philhilo

Evening all, Looks like a clear moonless night tonight (fingers crossed). Using a SW200PDS with an ASI1600MM under bortle 8 skies I have around 12 good hours of usable 30 second subs across LRGB on M81 (prob another 8 hours of unusable 120 and 240second subs). With that combo I can fit both M81 and M82 in (I didn't initially as M81 was the secondary object for the night and the rotation for the nebula was wrong for M81/2). Should I: Shoot another 12 hours of centered M82 and make a mosaic (not done this before but willing to learn). Shoot M81/2 in one frame and hope the gradients aren't going to kill the targets closer to the edges - it frames OK, could be slightly more space but OK. I have ordered an IDAS LP D2 filter in the hope that it will deal with some of the brutal LP gradients I get in the lum and red. If it does arrive should I use it in either of the above scenarios, and will it make merging data impossible? Phil

Hi Ivo, Apologies for the delay in responding (families, work, life etc) and a big thank you for responding, you don't get that with Photoshop! I do plan on getting a dataset over to you with my ideas, probably through the ST contact form rather than leave this hanging whilst I try to find the time to get something sorted. Cheers.

Hi Astrobena, Noticed you had no replies on this one, not sure why, however I think it would help if you included full details of the imaging set up from telescope to camera, settings for exposures, times, how many were stacked, ISO/gain, offset. It looks as if you are using DSS and PS? What were the stacking settings? What is the final outcome and problem? That will give people a better chance of understanding what is causing the issue. Does this issue occur in single subs, the stack, or just the end product? Currently its like saying my car won't go, why not? Need a little more detail. Also good to attach the actual image with the issue so folks can look for themselves (some issues are down to the display screen being used and don't exist in the image itself. Probably the stack and your 'finished' image. I find peoples questions often lead me to the answer. It is good to keep your stacks to single exposure lengths and ISOs - imagine trying to process a night time image and a daytime image. I used to do this but have learnt to just keep it to one set of settings, even though it pains me to disregard piles of data. You can combine data with different settings but do it as layers using masks - folks often do this with the bright core of the Orion nebula. Maybe 2 minute subs then 15 second subs for the bright core - process the 2 minute data for the bulk of the nebula, the 15 second data for the core then overlay the the core using a mask. Alas I have no idea why that is happening but I sure I have seen it in my own images from time to time. Good luck, hope someone picks this up.

Both clips and drawtube are messing with the stars. Clips is a piece of cardboard painted black circle cut out, glued onto clips - £1 for the cereal box for the cardboard. I have seen folks saw the end off the drawtube (scary), or replace focuser, £300, expensive.

I have a lot of faith in ST and Ivo - I think the interface is excellent and it produces great results from pretty well default settings. But show it an offcentre circular heavy gradient and wipe doesn't know what to do. I sort of hack away at it as I go through the modules and usually end up with various 'clouds' around my galaxies (only an issue in BB) or I loose a lot of detail. Fan on the primary - have you managed to baffle it so that light doesn't get in around the mirror cell? I looked at a fan but having made a point of light proofing the rear end I didn't want that problem back! I have added an aperture reducer/mask to the primary to get rid of the mirror clip issue, likewise I put on a Moonlite focuser to hold the mono+EFW tight and remove the focuser tube obstruction. Now I am looking at an EAF, not often the temp variation in the UK causes too much of an issue, but I would like to be able to have it refocus between filters as I often have it set up to do a nebula for the 1st half of the night, then swap to a galaxy that doesn't require framing in the same way - in the middle will do - for the second half. I find the D2 works well with the DSLR, but pretty well kills the red channel, currently looking for a solution for the mono cam, no clip in for that! Slip ring above the top ota ring? Is that to hold the tube shape around the aperture due to the weight of the focuser etc + guide or spotting scope? I have lots of offcentre vignetting which is a pain but down to the focuser tube diameter I believe. A dew solution for the secondary would be good, there seem to be plenty of DIY solutions, but none seem to be totally convincing and there are no commercial ones which is surprising for such a common OTA.

