ollypenrice

When I was a young NHS buyer we had a warning about a particular brand of office chair which was at risk of breaking and impaling its occupant. We also had a senior manager who blatantly ordered goods for his own use at the public expense. When this man ordered a new office chair, my colleague and I thought hard about which one to choose. Our decision must remain between ourselves and our consciences... 🤣 Personally, regarding your chair, I wouldn't risk it. You're out in the dark, the ground may be unstable or unfamiliar... Olly

Dew heater is the obvious first step... Olly

I don't think that you can really expect good results from an F4.5 achromat. At around 100mm aperture, F4.5 is a big ask for an apochromat. Even Takahashi, with their legendary FSQ106, settled for F5. The larger the aperture, the harder it is to achieve good colour correction in a refractor. The light which is creating the magenta halos should be focused into the star itself. Nothing you can do in post-processing will put it back there. For broadband astrophotography I'd look for a more suitable set of optics. Olly

Here we go again, as with your other thread. Because you are out of your depth, you are asking the wrong questions. Through my job I know, host and work with dozens of excellent imagers and I do not believe that any of them works to a spreadsheet of lunar position, phase or target proximity. I have literally thousands of hours of deep sky exposure time under my belt, yet I have no idea how to fill in your questionnaire. It reminds me of the nonsense OFSTED wanted me to tick-box when I was a teacher. The real world simply does not work that way. Rule Number One: Tick no boxes. The fact that you do not include, in your questionnaire, any distinction between broadband and narrowband, or any refinement of narrowband into bandpass width, clearly indicates that you should come back with more knowledge. Leave the production of astrophotography tutorials to astrophotographers. Become one, by all means, and you'll get endless help on here, as I have done. Then, when you have something original to contribute (as you will if you persevere) then contribute it and it will be well received. Even before the internet was thriving, friends and I used to joke about 'The advice mountain,' rather like 'The wine lake' of the time. There is far more advice at large in the world than the world has any need for. Don't add to it. Olly

You will also need to learn to use charts and find your way around. Take a look at a free planetarium like Carte du Ciel or Stellarium. Just going outside with a telescope and no plan would not be productive. There will be an astronomical society near you: there always is! Olly

I don't believe any of us means to be harsh but you are swimming in troubled waters, I think, given the current state of the internet. There is so much ill-informed or under-informed stuff out there that people with enough personal expertise to see through it are getting rather short-tempered about it. And there is now this new breed of self-styled 'influencer' to add to the virtual detritus in which cyber space is drowning. There are two schools of thought regarding beginners posting advice. Some take the positive view that they are inviting their viewers to 'learn with me.' Others think that they should desist from posting advice till they know what they're doing. I was a teacher, too, for 23 years and I lean towards the latter view without entirely dismissing the former. Olly

Indeed. It just wasn't obvious to me that this was your rhetorical device, for which I apologize. We could be misjudging the OP, as you suggest, but I'm not entirely sure how we might be making such an error. He says, 'I am mainly thinking of DSO ie. small or wide-field nebulae and galaxies.' I cannot for the life of me see why a person who does not know the difference between the imaging of small nebulae... ...widefield nebulae... ...or galaxies... ...should feel the need to publish information on this subject when those who do know have done so already. Olly

I don't see the connection, to be honest. I just feel that social media are full of tutorials made by beginners who - OK, I'll say it - don't know what they are talking about. Yes, I know I take an unfashionable view of this. Olly

My chances of getting a 3D printer to work are... zilch! I could make a fine focus out of proper materials, though: wood and metal. I just don't want to!!! lly

Ouch! We are using a (very crappy!) toothed belt system and hoping to get it to work. I can imagine designing and building a much finer adjustment system but I am hoping not to have to!! lly

That is like asking, 'What car would you buy for club racing, track days, towing a caravan and collecting materials for building a new house?' The question cannot be answered. May I ask you a blunt question? I don't wish to be rude, but if you don't know this, why are you writing an article about astrophotography? Olly

I'm a mono diehard but I think that, maybe, I may eventually have died! I'm working with a 2600MC in a RASA 8 and it's a quite incredible camera. I'm also setting up the significantly less expensive TS version of a camera with the same chip but can't comment on that, so far, since we're not up and running with it. Anyway, the 2600MC is a knockout. Olly

Thanks Vlad. We'd considered this but we want to use the lens wide open at F2 so we wonder if we really have any room to look for more extra-focal distance without introducing off-axis distortions. We can experiment, of course, because we have an adjustable back-focus gadget. Olly

Hi All, We are setting up a Samyang 135 with a ZWO focus motor for unattended robotic imaging. Has anyone done this? The problem is that the lens can't be driven a long way past the infinity stop in order to build a vee curve, whereas it can on a telescope. We'd be grateful for any pointers on how to go about this, with what software, etc. Thanks, Olly, Paul and Peter.

