ollypenrice

I can only agree with the others. The good news for camera lens imagers, though, is that star removal tools like StarXterminator or Starnet++ allow you to push the object very hard and then replace thestars with ones pushed far less hard. Make regular use of 'Save As' during the processing. I just use the suffix P1 then P2, etc, meaning 'Processing 1' and so on. That way I can always go back. Also use Layers if you can so you can process a top layer and blink it off and on to see whether it's better or worse. Also look at lots of good images and think about why you like them. Train your eye to observe keenly. I really think this is important. Olly

In considering possible alien life I always reflect upon the Earth's being home to predation. Predation is not nice and goes squarely against most of our professed ethics about killing and inflicting suffering - but it is natural here. I can imagine an alien talking to me, though, and saying 'You eat what???' It would certainly be a shame to introduce predation where none existed before and there is no reason to assume that it will be universal. Olly

I'm not so sure about our ethics... Olly

Thanks. In that case I'm truly mystified by the difference. Olly

Who is 'we?' Are you proposing that there will be no significant difference between us and an artificial life form? In using the term 'we' as you do I have to conclude that you do think artificial life forms and ourselves will be at least highly equivalent. If so, could you elaborate on this? Olly

I certainly prefer the revamp. Your rendition and mine are most unalike with yours having much more hydrogen and mine having more obscuring dust. What combination of filters went into yours, Goran? Olly PS I put some thoughts on exploiting star removeal-replacement here:

Here are two different stretches of the same Rosette linear data in 3nm Ha. The lower one was stretched conventionally in Levels by moving the mid point slider to the left in a series of iterations and adjusting the black point each time. The upper one was stretched only twice, using a very aggressive stretch followed by a slightly less aggressive one as shown here: I don't know which rendition you prefer but anyone wanting to enhance an LRGB or OSC image by blending this Ha into red would do well to use the top one. Now the big drawback of the aggressive stretch is that it gives large, bright stars. In this case it isn't much of an issue because the 3nm Astrodon filter gives tiny stars at capture, but you'd be likely to struggle if stretching luminance data this way. For this reason I tended to use the aggressive stretch only on narrowband data though I would often have liked it in luminance for its feisty contrasts. Enter StarXterminator (the first star removal software to work convincingly and often for me.) Since you can remove and replace the stars with softly stretched ones, the case against the hard stretch breaks down. You can replace the stars with any stretch you like, including a log stretch if you prefer. This is the hard stretch re-starred with tiny stars but you have total control to do as you please. Star removal is a game changer and invites us to re-think our workflow right from the start. Processing here has been pushed to extremes to illustrate my points. These are not images I'd publish as they stand. Olly

Transformed. I don't trust Photometric CC. Sometimes it gives a credible result, sometimes not. I never know why. I think what I'd do now, with this, would be to enhance its local contrasts. In PI that would probably be with Local Histogram Equalization, the idea being to pull out the shark shape. Olly

But how much is a Sony mirrorless camera? Oll

I'm going to disagree. Older, used, CCD cameras are available at remarkably low prices and will wipe the floor with DSLRs. They will have smaller chips but the sky is full of targets of all sizes and a proper astro camera gets more signal with less noise in less time. If one turns up, go for it. If it doesn't, put up with a DSLR. Olly

Imagers have fans right on their cameras all the time without issue. You need the right kind, with contactless bearings. Olly

An unheated fan blowing across the mirror might do it. Nobody seems to do this, but a Sky and Telescope article years ago said fans should blow across the mirror to break the boundary layer. Moving air is also much less prone to depositing dew. Olly

Thanks. Why would NB sharpen the dark nebulosity, though? When I played around with it on the close-up image I found it rather softened the dark dust because the Ha had picked up some signal which seemed to overlap it, slightly reddening its edges. I see the dust in the Ha as softer and more nuanced than in broadband. Olly

After Vdb123, why not Vdb132? 😁 The reflection nebula is NGC6914. The first is a widefield OSC imaged with Paul Kummer, using his RASA8-ASI2600MC on my Avalon Linear. 75x3 minutes. After ABE in Pixinsight, processing was all Photoshop. There's no NB data in this. Then there's a closer look made by combining old TEC140 HaLRGB data with a crop from the image above, weighted about 50-50. An enormous amount of signal but I failed to note down the exposure time of the TEC image. Interestingly, though, the blue reflection nebula was roundlly better in the RASA, so much so that I included no TEC data for that part. Olly

I love the resolution and depth but, for me, the colour's out of kilter. On my screen the dust is more green* than brown and yet, contrarily, the blues are rather magenta. Too little green in the blues and too much elsewhere seems very odd. Is it just me? Olly *Edit. In the sense khaki, really.