Hi, yes I stacked in ASTAP as well (I had forgotten it stacked, it normally just says hello when plate solving as you say). On a very quick, 'throw it in, hit go, stack' I think the result was not as good as APP but it needs another go, especially as it is free (although so is DSS but I seem to be coming to the end of the road with that). One potential bonus with APP is folks use it clear heavy gradients before putting the image into Startools, as ST does seem to struggle - I can vouch for that with Jag Land Rover, B'ham airport, Solihull and Birmingham around me, I have gradients! This arrangement is bizarre though, it is like buying a Mercedes sports car (APP), taking the wheels off and putting them on a Mini (ST) for trackday racing, or spending slightly more and buying a very hard to drive Porsche (PI). Very odd. I guess it is a more extreme version of using Sharpcap for polar aligning but not using its camera control +++ capabilities (which is exactly what I do as I use APT). I notice you are a fellow 200PDS and IDAS LP D2 owner not far away in E Mids - I wanted to check out the E Mids astronomy club before Covid arrived. Would be good to compare notes on getting the most out of the 200PDS. Cheers, Phil

Evening all, apols for the delay (life, 3 year old etc), rude of me not to put something up, even if only a 'working on it', but there was a lot to work on,, however I have an answer, well at least a solution to the biggest part of the problem 1st up, thanks to Geordie for your help, very much appreciated in times of arghhhh! An extra big thanks to you Vlaiv for your detailed response (as ever), it really got me thinking I still cant quite figure if there is a tartan in the flats, it is there, but definitely does strange things once you enlarge it. I did try flats with and without the guide camera plugged in, but no difference. Alas I don't have my number two laptop set up for imaging (well sort of but still have to resolve a few settings) I thought about a new USB3 cable but held off on the spending money option till later To address Vlaiv's suggestions: How do I calibrate, 50 of each - Flats for each filter and any rotational change using APT flats aid at whatever recommended % of ADU using a flat panel, Dark flats at same settings as flats Darks at same settings as lights - done in extreme dark checking that the histogram is close to zero, checking for any hints of light leaks I do seem to have an issue with the rig maintaining polar alignment - I use Sharpcap and despite getting it to 'excellent' it still clearly drifts, more so after a flip. Having a mount loaded to the max probably isn't helping, and I think there is a question around flexure in the tube of the 200mm Newt that could be addressed with a beefier dovetail, and another added to the top (even heavier for the mount, lol). I might also need to have a look at the level too. I did try stacking separate before and after sets, however it still had the tartan effect, but there was rotation in each set. Using a different stacker - I was imaging the rosette, 6 hours of Ha looks great, no problems, 30 mins of S was good (no rotation), 1hr of S tartan starting to appear, 2 hours of S and any fainter areas looked like a Scotsman's kilt, brutal tartan! i downloaded the free trial of APP, stacked the 3 hours of S, processed the result in Startools and NO TRACE OF TARTAN. So it appears that DSS doesn't handle the slight field rotation exactly as Vlaiv suggested. What surprises me is that more people haven't had this issue as I have flagged it up in other places and got no answers to a very glaring effect, no subtle slightly bigger or smaller, shades of colour, just glaring and completely show stopping tartan in a set up and processes that felt very standard. My dilemma now is do I fork out the annual fee (£60) for APP or buy it (£200), at which point with the cost of Startools I am getting close to the cost of PI - however there is the headspace issue. My quiet time is very limited until next winter - that might be the time to get PI, even though I loath the idea of paying top dollar for something with such a badly designed UI - but that's another story. Attached is an APP stacked and then processed in Startools version of the Ha only data I originally posted - no tartan (although there are faint linear features at 90' in the base of the cone - which it turns out are real). Hopefully won't be back with this problem, and thanks again for all your help, or anyone that even looked and couldn't. Cheers, Phil (I might well post a final image up) Full_Cone_Ha_21.01-Luminance-session_1 180m stack APP process ST.tiff

Hi Vlaiv, 1st up thanks for your help on this, really appreciate your time and effort on this - I don't often ask for help but this one has me stumped. Yes, that is clear - that was my 1st suspect. Interesting about the background calibration, it had occurred to me that different sessions were going to suffer from quite different seeing (even more so in high lp). Will be playing with that (not the 1st time that processing documentation isn't quite up to speed, but they aren't rules). I do have a permanent set up, and tend to keep the camera set in the same position for extended periods whilst working on a particular target - usually a nebula for which I need a particular angle for framing, and a galaxy for later in the night when orientation is less important (no rotator....yet). Not sure, I think I can still see a pattern, but as I said to Alan I am going to try both your approach's as I want a solution, life is hard enough with Bortle 8 lp (M81 circle) without tartan to add to the non signal! WOW! That is very dramatic and very much in line with my issue. Interestingly I have just done a quick dirty 1 hr on the rosette, 12 images with very little rotation and there is no tartan effect,

Thanks Alan, I am going to take both yours and Vlaiv's approachs in the hope that one works (as in a bortle 8 area life is hard enough without extra non signal - especially after spending £££ on upgrading everything!) . As for that flat, not sure I believe my own eyes any more, I think I can see pattern, but it does do strange things when enlarged, suggesting a screen effect - not sure what to think! The cooler comes straight off the dew heater hub, but the camera is separate and comes through the USB3 cable from the laptop into the 1600, then the guide camera comes out via the 1600 hub. I will run some flats this afternoon to see what effect unplugging the guide camera has, and as we have some clear skies tonight will run some sequences with the guide running through the 1600, and some running it through a separate cable, alas I don't have a spare USB3 cable. Also will be working through Vlaivs suggestions (and cooking dinner and keeping 3 yo under control lol) Will update later. Thanks again. Phil

