ollypenrice

The OP is in India where I guess the nights are very warm. This might be a big problem for any uncooled camera doing longer exposures. Olly

Most certainly! Olly

Yes and, somewhat later than my Nimrod pilot, we had a retired RAF navigation officer staying who knew our pilot and had flown with him. He told me about his training in astro-navigation. Fascinating stuff. I've just this minute finished David McCullough's Wright brothers biography and can honestly say that I've never read a more moving book. https://www.amazon.com/Wright-Brothers-David-McCullough/dp/1476728755 Olly

Or is it some kind of Icarus complex, or even Faustian? Indeed, in Marlowe's Dr Faustus, Faustus has mastered astronomy and, after his pact with the devil, has himself borne aloft on a flying chariot. Olly

I'm not so sure. Firstly we are not astro-specific since many people come here for general rural holidays in the hills and, secondly, we are not at all expensive! (Our immediate region has two major tourist attractions, free flying and rock climbing. Astronomy is a distant third.) In the first fifty years of my life I had never met anyone who had built his own aeroplane. Since coming here fourteen years ago I've met four. You're quite right, though, that sampling it the other way round would be instructive. For all that, I had the Flying Gnomuses last week and I have another PPL staying this week. And you yourself are keen on both. In my robotic shed three out of four scopes were owned by fliers until we lost Per. I'm going to take some convincing that this is coincidental. BTW, I accidentally set up camp on a gliding-specific campsite the summer when I moved in here. I hadn't seen the sign saying it was for gliding club members. Nobody minded and I set up a scope that evening. The level of interest shown by the other campers was out of all proportion to that which I'd experienced on any of the many campsites on which I'd done the same thing, and the level of the questions I was being asked was very high indeed. It was a great evening, in fact, and I was invited to the annual dinner! Olly PS I've flown paragliders myself but never got to the stage of buying my own because I could see that it would be yet another opportunity to waste days, weeks and months waiting for the UK weather to sort itself out... I enjoyed it, though.

So there is indeed this strong mental connection between astronomy and flight. Indeed, my very first guest at Les Granges was a retired Nimrod pilot. The connection is certainly there. Olly

At a slight tangent to History of Astronomy, this, but I'm reading The Wright Brothers by David McCullough. It's a truly outstanding read with some entertaining astronomical connections. Simon Newcome was one contemporary astronomer who spoke out on the absurdity of striving for powered flight, asserting that it would never happen. On the other hand another former astronomer, Samuel Langley, was the driving force behind several unseccessful powered flying machines and clearly believed it would be possible. Given that it took only 66 years to go from the first sand-skimmings at Kitty Hawk to the moon landing, Simon Newcome was wrong with a capital W! By the way, I find as an astronomy provider that a passion for flight seems to go hand in hand with an interest in astronomy. Perhaps twenty of our guests in the last ten years have held PPLs, helicopter or gliding licenses and three have built their own aeroplanes. (One was on his fourth.) Olly

This is one of the very few targets which cannot be imaged well in a single exposure time. Personally, I blended sets of exposures of 11 seconds, 50 seconds and 10 minutes (15 would have been better.) Each setup will vary so you do need to experiment. Once it comes to combining them, some thought is needed. I prefer to do this in Photoshop using this tutorial. http://www.astropix.com/html/j_digit/laymask.html Jerry has updated his website since I first learned the layer masking technique from him but the basics remain unchanged. In the latest version he blends two exposure lengths but I would still shoot three, I think, with my setups. Olly

Doh. I'll just go back to my original interpretation which was the same as Steve's! However, Optcorp did subtract 1mm when calculating my adapter. I didn't argue because if it didn't work it would be their fault, but it did work (and it's quite sensitive for a full frame chip with the TEC, I gather.) I'll let someone else draw the right set of graphics!! I'm on toothache antbiotics so no sangria for me... Well, maybe just one! Olly

