Stub Mandrel

Amazing!

The ground rods arrived today, took about an hour to cut to size, swap over and then rebuild/calibrate the printer.

Then a test print.

Then ages bed levelling as 200mm circle requires the bed to be dead level right across!

Then over five hours to heat up and print the secondary support, took it to the workshop and in utter disbelief it was a perfect light push fit onto my reduced diameter tube!

I was really expecting to have to tweak the diameter. Plus it feels really rigid, no worries about the strength/stiffness of the vanes.

Photo to follow tomorrow!

Well done Geof, that goes very deep. Wish I had the patience to collect that much data!

Here's a composite image with all the pictures at half resolution of 600 x 450 (larger objects like M31 and M81 and M101 are already downsampled to fit the 1200 x 900 format):

As part of my 'Messier project' I've converted my best picture of each object (the 70 I've photographed so far) into a 1200 x 900 jpeg file and put them all on my website with short descriptions, linked from here:

http://www.stubmandrel.co.uk/astronomy/3-messier-objects

The pictures range from the awful to ones I am really proud of. Filling the gaps and gradually getting all the pictures up to scratch is a great motivator. I hope you find them interesting.

1 hour ago, Chriske said:

I did a quick drawing, ok no holes, a spider for a 200 mm scope stl file was 389KB slicing that thing it was just 9.8Mb

Yes, but that's a prismatic object with constant cross section. I've got fillets all over the place to remove stress raisers, make it easier to assemble and more pleasant to handle. They hugesly increae the complexity of the STL but barely affect print time.

Imagine the difference between a crude cylinder, with say 20 segments, so 20 triangles for each face, top and bottom that's 40. Plus 2 for each of the 20 'sides' of the curved part - total 80 triangles.

Now put a fillet around the top, 90 degrees, so 1/4 circle that's 5 rows of 20 segments to render, Each segment will require two triangles, so that's an extra 5 x 20 x 2 = 200 triangles.

The crude cylinder now has 280 triangles, more than doubled from adding a fillet.

If you use a realistic number of segments, say at least least 100, maybe 360, to get smooth curves on large objects, and the number of fillets increases as the square of the number of segments. 

100 segment cylinder has 400 traingles, five times as many.

Add the fillet and its 25 x 100 x 2 = 5,000 triangles, so now it's more than a ten-fold increase in file size.

Of course some triangles will be too small to render and be ignored, but I'm using a 1-degeree segment as I don't want a faceted look so it's easy to see how a 9.8Mb stl can become a >100Mb stl just by adding fillets.

1 hour ago, johninderby said:

And the print time? 🙀🙀🙀

Probably only about 4 hours. I've found that if I run the printer quite fast I actually get better prints, plus most of the complexity is an abundance of fillets. That means lots of 3D curves which an STL has to represent with (literally) millions of little flat triangles.

On 20/04/2020 at 20:18, Mick H said:

Could it be that the air is now getting cleaner with this lockdown, so it appears a little brighter?

As you can see, I'm no Scientist. 😳

Apparent magnitude varies a lot with things like elevation and sky transparency anyway, so magnitude measurements are made by comparing to reference stars which rules out changes in 'sky quality' affecting the measurements.

7 hours ago, Chriske said:

This is how it should be build to 'remove' all traces of diffraction.
To be clear : these two circles are the primary and secondary mirror.
I think the spider's scope above is very close, if not perfect.

 

Ah yes, I understand now, as each vane makes two spikes they will cover 360 degrees. I've revised my design.

Blimey, I've just noticed the STL is 131 MB!

On 24/04/2020 at 19:04, Chriske said:

Good choice. Remember the sum of the angles of the curves must be 180° to 'rule out' diffraction.

I'm going to try somewhere between a full circle and the Orion scope in John's picture above, and see how it goes.

25 minutes ago, silentrunning said:

It wasn't dew was it? I have had something in the past that looked like that and it turned out to be dew.

I dont think so, the shape is consistent between sessions and it doesn't affect sharpness.

I've got a very odd pattern appearing and I can't get rid of it with flats.

Here's an example of a stacked image with a severe stretch. there's a round patch left and above centre roughly half the image height in diameter. I'm guessing the offset is a collimation issue.

I have processed data with the identical setup using flats taken both before and after imaging and using an on-scope flat field and the open sky at zenith around sunset.

The 'patch' doesn't show on flats (or darks or dark flats)

In the real world, it's fairly easy to lose with good processing as it usually only shows up on the dark background, but it does make life harder.

I've tried processing without darks, dark flats and flats and with no frames. Here's a stack with no control fames and aside from the vignetting you can just make out the offending shape within the brighter area:

So it seems this is an artefact that appears on subs but not on flats?

The scope is a 150PL and the camera is an ASI1600 with EFW and 1.125" filters and nosepiece - my thought is it could be stray light from behind the mirror (unlikely) or off-axis light  getting into the tube (more likely).

But does anyone have any ideas how I could solve this?

3 hours ago, ScouseSpaceCadet said:

Believe me it's not exciting or innovative but necessary...

Let me guess, you're going to be tossed up in a basket to sweep the cobwebs off the sky?

Or maybe prop up a sheet to keep out  next door's security light?

2 minutes ago, johninderby said:

Think they were 3mm thick on the old TAL200K Good scope but a very heavy lump! Pity the AZ100 wasn’t around then. 🙂

I've gone up to 2.4mm, that will give me six wall layers at 0.4mm, which is effectively solid PLA, should be plenty at 25mm depth. Now I have to do all the fillets again!