Hi Vlaiv, These are the DSS settings Startools recommends: Choose No White Balance Processing in the RAW/FITS dialog Choose Bilinear Interpolation for the Bayer Matrix Transformation algorithm Save your final stack as 32-bit/channel integer FITS files, with adjustments not applied. Stack with Intersection mode - this reduces (but may not completely eliminate) stacking artifacts Do not choose Drizzling, unless you are 100% sure your that; your dataset is undersampled, you have shot many frames, and you dithered at the sub-pixel level between every frame Turn off any sort of Background Calibration Some users have reported that they need to check the 'Set black point to 0' checkbox in the 'RAW/FITS Digital Development Process Settings' dialog to get any workable image. Choose Kappa Sigma rejection if you have more than ~20 frames, use Median if you have fewer. Ensure hot pixel removal is not selected on the Cosmetics tab. That's what I am using. The Cone images utilised different data sets from multiple sessions, even an offcentre set (ran out set rig off for target - forgot I had slightly reframed the object the previous session). Where I have multiple sessions of the same subs, but utilising the same calibration frames, I have always processed them in DSS as one group, even more so now I have a dark library, could this be an issue? OK, had another look at that flat and that could be the screen effect - it radically changes depending on the scale (I have started to see tartan in everything), At full scale it looks like pimples on a golf ball, about 3 pale squares across the dust bunny, zoom in a bit and it becomes a real fierce diagonal grid about 9 squares across the dust bunny. I had a look at the 'M81 red stack', some 223 30s subs over 3 hours in one evening. I can see the angle creeps steadily down by about 0.1 degree over the 1st couple of hours, then has a lurch of another 0.1 over a few frames just before the meridian, then creeps slowly about 0.01 degrees every 5 minutes for the last 30 minutes. Does that tally with the sort of rotation you were thinking of?

Cheers Geordie, Where is that likely going to be, I don't recollect ever having to specify bayered or debayered in any software - Drivers/APT/DSS/Startools? No option in Startools, can't see anything in DSS. Phil

Evening all, I am calling on the great combined experience in Stargazers Lounge to try and stop me spending yet another evening (tomorrow) creating a tribute to Scotland, namely Tartan images! Someone must have had this issue as I am not running an exotic set up. I have tried to detail everything and would be happy to I got a ZWO ASI1600MM Pro in the autumn after using a DSLR for a couple of years and have since been plagued with a tartan pattern creeping into most images. I have researched this at length (weeks) and have seen various suggested causes, but this seems to be a problem normally associated with debayering in colour imaging so what is it doing in my images? It does not appear to be a display issue as it is properly baked into the image whatever screen it is displayed on (I am used to seeing a chessboard pattern when opening the files in Fits Liberator, which instantly vanishes when I start to enlarge) I can usually find it in lights and it is in my flats. It doesn't appear to be frost, many were taken in warm conditions. . Is it to do with my running at gain 139 and offset 20? The ASI1600MM is acting as a hub for the ASI1200MM mini guide camera. 200PDS f4.5 Newt ZWO ASI 1600MM Pro imaging ZWO ASI 1200MM mini guide feeds into 1600 hub Dithered Controlled by Astrophotography Tool (APT) on laptop Stacked in DSS using Startools recommended settings Processed in Startools putting the data in as linear unstretched or using the compose module for multi channel images Gain 139 Offset 20 T = -30c or -20c Full images calibrated with 50 flats, 50 dark flats, 50 darks Images attached are: Fully processed Cone in Hubble palette - very tartan 11hrs 300s H, 3hrs 300s O 3hrs 300s S Part processed Cone in Ha, no flats - plenty of tartan bottom right M81 red only stack (also epic gradient as well, LP I think....but that's another story). Master flat, Gain 139 offset 20 stretched in Startools, lots of tartan in the midtones. What I have established: Pattern seen in: In Lights, Less prominent in galaxy BB data - small bright objects, and even bright nebula like the Pacman, but more prominent in faint mid tone images like Cone nebula. In Flats, so no guiding so unlikely interference from guide cam. Seen in Startools on 1st stretch so not coming from some later process Flats at 20k adu using electro luminscent panel so all pixels well illuminated - minimum values of Lights at different ambient temps, some +10c as well as during the cold snap so unlikely freezing in optics Its all mono so not sure how debayering would get involved? Pattern in stacks yes, single frames - not sure, maybe, but its not obvious. Certainly some chequerboard pattern at a pixel level in some single images. So is it something to do with: Offset too low? Driver issue? DSS setting? Camera issue? Startools issue? Cone short Ha 21 stack.tiff Ha 21.02 NO FLATS part processed.tiff m81 red tartan cicle.tiff MasterFlat_Gain139 Off 20 tartan.tiff

Great image and yes a hard target (or so i have found). 900s with RGB and f3.8 - do you live in the middle of Outer Mongolia or the North Pole, maybe the dark side of the moon?

