geoflewis

Hi @miguel87, well now we know exactly where you live - you need to be careful about posting those GPS coordinates 😉. I agree with you though, but then what you can actually see is largely affected by the quality of your eyesight. What I could see when I was 10 years old is vastly different than what I can see in my mid 60s... I know the skies have deteriorated, but as I child I could count naked eye stars in the Pleiades in the high teens (I think either 17 was my record), now I just see the main 6 or 7, sometimes 8. I have an an app on my phone called 'Loss of the Night Sky' (http://lossofthenight.blogspot.com/2015/01/brief-introduction-to-loss-of-night-app.html). It gets you to look at a series of stars of varying, but gradually diminishing brightness and calculates what your personal limiting magnitude is. I get a very different result than what Bortle suggests I can see. My skies are Bortle 4, bordering on Bortle 3 (typical SQM 21.2-21.4), but the best I can see in seemingly perfect conditions is something like mag 5.5, so not even close to the suggested NELM of 6.1-6.5.

Hi Olly, Thanks for the feedback and advice, it sounds like I really must get to grips with using lighten blend mode for HaRGB combine, something for me to do over the forecast run of cloudy nights and rainy days coming up. No not Bin 1, I shoot all my data with the C14 at Bin 2 due to the significant oversampling that I'd get at Bin 1 with the QSI583 camera.

Thanks Martin, that's the kind of feedback I love, I'm so glad that you like the revisions, it makes it all worthwhile.

Thanks Bob, the quality of the image has a lot to do with the advice and guidance I've received from folks on this forum, not only for this image, but over several years.

For anyone interested I took Ragnar's (@lux eterna) advice and adjusted the colour balance to get rid of the magenta hue and also ran it through Topaz Denoise. I've uploaded the revised image below the original at the start of this thread, so that it is easier to compare them. I will likely do a complete rework to see if I can improve the original Ha blend using a lighten blend as suggested by @Laurin Dave, but not today. Thanks everyone for the very helpful feedback; more is also welcome...

Thanks Bryan, So for clarification I have an Optec telecompressor lens designed specifically for the classic (non Edge) C14 which does a great job, though still not totally flat field. It aso reduces the FL to around 2.6m. Even then the system would be significantly oversampled with the QSI583, so I also bin 2x2 for all subs, getting me to about 0.86"/px. Guiding with the Lodestar X2 was in the range 0.4"-0.5", so well inside the imaging scale, which is good. The major player in imaging at this scale is the Astro-Physics 1200 mount, which is massive with minimal PE or backlash, so I can let it get on with the job with few worries.

It looks like you have some headroom to extract more of the tail, by using an overstretched image like this (maybe somewhat less stretched) as a luminance mask to control the areas in the image that are revealed.

Hi Dave, I agree with Brendan that it's an excellent image, so don't be too hard on yourself. I also think that you'll probably need to use masked stretching to extract more of the tail whilst preserving the cores of M65 and M66. Ultimately though you can only push the data so far, so how clean is the background of luminance data, as that's where you'll need to push the processing to lift the tail out of the background. Good luck.

Thanks Carole, I'm very pleased to get a better version of this beautiful galaxy.

Yes, IP has all the same blend modes as PS. I have tried lighten blend previously, but will give it another try. Thanks for the suggested workflow, I’ll take another look at processing it. This is where this forum is so helpful. Many thanks

Thanks Dave, Yes, ImagesPlus (IP) does allow blending Ha with R first before building the RGB image, in fact in many respects IP mirrors what can be done in PS. There seem to be so many methods for combining Ha with RGB data, but I struggle with them all.... 🥴. I guess practice will get me closer to perfect, not sure how close though.....

Thanks Gina, it really is a beautiful galaxy and I couldn't believe how long it had been since I imaged it. I think I've been too focused on capturing as many different Messier targets for my collection as I can, that I forget to go back and improve on the ones I did several years ago. This year I've redone M81, M82 and now M51, so next year I think I'll have another go at M101.

Thanks Ragnar, no I don't mind at all. I also saw the magenta hues and have been playing with it in PS too, but think I got processing blindness from looking at it too long, so out it up for feedback, so your's is much appreciated. Adding the Ha data really threw the colours off, so I'll take another look at it later.

