ollypenrice

Here's your widefield image with my rather less widefield superimposed on it. The Heart and Soul are in there, as you can see, but you have to get them to show via processing. Olly

And then... and then... there's Photoshop! So nice... 👹lly

Good capture. Regarding processing (and do please ignore this as no more than my personal feelings) I'd go easy on the black point. The sky is a bit black and flat for my taste. I'd let it up quite a lot for a more natural look. Also, I know that lots of new astro software likes to be 'true to the data' but, in a shot like this, it makes no sense to me to process the galaxy and the stars in the same way. To my mind this cries out for a 'Layers' approach using a common background but a separate stretch and processing job for the stars. This might not be true to the data but it might be more true to the sky. Nutshell: I like Alacant's galaxy but I would want to set it on a completely revamped background and field stars. I only say this because I think it's a cracking image to start with. Olly

Your histogram tells a story: The peak in the Levels graph is made up of the galaxy itself. The flat line to its right is from the stars. In the original data that peak would have had a left hand side rising gradually, not unlike a mirror image of the right hand side. However, in moving the black point slider too far to the right you have thrown all those faint data away. This is called black clipping and most newcomers to AP do it. It cannot be recovered other than by going back to the original and stretching from scratch. Olly

LDN1235 to paddleboard, LDN1235 to paddleboard: You need a bigger boat.

Two panel mosaic (right and left halves in this orientation) with 64x3 mins on the left and 53x3 mins on the right. Some high haze for the right hand side meant the right had more noise. This is a crop. RASA 8, ASI2600 OSC, Avalon Linear Fast Reverse, joint venture with Paul Kummer. Instrument based in our robotic shed and driven by Paul from the UK. After ABE and SCNR green in PI, this is my Photoshop processing. Images stitched in Registar. Olly Edit: scroll down the thread for a more punchy processing.

I doubt it. The present final lens group is already very radical and trying to undo its effects would be optically messy, I suspect. While @vlaiv is here I'd like to come back to an earlier discussion with Catanonia over sampling rate in the RASA. Although the usual calculation suggests that our RASA 8 with ASI 2600 should be OK working at about 1.8"PP, vlaiv suggested it would be over-sampled. As things stand with our rig, he is absolutely right. It is not going to give us results to present at 100%, though at 66% it is looking good. Further work on collimation and tilt might tighten it up but my instinct is to think it won't. Since we intended our rig to do widefield it's not a problem but I don't think the RASA is going to make a great high res instrument. F2 is what it is and, like all optical configurations, comes with its strengths and weaknesses. Olly

Nice clean result with tight stars. Olly

OK here's a version done from the 2x2 'superpixel' stacking algorithm. Obviously you've more depth to play with. Stars weren't so good though, tending to have a blue edge and a yellowish edge on the other side. It would be a lot easier if I weren't trying to extract NB signal from a broadband image. Using the dual or triband filter on targets like this would remove this pressure. This is still reduced to 5mb but will take an age to upload! Olly

Thanks. I just processed a super pixel stack and think it's considerably better, certainly on this target and with just 1.5 hours per panel. I'll need to do it again because I made a bad decision early on which has created colour artifacts in stars but the reduced noise lets me get a lot more out of it. Lots to learn with a new rig. Olly

I just followed your choices because they worked, Goran! I would not consider this cheaper camera for the RASA. I think tilt adjustment is essential for F2. I'm not at all sure that my tilt tuning was correct. All I know is that, in one orientation, it gave acceptable corners (acceptable to me) for the first time. The fact that it didn't do so well at 90 degrees suggests something is still out. Possibly one tilt is correcting another as things stand. For now we just want to get on with it. Olly

