ollypenrice

Worth remembering, also, that the steeper light cone will require more precise focus and that the focus drift with temperature change (to which the FSQs are sensitive) will become even more significant. Olly

Don't do that! Cleanliness is everything in a roller drive system. Both of my Mesus are veritable first generation examples with the cases for the drives made in a single piece. How Lucas put the wheels in is a mystery. 🤔 Olly

I was a very early adopter of the Mesu - or more accurately Yves Van den Broek was, since the one that first came here belonged to him - and right from the start some people have commented on how 'basic' it looked. My own view is that it is 100% graphic designer free. Hooray! It sets out in search of the simplest solution possible to the phenomenal engineering problem of precise sidereal tracking. We live in a ridiculous world in which the simplest things are made to look 'techy.' My bicycle handlebars have a scale on them so that their angle can be set relative the clamp which holds them. What ridiculous nonsense! I set my handlebars at 32.34 degrees to the horizontal. You do? You are losing climbing power at 0.00567 Watts per revolution, you nonentity! ...and so on. No, the Mesu is a machine. It looks like a machine. It should look like a machine. I now have two of them and host three more. They work. That's it. What do they look like? I can't remember. I only ever see them in the dark when I go out and switch them on... Olly

Ah, a nice easy question to answer, for a change! Polaris is very close to the celestial pole. If you watched it all day it would describe a very tiny circle around the celestial pole. It's only about three quarters of a degree off the celestial pole (the centre of the Earth's rotation) so its apparent movement describes a tiny circle about 1.5 degrees across. This means that 1.5 degrees is all that distinguishes its movement in right ascension during one full rotation. Imagine trying to distinguish between twelve o'clock and six o'clock on a watch face a mile away. Tricky. But fixing the position of the watch itself relative to the horizon would be easy. So Polaris gives perfectly good information in deciding declination but terrible information in deciding right ascension. Olly

What can we say? Bravo, a lovely job. Stunning. Olly

I have both Baader and Astronomik OIII filters. Neither is very good. Halos a go-go. Chroma have good reviews. I was up for trying the Baader 5nm but they don't seem to exist in 1.25 mounted. I guess there's a technical problem stopping production. Olly

Yes, but I'm rather intimidated by the business of setting it up! Olly

Version two is flatter and more evenly illuminated, which is less like the eyepiece view (such as there is one!) The core is the only part that we were able to see in a 14 inch and even then it was faint. So the revised version is probably more honest but I like both, I must say. Olly

Nice. I love imaging at 1.9"PP or thereabouts because it's a sweet compromise between the tolerant and the detailed. Olly

The real size of the corrected field of the Edge scopes was initially unclear and Celestron revised it. They now say 42mm without reducer and 26.7mm with it. https://www.celestron.com/blogs/knowledgebase/what-is-the-optimized-image-circle-for-the-edgehd-otas-and-reducers They claim that this will illuminate a 35mm sensor, unreduced, but it strikes me that this is optimistic. I think my Kodak 11 meg CCD needs about 45mm. Olly

You won't gather more light with a reducer. You'll just put the same number of object photons onto fewer pixels and widen the field of view. If that's what you want to do then fine, but you won't gather more light. Olly

On reading down the thread I found myself asking what the RA-Dec alignment was with regard to the the trailing. Paul (Pompey Monkey) was clearly thinking along the same lines. I think his analysis is excellent (not for the first time!) Olly

If my images are as close to nature as an impressionist painting I guess I'll be happy enough. The impressionists were, after all, figurative painters though their intention was not so much to capture 'what was there' as what they perceived to be there. Still, I reckon this gives a remarkably precise impression of Sunday breakfast at my place... 🤩lly

I haven't tried this in PI. More homework! Olly

Thanks Vlaiv. I'll go through all this over the weekend and give the separate stretching a try. Olly

Takahashi FSQ106N/Atik 11000 mono CCD camera/Mesu 200 mount for most of the image. The innermost part of the core was enhanced using shorter sub exposures from a TEC140 with the same camera. It's not a high resolution image. For that you should check out Jonas Grinde's huge mosaic or Pieter Vandevelde's recent monochrome rendition. An Ha filter will only work if your DSLR has been modified. The standard in-camera filters block the red channel at wavelengths just short of the Ha line. The modification involves removing and sometimes replacing this cut-off filter. Then a clip in filter will pass only the Ha line and it can be recorded by your red-filtered pixels (ie a quarter of the total). The blue and green filtered pixels will remain blind to Ha but still the result can be well worth having. Olly

