Stub Mandrel

Thanks for the link. Hubble makes the Saturn V look tiny! Would be great to visit the museum one day. (You do realise there are places that would pay you to make exhibition models of that quality...)

Excellent! Is that a freely available STL file?

What would be most effcient would be a hot end fed with powdered/shredded PLA that fed a metered flow of molten plastic directly to a hotend. You would probably want a fixed hotend so a table moving in X and Y (and maybe Z) but that woudln't be difficult to arrange. I suspect a dual feed so an archimedes screw to feed the pellets into the melter, and I wonder if some sort of peristaltic pump could work at a high enough temperature to give precisely metered delivery ?

I started this thread, and as one of the most discursive people on the planet, I can't complain if it goes awry!

LOL! I'm a chartered environmentalist. My main guilt is the large amount of failed 3D print prototypes I have building up; quite keen to look at a way of turning them back into filament. But... the environmental cost of a kg of PLA every month and the relatively modest amount of power used by the printer? Compare to any hobby or pastime that requires you to drive. As for my hobbies in general they don't involve large amounts of material and put me in good position to keep, repurpose, repair, reuse, recycle...

More harrassment than cost, you need to safely access and store sulphuric acid luckily a dilution just below the level where you need a licence for it is ideal (about 12%). Also sodium hydroxide, for stripping and degreasing. So a sealable plastic box as a tank for the acid, that lives in a bowl with washing soda in it to neutralise any drips. Lots of PPE - goggles, gloves, plus croc clips, wires... I bought proper dies (which will last a long time before being exhausted) and sealer, as these make the colours more consistent. I made a cathode by melting down lead pipe and pouring it into a (very dry) wooden mould. I have a long titanium rod for mounting workpeices, it needs to be polished to a clean finish with wet and dry to ensure good electrical contact. Other equipment is a 4A transformer from an old battery charger and an old style moving iron 5A meter. The meter swings full scale then rapidly drops, rather than set the current I keep going until it starts to drop.

I've only had one chance to use it so far! It was quite nice but the tube wasn't flocked and the sky was a bit bright so I only saw a few brighter objects. I want it to be my main visual scope, on the EQ3, while I'm imaging.

For the amount I need, it would be cheaper to use an existing offcut, or I can copy ZWO and just screw two bits together. But I'll probably 3D print it for now and make a pretty one when my anodising is set up again.

I might make another one, for my 150PL, if I do that will need some sort of belt drive because it's the focuser you can't the the knobs off. It looks like if you take the rubber grip off the knobs, they are like a big pulley.

I'll need to do my own design, because it's a self-made focuser.

I'm going to use direct coupling like the ZWO units. Yes I might end up with a 3D printed bracket, rather than mill away 95% of a lump of alloy!

My 3D printed (mostly) 6" f6 Newt.

Here we go, these are the new rollers. You can see they are a much simpler shape and how the 'new' sectors allow them to be horizontal. Instead of a precise location, they just need to be placed in contact with the supported and unloaded platform and slightly angled to get line contact and avoid any risk of the sector hitting the box. I've decided to stick with the simple 5: ratio for now,as slightly smaller rollers will give me a step size of about 0.016m and I suspect that for a simple platform rather than a precision engineered mount a resolution smaller than this is pointless. At my sector diameter of 788mm, one arc-second is almost 0.002mm, so I will have 8 arc-seconds per step, 550 milliseconds per step. Obviously these are best estimates to be fine tuned in use. I will be able tune to +/- 0.2% using the millisecond counter in Arduino. The new parts fill the old upper platform but it doesn't take advantage of the extra surface on the new sectors: I'm going to make a new platform, with a more rounded shape that will also allow me to move the pivot point further forward again. I will be getting close to the axis through CofG ideal by accident rather than design! I've just got to wait for some ball races to replace the ones I lost for the tension idler.

You win the 2020 Turner Prize.