The full sized image is far too big to upload easily with my internet connection so this is just resized in Photoshop. I also pushed the Ha signal pretty hard with a view to a final presentation below full size. Since this is a widefield image without anything crying out for a high resolution view I would normally have stacked it in a different mode giving a binned output, but I was curious to see how the data would perform at full size. I'll try processing a binned version to see if it will let me push the Ha signal harder. I suppose it will. I haven't yet read up on what AstroArt is offering to do with the raw OSC data. This has all changed since I last stacked any OSC several years ago. In RGB debayer it offers me - binning 2x2 - bilinear 1x1 - 2 gradients 1x1 - 4 gradients 1x1 If I knew what the last three meant I'd be a wiser man than I am! Homework time... I'm not a pixel peeper and post plenty of images at full size when appropriate, mostly galaxy crops from the high res rig, but I'll put in some crops from this at full size to give folks an idea of what to expect. I'll also re-do the image from a binned stacking and post that later. Noise floor in Ha regions Corner crop, top left. Corner crop, top right... If the idea were to present at full size I would want more than an hour and a half per panel and, while the corners aren't perfect, I'm happy with them. Getting this far at F2 wasn't easy and we are outside the official limits of the image circle according to Celestron. Anyone wanting perfect stars should, I think, choose a refractor and take six times longer than the RASA. I'll chuck in one more: both the mosaic overlaps lie in the crop below, and this was on unflattened panels: Olly

Our first 'proper' image from the RASA/ASI2600/Avalon. Two panel mosaic, 36x3 minutes per panel, so just 3.6 hours for the lot! Notes: This is an Ha-dominated target so a broadband capture can only take you so far. If I lean on the Ha signal in the data any harder it does give more but at a cost of noise in the red channel. We aim to try a dual or tri-and filter later. No darks or flats, yet colour gradients and vignetting were minimal, so no DBE or other gradient removal. The two panels were stretched, eyeballed for colour balance and blackpoint, and Registar just joined them seamlessly. Remarkable. Paul manned the plethora of software packages from the UK while I bolted the bits together (which is the easy bit...) Olly Edit: scroll down for a version made from data software binned 2x2 in 'superpixel' mode.

This isn't really my recommendation but one very widely circulated in astro circles. I would keep well away from WD40 which will a) get everywhere and b) be squeezed out of the threads over time. You want something which stays put and a little boot polish has many who recommend it. Olly

We think it worked. At least, after the adjustment we got by far the best corner and edge stars we've had since using the RASA 8. There is no doubt at all that my reflection went from describing a circle to turning on the spot. Was it the right reflection??? Who knows? The camera has three pairs of antagonistic (push-pull) screws 120 degrees apart. I simply fitted the RASA camera holder, sat the camera on the top of the box above the hole and rotated it. To adjust it I lifted it off, removed the RASA plate and tweaked the screws by the smallest imaginable amount. (Note, I had three little wooden blocks glued to the top of the box to oblige the camera to turn in a perfect circle but the Celestron camera plate wasn't truly round so it went tight-slack during a revolution. The Artsky plate proved better but still not perfectly round so I kept a little finger pressure pushing the camera against the same two of my three blocks. That worked OK.) I put some masking tape round the camera and numbered each pair of screws so I could write down each adjustment and undo it if necessary. As it happens the second adjustment nailed it. Nice surprise! Parallel surfaces? To make the two sides of the box I screwed two pieces of ply together face to face and cut them in my large chop saw as if they were one. This means they are going to be close to identical in length. However, my thinking is that it doesn't matter as much as you might think. If they are not parallel the mis-directed beam reflection from a tilted chip will not describe a perfect circle but an eccentric one. This doesn't matter because you're not trying to make it describe a perfect circle but to rotate on the spot. Once it's doing so the degree of eccentricity over the size of a spot reflection arising from slight out-of-parallel effects will be negligible and below the sensitivity of the test. So 'reasonably parallel' is all you need. Chip damage? I didn't use an astro green laser pointer, just a mild lecturer's red one. The test is recommended by Starlight Xpress and is used in their camera production so it must be harmless. Olly

Can't help on the filter but I wonder what the neighbours think about that light. It's absurdly high and seems to shine straight into a lot of bedroom windows. Might it be possible to get together and approach the local authority? Olly

Those are great images. I'm very much looking forward to doing some of these dusties with our setup. The reflection nebulosity in the first one is particularly attractive. Olly

You say you did your master darks in your darkroom. Our ASI camera has a metal chip cover. You should certainly use this for taking darks, but perhaps you did. Keeping light out of sensitive cameras by any other means is difficult to impossible in my experience. The effect you're getting would be a doddle to fix using Pixinsisght's Dynamic Background Extraction. Olly Edit: Perfect repair by Tomato to my eye.

