ollypenrice

There's precious little in it, as you say. Broadband might be a harder test for the small scope. Still, your findings match my own. Olly

Yes, good point. I dithered over the overall brightness and will look again. Cheers, Rodd. Olly

On reflection the earlier image was more milk shake than whisky so I dedicate this one to Louis D. Olly

You can always do this in any graphics program but whether or not you do so is a matter of choice. You've done two things: 1) Cut out the faint signal which took a lot of capturing. That's to say the galaxy's faint outer glow. That's a net loss in any terms. This happens when you bring the black point in too far and clip the left hand side of the histogram. It also results in a flat, jet black sky. 2) Increased the colour saturation. This is a matter of taste but the truth is that M33 is not a very colourful galaxy, probably because of its astrophysics. It does not have particularly well defined spiral arms so is not as active as some spirals in terms of star formation. However, saturation is a matter of choice and my processing was something of a reaction against my original M33 which had higher saturation. I was also making a statement against the intense colour which is becoming the norm in AP. I probably over-did it (or under did it. ) Anyway, it's nice to know that the colour is there if the imager wants it! Olly

It is vital to get behind the phrase, 'Get up close to small objects,' because it has two meanings, one of them misleading and the other one valid. Misleading: a long focal length allows a small object to fill the frame. It does, but with what does it fill it? If you are over-sampled (ie trying to resolve details which are lost to atmospheric turbulence even before they reach your telescope) then it fills the chip with mush. This is called 'empty resolution.' Your pictured object is bigger but contains no more detail than it would from a shorter focal length (or bigger pixels.) It is no different from taking a small picture and resampling it upwards. In fact the latter would probably be better because the initial image would be likely to have more signal per pixel. Valid: The closest you can get to an object is to image it at the maximum sampling rate that the seeing, guiding accuracy and lens-camera quality will allow. This has literally nothing to do with how big the object is in the frame. It is exclusively derived from sampling rate in arcseconds per pixel. What area of sky lands on each pixel? That's it. That's as close as you can get. So, yes, you'd be better off not oversampling in the first place and so get more light per pixel. With more signal the real detail you can extract in processing will go up. When it comes to presentation the best you can do is expose for long enough to get an S/N ratio good enough to present the image at full size (1 camera pixel given 1 screen pixel) and crop as necessary. I used to shoot small objects in a 14 inch ODK with an FL of about 2.5 metres. I then switched to a TEC140 with a FL of a metre. I found no significant difference in resolution and the TEC was less troubled by very bright stars and never required any maintenance. Olly

I think it's there already though not as clear of the background sky. That's just a matter of exp. time. Olly

On the other hand, consider the various incarnations of front-camera imaging variants of this scope. They all have whacking great cables routed in front of the corrector. And look at that big secondary mirror in the light path. Try it before you panic. Olly

I've been experimenting with all sorts of ways of recombining extracted stars after de-starring and have concluded that the best method is the one outlined by Xiga in the link below. However, I think you also need to think about when, in the processing, you extract the stars. If you leave it too late you'll have the problem that they are already too big and will need reverse-processing. So far, I'm favouring a partial stretch to the point at which the stars are about where I want them to be at the end. At this point I remove them and continue to push the starless stretching as hard as I can. I then follow the method in the link, giving a tweak in Curves if necessary. I never expect anything in processing to be formulaic. Every step also needs a bit of thought. The key point is that there is no point in removing the stars and then putting the same ones back! At the moment I'm favouring a fairly early removal, a continued stretch of the starless and then a replacement.

As I'm sure you know, you have no hope of resolving detail at 0.47"PP. The seeing will blur you out to two or three times lower resolution in long exposures. However, that blurring will not be directional. We'd expect it to give you larger stars but not eggy ones. To my mind, the same would probably apply to a system guided at too coarse a pixel scale. Why would the error be greater in one axis than the other? Because that's where the greater error is? Yes, maybe - but no more than maybe. A guide RMS of 0.5" to 0.8" should cover what the seeing will allow. The quick test is to double it, meaning your worst case scenario is to lose resolution after 1.6". Are you resolving below 1.6"PP? Have you plotted the long axis of the egginess you see against the orientation of RA and Dec? This is most important. If it doesn't align then, as already suggested, look to tilt. And, after all that, where is this egginess? I struggle to see it. If you have to pixel peep to see it then your problem is... pixel peeping! Don't do it. Its only purpose in life is to spoil your enjoyment of a good image. Olly

Team Viewer for free is OK for a while but they very soon flag you as a 'professional' user and block you out. A nasty business model intended to trap 'free' users. If I were a user I'd accept that I am, indeed, a professional user but I don't use it. It's my entirely amateur friends who do so. Olly

Some wild colours out there! I take your point about my relatively well defined outer glow but I'll say in defence of my image that I think there are hints of very faint spiral structure in that glow which I haven't seen elsewhere - though that will only be down to my random selection of views. Olly