I'm sure all at FLO are worked off their feet. Bon courage! Olly

80% is just a rough guess as to how much more stretching an image is likely to take. Basically I give it the StarX treatment when I think I'm nearly but not quite fully stretched. It's flexible. It's easier to judge the fully full stretch with the stars out of the way. Then, rather than stretch the background beyond its final ideal brightness, I prefer to go from Levels into Curves, pin the background where it is (Alt click on a bit of background) put a fixing point below that and stretch above it. This example has made an unholy mess of the image but I'm just explaining the method. In many stretching tutorials the imager stays in Levels and continues to stretch, taking the background too high and bringing it back down by moving in the black point. I can see no reason to do this because you are just lifting the background above the noise floor. You do need to be careful, when stretching only above the background, not to create an artificial step in the transition from background to faint stuff. To avoid this I'm very careful when choosing my background sample and I do a lot of small lifts rather than one big one. Olly

I wrote this Photoshop workflow down for guests and thought I'd post it here as well. This is my current StarXterminator workflow, though it's not set in stone and owes much to Ciaran here on SGL. Star Xterminator 1 Log stretch the image to about 80% of full stretch and set the black point not too dark. Save as Stretch1. 2 Run StarX. Save as Starless. Process Starless as you see fit. I use Noise Xterminator as a bottom layer and erase the bright, sharp bits which don’t need it. I also fix the background and stretch a little more above that, using Curves. Do all contrast enhancement and sharpening to the starless image. Save. 3 Paste Starless over Stretch I. From here on I have made an Action: 4 Ctrl I to invert both layers. 5 Top layer active, set blend mode to Divide. 6 Stamp down. (Alt Ctrl E) This gives a new top layer. 7 Ctrl I to invert that layer. 8 Flatten image. (Do this under the layers palette from the top toolbar. Ctrl E does not work for me.) 9 Save as Stars. End action. 10 Paste Stars onto the processed Starless, blend mode screen. 11 Use Levels mid-point slider to reduce stars. 12 Small stars benefit from contrast reduction. (Just the basic Image-Adjustments-Brightness and contrast from the toolbar.) Large soft stars benefit from contrast increase. Usually there are only a few large soft stars so I lasso them, increase contrast, then invert the selection and reduce contrast to soften small, hard pointy stars. Another way to soften them is to give a touch of Gaussian blur or to reduce the opacity of the star layer by a tiny amount. Stars which still stand out un-naturally against nebulosity can be settled into the image by giving the starless layer a dab with the burn tool right under the star to restore a bit of stellar 'glow.' Olly

Great result. In my view, Blur X gives you noiseless sharpening and finds the same fine details that emerge from unsharp masking, except that they are finer still and don't introduce the severe noise of USM, which can only be used on bright regions where there is enough signal to resist this noise. I'm also persuaded (or very nearly persuaded) that BlurX improves the smoothness and contrast of faint signal just above the background. Olly

I work from linear TIFFS. Olly

It IS exactly what you are looking for! I haven't been imaging galaxies recently because our present rigs are 'fast and wide,' but I'm working through my old galaxy collection and enjoying the combined benefits of deconvolution and star removal-replacement. Olly

I know what you mean but this is so easy. You open the image, give it a screen stretch (Ctrl A will do), open BlurXterminator and apply the defaults. There are not many slider choices and you can ignore them if you feel like it. From there onwards processing is significantly easier. Olly

I won't be doing any star shrinking now that I can process a starless object. It has to be the way to go. You can stretch differently and more honestly when you don't have to constrain the upper brightnesses in order to manage the stars. The clean separation of stars from object is an incredible breakthrough, I think, and one which also makes processing more enjoyable. No more agonizing over where to flatten the curve when stretching! Olly

As others have said, IC342 is an obvious candidate. I already had a StarX version but starting everything from scratch and anticipating what the three Russ Croman tools would do, I was able to process accordingly. This gives us an entirely new way of imaging the Hidden Galaxy. If you haven't tried it before the starfield is brutal. Not any more it ain't. Big thanks to Russ Croman. This is full size on my Smugmug page if you go to full screen and click on the image. The BlurXT version was, again, smoother, sharper and deeper than my original. https://ollypenrice.smugmug.com/Other/Galaxies/i-Chmdm43/A Olly

I would struggle to do without PI's ABE, DBE, SCNR green and now BlurXT. I also use LHE but as a layer in Photoshop! That's all I use but I rate them as 100% essential. Olly

I can't post the magazine article online, I'm afraid. It belongs to Astronomy Now. However, I have started playing with some old 14 inch linear data and putting it through BlurXT. My initial impression is is that it is less spectacular on the over-sampled data of the big scope, suggesting that the improvement levels off as you move up the scale of resolution. I thought it helped the nebulous stuff more than the stars. During the week, though, I'll see if I can put more time into this and post my findings. I could be wrong but my first guess is that the new processing is going to close what is already a small gap between large apertures and small. Olly