geoflewis

Hi Olly, Thanks for your observations. 0.43"/px is precisely why I bin 2x2 with the C14 and as you suggest I have considered 3x3, but never used that other than for plate solving where I actually use 4x4. My guide RMS is typically around 0.5"-0.6" total, with lower values for RA and Dec (typically 0.3"-0.5" each). That is clearly more than half my image scale of 0.85" when binned 2x2, so please could you explain the target of half image scale. As you will have concluded from my discussion with Vlaiv on this thread I really understand very little of the science of this hobby 😖. Up until now I've just guessed, but now I'm trying to better understand what I should be doing and why. Thanks for the explanation of how to improve star colours. I'm not familiar with MartinB's tutorial, so will look for that. I have just purchased Noel's tools last week and had a play, including with his 'increase star colour', but it didn't seem to have much effect - maybe I was expecting too much. I like the layer approach in PS that you [proposed, so I will give that a try, though I'm something of a novice with PS too.... Many thanks, Geof

Hi Vlaiv, I've now checked into my holiday lodge, but there is no wifi here, so I'm using my phone as hotspot, so that may be a little unreliable. I checked my darks and was very surprised to discover that the master dark was only 8 bit, so I've reprocessed the dark stack as 24 bit. Here is a single dark off the camera and the master dark from 20 dark frames. QSI-Darks(-10C)_300sec_Bin2x2_frame1.fit MasterDark.fit I checked and there are no zero values in the single dark, where the minimum seems to be ~400 ADU. The minimum value for the master dark is ~500 ADU. I then looked at singe uncalibrated frame and the same frame after calibration. M57_300sec_2x2_Ha_frame1.fit C_M57_300sec_2x2_Ha_frame1.fit The raw file off the camera shows minimum at ~400 ADU, this just 1 or 2 pixels, rising to ~500 ADU by the time 1000+ pixels at that level. Checking the calibrated same image shows a huge number of pixels with 0 ADU, so for sure the calibration seems to be making the difference. If calibration simple deducts the dark frame value per pixel this makes sense, as anything in the raw file with ADU <500 will move to 0 if the dark master has min ADU value of ~500. It makes me wonder how a dark frame has >ADU per pixel than a light frame even when using Ha filter, but perhaps I'm still not understanding this well enough. Truth to say, I've never really thought much about this previously, so this is definitely a journey of discovery for me and I very much appreciate your help and look forward to your reply. Best regards, Geof

Thanks Steve, it is very helpful to have your input. As I found in my discussion with Vlaiv, I was wrong in thinking that more shorter exposures gives better SNR than few longer exposures. I will go back to 10 min or maybe even 15 minute exposures, but I'm also very interest to learn more from Vlaiv more about this so will continue the thread with him by providing the dark frames that he requested. Cheers, Geof

Hi Vlaiv, I am just leaving home to go on holiday for one week - actually to a local uk star party, so I cannot send these to you immediately, but I will take my laptop with me and see if I can upload them later today. I very much appreciate you helping me diagnose all this for me and helping me better understand what is going on. Regards, Geof

Hi Vlaiv, Thanks again, here is a 32bit FIT file - at least I think that it is. C_M57_300sec_2x2_Ha_frame1.fit I usually perform processing (calibration, align, combine) at 32 bit Fit in Images Plus, then save as 16 bit Tiff for post processing as tools that I use, e.g Registar and Photoshop (CS2) do not read the Fit files. Even at 32 bit level I think I'm seeing 16% (~339k) at 0, so what does this mean? Regards, Geof

Hi Vlaiv, One more time please? I checked the background ADU for a series of Ha image that I captured last night. The exposures were 300sec and background ADU is ~50. So if target ADU is ~4100, then approx optimum exposure is 300s x 4100 / 50 = 24,600s or 410min (6.8 hours) - surely ~7 hour exposures cannot be right, so what did I do wrong? Does a background ADU of just 50 at 300s seem likely? I live in a bortle 4 location with readings that night of 21 SQM, so reasonably dark. I've attached the calibrated Tiff for you to check if that is possible please. C_M57_300SEC_2X2_HA_FRAME1.tif Thanks again, Geof