Now I must wait for my bits to come, eBay is givi9ng a 28 day window for second class delivery, hopefully it will be faster than that.

58 minutes ago, johninderby said:

Some scopes have thicker vanes and doesn’t seem to hurt performance.

That's useful to know, doubling the thickness will make them four times stiffer and I'd like to go with curved ones.

This is a big project!

I was generously given a 6" mirror and secondary of some age. I had the main mirror recoated but the secondary is fine.

I'm making them into a newtonian, using as much 3D printing as possible, although I have a vintage r&p focuser I want to use.

The tube is an 8" diameter PVC ventilation duct that I split and reduced to 7" diameter with a reinforcing strap along the joint. Prototype reinforcing rings on the ends added lots of rigidity, but I realised that I coudl incorporate these into the mirror cell and secondary support.

Here are my designs for the mirror cell and secondary supports. Annoyingly my 3D rpinter hasn't got enough Y-travel to allow me to print the full diameter, although the bed is big enough. I've ordered the ground rod, allthread and timing belt to let me add an extra ~50mm of travel. This will give me a bed large enough that I can print tube rings which will complete the stiffening of the tube. My one concern is that the 1.2mm thick spider may not be wide enough, although I printed a 0.8mm thick lens hood for a webcam which suggsts it will be strong enough, the question is will it be stiff enough? I can always make it thicker or straight.

Note nut pocket for M5 collimation screw.

The cover for the end tube includes a light tight baffled vent, ideal for 3D printing!

The mirror cell clips into the mirror without obscuring any of the silvered surface, however I will be using adhesive as well, just in case.

My printer has enough area to make the cell, a lovely job in Monoprice PLA Plus, totally unretouched straight off the printer 🙂

I got Juno last night, confusing at first as it wasn't exactly where Stellarium said it should be...

You can see the prominent asterism like an 'L' on its back, with Juno to the right - with a 1/4 magnitude of the corner star.

It took me far to long to figure out the missing asteroid was the extra star between the two in the horizontal arm of the L in my pic:

I've done a few asteroids now, I should do more, they are fun to track down. (I have a strange idea of fun...)

On 21/04/2020 at 15:42, Ships and Stars said:

I'd like to increase contrast without losing detail,

Astra image would work wonders on that nice image.

18 hours ago, Louis D said:

I didn't even realize aerosol deodorant still existed after it fell out of favor in the 70s and 80s.  It's pretty rare here in the states at maybe 2% to 5% of total shelf space and sales.

Perhaps we don't smell as good 😞

I've been filling in the gaps in my photos of Messier Objects, mostly galaxies. Many of them are delightful objects, especially compared to those dull-as-dishwater (in isolation) elliptical galaxies in Markarian's Chain whose delight solely comes from how they are arranged.

All of these are LRGB images, about half an hour of luminance and 6-15 minutes for each of RGB,  aside from M40 which is only about 10 minutes of L and a few minutes for each of RGB.

First M40, which is just two stars that happen to be lined up, but nearby two pretty little galaxies you can't help wishing Messier spotted.

Next M94, the Croc's Eye, a galaxy so outrageously dressed up in concentric rings it's like a cake. This one would benefit from much more exposure time.

M99 is far less neat and tidy, flinging arms in all directions like a miniature M101 justifying the name of 'Coma Pinwheel'.

M102 is so small that you wonder how Messier spotted it, it doesn't even appear on Wikipedia's map of Messier Objects! One name is 'cat scratch galaxy' look closely and you'll see why.

M104 is a more popular target, the Sombrero Galaxy, but a challenge for me as it floats through light pollution.

M109 is really pretty, but for some reason it doesn't get a popular name.

You could try the banding reduction action here (comes with many other useful routines).

https://www.prodigitalsoftware.com/AstronomyToolsActions.html

I had a go on a screen grab, made it better but didn't completely remove it.

Best other options are temperature matched darks (warm, cool, cold night darks should be OK) or a cooled camera.

Plus flats and darkening the background will help a lot by making them less prominent.

Incoming googly...

@Whistlin Bob gets really great results with a 200P-DS on a HEQ5, although he does benefit from the shelter of a shed with fold back roof and has the belt drive conversion.

I've been using my 150PL (1200mm f/l) on my HEQ5 for the last few weeks, no belt drive, just well set up gears - judge results for yourself:

30 minutes ago, Bigwings said:

Thanks guys. It's the second version in Fig 1. 

Guess I have to work with it.

 

Take a look here:

New Style Reticle for PolarFinder ...

Might help.

16 minutes ago, FLO said:

I don’t need a wooden case for my eyepieces, but I’d happily buy one 🙂 

Steve

No... read my post very slowly and carefully! 🙂

16 minutes ago, FLO said:

I am confident I didn’t say that 🙂

Though I fully understand someone choosing to pay more for premium craftsmanship and engineering. I.e. a fountain pen, not a ballpoint. 

Steve

Sorry the sentence got changed a few times and drifted in its content...

What I really want to know is - who is it who needs a case for their  wooden eyepieces?

I see LOTS of home made tooling. In the UK people love iron castings, and if not fabricate from steel. Americans use aluminium alloys for almost everything.

We tend to look for function before form and see ornate decoration of practical objects as pretentious which is not to criticise.  As an example I've seen excellent tooling where every surface is hand scraped, a great demonstration of skill but many would consider it a waste of time.

Yet as FLO say, there are plenty of UK people who will pay several times over the odds to buy something functionally identical but in red with a made in Italy sticker...