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Everything posted by BrendanC

  1. Hi all, I'm occasionally getting bright streaks on my subs, and I've identified the problem: reflections from the spider vanes in very specific circumstances. I pinpointed this by covering each vane with my hand and taking a shot. It's consistent and repeatable (and I'm so glad I've found the cause!) So, next up: the fix. I've got some tape on the vanes currently which works, but it's a bit, ummm, agricultural. I'd like something that looks a bit better. It seems to me that a nice, matt black paint would be best, but I don't really want to have to brush this on, let alone spray it. I want just to be able to spend a minute or so applying it, without having to remove the vanes or risk paint getting everywhere, or inconsistent application. I'd also rather not have to bother with flocking etc. I know the fix, and it doesn't require over-engineering. So I'm wondering if anyone could recommend a small paint PEN that could do the trick, available in the UK? I've come across some but they're only brands for sale in the US such as Testors. I'm sure they market themselves under a different brand in the UK/Europe but I haven't seen any solid recommendations from scouring the forums. There are plenty of black pens, obviously, but I'd just like a recommendation from anyone who happens to have used a specific one on their Newts? I also know there are super-duper blacks out there such as VantaBlack and Black 3.0, but they don't come as pens that I can see. They're also expensive (and, as far as I can tell, Anish Kapoor won't let anyone use the VantaBlack!) Thanks, Brendan
  2. Nope, but that's another good idea. I could check the raw subs, and stretch them in Photoshop to see what's going on. My feeling is that they'll still be there, but I could check. All I've done is process in StarTools and Topaz DeNoise, so I don't see how they would have done this to the spikes. Btw the 130PDS thread shows some shots with uneven spikes and some with, so I guess it's down to individual setups. I have a strong feeling it's because the secondary might be very slightly canted in one direction, so I guess I'll have to get the Concenter out and give that pesky secondary another go. I hate collimating.
  3. Good point! I haven't really looked. I know of the 130PDS thread on this forum so I'll take a look. Totally prepared to believe it's just something that happens with this scope. I know it's a very minor issue but after the long, hard struggle to get this far, I'm now considering these ongoing cosmetic irritations.
  4. Hi all, Now that I've fixed the 999,999,999,999 other problems I've had over the past year, I'm working on the next one. I keep noticing that the diffraction spikes on my stars tend to be longer along one axis than another - example attached. To my eye, the vertical spikes are longer than the horizontal ones. I've collimated the heck out of my 130PDS - even bought a Concenter to help with the secondary mirror and the out-of-focus star test yields concentric circles - so does anyone know what could be causing this? It's not a huge issue but it does sort of bug me. Thanks, Brendan
  5. Hi all, Sorted. It was the darks getting mixed up, and re-shooting the flats did the rest. Thanks for everyone's help!
  6. Yep. After much scratching of head and getting a bit sweary, I think I know what to do to fix this all now. If there are any other issues going on, then after fixing these two, I'm sure they'll rear their ugly heads next!
  7. Thank you, this seems to me to be bang on the money. So, I've identified two things (I've been up since 6am working on this - yes, it worries me that much!) There were some rogue 180s files in my 120s darks library. I've removed them, and that's fixed this problem. HOWEVER, it hasn't fixed other images that I've taken over the past two nights. I've stacked those images with no calibration at all, and the result is much, much better. So that tells me it's not acquisition or the camera. Now, given that the darks should be ok - and that I get the same result if I use the older darks - I'm starting to think that this is a separate problem with the flats. So, I'm going to retake the flats (the camera is still in the same orientation) and see what happens there. The reason I extended the darks library was that I didn't have many subs at certain temperatures, so I just added some. But, as per my bullet above, I accidentally moved some of the new ones to the wrong folder. Doh! So yes, a thorny problem which I believe is possibly two separate problems. Main thing is, as you say, the actual data is/are fine and if/when I nail this, I've got lots to be doing.
  8. I think you're right. It's almost as if there's an overcorrection happening. The flats are definitely fine, I just took them in exactly the same way I always do. Any more opinions on this one? Thanks again for the help.
