Captain Scarlet

It feels to me to be a good time to start getting to grips with, say, VBA, and “sub-contract” a lot of the processing out of the spreadsheet, particularly large sheet operations like sorting etc.

Macros for the sheet manipulation and Functions for some of the cumbersome calculations.

The learning curve is steep for only a short while then it becomes a joy...

I think the results are less important than the publicity. Anything that gets the topic in the public mind is a good thing. It’s a shame there’s no easy way to show people in Bortle 8 areas the majesty of an unpolluted night sky: just what it is they’re missing and what it is their area-conditions are hiding. And further, more difficult to my mind, to show those people lucky enough to live in a dark rural area, what it is they see and take for granted and how easily it can be made to disappear, and to get them to care about it.

Cheers, Magnus

I can suggest a guaranteed way of stopping the rain. Sell the mount.

5 hours ago, alex_stars said:

@vlaiv and all,

Regarding the math connecting the LSF with the PSF and the MTF, I think this is beyond the general interest of the forum (just a guess) ...

... perhaps but don’t let that hold you and the others back, please.

I've always wondered what de-convolution (and convolution obvs) was as a Sharpening software tool option, now I have a much better idea.

looking up Convolution in wiki for example is initially not very enlightening, it just gives proofs and definition leading one to think “yes but so what”

this thread puts it all into superb context, so very useful, thanks!

Magnus

Fantastic thank you for that tour. There are some mixed-forecast nights coming up here, I might just do exactly what you have done but with your notes as my guide! I’ll be able to tick off a few Messiers I’ve never got around to looking for yet. I’ll be using my 12x50s, but it is very dark here...

thanks, Magnus

You can force Boolean results, arrays or cells, to be numeric by either adding 0 or multiplying by 1, so (FALSE)+0 should evaluate to 0

In London I have a bog-standard SW 200p f/5 8" newt, and a superb Leica 60mm spotting scope. On one occasion I put them side by side on my Skytee2, and pointed at Polaris. Polaris B was trivially easy to see through the 8", a lovely obvious little blue pinpoint. I simply could not see it through the Leica, and I tried really hard!

M

All utterly fascinating.  I think one of the unquantifiable factors influencing our in-the-field-perceptions of frac vs bigger reflector is that fracs are generally supplied having been assembled collimated and calibrated on an optical bench by professionals. Whereas the reflectors, especially Newtonians but even the Cassegrains, have been supplied as barely more than a bag of bits with a useless set of instructions essentially saying "you put it together".

M

Unfortunately I haven't yet attacked my Skymax 150, I haven't even managed to get back from Ireland to the UK yet!

With the 180, although I have cleaned my secondary, it was because it became necessary after discovering my own secondary baffle had been attached seriously off-centre. At that point I simply pulled the baffle off, leaving behind a ring of glued-on foam. To deal with that ring of foam, I soaked and kept soaked the area in pure acetone, and as it softened gently manipulated with a soft plastic spatula until the last shreds detached and could be lifted away. The whole area, back-plate and mirrored surface seem to be coated with a very hard coating, most likely SiO2 (i.e. quartz). So it can even tolerate rather poor treatment I think.

I replaced that baffle with one I made up myself of clear 220 micron acetate, painted matt black, and which I glued on with 3 dots of standard 2-part epoxy. I made sure that such epoxies are soluble in acetone. I have since removed that replacement baffle, cleaned up with acetone again, added flocking to the baffle both sides and then re-attached with the same epoxy.

It gives lovely views.

My points are is that it may well be that a previous owner had noticed, like me, that the original baffle was not centred and decided to remedy it. I would imagine a non-central baffle would have a disproportionate effect on transmission! Getting it back on perfectly central though is actually quite a difficult thing to judge, and my cynical self would suspect that the word "plonk" might have applied at that SW manufacturing stage.  Also that acetone is the right thing to use here, there's not anything around for it to damage, with sufficient care (and pure water and dust-free swabs!). If you do get it wrong, as I did at one stage, simply dissolving away the dabs of glue and starting again is quite easy, although time-consuming.

Cheers, Magnus

Thank you vlaiv. Just two things, one suggestion, one general observation from my reading around this topic.

Suggestion: You start off by assuming everyone knows what MTF actually is ... perhaps elaborate exactly what MTF is, even mathematically perhaps, I think the formula for it isn't too complicated for your readers.

General observation: whenever I come across MTF plots in the literature, almost without exception the frequency x-axis is scaled from 0 to 1, i.e. the proportion of maximum possible frequency for the scope in question. This is for comparing different configurations of the same scope, perhaps deformed mirror vs perfect mirror for example.

Almost never do you see an MTF plot of one aperture scope vs another aperture, i.e. with two different "maximum possible frequencies", for which the x-axis would need to be in absolute frequency-units rather than "relative to the ideal for one scope" units. Plotting vs absolute frequencies then allows one to see quite how much better a larger aperture scope is than a smaller one (for contrast and resolution). Even that a badly abberrated large scope can outperform a better-engineered small scope.

