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v4169sgr

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  1. Thanks for the reply, Michael. The results above already show that they aren't consistent over the test you are suggesting. I therefore agree a screw fitting will be more consistent, but am mystified how one is supposed to screw in a Baader MPCC into a BDS focuser? The camera has not been modded in any way.
  2. Next two images are a corner of the first and sixth frames, magnified by 208%. Remember there's been no processing.
  3. Results of a few little experiments Saturday evening. All measurements taken interactively as I went, informing me of sensible next steps. All single frames, without calibration or any other processing. Aim is to understand a little more about how tile and aberrations affect star images towards the edges of the frame. The assembly is: Canon 450D + WO 'Copper' T-adapter + 2mm spacer + Baader MPCC + Baader twist lock clamp, fitted to a Baader Diamond Steeltrack focuser on my OO UK CT8 Newt. The whole arrangement designed to minimise the effect of uneven or unequal tightening of grubscrews etc. Images shown are the results of applying the 'tilt' command in Siril, that "computes the sensor tilt as the FWHM difference between the best and worst corner truncated mean values ... expressed by the difference in FWHM between the stars in the center and the stars on the edges of the sensor." Worth bearing in mind that "the drawn quadrilateral has its proportions exaggerated, in order to be more visible on the screen." Order of images shown is top to bottom, left to right, in order of images taken. I tried rotating the camera by 90 degrees (refocusing each time between images), then repositioning it back to the original orientation, then taking it out of the clamp and replacing it, then simply taking another frame changing nothing to understand the consistency of the measurement. After that, I disassembled the camera and coma corrector assembly, took out the 2 mm spacer, re-assembled, then took the final two frames. All the images shown are screenshots. My impressions: 1. Taking the camera + CC out of the clamp and replacing it, however carefully done, introduces noticeable tilt. This seems unavoidable. Getting a good 'un seems to be more luck than judgement. 2. I'm not sure I can see much of a difference in aberration between two frames of approximately equal tilt before and after taking out the spacer - more details in a reply to follow. Happy to hear how others approach the whole issue of non-circular stars in their frames. I think I've done what I can short of replacing the coma corrector.
  4. Thanks again. Focus is no issue ... I use a Bhatinov mask to achieve critical focus - and the Pleiades are bright enough that I don't then need to slew to target. I've taken some measurements ... within the precision of the tools I have available, I estimate 56-57 mm between the image plane and the M48 thread. Might not be spot on with this one and could easily be a mm or so more as I found it difficult to determine with any greater precision where the M48 thread is in the assembly. However this should not be any great surprise since the T adapter and MPCC are obviously designed to work together with a DSLR. So the spacing should be good enough. I use Siril to preprocess my images already, so quite a revelation that I could simply type in 'tilt' in the command line and see for myself. In answer to a comment above, I verified that the stacked image is in line with (produces the same result as) one of the subs. I've seen stacking issues before - they are not pretty - but that doesn't seem to be an issue here. If the weather holds up I should be able to carry out some experiments in the next couple of nights with single frames under various conditions. An obvious question that arises is what sort of results I should *expect* from the equipment I have? Is it really legitimate that the MPCC II doesn't remove all the coma towards the edges of the frames? How precise should I expect the match between the image plane and the detector plane in my DSLR to be?
  5. Thank you for all the responses! Food for thought. Happy to acknowledge the limitations of my equipment, however given my motivating interest on photometry, I'd like to see if I can achieve nice circular stellar images throughout as much of the frame as possible. Added to which for me it is as much about the process as the result. In efforts to eliminate tilt (clearly not successful!) I use a Hotech Laser Collimator to ensure all the optical elements of the OTA are lined up - and crucially use the same focuser configuration and clamping mechanism as I use to hold the camera, adapter and coma corrector. I use a Baader Clicklock Clamp attached to my BDS-NT focuser to ensure circularisation so that I am not playing with unevenly tightened grubscrews. I attach the coma corrector to the camera body using a WO high precision "copper" M48 T-mount, so I am not using the M42 threads. In the first photograph below I show the MPCC itself without any covers (and in the edge of the picture a stack of two of the thin spacers I am adding). The second photograph shows the MPCC (capped) mounted to the camera body using the M48 T adapter. The third photograph shows the full assembly: I push home the camera + CC assembly as far as it will go into the clamp, then secure it with the locking mechanism. Which software do you use to determine the tile, by the way? Would it run on Linux? I run Linux Mint (Ubuntu based). My principal concern though is in determining the correct spacing. I don't think I am particularly close at the moment, and welcome insights. This is the reason I am introducing the 2 mm of spacing, to try to achieve the correct 57.5 mm separation between MPCC and detector, since I am using the M48 thread. I welcome any thoughts.
  6. All, Will be very grateful for any insights. Equipment: 20 cm f 4.5 Newt on an NEQ6; Canon 450D fitted with Baader MPCC (probably type II). The first image below was taken with the assembly as-is. The second with the addition of two very thin spacers on the camera side of the MCC (the max. I could fit in and still have some thread left!). Is there any improvement in the second image - accounting for the orientation and slight processing differences? I'm inclined to think not, and even to believe the situation has been made worse. What do you think?
  7. Thanks again for all the replies ! 😎 I did get some time at the scope again last night & while messing about with the focuser clamp collected some 60s subs + all the calibration frames. No good at all for lights stacking because of the (quite deliberate) errors I was introducing, but it did give me a chance to corroborate my working assumption. Longer subs - especially near the moon 😆 - do definitely make the negative pixel warnings on dark subs go away & that's with the same image reduction script. That's OK because I would have no intention whatever of using 10s subs. I was only using them at the time to get a feel for how tracking errors might be influencing the image (they aren't, at least not up to a minute). On other points raised: it was quite notable that random noise increased in the darks for longer exposure times (as expected) but also that the median values hardly budged, which - combined with a visual inspection of the master dark - confirm that merely capping the scope doesn't let light in. And I was pointing almost directly at the moon - it was BRIGHT!
