ollypenrice

It might be best to get your head round the notion of resolution now rather than later. Forget, entirely, the notion of 'crop factor.' It has no meaning whatever in astrophotography. It carries with it the implication that you increase the resolution with a smaller sensor, but you don't. Nor is resolution (of detail) governed only by focal length. It's just as much under the control of pixel size. What you need to know to define your resolution is how large an area of sky lands on each pixel. The more sky per pixel, the lower your resolution. Increasing pixel size and/or reducing focal length will lower your resolution and make life easier at the expense of detail. Increasing focal length and/or reducing pixel size will increase your resolution but will need better tracking, better seeing, better focus etc. The key unit is arcseconds per pixel which can be found using an assortment of online calculators such as this: http://www.12dstring.me.uk/fovcalc.php As a rule of thumb, amateur images of small targets in high resolution will be taken at around 1 arcsc per pixel or a little less. Below this atmospheric turbulence imposes its own limits. This is the tricky end of imaging! Very widefield telescopic images may be at 3.5"PP. Beyond 3.5"PP your stars risk looking 'blocky' when shown at full size but you can get attractive images beyond 3.5"PP if you don't show them full size. Chip size affects only how much sky you can frame. Having an object fill a small chip does not 'zoom you in' as crop factor implies. Your resolution is defined exclusively as in the previous paragraph. Olly

Best to convert the image to JPEG and load it straight onto here. Olly

Seamless, well judged sharpening and a good call on the framing. Olly

I used to use it and only stopped doing so because guests preferred the more familiar PHD2. It did involve opening a lot of different windows but it worked well. I particularly liked the scattergraph. Olly

Shoudln't be too difficult. If you have Noels' Actions (now called Pro Digital Astronomy Tools, I think) there's one called Remove Horizontal (or Vertical) Banding. I use it to remove a 3 pixel wide dead column on one old CCD camera so it should fix yours. I copy the image to make two layers and run the action only on the bottom layer. Then I activate the top layer and run the eraser over the repaired part, so the action is applied only where needed. If necessary you can rotate the image to make the line precisely horizontal though that might not be necessary. Olly

Looks good to me. Olly

That's something I, too, thought odd. It seems more like an optical phenomenon for that reason. You'd say a flaring satellite except that it's repeated on multiple frames (or so I understood?) This similarity with Adam's line is also striking. Olly

But wouldn't this create spikes coming out of all the stars? (Like Newt diff spikes?) Olly

What more could you ask? Olly

Good stuff. It would be worth having a look at your colour balance in processing because, at the moment, you have a quite insistent blue bias. Olly

I'd try that as well. Before you try it, though, have a good look at the areas of overlap and, ideally, measure their brightness in the same place. Adjust one or both images to get them as close as you can and give ICE a hand that way. Olly

It looks pretty horizontal on here but in a single uncropped sub is the line literally pixel-perfect horizontal? If it isn't I doubt it will be electronic in origin. Olly

I'd be applying the curve to the still-linear original while it was pasted onto the processed starless. In blend mode lighten it won't be visible at all because none of it will be brighter than the processed layer below. If you now stretch it in Levels it will produce a pure log stretch, steeper at the bottom and leveling off higher up. You won't see this curve but it's the same shape as the curve in PI's histogram transformation. If this is giving hard-edged stars which look dropped in it may be because the curve is too steep where the outer edges of the stars lie. I'd call the curve below a 'soft star curve' because it will brighten the fainter outer parts of the stars by far more than it will brighten the cores. It would need several iterations and it might not work at all! I'm a great fan of the custom curve. For example, many people are scandalized by my Ha curve, which is the opposite of the above. It gives very high contrasts which I think are advantageous when you're aiming to combine Ha with red. In fact it isn't 'my' curve at all, I learned it years ago from a video by a famous imager, and I know Tom O'Donghue uses it as well. This gave me... I found this aggressive stretch gave a far more punchy result than a log stretch which, while looking nicely natural, seemed a bit soft and featureless. You should have a play with curves, and with pinning them at a fixed point and then changing the curve above and below the fixed part. That's superbly useful. Olly