That really is a great rendition, Wim. The IFN is coming through very naturally and contributes to the image in this case. Outstanding. Olly

Most of us have learned that our first and most fatal error as beginners lies in black clipping. We bring in the black point (the left hand slider in Levels moved too far to the right) and this clips out the fainter signal. The temptation to do this often arises from the desire to get rid of gradients, but the black point slider is not the way to do this. This screen grab shows your current histogram in Levels (Photoshop.) It is massively black clipped, meaning the left had side of the histogram peak is jammed up against the left hand edge. Your faint data are now lost and cannot be recovered. There should always be a small amount of flat black line on the left before the peak begins to rise. The way to check this is to look at the Levels histogram after every operation in stretching. You can also use the eyedropper in Ps to place Colour Sampler marks on the background. Keep it high, around 23 to 25, during processing. You can always bring it in as a very last operation but you need the elbow room above the black point for many operations. 21 to 23 is a decent background value because the night sky is not jet black. The next thing would be colour balance. Green is too strong, as often happens. Pixinsight has SCNR green but an alternative, on Rogelio Bernal Andreo's website, is free Hasta La Vista Green. These routines are vital. They pull out unwanted green and green noise. Do not shoot short subs for the core if you don't need them. Open the linear image in Photoshop, open Curves, and click the cursor on the core. If the point appearing on the curve is not right at the top you are not saturated. The need for short subs is greatly overestimated n my view, though I don't know here. I downloaded your data but can't open it, unfotunately. ('Incompatible File Format' for some reason.) However, here's the histogram on my own M31. Note the distance between the histo peak and the left hand edge of the graph. Olly

135/49=2.7. It sounds as if this will be close to your true F ratio. I'd say the lens was doing pretty darned well at that and a bit of star-rounding in Photoshop will sort out most of the problem - if it qualifies as a problem. Olly

71x3 minutes, RASA 8-ASI2600MC-Avalon Linear. Captured remotely (and pre-processed) by Paul from our robotic shed here in SE France. Post processing is mine, entirely in Photoshop. Most enjoyable data to work on. We may extend it because the area is well stocked with interesting objects including a diffuse planetary just out of shot on the right. I was most impressed by the way the RASA data held up to a pretty brutal stretch without breaking down. Olly

Super! Olly

Lovely crisp, clean image, Emil. I like literally everything about it but the golden star colour might be a favourite aspect. I'd call that perfect processing. Olly

I'd be too nervous about the physical vulnerability with the camera on, and too nervous about it holding its adjustments if taking the camera on and off. This doesn't mean I have any experience to justify this nervousness and if folks do it, and it works, then better still. I find it interesting that, contrary to what we might expect, astro camera technology has not seen particularly rapid evolution. The CCD cameras available when I started 13 years ago are not very different from those still on sale today. Chips got a bit bigger and pixels a bit smaller but nothing very fundamental changed till CMOS. Olly

It is certainly true that refractors are the easiest and most reliable optical systems to use and the case for using them is as sound as ever. However, the RASA 8 has changed my view of fast optics. The arrival of StarXterminator is a significant factor in this equation, though. The RASA was tricky to collimate but one 'fast optics' problem which the RASA has overcome is sensitivity to focus. It actually holds focus better than the Tak FSQ106N and a lot better than the later ED FSQs. This came as a real surprise, though Gorann had said the same. I agree about filters, certainly. And I would not consider for ten seconds the idea of using a RASA in a mobile setup. Call me a coward! The improvement in CMOS OSC over CCD OSC is another important factor in my admiration for the RASA. I don't know why CMOS OSC is so much better but I really think it is, though I haven't done a rigorous back to back comparison. Technology moves on, sometimes in the right direction. Olly

I've never combined them but I've read convincing arguments in favour of using both together if you have a problem. Olly

I've just spent what might be the most enjoyable afternoon's processing I can remember. 3.65 hours of OSC on VdB123. It's hardly a 'showcase' object but it's there in the sky, it's interesting and it can be done well or badly. Paul Kummer looked after the capture remotely (for him, but the rig is at my place) and did the stacking. All I did this afternoon was wring the neck out of what was there in the stack and it kept on giving. The camera is an ASI 2600 OSC. At about 1.8 arcsecs per pixel, this is a setup which needs nothing better than a decent EQ6 to give well resolved subs. We'll post the image later, maybe after a bit of re-framing with a second panel, but the point of this thread is to say that, despite having a dark site and an awful lot of clear nights each year, I am loving the RASA 8/CMOS OSC. You don't quite get Takahashi stars but you can tweak what you do get, and you get many times more photons per pixel. This rig has rekindled the fire in my imaging heart, and that's at a great site. If I had only limited imaging time the bonus would be considerably multiplied. I've just checked the RASA price at FLO and, at £2,345.00, it is cheaper than premium apos of comparable focal length and it's harder to set up. However, in combination with CMOS OSC, dual or tri-band filters and StarXterminator for star control, it has (for me) changed the game. Maybe I've just got too old for 20 hours per image? Olly