ollypenrice

Possibly, though with an electric wheel how would dust get in if the camera is never removed? I'd have thought this possible for many. Olly

Not necessarily true in practice. My experience suggests that the need to refocus comes from the optics, not the filters. This just means that you can refocus per colour with mono and can't with OSC. It also means that you can't when shooting luminance - at least, all you can do is compromise somewhere across the colour correction of the optics. Anyway, being a hare out of focus is really no big deal in RGB. After all, you can bin colour and still get a sharp result. Likewise I rarely find that there's any need to shoot flats per filter. It's possible to get a dust bunny from a contaminant on one filter but I've found over thousands of hours of imaging that I very rarely do. Nearly all my imaging is stacked using the luminance flat for everything. In reality it works. Because I don't use robotic focus on my own rigs I sometimes just scroll LRGB, LRGB, at the luminance focus and that works fine, though I do prefer to optimize the altitude when shooting L and blue if the target is low enough for this to make a significant difference. The book says flats and focus per filter, I know, but sometimes it can be safely ignored. (I know you won't like this! ) Olly Edit, I agree that OSC is a boon for the heroic mobile imager...

Are you really sure you want to rotate to frame? Rarely, if ever, do I find it necessary. I'd much rather shoot in one of two orientations, 'landscape' (long side along RA) or 'portrait' (long side along declination. That way I can easily add more data at a future date. Recreating a random camera angle takes forever. Olly

Very impressive and much better than I'd have thought possible. Olly

Like Vlaiv, I wonder why you'd go for a Mak? Long focal lengths are good for the planets but most people can see those at home. I watched a shadow transit of Jupiter from beneath a street light in a town, years ago. When you holiday under dark skies it is likely to be at a time of year with the Milky Way overhead and lots of gloriously starry fields on show. A small scope will never be a great tool for viewing smaller deep sky objects but what a short FL can do well is give a wide field. Also, if you have a larger scope at home, might there not be something to be said for having a very different second scope like a refractor? Olly

I'm not sure how many people argue that mono is faster, but those who do are correct! It is far more common to hear people argue the reverse, that they 'don't have time' for LRGB so prefer one shot colour. The problem is that 'one shot colour' does not exist. What a so-called one shot colour camera delivers is really more like 'quarter of a shot red, half a shot green and quarter of a shot blue.' However, edarter makes an interesting point. I'd have thought that the first NB filter in the system will block the light the second one is capable of passing - unless they overlap. I'm now off to see if the internet can tell me how dual band filters work... My initial guess is that the filtration of each passband will be somehow dependent on the other. Olly

I'm happy with the Baader LRGB set and I'm very fussy... Olly

Sure, but is this offset from the filters themselves or from the optics? I ended up concluding that the filter difference was negligible with good optics (Tak FSQ106 and TEC 140) meaning the Baader LRGB filters were parfocal. Olly

I'm a deep sky photographer rather than a lunar/planetary type but I took this for fun to test my newly arrived (but second hand) Canon 400L lens. Single image, hand held but leaning against the side of the house. Lens stabilization, autofocus, click! It's better than I thought it would be. I'm not sure what this tells us other than that the 400L is very good and, above all, that good seeing makes all the difference. I didn't quantify it that night but it must have been good. So the upshot is, choose your night and your site. Don't shoot over anything warm, like houses, large areas of man made environment, etc. If you can, get to a higher altitude. We're at 3000 feet. Also, pick a season when the moon is high. And remember that good seeing can be had on nights of fairly poor transparency. A bit of haze may not be a bad thing. Olly

Part of the answer is dead simple: go for the Baader LRGB. They are excellent. I've also processed data from the much more expensive Astrodon LRGB set and felt there was no big difference. The Baader LRGB are so reliable, and used by so many well known imagers, that I would look no further. The Baader 7nm Ha filter is OK but is blown into the weeds by the Astrodon 3nm. (I have both.) So it should be, given the spectacular price of the Astrodon. I have also used the 5nm Astrodon and been less impressed. The gap to the Baader is smaller. What you get with the 3nm is the tiniest of stars and the most striking of local contrasts or structural details. However, modern processing using star removal and replacement gives a new degree of star control in post processing so you can fight back, as it were. I've had bad OIII filters twice from Astronomik and once from Baader. The halo problem is well known. Because I only use OIII to enhance LRGB, rather than to make pure narrowband images, I can process out the halos but it would be much nicer not to have to. So I don't know what to recommend for OIII, though I hear that some more recent Baaders are OK. We've had a fair numbers of doubts about the ZWO filters expressed on here. I've only read the posts and never tried them. Likewise, Chroma get a good press. Olly

Thanks. I'm not a great theorist but it seems to me that the information we really need, and don't have unless we work it out ourselves, is the value for area of aperture relative to area of pixel. F ratio was OK in the days of film but when we introduce pixels it's the flux per pixel which matters. Olly