Two of the best clusters, Mick! 🤣 (Actually I once showed them to a friend who was into birding but not astronomy and he flatly refused to see anything 'double' about them. I never could understand this.) Lovely image with the background light enough to allow faint dust lanes to show. Olly

Super, with good colour contrast from the gasses. Olly

I don't think it's poor at all. The processing hasn't tried to take the data beyond what it wants to give and that's always a key issue. The black point has been left nice and high and the colour isn't over-saturated. I can see that you might want to lose the golden outer glow around the stars, though. I'm afraid I don't know how to do this since I don't do any false colour imaging but I think I remember reading about how people lose the magenta halos from Hubble Palette images in PI. They invert the image so that magentas become green and then run SCNR green. There might be some way of adapting this principle toy your palette, I don't know. Olly

Hmmm, it has worked quite nicely for me but processing is a funny business. Maybe the choice of curve is critical. If the stars look 'dropped in' (and I know just what you mean) it might be worth trying a hand-shaped curve which rises quite steeply at the bottom and flattens to a straight line early. This should give softer stars. Olly

Cor blimey, Rob, that doesn't look like a lens image! The stars are tiny. I can safely say that I'm very impressed! Olly

You're getting there! Green-Magenta lie on one colour axis and now we're seeing a swing a little too far away from green towards magenta. Just dial that back a bit and you'll have it. Good dust lanes! Olly

Great! Personally I'd be inclined to combine the starless and starry versions in search of one with nice tiny stars. (I'd do it in Ps by pasting the linear original on top of the final starless in layers and changing the blend mode to lighten. I'd then gently stretch the top layer till the stars started to appear and stop when I had them at the desired size. Only the stars will appear in the blend if you choose blend mode lighten.) Olly

I prefer the original. The darkest parts look clipped to black and the smoothing is visible. For me you had it right in the first one. Olly

Sorry, I wasn't clear. Anyway the rule of thumb is that your guide RMS in arcseconds needs to be no more than half your imaging resolution in arcseconds (per pixel.) If the error is more than half you won't achieve the scope-camera resolution (though this doesn't mean you won't get a decent result. It just won't be optimal for the scope-camera.) Olly

Surely those are encouraging results. An hour's integration isn't much and you'd be able to go deeper, and do more sharpening, if you upped that considerably. There's something going on in the M45 image: there are some not-quite-vertical striations running down the middle part of the frame. They may go right across it but they only show where it's lighter. We don't see anything like this in M31 and that target is fainter, which is odd. Could these be stacking/calibrating artifacts? Try looking at some raw subs under a good screen stretch to see if they're present. The other thing I'd be thinking about would be extracting more colour, particularly from the stars. I can't help on how to go about in PI since I do it in Photoshop but perhaps someone will come along with advice. Olly

If I have this right, your camera in an Esprit 120 will be working at 0.87"PP. That's pretty much the same as my own TEC140/Atik 460 setup which gives decent results on galaxies. However, you'll need a guide RMS of 0.45 arcseconds to support that, (on nights when the seeing allows it anyway.) This is very close to the best an EQ6 can deliver under guiding. With everything working optimally on the mount I think you could get very close to required guiding precision but it will require careful setting up and tuning of the system. I suspect, though, that you'd see no real benefit from the 150 Esprit, not because of its weight but because its longer FL would take you below the resolution you could realistically achieve given the limitations of guiding and seeing. I think you'll get good results. Olly

Excellent replies both from Andrew and Jim. I think it more than a little interesting that Newton himself, in a conversation with Halley, said that he did not wish the idea of a force operating instantaneously at a distance be attributed to him. This seems to anticipate the revision constructed by Einstein since it resolves the two points which troubled Newton. Olly