  8. Thanks for the responses. I've inspected the stretched master dark and can find no evidence of light leak. Additionally I've noted the median statistic of the master dark and the master flat dark - they are very close to each other, confirming this conclusion. The 450D body is relatively old, and does not have built-in dark current subtraction. The EXIF CCD Temperature varied in a uniform way between +3 and +7 C over the course of the multiple frames, in the same way both for the lights and the darks, confirming there's no problem with systematic thermal noise offset between the lights and darks. Using Siril manually is slower for me than running scripts, and there is nothing to suggest so far that default processing is giving me issues (other than the nomenclature for flat darks, which I can easily adjust). My working assumptions are that dark subtraction is sensible and necessary, and that I simply didn't rack up enough sky background in the lights of 10 seconds to make a difference from the darks. My Bortle score is 3.6 - skies are very dark. I hope to go out again and take some longer exposures tonight or tomorrow (while conducting other tests). We shall see!
  9. Hello everyone, I am somewhere in the foothills of my learning curve on how to acquire and process images. My main aims at the moment are: (a) acquire nice round stellar images; and (b) properly implement dark subtraction and division by flats, both for the purpose of getting into photometry of variable stars. My equipment is an 8" Newt (f4.5, 900 mm focal length) on a NEQ6 and a Canon 450D, unmodded, with coma correction. I use Kstars to download the images and write to FITS, and Siril (v 1.2.0) for data processing. I've chosen M45 for the purpose of learning: a nice wide bright star field, not far from the zenith, with plenty of interest in the background, and which moat important is a very well recorded target. My mistakes and wrong turns should be all the more obvious. I am conducting star tests at the moment, with the aim of understanding & being able to eliminate as much as possible any deviations from circular stars. On Monday I'd decided to acquire 120 10 second subs of the target, to contrast them with the 60 second subs I'd taken of the same target a week ago. I would not normally suggest 10 second subs for this target, but wanted to reduce any contribution of tracking errors. To reduce the data, as a default, I am using the 'OSC_Preprocessing.ssf' script naively without modifications, to see what I can learn. Along with the lights, I also took 120 darks of the same exposure with the telescope cover on but pointing in the same direction, 120 flats of 0.01 seconds each of a light box placed over the end of the telescope tube, and 120 'biases' of the same exposure, as flat darks. 12 GB of data, but so worth it for the learning experience! 🤣 While running the script I noticed Siril complaining that calibrating the lights with the dark and flat masters the script made produced 20 % negative pixel values over the frame, consistently. Investigating further, I found that the median pixel value in the master dark was 1025, while the same on a representative light was between 1030 and 1045, over the RGB channels. The scripted calibration command is: calibrate light -dark=../masters/dark_stacked -flat=../masters/pp_flat_stacked -cc=dark -cfa -equalize_cfa -debayer As far as I can tell, my method for acquiring the calibration frames seems OK to me. Similarly, there are so many eyes on this script that if something was off them it would have shown up by now. The only reasonable explanation I can find is that my subs were so short that systemic contributions to the dark from the bias made a more than is usual contribution to the data levels in the dark. Next opportunity I get I am going to try some 30 second exposures to see if this makes any sense. Any thoughts?
  10. Thanks Stefan for the perspective - I guess this is what I was looking for i.e. how much of an issue is this? Seems to be not much - just try again if it doesn't look right and don't sweat. From a practical POV I am not sure what screwing the camera in to the focuser would look like LOL
  11. Hello, I am experimenting with a coma corrector on my DSLR attached via the focuser on a smallish Newt. I noticed that there was still some residual coma in some of the corners of trial images after fitting the corrector. To eliminate the potential of sag I pointed the OTA in various directions and critically compared resulting trial images - no changes were observed. The DSLR and corrector are held in place in the focuser using a compression ring tightened via three grub screws. Changing the order in which they are tightened DOES produce a variation in star shapes in corners of trial images. A fortunate trial choice virtually eliminates coma. The coma correector itself screws into the T adapter, a very solid metal piece. So no issues there. Anyone have any recommendations on achieving circularisation (via a screw thread) at the focuser?
  12. Would like to take this opportunity to put in a good word for the developers and help desk at QHYCCD for making available this recently updated version of their software for Ubuntu Linux and derivatives. Works flawlessly on Linux Mint 21.2 making polar alignment a breeze - even for me. Link: https://www.qhyccd.com/file/repository/latestSoftAndDirver/Soft/PoleMaster_QtforLinux64Ubuntu_V21.05.18.zip . Please of course familiarise yourself with their documentation.
  13. Found this thread - looks promising! https://www.cloudynights.com/topic/388671-updating-synscan-firmware-in-linux/ Will give it a try in the next few days ...
  14. Good evening, Managed to connect Kstars to my Skywatcher NEQ6 mount for the first time this evening. It complained in start up that I needed synscan handset firmware v 4.38 or higher, but the handset I have runs 3.27 at the moment. My set up is ancient. The mount is probably getting on for 20 years old (got it second hand more than a decade ago). First, is this upgrade path even possible? I've read that with some older handsets, the internal hardware cannot run more recent firmware. Second, can a firmware upgrade be performed without Windows? I do not, and will not, run Windows. (My system is currently Linux Mint 21.2 which is very good). Not a showstopper apparently as I still have GOTO from Kstars. I connect using a USB to RS232 cable connected via the handset, and the Indi Synscan Legacy driver. Any information appreciated!
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