The way you stretch may also play a part. I used to use a custom shaped curve of diminishing aggressivity and bring in the black point after each stretch. I don't do that any more. I stretch until I get the background to a certain brightness (23 in Photoshop speak) then I pin and fix the curve at 23 and below and only stretch above that. This means I don't keep stretching the faint stuff beyond its noise floor. Olly

Well, as a Photoshop user I'd try this: get the old and new backgrounds to the same brightness, if they are not already. Paste the new on top of the old with the new active. Use the colour select tool to pick out everything you regard as background and erase it. What this would do is give you your old background back everywhere except for just a small circular region around the now-smaller stars. If it worked (and I don't know if it would or not) you'd get a large part of the best of both worlds. Olly

Newts are not intrinsically light-proof in the way that refractors are. Light can enter the scope from the bottom, for instance. Olly

What do you consider to be the importance of F ratio? What about pixel size? Olly

That's a terrific image of an astonishing object, one I don't recall seeing before. I can't think of anything like it. Olly

I absolutely agree. In these circumstances I'd look into de-starring the nebula for one process and then process a star layer differently. This frees you from the need for small stars at capture. You can re-insert them as large or as small as you like and with more data on the nebula you can process for more larger-scale contrast and local contrast without getting into the noise. Olly

Much nicer without the joins. A great way to check for them before going too far in processing is to look at the mosaic in Photoshop's Adjustments - Equalize. Although you'll discard this image it really does show you any joints and colour changes. It's a brilliant diagnostic tool. I'm not sure which I prefer regarding the darkness. The darker one is more dramatic to my eye but they are both great. Olly

Thanks Goran. I think the dark ring problem you've met and the spikey, hard-edged star problem I had may effectively be the same thing - too much contrast between background and star. That's why I used many iterations of a curve like the one below when stretching the star layer. Basically I'm hoping to lift the outer part of the star more than the core. Olly

One more note: in case this version might be too 'hard' for some tastes I just produced a much softer stretch. All you have to do is paste one onto the other and you can be as extreme or as conservative as you like by moving the opacity slider. This stretch certainly is extreme. I might tone it down a bit with fresh eyes in a day or two but there's a lot to be said for the 'adjustable image.' lly

I've read Russel Croman's suggested method for replacing the removed stars but wasn't inclined to try it this time since I had enough new processing tools on the go as it was. Instead I processed the starless image to its end point and pasted the linear original image on top of it in Blend Mode Colour Dodge (Add). I didn't compare this with Blend Mode Lighten but I doubt the difference is huge. In either mode the new linear top layer is invisible because none of it is lighter than the stretched starless one below. I then stretched the top layer till the stars began to appear. They tend to look a bit hard and spikey so I used a curve stretch in which I only lifted the bottom of the curve and restored it to a straight line above that. The theory was to lift the outer parts of the stars more than their cores in order to soften them. Even so I gave the top (star) layer a bit of Gaussian blur and played both with the stretch and the opacity till I got a decent look. More stretch at reduced opacity gave some control here. Olly

I noticed the slight drift in tone as well, though on such a dusty background sky it could be genuine. I combined the linear stacks (after DBE) in Registar then checked the output file in Ps Equalize, which really shows up joints and gradients. It was a s good as I've ever seen it so I stretched the mosaic from there. As you say, starless processing is the way to go with a RASA and lets it do what it's good at. Thanks. I agree that the stars are the RASA weakness but it seems it can be worked around this way. More images will tell. I think this was a challenge for StarXterminator, though, because there were a of stars and the stretch was extreme. I'm optimistic. I'm convinced by these and looked again after Maurice Toet approved of NoiseX. He's a superb imager. Olly

I haven't but I don't want the palaver of it disappearing again! Once I have a starless image my entire workflow after that is Photoshop and Layers. That's my natural habitat! lly

After I spent an age installing it, it simply vanished from my copy of PI. I read on here that someone else had had the same thing and that it had been deleted by PI. However, it never worked well for me and couldn't handle the large CMOS files, or my computer couldn't. If I'm maligning the PI people I apologize but it vanished for me. Olly

Another Project with Paul Kummer who owns most of the rig and runs the capture side in our robotic shed, here. This is a two panel mosaic and one panel had less than 2.5 hours of OSC. That's not a lot for a dark nebula... What's new in the processing are two Russell Croman products, Star Xterminator and Noise Xterminator. Both are excellent and, together, they are beyond excellent. Star Xterminator is a game changer for instruments which don't produce good stars out of the box. (Scopes which do are called expensive ones. ) I've previously tried Straton and got nowhere, then Starnet++ which was kindly deleted by the powers that be at Pixinsight. Star Xterminator is a class ahead and I have it in Photoshop's civilized environent allowing Layers to blend the stellar stretch and the starless stretch easily. Olly