Here is my version of M51 a target that I've only imaged twice before, once when I was just starting out imaging in 2013 with a DSLR attached to my 10" Meade LX200 and then again some 5 years ago in April 2015 also with a DSLR but attached to my then new 4" TSAPO100Q, a much wider field view, so I thought that was about time that I revisited it with my C14 and mono QSI585wsg-5 camera. The image comprises L=36x10m, Ha=11x15m, RGB(each)=24x5m for a total integration of just under 15 hours. I used ImagesPlus mix LRGB tool to create a colour image blending 20%Ha and 80%R for the red channel, so as not to overly saturate the active Ha regions in the galaxy (it may still be too much). The L was separately processed and layered over the HaRGB using ImagesPlus with final tweaks in PS(CS2). Revision with reduced magenta and pass through Topaz denoise which trial I've just downloaded.... Thanks for looking, as always comments and feedback are very welcome.

Sorry, just been out for a 4 mile walk with my wife and very pleasant it was too despite the fairly strong chill east wind - I hope that drops by this evening BTW. OK so the primary issue seen with RA is periodic error (PE), which arises from errors in the gear train, e.g worn, or poorly manufactured gears normal for other than very high end mounts and hence the use of PEC (periodic error correction) models. The worm gear is constantly turning and any errors in that will show up when that part of the worm engages the gear. Similarly errors in the individual gears will also show periodically and a pattern of errors will show repeating every complete worm cycle with the main frequency spike usually being the period of the worm itself completing a full rotation. PHD2 log viewer allows you to perform frequency analysis on sections of your guide log, but I'm not experienced in interpreting these, so again I would point you to the PHD Google Group for assistance, unless someone else on here can assist better than me. The other thing to be wary off with both RA and Dec is overtightening of the gear train as that may lead to stiction, (static friction) where the gears stick until sufficient force is applied to move them, this is seen by a build of in guide pulses that have no effect, then sudden large moves as the stiction is eventually overcome and the gears leap forward.

Backlash in RA has no impact on guiding, as the gear drive is always moving in the same direction - for RA the guide pulses just change the rate of movement, i.e. speed up or slow down the gear. Backlash in Dec is the problem as when a change in direction from north to south is required then the guide pulses have to take up the backlash before the mount actually changes direction, hence there is a delay, quite often followed by an overshoot and then a reverse correction leading to guiding oscillations. Good luck tonight.

I'm no expert, but I downloaded your PHD2 log and reviewed it using Andy Galasso's PHD2 Log Viewer (available to download from https://adgsoftware.com/phd2utils/), so I'll make a few observations, but would recommend that you post your logs to the to Open PHD Guiding Google group where you will definitely get expert advice, quite possibly from Andy himself, or Bruce, or Brian - https://groups.google.com/forum/#!forum/open-phd-guiding The things that I noticed from your log is that you had several failed attempts at calibrating with the 8" F4, with GA runs that reported errors in calibration, polar alignment and guide star focus, but there are no lengthy guide runs to see how the mount performed, just many short runs of up to ~5 minutes, many, much shorter, which really won't tell you much, if anything. As soon as your swapped to the ZS73 you got a good calibration and for the long 1h 20m guide session PHD Log Viewer reported excellent polar alignment error of 0.1', so I'm curious about the rig's configuration, e.g. is this the same mount? is the WO piggybacked on the 8" OTA or did you swap out the OTAs? If everything is mounted on the same mount and you just moved the camera from one OTA to the other then the immediately improved calibration and reported significant improvement in polar alignment is interesting, however, I did not see any new GA run after you swapped scopes. As already mentioned, in addition to the reported poor calibration and polar alignment with the 8", the GA also made recommendations to improve guide star focus. I've never imaged with an F4 scope, but I recall reading that these fast mirror scopes may suffer from significant coma at edge of the FOV (my recollection may be wrong, so just putting my thought out there), so with the OAG prism sampling the guide star from the edge FOV I'm wondering whether this is a contributory factor. Another thought is whether everything is secure within the scope itself, i.e. primary and secondary mirrors. I used to own a Wise Optics 8.75" F4 Newt and it would never hold collimation, as the springs on the primary mirror adjusting screws were too weak, such that as soon as I moved the scope from one location to another it lost collimation (every time). It was a 2nd hand scope that I acquired in the early 1980s, which I only used for visual observing and just lived with it until about 10 years ago..... The long guide run with the ZS73 was good, not great, with total RMS just over 1" and different rates for RA and Dec resulting in a somewhat elliptical scatter graph, which might result in non round stars. There is also a clear sin wave form in RA guiding (blue plot line) indicative of the mount's periodic error. I'm not sure if my musings are of any help, so will repeat that the best place to go for advice is the Open PHD Guiding Google Group where the developers and other experts will be able to give you far more reliable advice. NB they will want to see your log files and probably debug files which may be uploaded to their sever from within PHD2 itself, just make sure you submit log and debug files with matching date and time stamp. Good luck.