Great thread, Magnus

34 minutes ago, JeremyS said:

Question to AZ100 owners. Is it feasible to lift the combo of the AZ100 and Berlebach Uni 28 in one go? Or is it too heavy/awkward to countenance that?

Before I got to this post I had precisely the same question bouncing around my head. And seeing @John’s reply my heart sank ... I so wanted the answer to be “no no no FAR too heavy”.

Magnus

29 minutes ago, JeremyS said:

One way to avoid the worry of getting a bad mirror: get a refractor 🤣

Dammit can’t find the Report button in this new version...

5 hours ago, Jasonb said:

... I really have no plans to do imaging (I think that's a rabbit hole I'd never escape from).

... but at least you’d have plenty of company down there 😉

I ordered a 300mm 1/10w mirror from OO last March, it arrived in October. While I have no complaints about the views it's given me (quite the contrary actually), I did complain about its packaging and the state in which it arrived. It arrived in a box filled with nurdles, and was kept away from the edges of the box by several large soft plastic doughnuts. So far, so good. But the mirror itself was directly wrapped in a large swathe of cotton wool, further surrounded by tissue and bubble-wrap. The trouble was, the cotton wool was directly in contact with the face of the mirror, that can't be good, I thought as I carefully pulled everything away.

Sure enough, on revealing the supposedly pristine surface of the mirror, I noticed a pair of more-or-less parallel scratches, too big to be called "sleeks", about 1-2cm long and 0.1 - 0.15mm wide, about 60% from the centre to the edge. One of them had at one end a sort of orbital pattern, suggesting that there was grit or somesuch on the cotton wool as it was placed on the mirror, which then travelled around a bit during transportation. Christ!

I complained, obviously, and got a terse reply saying essentially "read our terms and conditions, it's within tolerances". No hint of regret or apology or redress.

The scratches have no effect whatsoever on the views of course, which have been superb, but surely they can think of a better way to keep the surface protected during transit and packing having spent literally months making it close to perfection?

Before too long I shall be in the market for a 20" mirror, and my first port of call will be John Nichol.

Magnus

1 hour ago, JamesF said:

I have nothing to add, but now you've made me feel the need to post this.  It's even relevant to astronomy, not least because Matt Parker is married to Lucie Green, the solar scientist and occasional presenter on The Sky at Night.

James

Very good 

In such situations I always use the MMULT function, which stands for Matrix Multiply, and follows the strict rules of matrix multiplication. Combine that with the fact that you can also use <, >, =, >=, and <> as actual operators like + - / * , and you have a very powerful tool.

Such as

MMULT(TRANSPOSE(AND($A$2:$A$20>$A$1,$A$2:$A$20<=$B$1)*1),$B$2:$B$20)

... where A2:A20 contain, say, dates, B2:B20 contain values and A1 and B1 contain the min and max dates you want to use to filter that list.

TRANSPOSE is there because it’s strict matrix mult rules so you need 1x19 and 19x1 to be able to multiply.

the mysterious “*1” is there because (1>2) evaluates within a formula to FALSE, and the *1 forces that to become 0

4 minutes ago, Saganite said:

... 4th outing in 5 nights which can't be bad !

By the time I get to that stage I’m praying for clouds 💤 

... and in the same vein, the weather keeps playing ball. This one around 2am the next night:

Well done for seeing those things on a Moonlit night! You’ve set yourself up for a treat I think, as now you’ve seen them under far less than ideal conditions, you have something to compare for when you observe them with no Moon around! The difference should be very noticeable.

Cheers, Magnus

20 hours ago, John said:

I'd like to apologize for the above fib

I got tempted by all those shiny things gleaming in the sky

 

Tbh it did read as though you were writing to yourself: “Dear conscience please don’t make me feel guilty about staying inside “

I remember I found this and split its components shortly after you started this thread. Now it's come back around the block and you've reminded me of it, it was on tonight's list. But clouds rolled in around 6pm. I'll have another chance within the next few nights though I think.

M

Canon EOS 6D and Samyang 24/1.4 1/10s ISO 6400 handheld. There seems to be a huge white Fox looming in from the left. A little noisy, but that's price to pay for hand-holding at high ISO.

Thanks for looking, Magnus

Wow imagine being able to communicate with messrs Dorsey or Zuckerwotsit and ask can this be a bit bigger and this further left please? And getting it done there and then. Absolutely superb!

Magnus

It took me ages to split Rigel my first time, and I was equally excited! It’s now one of my habitual go-tos at this season, including tonight! So well done.

Next time you look at M37, look for a somewhat brighter central star than the others in the cluster, can you see its colour? That made M37 for me the first time.

M

Even worse than being cloudy ... this forum will be down ☹️😉