ollypenrice

Normally the dust with which flats deal successfully is on some surface forward of the sensor in the light path. Chip window, filter, flattener, etc. These produce doughnut-like shadows which flats correct. A contaminant (unless very tiny indeed) on the chip itself will block light from reaching a pixel and, since the flats won't have any signal there either, a division of light by flat values will be worthless. Flats only work where the pixels receive some signal. The small dark circle you point to with your arrow will not be from dust on the sensor. It covers many pixels, is not completely dark and is round. It will be on a surface above the sensor but, being small, it will be close to the sensor. (There's a formula somewhere for calculating the distance of the contaminant from the chip. I dare say it would Google but the answer probably wouldn't be much help. The link I had on file is no longer active.) I'm wondering if the unsuccessful correction comes from the possibility that the contaminant is slightly reflective and responds differently to the bright light of the panel than it does to the dark night sky. It might be worth dimming the panel with typing paper and upping the exposure time as Alacant suggested for other reasons. Olly

Yes, this is what makes the most sense to me, looking at the bandpasses. So the filter might be good on targets rich in Ha and OIII but will be destructive of reflection nebulae because the broadband blue is blocked. This will also slew the star colour towards red, as AKB points out. Olly

Flats won't remove gradients from the sky and, even at my site (SQM reaches 22), I have residual gradients on almost all broadband images, which I fix with DBE in Pixinsight. Even on the zenith you're pretty well bound to get them. Nor will flats correct for dust actually on the chip because the affected pixels receive no light. For all that, I have, like you, had occasions when my flats would suddenly stop working and I never did get to the bottom of it. The problem was unique to a rig which was capturing in Nebulosity, which makes me think it was to do with the capture process. I shot a set of flats capturing in AstroArt and these worked perfectly for some time - and then didn't. Mystery. Olly

Steve has it. Actually I think that most cases of non-parfocality arise not from the filters but from the optics. No Apos are literally apochromatic so different wavelenths have slightly different focal lengths. The blue channel always sorts the men from the boys amongst the apos! They have to focus all the blue wavelengths to the same point and can struggle. On top of that you may be picking up a little poorly focused signal from the violet. Like a number of TEC140 users I find that the official field flattenener reduces bloat in the blue even though the manufacturer insists that it doesn't. Anyway, the great thing about LRGB is that the L channel controls the final sharpness and, although it obviously contains blue, it isn't dominated by it. Olly

They do, but for some reason hardly anyone follows the findings of research published in Sky and Telescope years ago. It suggested that drawing air in from one side, just above the primary, and blowing across the mirror and out of the other, was the best way to break the boundary layer over the mirror. This strikes me as far more logical than blowing air up the tube from the bottom, as most do. The most radical solution I've seen came from the fertile mind of Ralf Ottow who made a watercooled primary mirror for his Newt. The mirror has a second glass blank beneath it, attached by a spiral coil of silicone leading from edge to centre. Cooled water is pumped through this for a few minutes prior to observing. The telescope's images are out of this world. Stunning. Olly

I haven't tried it but would be amazed if you got a distortion-free field on full frame with this scope. I'd put it down as extremely unlikely. However, you can always crop if your main purpose for buying the camera is to use in for landscapes. I've been using full frame chips in astronomy for some time now and relatively few scopes can cover them. This includes a few which say they can but can't! Olly

It's a very sound image. It would improve with more data and that's about it. The background sky has significant colour noise and looks a bit 'busy' as a result. More data would tame it but if you have Photoshop or similar you can select the background sky using the Colour Range selector ...and then, with just the background selected as above, you can either go to Colour-Saturation and redice the saturation or, as I did here, go to Noise-Reduce Noise and set the adjustments as seen below. (I didn't want to make the sky oily-smooth so the basic noise reduction is set to zero, but colour noise reduction is set to maximum. Ignore the Sharpen Details setting. I just forgot to set it to zero) I thought this made an improvement when applied. Olly

