ollypenrice

? Well, I'll admit it, wild horses wouldn't drag me into doing flats at the end of ten hours out under the winter stars! The darned things can wait, and always have done, other than in summer when it is impossible, here, to cool the cameras by day. If, in summer, I need new flats then I do have to shoot them in the wee hours because shooting them in an observatory at 55 degrees C is not really an option! But as for being superstitious - sure. Oh yes. Like most imagers I have a shedload of personal superstitions. Eg, Never use software to do anything you can do manually, Never add a gadget to 'simplify' your rig, Never use a hub when you can add another cable, Never listen to theory when you can use experiment... I could go on!!! But I'm a dinosaur and know it. Olly

I use both Petzval scopes (whose flatteners are on the objective side of the focuser) and flattened triplets (whose flatteners are on the camera side of the focuser) and have never found that flats were sensitive to fine focus. And think about all those robotic scope users. They can't shoot flats 'per focus.' No, I simply don't believe that flats are sensitive to fine focus at the level carried out during a night's imaging. It simply flies in the face of everyones' experience. Olly

Yes, I use a master bias as my 'dark for flats.' The flats need this and only this by way of calibration. Don't subtract the bias a second time, once is just right! And yes, I always make my master flat before using it on a set of lights. I need to believe in it. To believe in it I need to look at it - though I can sometimes be wrong in thinking a flat is OK when it isn't or thinking it isn't when it is. This doesn't happen often but it does happen occasionally. Even with a full frame camera the TEC with flattener gives a seriously flat field, almost free from vignetting. Any vignetting that I see comes from my tight fisted use of 2 inch mounted filters. When I use the Atik 460 in the flattened TEC I would describe the vignetting as zero. You won't like this because you've already said previously that you don't like the 'one flat fits all filters' model, but when I find I have a dodgy flat for, say, green I just dump it and run the luminance flat for green. I do a lot of multi-panel mosaics and these need flat background skies. I've never had a problem doing it this way... Olly Edit: my calibration files may not be immortal but they are certainly geriatric! Flats for every night in an observatory based mount? Nooooooooo. One month's lifespan is unlucky, six months is lucky. A year is not unkown, not that I'd ever admit it on a forum... ?

John, PS does have this ability but it also has layers and the eraser tool. For many, many processing adjustments I find this a far simpler method than masking for precisely the reasons you imply when you say, 'You might need to make several attempts at getting the mask the right size/blurriness, though.' If, instead of worrying about shaping a mask, you carry out a modification globally to a bottom layer, you can then use a soft edged eraser to remove the top layer where you prefer the bottom, modified, one. And you can see the result in real time as you do so. (As Sara once said to me, 'All you ever do is use the bloody eraser!' Guilty as charged, m'lud.) Olly

Firstly any anomalies are unconnected with dust on your objective, which is far too far out of focus to have any effect. (Look at that big central obstruction in the middle of the lightpath of a Ritchey Chrétien!) Whatever is stopping your flats from working perfectly, it isn't that. Dust bunnies are created from contaminants much closer to the chip. And, although I follow Oddsocks' logic, I have never ever detected any issues arising from changes in focus between flats and capture. We refocus regularly but nobody shoots a set of flats prior to doing a refocus - do they? I've never heard of anyone doing so and they'd be pretty unpopular at star parties. ? If, inadvertently, you'd shot your flats at a very different point of focus then, yes, they would probably have an issue but the tiny adjustments we make to focus on an imaging run simply do not require replicating when shooting flats. Is there any chance of a big accidental change in focus? Are you using the TEC flattener? I do find this needs to be kept clean because it's a huge piece of glass a good way from the sensor so it can create very large, faint bunnies. PI always strikes me as hard work for stacking and calibrating and, on the two occasions when guests have tried to persuade me to use it, they've demonstrated it and found they'd done something wrong so it didn't work.... In AstroArt I just make a master flat by average combining the individual flats and putting in a master bias as a dark flat. Lots of people use this short cut. It works perfectly for me. The idea is that, for short flats exposures, there is no significant difference between a dark and a bias. I never assemble flats in the same pass as stacking lights, though. With experience you get a feeling for when a flat is 'right' and when it's suspect. I always want to look at a master flat before applying it. Why they are sometimes wrong I don't know, but occasionally they are, and I just reshoot them. Your 'cresent moon' artefact would be an easy cosmetic fix in Photoshop (he claims! Famous last words.) Copy layer, top layer invisible and inactive. Open curves. Put a fixing point on the curve at the value of the background sky next to the crescent. (Put the cursor on a bit of this background sky and alt click.) Put a second fixing point on the curve below that. Pull down the curve above the top fixing point till the crescent is no longer brighter than the background. Top layer active and visible, use the feathered eraser to remove just the crescent. Dodge and Burn brushes at 1% set to shadows will provide a final tweak. I tried on a screen grab: Any cosmetic fix is a last resort, of course. I never use them myself. Ahem. ? Olly

Exactly so. Olly

Superb job with more outer glow coming into view. I'd still be tempted to brighten and warm up the core reds a tad but this must be close to what the data has to offer (which is a lot - it's great.) My gut feeling is that this is at the limit of saturation and bang up against the noise floor. Really excellent. Because one of our cameras is very old and has a plethora of dead columns I'm used to clean-up operations, as Mrs G mentioned. I really think that there is very little which can't be invisibly mended! For a background repair in this case I'd just work on the LRGB, ignoring the defect, then do a quick stretch of the RGB to get the background up to exactly the same RGB values as the LRGB (Colour sampler tool in Ps for me) then paste the LRGB onto the RGB and erase the defect. Regarding the PI and Ps approaches I think another important thing is to pick the one you enjoy using. For me the processing is the fun part of AP and I want to enjoy it. If you enjoy using masks more than layers, or vice versa, base your choice on that. What a great thread and happy result. Olly