Vlaiv, Thank you so much for taking the time to explain this using my example ADU readings. I think that I finally get it, or at least I feel much more comfortable in my understanding. Thanks also for explaining your use of the x5 multiplier, which makes sense. I will continue to re-read this thread (probably many times to get it fixed in my brain), but at last I feel that I have some logical methodology for determining exposure durations for my different rigs and different binning. Oh and BTW (by the way) my reference to NB for M13 was not Narrow Band, but Nota Bene (Latin for note well). Of course I do not shoot narrow band for globular clusters 😉. Many, many thanks. Geof

Vlaiv, Many thanks again. I have found a statistics tool in my astro software ImagesPlus, so tried some tests on both binned 2x2 and unbinned 1x1 images. I only use the 1x1 when imaging with my 4" APO, whereas binned 2x2 is always with my C14. I'm not sure what if any significance these different configurations make as it is the same camera. Here is what I found checking some L subs.... 4" APO unbinned 600 sec sub - ADU = ~3200 If I understood you correctly I need to multiply that by 4 for comparison with binned 2x2 which gives 12,800 - I must say I'm not understanding this part....?? C14+Optec lens binned 2x2: -300 sec sub - ADU = ~1400 -120 sec sub - ADU = ~800 (NB for an image of M13 the background ADU was ~600, but if I shoot much longer surely the globular cluster core would become blown out) Of course the results vary depending whether there was a moon in the sky, hence recent subs from M57 had ADU of ~1800 at 120 sec. Based on my understanding of what you are saying the 600 sec sub binned 1x1 with the 4" APO looks to be too long duration, which I find very surprising, whereas both 120s and 300s subs with the C14 binned 2x2 is much too short. Please can you explain some more. Many thanks, Geof

I'm finding the same Neil, so have also been updating old crappy versions with better ones, but likely it will be a never ending project.....

Thanks Vlaiv, I understand the advice about LP noise v read noise, but I have no idea how to measure them, nor how to convert ADU to electrons - actually I don't even understand what that means. What software do I need for that? I also understand that more shorter exposures is better than few longer exposures for improved S/N, provided each exposure is sufficient to dominate read noise, so why do many of the best imagers I see shoot exposures lasting 10, 15, even 30 minutes? I've never been able to get my head around that? I also understand that short exposures can be used to restore star colours, but I've never been much good at that, so I guess that don't know the correct processing steps. One of the problems of beinf self taught I guess.... I sure wish that I understood all this much better than I do currently.... 😖 Cheers, Geof

Thanks Nigel, I'm still trying to get my head around this, but it's gradually seeping in - I hope.... Cheers, Geof

Hi Mark, Yes, I believe that they are all visible from the UK provided you have a clear southerly horizon. I saw them using my 15x70 binoculars from my previous home in Surrey, but the extra degree or so further north here in Norfolk takes them really low; M6 and M7 being ~2-3 degrees altitude at best. Unfortunately I have an obstruction up to about 10 degrees due south and whilst I can see down to about 4 degrees SE and SW my observatory wall prevents my scope seeing below about 8 degrees, which isn't usually an issue, but is for these few very low Messier targets. It's good to have challenges to solve though - life shouldn't be easy and this hobby certainly isn't.... Cheers, Geof

Snap..!! I'ts a great project Neil and one that I've been working on for a few years. The low southern targets (particularly M6, M7, M54, M55, M69, M70) are a real challenge to image from my location, so whilst I believe I have seen most of them visually, I will have to travel south to image them. I'm currently at 88/110, having ticked off a few globs and open clusters this summer when in previous years I was dedicated to planetary imaging. I will try for more of the Coma/Virgo/Leo cluster galaxies next Spring, but it's difficult to get more than a few each season, due to UK weather and/or moonlight, so I suspect that it will be a few years yet before I have to make specific travel plans for those horizon hugging ones.... Good luck, Geof

