instead of quoting the absolute target ADU why not express it as a fraction of this fixed Saturation ADU. Ie specify the percentage of saturation you want rather than the actual value. What happens if the required exposure time for your target ADU falls outside the min or max exposure. I have used an EL for narrowband flats and the S2 filter was like 30s whilst the O3 was just a few. How does the software calculate the signal in the flat? Is it the average value or the max value? There might be some use in using the max value as then you can guarantee that no part of the flat is overexposed or nearly so. As for the range, is this Target Signal +- Range or is it the difference between max and min? To clarify using the image you posted is it 20,000 +- 2000 or is it 20,000 +- 1000, so that max-min = 2000 centred on the target ADU. Not that this matters much but some clarification may help users. Why not add an option to acquire the bias frames or flat darks at the same time. After all they are required for the flats to work properly. Perhaps an option for either flat darks or bias frames along with the number of these you want to acquire. Once the software has initially found the correct integration time to satisfy the user demands does it keep the same exposure time for all images or will it seek to adjust the exposure time to always satisfy the demand? That shouldn't be an issue for the el panel but perhaps for sky flats as the illumination falls. Let's say that during the shooting of sky flats the illumination falls outside the target range, will the software recognise this and adjust the exposure time? Or is the integration time then fixed once the capturing begins? Having the software compensate might be useful for sky flats but changing integration times would affect the usefulness of flat darks. Just a thought Hope that helps Cheers Paul
  20. Strange? Actually quite rude to you. Where there are the gullible you will find charlatans. Those that don't know any better buy in to it. If the guy tries to make money off of this then surely he is committing a crime. I hope the guy doesn't actually believe he is better than NASAs space probes, does he? I mean he must know its bogus. Surely.
  21. I watched that Canopus video. Was he trying to say that was the actual surface? Wow. I thought I wonder what point he is trying to make here about seeing conditions. I never even thought he was suggesting that a defocussed image of a star was actually it's surface. Wow. Just wow.
  22. I googled Hidden Micro Image retrieval also. Nothing. If this was a legit technique there would be papers and such like. Also 60s for Pluto is impressive. It's average mag is about 15. Need more than 60s to go as deep as that. Angular size of Pluto is, based on size an semi major axis 0.04". To even resolve Pluto he would need to better the diffraction limit of his 14" by a factor of 8. His "Pluto" images show surface details, so this factor must be even larger. Even the HST struggles with Pluto!
  23. Thanks Carole, Stephen. How do you determine what works best and what doesn't. How do you quantify it? Paul
  24. Hi All, I'm curious as to how bright your flats are and how you came to this decision. I see lots of different numbers being quoted and I'm interested as to how you came across these. The quality of a flat field can be expressed as Quality=Signal of single flat x Number of Flats. This quality term actually makes an appearance in the mathematics of flat fielding By using a low value for signal you only end up hurting yourself. You need a high quality flat to minimise the injection of random noise. Using 1/3rd of saturation and 10 flats just won't cut it really. You do want to keep your flats in the linear portion of the CCD but even with antiblooming CCDs are still linear over most of the dynamic range. So please post how you take your flats, the signal level and number of images. Perhaps we can all reach an informed consensus and cut through some of the drivel and misinformation you can find on the internet Cheers Paul
  25. Further information from Richard Crisps site. http://www.narrowbandimaging.com/images/Flat%20Fielding.pdf Cheers Paul
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