Glad you got something sorted.

I have the clip in Canon D2, not cheap but effective in a bortle 8+ area when imaging broad band targets. Although the LEDs are broadband, I think there is an overall reduction in light pollution as the streetlight designs are more focused, the house fronts and gardens in the streets with LEDs are noticeably darker.

i have come across this thread and am interested in the outcomes from adding a fan to the rear of a Newt for imaging My position is not about getting the OTA to ambient temperature as it lives outside, however I do have a problem with gradients in images, and I know some of these are caused by dew on the secondary and primary (despite being told its very rare for the primary to dew up, tell me that when I am stood with a hairdryer, again!). I have looked into secondary heating, but if I can do it with one mod then even better. I have read many articles extolling the virtues of a fan, cool down times, dew prevention, improved resolution due a disruption of the boundary layer on the primary (better when blowing rather than sucking). My concerns with the fan are three fold: How does it impact guiding - you are applying a force to the tube with the fan blowing, and with an elastic mount momentum during corrections? Can the vibration be eliminated sufficiently to not be seen in the images? I have spent time trying to stop light getting in through the rear of the OTA, can a fan be installed without compromising the light proofing? Cheers, Phil

Cheers, I had started to think I might need to get a bigger secondary ...... just after I rebuilt the dang thing.

Very nice, and gives me a chance to ask a fellow 200PDS owner about vignetting. I am using the ASI1600MM Pro with 36mm filters and the vignetting is heavy and offset causing me headaches when processing.

If you have a look at Chuck Ayoubs Spaghetti on Astrobin its around 20 hours and he is in Detroit in an 8 I think. He was using an 80mm at around f5.

Should be. I am using a generic coma corrector that doesn't act as a reducer, I figured it was fast enough and I wanted fl for galaxy imaging. Erling, I was most impressed by your image of M33, especially with your 200PDS/HEQ5 Pro/DSLR set up, the same as me. I thought Denmark was the land of eternal cloud, but I guess you at least have low light pollution unless you are in Copenhagen? Have you done any upgrades to your set up apart from the rowan belt mod? I still think the 200PDS is under rated, and it's a huge step up in price to get the same fl in a refractor or SCT, which is why I am trying to hypertune mine (also need all the help I can get in bortle 8), however I have finally gone for a mono astro cam as I was sick of trying to remove epic noise, just hoping it is the right decision going mono rather than OSC. Here is my 5 hour Whirlpool which I think is OK for the budget OTA 200PDS and a DSLR (just need to get processing nailed). M101final5hr.tiff

The 200PDS has the tube slightly shortened for astro imaging to bring the focal point further out (I think) - one of the drawbacks with the 200P where the focuser can't rack in far enough for prime focus. They didn't bother to change the stickers on the side of the OTA. Astrophotography tool gives me a calculated fl of 911.8mm from plate solving images as I remember.

Got it, the mirror is offset in the holder! Yes I left the mirror on the holder deliberately as I could clean it with it still attached (and more safely suspended in washing solution) and it was one less variable to deal with later. Thank you folks, hopefully ABs guide will get me through. Cheers.

But alas as part of the flocking process I had to remove the secondary, spider and all, unscrewing the tensioning bolts that position the mirror. Now when I come to put it back I need to figure out if it was central or offset, assuming this was originally achieved by adjusting the spider? What I should have done was measure the position of the secondary before I removed it, emphasis on should have done!

I have put on a Moonlite designed for 200mm Newts, seemed the way to go to reduce the diffraction spikes and better at holding my shiny new mono cam and efw ... allegedly.

I have stripped, cleaned, flocked, masked the primary mirror clips, and put a new focuser on my SW 200PDS. Now I need to collimate (something I seemed to get away with before using a basic laser collimator), and the 1st step is ensuring I have the secondary in the right place - but where is the right place, central or offset? Astrobabys great instructions say consult the manufacturers instructions - there are instructions for the 200P - central, the Quattro - offset, but not the 200PDS which lies between the two in terms of aperture and focal length (Quattro fl 800 F4, PDS fl 900 f4.5, P fl 1000 F5). Any 200PDS users done a collimation from scratch?