I agree. And the field illumination of the RASA 8 on an APSc chip is much flatter than that of my Tak 106 on a full frame chip. The Tak has a 23% light fall-off in the corners, making flats essential. I haven't done RASA flats yet but I've processed several images from it and haven't noticed any vignetting. It will be there but it can't be anything like 23%. And what about dust bunnies? I see none at all, but could this arise from the F ratio? The more out of focus the source of the bunny, the larger and softer will be its shadow, the bunny. In a steep F2 light cone the dust particles are going to be massively out of focus if I've got this right. Olly

This cannot reasonably be a problem coming from the sky since it is aligned perfectly with your chip, nicely parallel with the two short sides. That could happen - but wouldn't! I think it may also be present in the single calibrated sub you present here but, in a single sub, it is much less obvious. You could check by measuring the background brightness along a horizontal line starting at the left hand edge and working inwards. Is the background in the single sub consistently brighter near the edge? My guess is over-correction in the flats, a well known problem without, unfortunately, a well-known universal remedy. Often it comes from not using flat darks but you say you've used them. Do your flats show a change in brightness along the two short sides? Maybe post up a stretched flat here? I wonder what would happen if you made your flat darks slightly longer (or possibly shorter) than the flats exposure... Olly

I went for this setup because Goran has demonstrated that it can work. I don't think there's much compromise being tolerated once the rig has been persuaded to work. Our setup is not yet working as well as his but we now feel happy with it, but we won't be trying a bigger chip in these optics. It's true that I'm fussy about image quality but I'm not, and never have been, a pixel peeper. That's not my notion of a good image. My idea of a good image is one which has something to say and, ideally, something new. I don't like noise and nor do I like noise reduction so the RASA-CMOS combination ticks those boxes. Today I was processing 35 x 3 mins from this rig and, after a hard stretch, it looks slightly noise reduced when it's had none at all, which is quite impressive. Another plus is the sheer depth that the large aperture makes possible. And then there's the different 'look' that fast optics and OSC CMOS gives. It's a change, which is stimulating. I think the biggest down side so far is that bright stars are themselves tight but they have an extended outer glow which is unlike refractor stars. Above all, perhaps, this new rig has brought a fresh spark of excitement into my game. Olly

Well done. This is a dark sky target in my book but you have it. Olly

The star alignment routines are entirely unconnected with your tracking accuracy. They are only related to the precision with which the GoTo operates. Accurate polar alignment will help but, as Vlaiv points out, you simply need to autoguide. The software, PHD2, is free and intuitive. You just need a guidescope and guide camera. I would just use an ST4 cable connection to connect guide camera to mount. Olly

I can see the simplicity of sticking to a smaller chip size but, for me, 400mm isn't a focal length I'd instinctively use in search of high resolution. We're at 1.9"PP which won't be very seeing dependent and makes the system a good compromise between speed (flux per pixel) and resolution. On the other hand the RASA should have the aperture to deliver higher resolution, certainly, when you have the seeing. Your sampling rate of 1.24 is, in principle, a viable galaxy imaging resolution. I'll be more than a little interested to see what you get on small, high res targets. The idea of just swapping the camera to go from widefield to high res has to be appealing! Olly

I only ever rotate the camera between landscape and portrait. I never feel the need to use a random angle and doing so makes returning to the target some time later a nightmare. M31 won't fit on my widefield rigs anyway without cropping the outer glow, which I would hate to do, so I regard it as a 2-panel target even with a 4 degree-wide field. Last night we corrected the angle of the camera to accurate Portrait format and star shapes were still good. However, we probably can't use Landscape with the RASA as it is since we get distorted corners that way. We can live with this. It will doubtless do mostly mosaics anyway, which is one of the ironies of widefield setups. You have a wide field and you want wider... I never do mosaics in the TEC. This is a possibility but I really don't like diffraction spikes, especially on widefield images. I think of it as the 'World war 2 cemetery look.' Last night's images, after tweaking the cable loop, seems to have round stellar glows. Olly