Stub Mandrel

Lessons learnt! It's too easy to nudge the main mirror collimation knobs. This is true of most scopes, but most have lock screws. Also the secondary adjustment screws are menace when they protrude, tehy also mean a bhatinov mask would need a big hole in the centre. So I'm doing the opposite of 'Bob's Knobs'. I've ordered long M5 grub screws for secondary adjustment. I will also use these to lock the primary adjustment, while adding circular 'guards' around the adjustment nuts that will also act as feet if standing the scope on end. The joy of 3D printing is that if I had milled out some aluminium shapes it would be very hard to abandon things, but instead I can put £2 worth of PLA in the recycling (it would be nice to have a filament shredder/filament extruder!) and print again.

Tonight was first light for my new 3d printed 6" Newt. Details in the thread below!

That's deliberate, I set it so the focal plane is about 1/2 from racked all the way out so it will focus all my EPs without intruding into the tube. This means there's 1 1/2" of backfocus available if I want to try it with a camera. I just had ago, I was able to split Mizar easily, even at low mags, although with the 2.5 and 5mm it was pair of airy discs (more like triangles to be honest, I think that's affected by the spider). There was no hope of galaxies with moonglow. I found M13 and although it was clearly quite big it was a faint patch of light grey on a pale grey background, so I packed up.

Probably a combination - I only have enough flock to do about 2/3 of the tube.

First Light tonight! Well the mirror I was very kindly given seems to be excellent. Hard to collimate with my laser collimator as the dot is almost invisible on the freshly coated mirror! I tried it with all my eyepieces on the moon. The 2.5mm UWA was usable (I can use it in my 10" scope, but my 6" x 1200mm scope doesn't like it), and it's the first time my cheap 4mm plossl has given a view worth looking at. Every other ep from 5mm to 40mm gave its best, although a few of the cheaper ones (especially the 8-24 zoom) showed CA or softness at the edges. The 18mm ortho was, as ever, outstanding giving a full disk view, the 5mm UWA was great going along the terminator. The ortho, cheap aspheric 23mm and longer plossls all showed a touch of colour - subtle blues and browns on the maria but surprisingly the 23mm aspheric which cost about £5 showed the colour best! I'm sure contrast will get even better when painted/flocked inside! Really very pleased. It perhaps isn't rigid enough to be a serious astrophotography scope but being between my 1200 and 590mm fl imaging newts it's an ideal visual scope at just over 900mm. Going to see if I can find some galaxies now. Definitely needs flocking... also temporary collimation screws

I have the good fortune of some much light pollution that astro dark doesn't make a big difference...

Argh! I've sold you a pup, those are some of my first narrowband images. These are with the L-Enhance:

Hmm a 1mm layer of extra felt shoudl make it a firm fit on the ASI1600.

If you have a camera that's modded or with a strong response to Ha light (I think the A5000 does) then the Optolong L-Enhance filter would be an excellent investment for the nebula season. You can either use it for synthetic colour images like those below or as originally intended as an L-layer to go on top of RGB data. These were taken with a modded Canon 450D and the L-enhance. and a 130-PDS. <Edit I should add that before getting this filter I got a very basic moon and skyglow that cost about £15 and it worked absolute wonders for my images>

Hmmm ... ASI1600MM-pro is 78mm diameter.... how big is the gap when clamped up tight?

Slippery slope starts here...

A couple of pics:

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.

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.

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.

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.

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!

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

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?

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?

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.