I like both your images, Carole, and don't think there is a clear winner. However, narrowband stars are small and tight anyway and the nebulae more structurally defined than in broadband. This means that NB images are in less need of star control for two very significant reasons. It's in broadband images that the separation of stars from nebula comes into its own by allowing far more decisive processing. I don't see the new technique as being only, or even primarily, about reducing star size. Rather, it's about enabling a more assertive processing of the rest of the image, a processing which would damage the stars or cause them to become oppressive. It is so much easier to enhance local contrasts (to borrow a term from Noel ) with the stars removed. Perhaps they look unreal because we're used to seeing large stars which are, in fact, simply an artifact of the imaging system? To my eye a nebula looks far more real when it it not obscured by a bombardment of stars. Small stars in images have been with us for a very long time, of course. The technique for creating them was and is simple but expensive: use a multiple metre telescope with minute spot sizes. Do the professional images with small stars look unreal? Not to my eye. But, sure, like any technique it needs to be used sympathetically. I also think it's a wonderful technique for budget or portable imagers since it allows small telescopes to create the large telescope look. It also transforms camera lens images, the star size being the perennial give-away with lens shots. A Samyang 135 goes from good to astounding to my mind. I used to envy the NB imagers their tiny stars and strong local contrasts. Now I feel I'm entering this territory in broadband. Olly

Here's a hybrid combining my old TEC140 HaLRGB CCD image with the RASA. Opinions welcome. The RASA went deeper, without any doubt, finding the smooth outer glow which looks slightly artificial, perhaps, but which I think is genuine. The RASA had 6.65 hours, the TEC about 30. Makes you think... Olly

Thanks Goran. I have that link but am unable to locate the PsCC program file on my PC. I also have, and want to keep, PsCS3 which I can find. Anyway it's a 2 second job to write it as an action. Olly

Another one with Paul Kummer. You wouldn't normally choose a scope with a 400mm focal length to shoot galaxies but , hey, pixels are getting smaller to match. Anyway, what happens if you do? Here we go: This is quite a heavy crop of the starfield and has no additional Ha. It's RASA 8, ASI2600MC, Avalon Linear. After DBE in PI it was processed in Ps and incorporated Russ Croman's StarXterminator in the workflow. Thanks to Ciaran for suggesting a better way of recombining the starfield. It worked a treat and is explained in this thread. Merci Monsieur! (At some point I'm going to try to work out what I'm actually doing when I follow this method but this time I just did as I was told. ) Olly

Beware of the highly controversial F ratio myth.' Exposure time going as the square of the focal ratio is perfectly correct when you are altering the F ratio by altering the aperture, and the focal length remains constant. When you do increase or reduce the F ratio by altering the aperture you do, obviously, increase or decrease the amount of incoming light. That's why the rule works. But... when you alter the F ratio by using an extender or reducer at the back of the tube you have not altered the incoming light in any way. All you are doing with your rear element is putting the object photons onto fewer pixels (reducer) or more pixels (Barlow.) I think it's important to understand the difference in order to be able to decide whether a rear elemnt is worth it or not. When you say, 'the light levels being received drop to a quarter of what the originally were,' it would be better say that they are reduced to a quarter per pixel but that they land on four times as many pixels. Olly

The Barlow does not affect in any way the number of photons from a planet which arrive at your camera. The light entering the front of your OTA has no idea whether or not there is a Barlow at the back of it so it is the same light. What the Barlow does is distribute it over a larger number of pixels, meaning each one receives proportionally less light in exchange for higher resolution. Since we can collect photons over time this matters very little in planetary imaging since the total exposure time is short anyway. A deep sky imager might feel differently since exposures are measured in hours. Olly

Paul Kummer added a second panel to take the original image over to include the red emission nebula Sh2-64, along with further gas and dust in the Serpens Molecular Cloud. He also pre-processed the data. The post processing, here, is mine and mostly Phtoshop. RASA 8, ASI2600MC, Avalon Linear based at my place but driven from the UK. Olly

Thanks Ciaran, I'll give this a go. Although I say that I replace the stars using blend mode lighten, I do a lot of tinkering about, mostly in Curves, when I have them as a top layer like that. I don't find I can just drop in them in as they are. They tend to look very hard without adjustment. Olly

Exactly like yours, Goran. No dust bunnies, ever, with the RASA. In truth, flats make little difference since everything we get can be dealt with in ABE, though we do use flats. Like you, I think its the F ratio blurring them out, though the system is also very well sealed if using an OSC. I've had a RASA 11 in my hands and would be very doubtful about an EQ6 for it. Olly

I'm just off out, now, but I would strongly recommend 3 Photoshop astro plug ins. Astronomy Tools from Pro Digital (formerly called Noel's Actions.) StarXterminator and Noise Xterminator from Russell Croman. These are mighty additions to Photoshop. Off the top of my head your colour balance is leaning towards green* and local contrasts could be boosted but the data look promising. Olly * Use the Eyedropper set to Colour Sampler and 5x5 Average to measure 4 separated points in the background sky. I aim for parity in all colour channels, around 22 or 23 in R, G and B.

I don't know it at all. I'd just use a finder-guider with a camera known to PHD2 and use that. Once it's focused and calibrated (which is easy) it should just work. I have never found guiding difficult. Olly

I'd work on the guiding... Olly

What a shame that this production issue has arisen. Since the RASA 8 certainly can work, it surely can be sorted. But how fast? The 11 can, potentially, give a wider FOV despite its longer focal length but, of course, it will need a new mount. You all know what I'd recommend! Nothing in astronomy that I've ever owned or used beats the Mesu. I'd love an 11 inch RASA on a Mesu but, alas, it wouldn't fit in the robotic shed it would need to live in. We must all make our own calls on equipment choice and some subjectivity will come into it. Of the three iOptron mounts which have arrived here, two were dead on arrival and the third was performing badly within less than a year. The last one to arrive had a defective electronic component which iOptron could not replace because they were out of stock, so the owner sent it back for refund. I know this is purely anecdotal but, in my shoes, would you buy an iOptron mount? Olly

Yes, I'll potter away at it since I think that the quality of modern images is going to go through the roof. Olly