  9. Hi all, My past three shoots have yielded weird results - unaccountable vignetting and poor detail. In my efforts to understand what's going on, I tried restacking the last decent image I did, about a month ago. It came out differently. I don't know why. This is how it came out originally, about a month ago, just very quickly stretched in StarTools, no colour processing etc: This is how it came out just now, using the same files in DSS: See what I mean? It's almost as if the flats aren't being applied, or something. They're using the exact same files - darks, dark flat, flats, no bias. This leads me to believe that something, somewhere, has changed. My thoughts are: * Something's different in DSS, possibly to do with the flats. I've tried stacking on other machines and get the same results however. I'm going to give this another go to make sure. * Something's wrong with my darks. I extended my darks library while the weather was bad, so I'm wondering whether some of my darks have 'gone bad' somehow, and now everything's over-compensating. I've got an offsite backup of the original library so I'll be getting hold of that too and seeing if that gets me anywhere. Either way, I really, really, really need someone's help before I spent hours and hours trying to figure this one out. I've got lots of plans for the next few clear nights but without ironing this problem out, I'm in real trouble. Does anyone have any suggestion about something that might have changed in DSS to do this? Or, is my hypothesis about the changed darks library a possibility? Thanks, Brendan
  10. So I took the exact same shots last night and they came out much better. It must have been high cloud. That's my working hypothesis anyway, until/unless anyone else can offer another one!
  11. Hi all, Last night I took 16x120s of the part of the North America Nebula just to the right of the Cygnus Wall (I'm doing a mosaic), and 28x240s. The reason for doing this is that I've found taking shorter exposures while the object is lower in the sky, helps with light pollution where I live. Then, when it's higher, I can move onto the longer exposures. This worked just fine for the Cygnus Wall bit, which I did a month ago: However, last night's images have come out pretty badly. I've done a VERY quick stack in DSS and process in StarTools (no noise reduction or owt), and it's not looking good: It's using essentially exactly the same calibration approach as the other image - 25 flats taken on the night, 50 darks from the library, a master dark flat, no bias frames. What I'm finding is that the 120s exposures show bad vignetting, which I'd have thought the flats would have fixed... ... while the 240s exposures are oversaturated (and noisy): I've tried EVERYTHING to find out what's causing this. I've used different flats from another night, retrieved old darks from an older library, tried without any calibration at all, using different stacking algorithms, and it just seems to be there, in the subs. So, this is weird, and I don't quite understand it. The conditions seemed perfect last night. I've not had such bad vignetting or saturation, and I'm confused as to why this is a split between the 120s and 240s subs. One theory is that perhaps there was very high cloud last night? Could this have caused it? My guiding was pretty good, which isn't usually the case with high cloud. I've noticed that particularly with the 240s subs there's quite a variation between lighter subs and darker ones, which would bear this theory out. Or, is it just simply not enough data for this to give good results? It's similar to what I captured for the Cygnus Wall image. But frankly, if it isn't something like that, I'm stumped! Again! Thanks, Brendan
  12. Interesting! I'd read about them but never really understood what they're for. This could be really useful, thanks.
  13. Outstanding! Thank you so much! It must have been there staring me in the face all along...!
  14. Hi all, When I'm revisiting a previous target or doing a mosaic, and I really need to get the rotation angle just right, I plate solve in APT and then Show the result in Stellarium. This gives me an exact rotation angle, from where it's an iterative process of rotate, solve, show, repeat. However, it just occurred to me that it would be incredibly useful if APT could just show the angle of rotation instead. I'd still need to iterate, but wouldn't have to jump across to Stellarium (which isn't very easy to make out sometimes). I know that a compass icon is displayed top left after the plate solve, but ideally there would be an actual figure there too, for more precise alignment. I must admit I don't have APT in front of me right now and this might already exist! If so, could someone tell me where I should be looking please (ideally before tonight!) Thanks, Brendan
  15. Actually, I decided just to think about this for a moment, and I completely get it now. Of course it won't change the focal length but it will just make the scope a bit slower. I think I get it now. Thanks.
  16. Thanks! So, data before and after should still work together then?
  17. Hi all, I just got a baffle to fit to the primary on my 130PDS, in an attempt to get my stars a bit more defined. It goes around the outside of the primary and hides the primary mirror clips - very much like this: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p12358_Wega-Primary-Mirror-Baffle-for-Skywatcher-Newtonian-130PDS.html I've yet to fit it, but I just had a thought: if I do fit it, will it affect my focal length? And if so, will that mean data acquired after fitting the baffle, will be incompatible with data acquired before it? As in, will images acquired with the baffle fitted, register and stack ok in DSS with images acquired without the baffle fitted? I'd rather know either way before I fit it! Thanks, Brendan
  18. Thanks - that's why I was asking this, because I'm aware that the EXIF isn't from the sensor, it's from the processor. I've discovered that just leaving it in the fridge for a few minutes gets rid of the issue. So, I guess it's as I thought: an object lesson in the difference between sensor temps and processor temps. I'm just glad I spotted this before ruining my darks library!