I'm a fan of parts of PI but, in the important matter of layers versus masks, give me layers every time. Layers and masks don't resemble each other, on the face of it, but they serve the same purpose in allowing the imager to process selectively only one part of the image at a time. Masks have to be made to cover exactly what you want to be covered and this is very difficult. In Layers you modify the whole bottom layer and then simply erase, as fully or partially as you prefer, the top layer to let the modification into the result image. You can see the consequences of each touch of the eraser as you make it and can go back as you please. I also find the Ps colour selection tool a simple and powerful way of selecting certain parts of an image. In the early days of PI its users were often tempted into gross excess, particularly in the use of HDR wavelets, but now there are plenty of nicely processed PI images. Check out Barry Wilson's, for instance, whose processing is always subtle and invisible. Olly

Although I get the hell out of Pixinsight as soon as I can (as Mrs and Mr Gnomus know ) I heartlily agree with Mrs G's advice and her result is lovely. I also like Geordie's but I prefer Mrs G's higher black point, lower saturation and stretch which keeps below the noise floor. My PI approach to RGB is always very simple: combine the colours at equal weighting, edge crop, screen transfer function 'preview stretch' then DBE and SCNR green set as low as will do the job. (The original post was very green.) However, I've recently been trying PI's photometric colour calibration and it seems convincing. After that I head for Ps. The background sky is a peach in Mr' G's rendition. Dead even, just the right brightness and just the right amount of grain with no sense of noise reduction. All I can think of to try on this rendition to take it a touch further (and it might not work) would be to put a little upward kink in the Curve just above the (pinned) background sky to pull out the faint outlying tidal structures and a slight lowering of the cyans in red (Ps, Selective Colour) to perk up the Ha components. Because Mrs G has done such a good job on the stretch my impression that there might be a tiny bit more left in the data could be an illusion. For me the perfect stretch does look as if there's a bit more left in there. Olly Edit: To emphasize a point already made, I would never stretch the colours individually. Combine first, then stretch.

The project would have been worth it just for that lower right hand corner of swirling dust, which is sumptuous. I think this is a target which is bound to look unfamiliar in NB because so much of the broadband structure is from reflection rather than emission. To see in in emission only is exciting. I'm surprised that there is so much emission nebulosity, in fact. Olly

This must be one of the most informative posts ever seen on SGL. Every day's a school day when you read an Oddsocks post! Much appreciated here. Olly

I would do this. I recently installed a replacement Lodestar into a robotic rig I host and it produced elongated stars. I then lent the guys my spare Lodestar and that was fine in the same OAG, so the camera has a problem, probably a tilted chip. I'd check it a normal scope to eliminate/confirm camera and OAG problems. Olly

I think my observatories are in multiple ownership, then. There's a badger, a local dog, two cats and a fox making claims this way - though the fox uses a slightly different kind of marker... lly

I often think a big label saying 'Septic Tank' might be a deterrent... lly

I did once, on a whim, post a star-spiked variant of an image we did of clusters in Cass. I got a good telling off for it as I recall! Olly

No, we just like a larf in this 'orrible weather! Olly

But what do they use them for? lly

...assuming all the variables are optimized. But are they? I don't think anyone on this thread has argued against aperture - have they? I certainly haven't, and certainly wouldn't. Imagers can capture more light by taking longer exposures. What they want is to see that light landing on their chips in the right place. Olly

Ooooohhhh, things are warming up. To be fair, photons which have spent only a few minutes in flight from Jupiter probably feel they've hit the jackpot if they sail into Damian Peach's corrector plate! Immortality at a stroke... Olly

Thanks, that's so much better. I'll give you a free week's holiday if you tell me how you did it.* Olly *In Anchorage, Alaska in June.

It was a really warm night and he was trying to get it to ambient. Olly

Wot, on a refractor versus reflector thread? Nobody behaves on those. Especially those reflector crackpots! Olly PS For anyone suffering from chronic sense of humour failure, this was a joke. Not really!!!!

I really don't. Mine's a scruffy old thing with a home made tangent arm microfocuser and a handwritten sticker on it to remind me which one it is on the dual rig I share with Tom. I did clean it once when Steve Richards was about to drop in! I posted a refractor image which I wanted to speak for itself. To speak for it instead I would say this: in a Newtonian image of this target there would be little there apart from diffraction spikes! And if I tried it in an SCT it would need a six panel mosaic - and there would be no hope of holding down the stars which tend to be pretty soft in SCTs. This was taken in a small (but expensive) 3 inch refractor, smaller and more compact than an SCT and much easier to mount and guide. If all you are interested in, visually, is going deeper then aperture is king. But if all you are interested in is going deeper then get a bigger scope. Visual refractor enthusiasts are not obsessed with going deeper, they are are passionate about the quality of the view at an emotional level. Deeper or better? There is no right answer. Both are perfectly valid obsessions. I've no axe to grind. As a provider I have refractors, Newts and SCTs here and I like them all. Well, I like them all visually but for imaging I really like refractors. Olly

One thing does bug me about refractors, though. Try as I might I can't see those spikes sticking out of stars. Olly

The last thing in the world that I'd do to a working scope would be to update the software. Your efforts so far tell you one thing for sure - the update software doesn't work! I'd keep well away from it. Olly