ollypenrice

Sure. Resolution of detail is generally dominated by the sampling rate of the imaging setup, measured in arcseconds per pixel. There is a calculator here: http://www.12dstring.me.uk/fovcalc.php The resolution goes up as the pixel size goes down or the FL increases, or both. You may also be limited by the optical resolution of the telescope, particularly when using small refractors with small pixel cameras. There is little point in trying to image below about an arcsecond per pixel because other factors, notably the seeing and the guiding, will blur out the theoretically possible detail available below that. When you try to over-sample in this way you simply reduce the amount of light striking each pixel and slow down the imaging process. Your final image will give you a bigger object but a bigger one containing no detail not found in a properly sampled one. As pixels get smaller it becomes increasingly possible to over-sample. For example, you could put a Canon 5D Mk4 in a C11 and this would be sampling at 0.39"PP. This would be an utter waste of time because that level of detail cannot be resolved and, at a more realistic focal length, you could capture the same real detail while putting more than twice as much light on each pixel. My own high res imaging is done at a metre focal length (TEC140 refractor) and at 0.9"PP (Atik 460.) This gives a decent 'real world' result in my view. A 10 inch F5 Newt would give a similar result with slightly larger pixels and would be faster because of its greater aperture. Just keep your sampling rate realistic. Olly

I think that's a beautiful rendition, revealing less of the gas but more of the dust than we usually see. It absolutely must be seen at the higher res (click on the image and click again) because it holds up superbly and the details within the Trunk are gorgeous. Crazy-deep Ha has its place but it isn't the only way to go and this is one of the most subtle versions I've seen of this target. If you do want to emphasize the Ha a little more and have Ps (I don't know about Lightroom) the simple trick is to go into Selective Colour, Reds, and move the top slider left to lower the cyans in red. This always brings out Ha signal. Olly

No, it still hooks on using the standard two bolts which sit on the dewshield. I suppose it would be better to mount it on a new card so that it was centred on the lens but since it gives a perfect result as it is I've never bothered. Olly

I use a mask designed for an 85mm refractor on a 106mm refractor and find it works perfectly (checked by also measuring FWHM values at the same time.) Olly

The cure for aperture fever is focal length. In this telescope, at the nearby Observatoire des Baronnies, a 31mm Nagler is an excellent planetary eyepiece. In the end an enormous aperture inevitably ends in a small field of view. Personally I wouldn't want that. Olly

I'd begin by finding out what sampling rate you'll get at various focal lengths with the camera you intend to use. Because pixels are getting smaller you can reach high resolution with shorter focal lengths these days. Other factors: - You'll be lucky if your seeing allows you to get down to 1 arcsec per pixel and very lucky if it allows better. - Your guide RMS in arcseconds needs to be half or less of your imaging sampling rate. (So to image at 1"PP your guide RMS needs to be no higher than 0.5".) - If going for a 250 or 350 Newt, are you well protected from the wind? Olly

I've been mightily impressed by a QHY OSC camera recently but if you're mainly going to do narrowband then mono still makes more sense. Very good Heart nebula! Olly

The term 'magnification' isn't used in astrophotography and with good reason. It is literally meaningless. What is being magnified? Certainly not the Ring Nebula because that is quite a bit bigger than any picture of it ever created! We say something is magnified 100x when an eyepiece magnifies an image on our retina by 100x. That makes sense. A scope/camera doesn't produce an image on our retina so what are we magnifying? Nothing. We're not. So what are we doing? We are using a telescope to project an image onto a camera chip. The longer the focal length of the telescope, the larger that projected image will be. But -and this is very important- how many pixels do we put under that projected image? The more the pixels (i.e. the smaller the pixels) the larger the final image will be. The useful and meaningful unit here is arcseconds per pixel. How much sky lands on each pixel? The smaller the amount of sky per pixel, the larger the final image will be. This is the closest we can get to talking about 'magnification' in astrophotography. It is worth getting your head around this because, until you do, you'll be confused. Olly

There's little point in considering the optics without considering the camera and the mount since they make a single entity in use. So the first question is, 'What is your guide RMS in arcseconds?' (If you give PHD your guider's pixel size and focal length your RMS will be given in arcseconds.) Whatever is your guide RMS, mulitply it by two to get an idea of the resolution your mount will support. If your guide RMS is 0.5 arcsecs, don't try to image below 1 arcsec per pixel. The resolution of an imaging rig is not determined by focal length or by pixel size but by both. There are lots of online calculators but I use this one: http://www.12dstring.me.uk/fovcalc.php You then have to consider the chip size and whether or not 'scope x' can cover it. Not many scopes will cover a full frame (35mm) chip, for instance. Olly

Art? That's a bit hard on art! The second image is just wrong. Wrong does not equal art except in the parallel universe of that stupid astrophoto competition. 😁 In my understanding the offset in OSC imaging concerns the simple matter of which pixel has been filtered red, which green and which blue, across the chip. This is the Bayer Matrix offset. Not all chips have the same pattern so, for example, the top left pixel on your chip might be under a red filter, or a green, or a blue. Your stacking/calibrating/debayering software needs to know which pixel is filtered to give which colour or, obviously, it cannot produce a correct interpretation of the data. If 'offset' has been given another and different meaning since I last calibrated OSC data I may be entirely wrong. Olly