  19. Hi all, I thought it would be interesting to make a list of all the things I've had to learn along the way over the past two years or so, starting with scratching my head figuring out how to put my first scope and mount together (Sky-Watcher 130P Synscan) and now producing images I'm pleased with on a consistent basis. So, I just jotted them all down, sorted them A-Z, and here they are - no attempt to categorise, it's a mix of techniques, hardware, software etc. This is without even considering mono shooting, filters, and all that jazz. Align mount APT ASCOM drivers for DSLR Assemble scope and mount Attach camera to laptop Attach camera to scope Attach guide camera Attach guide scope Attach mount to laptop Bahtinov masks Calibration Collimation Coma Control everything from laptop Control remotely Dithering Drizzling DSS EQMOD Exposure times Focusing Guiding Image formats CR2 and FITS ISO Mount handset Magnitudes Mosaics PHD2 Photoshop Planning sessions Plate solving Polar align RA/Dec and Alt/Az Registax Sharcap StarTools Stellarium 'The sky' Topaz DeNoise Using camera Visual - star alignment, finder scope alignment, eyepieces/barlows What to do when things go wrong!
  20. Just a little bump of this one cos I still don't really know what's going on. I have a theory that it's evidence of how the Digic 3 processor, from which the EXIF temperature is derived, is demonstrably a different temperature from the sensor in certain conditions. It would be great if anyone could confirm this one, ideally by having experienced this themselves. I know that in theory this could account for it, but whereas in theory, theory and practice should agree, in practice, they don't!
  21. Hi all, Just experimenting with Siril. In DSS, I can use groups to match my lights and darks by temperature and/or exposure time. In Siril, I can't see how this is done. I've looked around online, inc the Siril forum, and can't find a definitive answer. Any ideas? Thanks, Brendan
  22. Well, after leaving it in the fridge for a bit longer, I started getting the same as the darker darks. So it could be something thermal. If so, it would be an object lesson in how EXIF temperatures differ from the thermal state of the sensor. Hmmmm.
  23. I'm not - it's just that the dark came through at that temperature. I was hoping it would go down during the night, but I was testing it now. Also, given that my camera typically is around 10 degrees above ambient when shooting, I can easily imagine an evening of 19C. I do have subs at 29C and above, believe it or not. The problem still remains though. Why is one taken at 29C markedly different from another?
  24. Hi all, I decided to extend my darks library while the clouds are still rolling in. I know, I know - I shouldn't be using a darks library with a DSLR but it seems to work for me. Anyway, my past MO has been to put the camera in the fridge and build up the library for 60s, 120s, 180s and 240s exposures, all at ISO800. Then I group them according to temperature and build master darks from 50 subs for each temperature. Here's an example of one at 29C that I took a while ago, stretched in APT to bring out the details: I've used these darks for a while and they produce good images (or at least I think so). The difficulty using this method is getting the higher temperatures (dur, cos it's in the fridge, right?), which is where the dark files are most handy. So I decided to put the camera in a sealed box outside, with the lens cap on. I got this (ignore the square top left, that's just an APT thing): It's the exact same exposure time - 240s - and EXIF again reports 29C. Looks like light leakage maybe? Realising the LED display was still on, I slapped my forehead, switched it off, thought that would be it. Nope. So I draped a thick towel over the box. Nope, still there. So I wrapped the camera in a big hat, and then in the towel. Absolutely no way light's getting in there. Still the same. And now I just put it back in the fridge, exactly as per the, er, darker dark, and I'm getting the same result - a sea of purple noise. Nice title for a Prince song maybe, not so great for calibration. So, I'm thinking this must be thermal noise, despite the EXIF reporting the same temperature. Is this the classic thing of the EXIF reporting the Digic 3 temperature, not the sensor temperature? In which case, am I stuffed? Thanks, Brendan
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