As I continue to work through Virgo cluster targets for my Messier collection, I imaged these two elliptical galaxies earlier this month, but only just got round to processing them today as its a cloudy night. There's nothing much to say about these large fuzzy blobs, hence posting them both on a single thread. As would be expected from galaxies in the heart of the huge Virgo cluster there are several other galaxies on view. Both images were captured with my QSI583wsg-5 camera, through my C14+Optec x0.67 telecompressor lens. M49 (L=9x10m; RGB=7x5m each) M59 (L=12x10m, RGB=7x5m each) Thanks for looking.

I'm not sure about posting this in the Deep Sky section, but I can't think anywhere else to post it - indeed one wonders if it should be posted anywhere at all...!! This is possibly the most bizarre of Charles Messier's list of 'it's not a comet' targets, though to be fair to him, in 1764 he was searching for a nebula that had been reported in the area by Johannes Hevelius, of which nothing has ever been found. What Messier found was an optical double, which I've only imaged as I need it for my personal Messier collection. It was rediscovered by Friedrich August Theodor Winnecke in 1863, hence the alternative designation of Winnecke 4. The star field is so boring that for the first time ever I used Noel Carboni's Astronomy Tools to add artificial diffraction spikes.... Anyway here you are Messier 40.... For anyone interested capture details are: C14+Optec x0.67 telecompressor lens, QSI585wsg-5, Astronomic Type II RGB filters each 12x1m.

Hi Dave, I agree it’s a bit blue, but it’s a huge improvement on the first pass that you posted, so I’m sure that it was worth recalibrating the data with correct flats for each filter, plus what ever other processing modifications you incorporated. I don’t think the background is overly bright, but then I prefer backgrounds that are not too black. All in all it’s a great image, well done.

Maybe somewhere in between and yes, it's always best to shoot flats and flat-darks for each filter. I reuse mine for several weeks, even months so long as the camera hasn't been removed or rotated; sometimes even if it has been rotated together with the Optec lens, as anything further up the optical train away from the sensor really doesn't show.

Well done Dave, whatever you think, it’s a very nice result and the tidal tail is showing, even viewing on my iPhone. Does it show better if you raise the black point a bit as the sky background looks pretty dark (on my phone that is)?

Looking at your original post again, the downloaded image in SGP (bright grey in the background) appears to have round stars, so what length exposure was that one? Also the period of the PHD2 graph is pretty short as I note that you're using 1s guide exposures and the graph is at only 100 guide pulses, so less than 2 minutes. Have you used PHD2 log viewer to read a much longer guide session to see if the guiding holds up over a longer period?

PHD2 should be able to manage 609ms backlash easily. Run the GA and accept the recommendations for backlash compensation. PHD2 will continue to monitor backlash as it guides and update the compensation based on real time feedback from guiding. Be sure NOT to have any backlash compensation set in the mount as that will throw PHD2 off.

Sorry, I'm not sure, but I'm thinking flexure, but that is less likely with an OAG, unless there is flexure between the OAG and imaging camera. An imaging camera gradually sagging would be one type of flexure, but that would have to be in relation to the guide camera, so it would be worth checking that everything is tight there and that the cable to the guide camera isn't too tight and straining the OAG union. I asked partly to eliminate field rotation, coma, etc. which won't give elongation in the same direction across the FOV.