OK but at least I can now understand the existence of the 'subtract' argument which I think I first heard of from QSI and which was adopted by Optcorp when I asked them for the correct spacer for my TEC140 flattener to full frame chip. (This works perfectly, for what it's worth.) So what's the error in my graph? In the second version the overlay at the bottom brings the focal point to that of the chip distance. The angle of convergence had been respected (because it was a cut and paste job from the original light path with filter.) On the other hand my overlay shows the filter intersecting the light path further up the light path (within the pink 'spacer' section) so that's not geometrically correct and could be the sorce of the error. What bugs me in this whole question is that the 'subtract' camp are not idiots but I've known myself for long enough to know that I might well be an idiot! Olly

But if we take as gospel the sentence 'angle of convergence remains the same' then we get this: ???? Olly

Nightmare! Yes, I now think you're right! I've always said 'add' myself but now I can't see where the 'subtract' argument comes from. Olly

I always struggle with this so I took Ray's diagram and added the hardware around it. The image below is how it came out. It shows why Davey T is right. The lengthening of the light path means you need a shorter spacer. Even as I write this it feels wrong, but see what you think of the diagram. For me, at least, it has brought a bit of clarity since, in the past, I though adding length to the light path meant adding it to the spacer. It seems not... but maybe I'm up a gum tree again! Olly

What about using it wide open and making a front aperture mask to stop it down? I did this to avoid diff spikes which are pretty intrusive on starry fields of view.

Thanks Mark, one to have a play with! Olly

The idea that focal length and chip size are related is an error imported from the daytime camera world via something called 'crop factor.' I would ignore all this completely. It is utterly meaningless. Keep it nice and simple in astrophotography and you won't go wrong. You have a focal length, determined by your scope's optics. This is a simple and non-negotiable fact. You have a chip size of x by y, also non negotiable. Then you have your pixel size, which (allied to you focal length) specifies your resolution in arcseconds per pixel. Your chip size simply speciifies how much sky you cover. It has absolutely no effect whatever on your resolution. (That derives from focal length and pixel size. The number of pixels you have is also irrelevant.) Olly Edit: Crossed with Adam J but we are saying the same things.

I would look at it this way: the mount has a maximum payload and a maximum tracking accuracy. Both, not just one, have to be respected. Payload is obviously easy - you just weigh what you are putting on the mount. Accuracy is more difficult. The unit that matters is resolution measured in arcseconds per pixel. This value is derived from focal length and pixel size, so focal length alone is not a useful term. (Long focal length with big pixels equals short focal length with small pixels in terms of resolution, stating it simply.) I think that the best information will come from published images in which the user states what camera, at what focal length, was being used. To turn this into arcseconds per pixel you can use a number of online calculators such as this one: http://www.12dstring.me.uk/fovcalc.php Olly

If you were happy with your QSI decision I can't see that it differs significantly from switching to the same chip from Moravian... Olly

We rarely see a tricolour M42 in narrowband. Very exciting. Olly

I'd prefer, 'If the Earth were flat...' but it isn't... Olly

It very much depends on your pixel scale. If your binned pixel scale is less than about 4 arcseconds per pixel then it might be worth binning the RGB. (Why 4"PP? No good reason, it's a guess plucked from the air to define the scale beyond which I personally would not bin colour. I don't expect everyone to agree.) Another factor concerns your processing method. Early on, you'll be happy to apply luminance globally over your RGB data. As you slide into the obsessive processing trap you may want to avoid applying luminance to your RGB stars, in which case you'll want nice unbinned RGB stars! Personally I never bin colour. I want to be able to bring those nice little RGB stars, with unsaturted cores, into my final image. Olly

I don't, I'm afraid. But I've just picked up the clamshell belonging to Tom O'Donoghue's FSQ106 (resident here) and I can only say, 'not much,' as in 'seriously trivial.' Given that you can put it on a short dovetail and still have enough fore-aft movement for balancing I'd expect it to weigh in at less than a longer dovetail and rings. Olly

For visual use I rather like the clamshells. They are quick to open and close and give lots of fast and easy fore-and-aft travel for balancing. (They might come up second hand because some imagers have found them not to hold the tube in perfectly constant alignment, which can spoil the guiding. This is not an issue in visual observing.) I have also found Ian King to be an excellent retailer. Olly