ARM stands for 'Acorn RISC Machine'. Acorn built the Electron and the original BBC Micros and the original ARM processor was produced as a co-processor for the Beeb. It's fair to say that the most ubiquitous computer processors in the world are a direct evolution of the BBC Micro. Beat that, Microsoft and Apple!

Took me numerous sessions to get that much M101 with a dslr. It's not an easy target.

Hi, The electronic bit Just Works (TM)! Fire up Sharpcap and it does everything you expect, even moving rapidly then slowing down at the end of a long move. Only thing is it was a tad slower to respond than my ZWO EAF, presumably because it uses a smaller stepper with a bigger gear ratio. I changed the stepper speed settings in line with Dave's suggestions to tune it up to be a bit faster. One thing that's interesting is it happily runs off the 5v USB supply with no 9V battery fitted. It will only draw about 145mA even when two coils are energised, so this should be fine - there's plenty of torque. I need to make a fixing bracket and adaptor, to be honest the only thing holding em back is it's the ED 66 scope I made myself and I'm reluctant to remove my lovely home-made knob!

I found this.. the little blur diagram looks a bit like the distorted stars.. http://50.87.30.54/goldfocus/collimation_refractor.php

On chromatic abberration this is what I figured... If you use an RGB sensor and have CA some colours are out of focus, so you get halos. If you use RGB filters with a mono camera all your subs will be sharp, so no haloes. BUT the focal length for each colour will be slightly different so the image scale for each colour will be different. Say the blue focuses further away from the lens, then the blue image will be smaller. This means that in the composite images there will be blue fringes on the inside edge of the stars in the corners, and the outside edge will look yellow. I'd expect bad alignment to cause a consistent shift in the same direction across the image. That said, having seen the odd star shapes Ken's getting, I think it's one or more lens elements out of alignment, so hopefully fixable on an optical bench.

Take the ring off, it unscrews from the other side 🙂

In a very dark room, white wall lit from a shaded lamp (with a hoodie over the top!) 4m away: Camera 6 seconds, f3.5, 800 iso. Formula gives a value of 0.0319. Meter varying between 0.0133 and 0.0128, but pretty clearly centred on 0.0130 Lux (correction factor set to 1.0). Comparing the first figures were 0.39 and 0.22, ratio 1.773. Second figures 0.0319 and 0.0130, ratio 2.454. That's a significant difference BUT the second experiment was done under much more consistent conditions. I'll put the 2.45 ratio into the device and then see how it measures up against real skies in due course.

Sammy Hagar fan?

🤣 Worked for me... not!

Cheapest way in if buying new is a Star Adventurer used with existing camera and lenses. The pro pack is about £270, but you can get by with the standard pack. Later it has enough oomph to take a small refractor. I actually started astrophotography with a 150PL - a long reflector, on a manual EQ3 tripod (£180 second hand) to which I fitted an RA drive (home made) but you can buy one for less than £100. I was able to do 30-60 second exposure unguided although a proportion were trailed. Not ideal, but the long scope meant that a field flattener or coma correcter weren't needed. I got results that made me want to achieve more, so I bought a s/h 130P-DS and ended up fitting the EQ3 with RA and DEC and basic goto/guiding. With guiding I was getting up to 5 minute subs even with an EQ3. Personally I would recommend the 130P-DS over a frac for a beginner in AP, with the SW coma corrector its 'plug and play', collimation is easy after the first time. With my frac there was a long sequence of test runs to get the field flattener spacing OK. Next I got an HEQ5 mount, again s/h. Then as ASI1600 mono camera, again, s/h. Each step has seen my results improve, but also each step has been really rewarding. Buy deciding what I wanted and then waiting for good s/h examples I built up my kit for significantly less than buying new. I still use the 150PL - I've been suing it exclusively for the last few months building up my collection of messier galaxies and clusters. So it can be cheaper than you expect, but there is always the urge to go for the next upgrade!

Wowser! "Build 'em big!"