Steve, it's a really cracking image, well done. Geof

Hi experts, I know that there's been a lot of discussion around binning on this forum, as I've read quite a bit of it this afternoon and previously, but the more I read the more confused I become. I've used the 'Resources' page to check CCD suitability for my C14 plus x0.67 Optec lens, when used with my QSI583 camera. The unbinned (or binned 1x1) resolution for this equipment combimation is 0.43"/px, which even in good seeing is borderline over sampled and in more typical UK seeing is definitely oversampled, so I typically capture all data at 2x2 binning, which gets me in the green sampling range of 0.85"/px. The question I now have is by how much should I vary my exposure times? Simple maths suggests that since I'm using 4 physical camera pixels in the 1 large (binned 2x2) pixel, that I'm capturing at x4, but I read that practical experience puts the ratio as more like x1.6 to x2. So, if I typically would use 10 min (600sec) exposures imaging unbinned, would that be equvalent to say 5 mins exposures when binning 2x2. I see many exposure durations far in excess of that being used by some folks, e.g. 900s, 1200s, 1800s albeit not imaging with a C14, but I'm seeing fully saturated stars with the C14 at even 300s binned 2x2 and for RGB images saturation of brighter stars occurs after even 120s. I want to shoot as long exposures as possible without saturating stars as there is a significant overhead in download times, storage and processing with many shorter exposures. I know I can experiment, but building a darks library for 10m, 15m, etc. exposures is not a 5 minute exercise, so I don't want to do that if there is no point. I'm hoping that my question makes sense, or if not someone can put me on the right track please. Cheers, Geof

This image was something of an afterthought as my intention initially was a single test shot before packing up at about 1:30am, but I liked what I saw so kept going for about 2 hours until the clouds got me. The below final image comprises 1.5 hours data (18x300sec Bin2) captured with my QSI583wsg-5 and Astronomic 6nm Ha filte, through my C14 with Optec telecompressor lens in train. I've just purchased Noel's actions to help with my very limited PS processing experience, so definitely was fumbling about in the dark. Calibation, grading, alignment, stacking and initial post processing was using Images Plus, then into PS for final tweaks. I have very little experience processing mono images, so all critique is very welcome. Cheers, Geof

I too have just purchased Noel's actions and have very little idea how to use them and no idea about using them as layers, so the tips here are great thank you 👌

Hi Dave, I too much prefer the 2nd version. Well done, Geof

My double garage has 2 cars in it....., but then consider me old school 👴

That's really good and a great way to ease yourself into the new season

Many thanks, Geof

Thanks Steve, Yes, it is a handful, but the AP1200 doesn't break a sweat with the C14 and (fingers crossed) I'm gaining confidence in the settings I'm using in PHD2 for guiding. I also used SGP's focus target tool for the first time as I've consitently found that using autofocus on target for globulars just isn't reliable. The focus tool requires manual intervent so hardly automatic; I had to stop guiding, slew to a focus target, run autofocus, then slew back, resart guiding and resume the sequence, but it definitely gives better focus than what I'd been doing focusing on the cluster itself. FYI below is a screenshot of PHD2 guide log analysis for just the red filter. Total RMS after excluding the dithers was sub 0.5", with RA 0.27"and Dec 0.35", being similar for all 3 filters. Cheers, Geof

Thanks James, I know what you mean as most of the brighter clusters I've imaged tend to be dominated by blue stars, e.g M2, M3, M13, M15,, etc. I did find this reference from an article on M71 in 'Universe Today', from Nov 2018.... 'In NGC 6838 the giant stars are red and become bluer with decreasing brightness.....', ....hence I'm fairly confident that I got a true representation of the star colours in my image. Cheers, Geof

I settled on imaging this cluster as the full Moon made the sky to bright for me to shoot any faint targets in RGB. It is just 9x120sec subs for each of RGB, so just under 1 hour total integration. The data was captured with my QSI583wsg camera through my classic C14+Optec telecompressor lens for an effective F7. Despite the very bright sky it turned out quite nice with good star colours. I think that it makes quite a striking view, being located amongst the rich star field of the Milky Way. I hope that you like it and thanks for looking. Geof

Hi Dougie, as Rob says, you need a barlow to increase the image scale. Does your DSLR offer a video mode and better still cropped video? If it does, then capture a couple of minutes video then use something like Autostakkert (AS3!), Registax, etc., to grade and stack the best frames (lucky imaging) and Registax wavelets to sharpen the resulting stack. It's possible to get pretty respectable images of the planets with a DSLR, but be aware that DSLR video is usually a compressed format not readily supported by AS3!, Registax, etc., so you may need to research software to convert the video file to a readable format. Another method is to stream bitmat images from the camera direct to a laptop, then grade and stack those. I've also done that, capturing about 8 frames per second, not the high frame rate of dedicated planetary cameras, but still worth trying if your DSLR and capture software supports that. Good luck, Geof