It's probably more accurate to say that cooling the scope down to ambient temperature is one way of ensuring that it is free from internal 'tube currents' which are what do the damage to the image. You'll be familiar with the way mirages work: light rays passing from a hot road surface, for instance, are 'stirred around' by the heat-disturbed air above the surface and produce the illusion of puddles etc. Turbulent warm air inside a scope tube has a similarly damaging effect. In an open-tubed scope like a Newtonian the only way to get rid of turbulent air in the tube is to let the whole system reach ambient. The primary mirror is a big source of stored heat. However, when a scope has a sealed tube there is another school of thought on how to prevent internal currents: you can insulate the tube so that all the components within it stay at the same temperature. I get the feeling that this hasn't gained much of a following in the UK but it's quite widely used here in mainland Europe. In a nutshell, when all the components in the tube are at the same temperature the light rays will pass without disturbance. Olly

Ouch, I've watched it about ten times and not seen anything move! When/where is it??? Olly

As I've said several times on here, the 'numbers' on the 11000 don't look very promising. However, the data from the camera is a joy to process. Those entirely addicted to theory will dismiss this as they might dismiss astrology, but I'll stand by it. So what's good about the data from this camera and why is it so nice to work with? - Provided you have decent integration the final noise is very low. (I calibrate with Bias as dark, BPM, flats and hot pixel filter.) - The background sky comes up to a decent level naturally. (My Sony-chipped Atik 460 data has to be badgered into reaching a decent value and has many pixels which are too dark in the background, obliging me to do a special curve stretch on the background-only parts.) - The dynamic range in the final image is easy to work with, the faint stuff coming up easily and the bright stuff not easily saturated. - Stars require no effort, there are no lensing artifacts etc. - Colour is just great. I can't explain this, but it just comes out 'right' without a fight. That's both star colour and nebula colour from bright to faint. Colour from the 460 is much harder work. The part of this game which I enjoy the most is post processing and I enjoy processing the 11000 data more than any other because it is somehow incredibly co-operative. And I like the results, some of which are here: https://www.astrobin.com/3wnqx9/?nc=user https://www.astrobin.com/phk0cx/?nc=user https://www.astrobin.com/383965/?nc=user https://www.astrobin.com/380941/?nc=user https://www.astrobin.com/295716/?image_list_page=2&nc=&nce= Maybe I'm just old fashioned. I also like my not-very-modern, not-very-fast Royal Enfield as well! Best to ignore me. 🤣 Olly PS While I wouldn't consider an OSC CCD I'm still open minded on the modern CMOS.

But that's great. It will respond to manic amounts of Ha if you're so minded... Olly

Oooh, nicely blended! The whole region has faint Ha signal if you're feeling inspired!! (Or bonkers...) Olly

I recently processed a 32 panel mosaic (!) captured by Yves Van den Broek with a full frame QHY OSC CMOS camera and about 90 minutes per panel. When I compare regions of this image with the same regions captured in far longer integration with my mono CCD in HaLRGB I find Yves' results generally preferable. I'm astonished by this, quite honestly. Some relevant details in the comparison: Site - the same. Yves' rig is in our robotic shed 20 metres from mine. Scopes: both FSQ106 Taks, mine the old fluorite, Yves' the new EDX. Mine at at native FL, Yves' with Tak reducer. Mounts, both Mesu 200. Integration: can't remember mine but can't be less than 6 hours per panel, HaLRGB, Atik 11000 mono, Baader filters. The Squid in both cases comes from my rig's OIII data. No sign of it without an OIII filter. The small blue reflection nebula between Bat and Squid was better in my data so I blended it into Yves'. (Question: how good will Yves' camera be on blue targets? Don't know.) Mono CCD is the upper image. How would a mono version of Yves' camera compare? Don't know. Send me one and I'll see what I can do!!! The images have a different 'look' and I prefer the CMOS because it has gone deeper in the faint signal, particularly the dust, and allowed the nebulae to rise more naturally from the darkness. Stars were smaller in the CMOS camera. (That's worth noting.) Of course the processing was done several years apart and introduces its own effects. However, I hope this comparison is helpful. Olly

