ollypenrice

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

Here's my 31 hour TEC 140 Vdb141 Ghost image after StarXterminator intervention. I doubt that anything I've ever done will end up so different from its original. It's not so much that the replaced stars are smaller, though the small ones certainly are. Rather, it's the fact that I could stretch the nebulosity far harder once they were removed. If you've never tried this target, the dusty structures are faint and the starfield is full of bright stars. Here's the new one. The net's so slow here today that I'll link to the original on Astrobin for now and edit when it's a bit faster. https://www.astrobin.com/7kt3vn/B/ Method: Not having the linear data, I just worked from the original in Photoshop. Copy Layer. Run StarX on the bottom Layer. (Large Tile option enabled.) Run Noise Xterminator on the bottom layer and use clone stamp, healing brush, colour balance, etc etc to rectify any artifacts left by StarX. There weren't many. Stretch bottom layer further than before. Top layer active, Blend Mode Lighten. Manipulate in Curves to pull down the stars at the top of the curve but shaping it so as not to give a hard edge to them as seen on screen. Gaussian blur to soften them to taste. Some stars still had a 'stuck on' look so I used an appropriately-sized Dodge brush to brighten the bottom layer just underneath them. This settles them back into the image, visually. Olly

Thanks for the comment, Martin. I'll have a look at that. Olly

I get you. On the other hand a long refractor can have a bigger moment, perhaps, than a folded light path instrument. Olly

I may be missing something but if the tracking precision (as in guide RMS from PHD) is 0.39" then surely that's what it is, as calculated using the guider's focal length and pixel size? The focal length of the imaging scope doesn't contribute to this calculation except in the case of an OAG, in which case it's also the guide scope and factored into the RMS calculation anyway. Olly

Actually I misunderstood the OP's question. I thought he wanted a photographic confirmation of good collimation but what he wants is an image of the optical train, I believe. Olly

How are you attaching the camera? Getting it centered and square is critical. You'd normally use a T-ring which fits into your camera as a lens does, then use a nosepiece, 2 inch or 1.25 inch, between that and the telescope. There are also adapters to hold mobiles but I've no idea how precisely they place the camera. My guess would be 'not very.' Olly

Yes, extremely dark skies here but I chose my location with that as a first priority. Olly

Lancashire, land of my birth! Born in Wigan, schooled in Bolton, lived longest in Chorley. You can stack images with rotation, certainly, and many of us do when we carry on after a meridian flip which gives images rotated 180. However, I always think it best to be aligned with RA and Dec. This is easy: do it by eye when putting the camera in then take a 5 second (ish) exposure while slewing slowly in RA or Dec only. You'll get star trails at your present camera angle. Just rotate the camera till the trails align with the chip. You don't have to get it perfect. Olly

F ratio also plays a big part in the precision required. A fast F ratio has a steep light cone which means a shallow depth of field. We see this in daytime photography all the time: for a deep focal range you need to stop down to a slow F stop. Even though we are shooting at infinity in AP the same rules apply. A slow system will be more tolerant of a tilted chip since critical focus only has to fall somewhere onto a single pixel. It doesn't matter where on that pixel it falls. When critical focus from one side doesn't find the same pixel as critical focus from the other you lose resolution. Olly

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Apart from the sat trails all you really need here are more subs. What you have is decent stuff and could give a very good image. Olly

Say your chip is wildly tilted from horizontal like this : \ A beam arriving from below will be reflected downwards towards the left. If you turn the chip through 180 degrees so it is angled like this / it will reflect the same incoming beam downwards towards the right. That is the test you are performing with the jig. I can't see that it matters where the incident beam hits the chip. Olly

Resolution is not measured in pixel count. It is measured in arcseconds per pixel. That's to say, how many arcseconds of sky land on each pixel. Less sky per pixel means higher resolution (all being equal...) If the optical train is a constant, that means that the only variable is pixel size. If you have larger pixels it doesn't matter how many of them you have, they will give you lower resolution. Olly

Modern fans, for a few Euros on the internet, are effectively vibrationless. I really don't see them being an issue. Olly

It isn't dead easy to align the laser precisely with the simple fixation that I used so I just went for more or less the centre. Why not? The angle of the reflecting surface (the chip) is the same right across so I can't see why it would matter. In my thinking the consequences of a tilted chip affect the image asymmetrically because all parts of the light cone create all parts of the image. In the case of the (roughly) point source of the laser only the angle of the reflecting surface matter. I'll happily stand corrected. Olly

How good is that? Perfection. Olly

What a glory! These projects can be very difficult to pull off but are worth it. I'm extremely impressed by APP as a mosaic-maker. Olly

To launch another kite, the term 'intelligence' has at least two meanings in English, as demonstrated by the way we like to laugh at an irony we detect in the term 'military intelligence.' This branch of the armed forces is concerned with information gathering and uses 'intelligence' to mean 'awareness of.' The word's other meaning refers to intellectual capacity, the ability to solve problems, etc. The curious thing is that living things can and do solve problems and detect information without involving 'awareness' in the sense we apply the term to ourselves. So when we discuss the possibility of intelligent alien life are we setting off on the wrong foot already? Should we not say that we are discussing the likelihood of non-automatic problem solvers evolving elsewhere? Olly

Just with regard to your first point, I think the importance of competition on Earth should not blind us to the idea that it might take a different form elsewhere. In the hypothetical example I gave earlier, it might be competition with a changing environment. This might require intelligence and co-operation for survival. Another assumption we may not be entitled to make is that evolution into multiple species is inevitable. What would happen if there were only one species, or a kind of highly evolved 'compound species?' Might there not even be a highly evolved single entitiy? The notion of evolution into multiple individuals is nothing more than an assumption and can only be defended as inevitable with reference to terrestrial examples - which is hardly satisfactory. In considering possible alien life the challenge is to make ourselves aware of all our unconscious and Earth-derived assumptions and to dispense with them. Olly

Indeed. So might we conclude that, on Earth, predation arises from the short cut it offers into higher energy densities and that intelligence is driven by predation's introduction of the need to attack and defend? If so this poses at least two questions. 1) What would happen to life on a planet in which energy was abundant and transferable? Stellar energy, perhaps, like an extremely efficient form of photosynthesis. If this removed the need for predation it would, we might argue, remove the need to develop intelligence. But... 2) What would happen if this life form were threatened by, say, a inorganic threat like an unstable environment. The drive to find ways around this instability might be a driver for intelligence? Olly

That's true here but I can conceive of different environmental circumstances in which a co-operative model might replace a competitive one. I also wonder if competition drives extinction as vigorously as it drives evolution? Co-operation could also drive evolution perfectly well, the best co-operators being the best survivors.Someone must have done a PHD on this! Olly

I think darks are greatly over-rated, even with my old-school Atik 11000 CCD whose darks looked like a snow storm. If you have amp glow then, yes, you will certainly need them but, if you don't, it might be worth trying hot pixel filtration when stacking and, maybe, a bad pixel map. Don't be persuaded that darks are compulsory. Do your own testing. When I did that I stopped using them - as many others have done. For example, no darks went into this: Olly

I had another think about this one and got the star removal to work - ish. It was good enough to let me get more of a stretch into the faint stuff before putting them back. RASA 8, ASI2600MC, Avalon linear. Joint project with Paul Kummer. Olly

Lovely! That's a brilliant composition as well, with 'movement' towards the upper right. Olly