Hubs have given me plenty of distress in the past... Olly

That looks super and out of this world for the exposure time. (My suspicion of the blue patches didn't begin by my not remembering them in other images. Rather it was their shape, colour and distribution which looked artificial, particularly their colour. It was only then that I looked for other images. The odd colour was easily explained later by a simple absence of red.) Olly

I've only just seen this but I used an idea found in Phil Harrington's book Star Ware. Essentially you make a triangular wooden palette to fit the footprint of the tripod. This stands on feet high enough to let you slip a sack truck under the palette. You pop a 'safety belt' around the scope to secure it to the sack truck then tip that backwards to allow you to wheel the lot to your site. (The scope-tripod is permanently attached to the palette.) This works if your store-to-site route is flat. Like a Dalek it would be easily defeated by a spiral staircase!!! 🤣lly

Great result and what's particularly reassuring is the strong blue signal from the faint reflection nebulae (and they are faint even if they don't look it here!) If you're feeling fired up there is lots more shapely dust below the Shark itself. Because the noise is so low I think you just about get away with that level of brightness but in order to give the image that 'something held in reserve' look I might ease it down a touch if it were mine. Olly

Something like this? I was lucky enough to get a personal tour of the Institute of Astro Physics in Marseille and saw this narrowband filter under development. It was destined for the VLT and subsequently for the OWL. Being a tad large for the average draw tube it's designed to sit in the middle of one of the azimuth bearings at the Nasmyth focus. It can isolate tiny fractions of a Nm at wavelengths going well beyond the visible spectrum in both directions. And therein lies our single ray of hope: you'd only need to buy one! 😁lly

It would take me 84 seconds to show you and the arduous four clicks involved might not be beyond you! 😁lly

Sorry, please delete.

This actually took 84 seconds in Photoshop, just using a screen grab. (Yes, I timed it honestly!) 🤣 Give me the full two minutes and I could do it properly. Olly

Don't tell me you've never been round the back to shoot it from a different angle? Olly

Photoshop, Layers, ten seconds! 👹🤣 Olly

That's excellent. The only thing I'd add would be a blurring of the inner core which looks slightly stellar. Olly

Same for me. Olly

'...and we can't really say that this is intentional by person taking the photo, can we?' Of course we can! You use the tools which give you the effect you're looking for. If the effect is positive, fine. If it's just an irksome artifact it will create an irksome image - which is just what happened with Andromeda. In the image you post here the distortions are coherent and aesthetically meaningful. They seem to roll around the subject in an harmonious way. Also, in this image, the foreground is sharp and the background soft so there is no conflict with the natural way we see things. It's a fine image - though it would be hard to go wrong with that young lady! The macro effect on depth of field is only OK for me when the whole subject is sharp. I simply don't like macro images in which that isn't so. Bokeh in the background is fine. It's how we see things in real life. And it's fine in macro for me if the subject is sharp because that mirrors concentrating on a small object in life. Olly

I find this image really quite hard to look at and positively unpleasant. Maybe it's just me but the inversion of sharpness foreground-background really makes me recoil and feel queezy. As a former English teacher I'm quite happy to argue for arguing's sake! I used to get paid for it... 🤣 OK, as an M31 it's very dull, partly out of focus, has little resolution, an unremarkable core and it doesn't go very deep. Without the tilt, would we be talking about it? So it's meant to have a 'macro' look? Why? What's the point? And the image replicates the galaxy's plane relative to us? Really? Lost on me. A wider point: Art and literary criticism cannot replicate scientific reasoning and is not the same kind of activity. However, it is rigorous in its own way because it must make reference to the work itself. So I have some specific questions making close reference to the picture. - What is achieved by having a full width horizontal band in focus right across the image? - What is the significance of the deviation from round seen in some but not all of the stars? What does the particular orientation of these elongations contribute to the image? Olly PS I feel particularly strongly about this because the art world was hijacked years ago by charlatans churning out easy gimmicks which were there to be talked about, not looked at. (See Tom Wolfe, The Painted Word.) I dislike the way this competition, in which Tom and I were once runners up, is trying to pull the same kind of hijack on AP.

Sure. Firstly, as a photograph of Andromeda, it is poor. I think we can probably agree on that but you might (quite reasonably) say, 'It's not trying to be a normal photo of Andromeda. It's trying to give an impression of Andromeda's distance behind the foreground stars.' So my second point would be that it fails, utterly, to do this. The distortions of the out of focus stars contribute nothing to the image's 'story,' they are just artifacts of the cheap trick used to create it. The distortions lie in two horizontal bands across top and bottom but not at either side midway up. This has nothing to do with the 'story' either. It's an artifact of the cheap trick... etc. (The distortions should be spherical in order to tell the story properly.) The sharp focus of the distant object and blur of the close gives precisely the opposite impression of distance. (Distant objects are less sharp than near ones.) In other words the distortions are pulling the mind in one direction and the focus in the opposite direction. Both the idea and the execution are crude and visible. In good art the artistry is 'invisible' in the sense that the viewer responds to what the technique is there to introduce rather than see the technique itself staring at them. We should first be moved and only later wonder about how it was done. Olly