A very exceptional set of images. Hearty congratulations. Olly

There is professional astronomy, in which a PhD is the first baby step, and amateur astronomy done for a living (which is what I do) and then there's retail in which the key skills are retail skills aligned with product knowledge. As DirkeSteele says, I don't think a specific journalism qualification is needed to become an astronomy writer. I've been employed to write a dozen or so articles without one but, more significantly, my late friend Alan Longstaff made a living out of astronomical journalism. As far as I know he had never studied journalism. But... he had a first degree in biology, a PhD in neuroscience, a hefty qualification in maths and another first class degree in astronomy. In short he was a heavyweight scientist with the kind of authoritative grasp that made him attractive to publishers. Olly

I wondered about this but Tony Hallas recommends bias and dither for DSLRs rather than darks. I know little about DSLR imaging I'm afraid. Olly

I just used Ctrl A to get the screen stretch, Ian, and yes, when I subtracted the posterized background model I got an equivalent posterization in the image screen stretched in PI and stretched as normal in Photoshop. This is the same workflow as I used on the Ha which worked well. Indeed it's what I always do. For 9 hours the OIII breaks down fast under stretching. My own CCD data goes deeper in less time so I do think something is wrong with the file. Olly

It was a second stretch for me when it fell into combing, Steve but... this is working for me! Nice one Ciaran!! EDIT. Sorry, spoke too soon. This is also breaking down under a hard stretch and also produces a massively posterized DBE model, which is new to me. The Ha didn't do this. See below. Olly PS My internet has suddenly started working at supernatural speed (for rural France.) Long may it continue.

Yes, don't get me wrong, I'm not trying to engage in a mono versus OSC debate. I think that recent CMOS cameras have changed the rules. In the CCD world I felt that mono was faster, easier (in the long run), more flexible and simply better. But having processed a 32 panel mosaic captured by Yves Van den Broek in a CMOS OSC I'm happy to say that this data bore no resemblance to the thin stuff I was used to in OSC CCD. It was sensational data. (From a dark site. Yves' gear is hosted at my dark site.) https://www.astrobin.com/g82xf7/B/?nc=user My question is really, 'What does the multi-band filter add to OSC and how is it best used?' When you say, 'I think that really is the objective, for people with OSC cameras to be able to produce HOO-like images,' that makes perfect sense. I don't know how effective the filter is in achieving this but I understand the objective. Olly

Thanks Dave. Looked promising to start with (I only downloaded the OIII) but, while it isn't white clipped any more, it still isn't a happy file. DBE rejected everything I tried. Thinking that I didn't need anything but the nebula itself I took the file straight into Photoshop, aiming to dump everything but the nebula in the final blend. However, it won't stretch and falls apart when I try do stretch it, viz: It's odd that I had no issues with the Ha file, which behaved normally, but I can get no sense out of the OIII. There has to be a clue in there. It can't be to do with the brightness at capture, it has to be to with filing/formats/other IT stuff I don't understand! Olly

Piece of work! You're making me nervous but I now have workable OIII. Great job there... Olly

Well, it downloaded in no time (amazing!) but I have the same trouble as you with the compression. It looks lovely in AstroArt at 32 bit but saving as 16 bit white clips it. The 32 bit TIFF won't open in PI for me. This is beyond me. (Not difficult with IT issues...) Can anyone help? So frustrating, the stack's lovely. Olly

I'm speaking sweetly to my internet connection and giving it all the encouragement I can. I may be some time... 🤣lly

Since Yves and I posted a mosaic heading the other way from the NAN I thought it would be interesting to see what it would look like combined with Ciaran's. Ours was OSC so this is the greyscale, posted with Ciaran's permission. I didn't try to adjust the field curvatures so there is some distortion, but this is a lot of sky! Olly

What kind of pictures do you aim to take? I'm never entirely sure what the end product of these multi band filters is meant to be. I recently processed some L-enhance OSC data and found, as you'd expect, that it passed the Ha and OIII but subdued the broadband blue. So what's the picture aiming to be? A kind of one shot HOO? I'm not knocking the filters, not at all, but I'm genuinely unsure of the objective. I could imagine using such a filter in conjunction with a stack of unfiltered OSC images rather in the way that I add Ha to enhance red and OIII to enhance green/blue but I don't know whether that would work. As I've said elsewhere, I understand that the L-enhance passes blue in the H-Beta line but that is not the blue of reflection nebulae and, besides, it only traces the same gasses as the Ha. Olly