Yes, and emphasized by a very gentle application of an Ha layer used to lighten the red channel. Thanks for your kind comments. On this image I worked mostly on trying to find structure close to the core and on trying to reveal the faintest outer parts of the galaxy. Olly

That would be me! In fact everyone I know does it that way, so far as I'm aware. I've generally taken the view that it ensures an equivalent stretch on all channels, though the black points may need a small adjustment. I never attempt complex custom stretches using Curves in RGB, it's always a bog standard log stretch in Levels, so I guess a log stretch could be done on the individual channels without creating imbalances up the brightness range. I'm very interested in your point about losing saturation. I do find, sometimes, that good solid integration times are producing very thin colour. Why does stretching the channels individually increase saturation? And how would you go about it? I'm guessing but one could give each channel a log stretch until the background sky reached 'value x' and then combine them. Tell us more! Olly

Side by side is stiffest. Piggyback relies on the integrity of the lower tube rings and also greatly increases the required counterweight. I agree, the Esprit would be another good choice. Old FSQs do appear. I found mine pretty much 'on demand' but the one in our linen cupboard isn't mine! It's destined for eventual dual rig duty on a robotic rig, based here. Olly

The astrophysics tells us that the the stars of the central bulge are what Walter Baader called 'Population 2,' so they tend to be older, cooler and redder. The spiral arms are home to the hot young blue giants and the HII regions of star formation which are rich in ionized hydrogen. This would square with a reddish core, bluish spirals and patches of red for the star-forming regions. This is pretty much what I get when I perform a colour calibration of my RGB data. The red star forming regions are not particularly striking in a straightforward red-green-blue capture. They reveal themselves when we image M31 through an Ha filter which blocks everything but the light from ionized hydrogen. The addition of Ha does not invent anything which isn't there, it simply gives it preferential emphasis. This is one way in which M31 images will certainly vary. In mine I used the Ha sparingly but others may be more lavish with it. When it comes to what precise shades of blue and red are the truest, it gets very difficult. We're used to the idea that faint parts of an object need lots of signal in order to appear at all. The same is true for objects naturally weak in colour intensity. The colours will only distinguish themselves when you have a lot of data. I'd feel happier if my blues had come out less cyan but they didn't and so I just accept them as they are. A friend using the same makes of scope, camera and filters got the same result independently. We do have other sources of information on any picture we look at. Is the sky a neutral dark grey? It should be. Are the stars showing convincing blue or red colours as is appropriate? (It's easy to look up the colour index of a few bright test stars.) Olly

^^^ Essential reading. Thanks, Magnum. Olly

Obviously this is a worry for me because I do amateur astronomy professionally. If the satellites prove fatal to astrophotography then I'll take a treble hit, losing my visiting customers, my robotic hosting operation and the value of my kit (very considerable and in effect, my 'lump sum' should I ever decide to retire.) However, there are astrophotography businesses far larger than mine. Cameras, mounts and telescopes need makers to make them and retailers to sell them so to this extent I disagree with Filroden's notion that it is just a hobby at stake. Amateur astronomy generates many livelihoods. (I'm not entirely sure that the internet brings vast social benefits either, but that's for another debate and another forum.) Fortunately I don't think the effect will be catastrophic, though I may be wrong. If the problem is going to increase by a factor of 10 then 10 x 0=0. At the moment satellites are a non-problem. Sigma clipping gets rid of them almost entirely and the big ones, which sometimes leave a trace, may need a line removal applied to the sub in question but then they'll vanish like the rest. With CMOS chips thriving on more and shorter subs the Sigma clipping will work better than ever and I don't doubt that the software folks can up their game as well. It may be possible to write a programme actively to look for lines and then remove them. Olly

Lots of things are absolutely right so this is a great start. The whole point of this game is that it takes a bit of learning. That's why it's worth doing... Olly

It's best to be as close as you can. If you move the tube rings forward on the dovetail you'll probably get it balanced. You'll probably need to drill new holes for this. You can also use a longer dovetail and bolt a small weight to the front of it. Anything will do. Olly

Aha. Maybe the problem with an OAG in a dual rig might be that it can throw the full or combined flexure error onto the slave scope. A little flexure in the primary's focuser, for example, will be corrected by the OAG at the expense of driving the slave into incorrect positions. If you have a guidescope and the primary's focuser flexes a little there will be no guide input, which will leave the flexure uncorrected. Similarly any secondary focuser flexure will be uncorrected. But with an OAG the combined error will appear in the slave. (This assumes that the error of the doesn't happen to cancel that of the primary but that seems unlikely.) Olly