vlaiv

Yep, that would be sensible place to start - to get fairly good dimensional accuracy.

+1 for designing your own model. Also, you need to do some tests / calibration to figure out tolerances of your printer and then adjust the model for those. I often use 0.12mm layer height for 0.75mm pitch, so you don't need to go very fine (and waste time) - 0.05mm will be more than sufficient. As far as I know - there is difference between different types of resin in amount of detail they can pull off - so it's worth checking out what type of resin is best suited for this work. If you wish, I can design wanted adapter for you in FreeCad (which is open source) - in parametric form so you can tweak tolerances later on to suit your printer?

Field of view and ability to use 2" eyepieces to the field stop? (not really doubles and planets territory - but hey, who does not like to take a look at MW in the summer from time to time? ).

It can show some CA for discerning observer - which 200mm newtonian can't

I'm using ASI185 with 1600mm of FL and OAG. It has 3.75um pixel size, and I bin that x2 and it works nicely.

Yep - with exception of: 20/20 vision is not really excellent eyesight - more "most common" or "median" or something like that. Exceptional eyesight would be 20/10 or 20/8. If you have poorer eyesight than that, but note that even if you wear eyeglasses - you might not have poor eyesight when using the telescope as focusing can compensate for certain diopter thus some people can observe without glasses, then you'll probably need a bit more magnification to clearly see all the detail. It's a bit like small letters. Some people are fine with reading the small letters and other people need glasses / magnifying glass to read the text.

You are likely to hear many different accounts on what works for people - and there is a reason for it. I'm going to tell you what is maximum useful magnification based on objective criteria (and it varies from person to person), but there is no way to account for subjective criteria (at least not that I know of). There is something called visual acuity of observer and it varies from a person to person: https://en.wikipedia.org/wiki/Visual_acuity There is a table on above wiki page - that lists MAR value. That is minimum angle of resolution. Person with 20/20 vision will have MAR of 1 arc minute. Person will be able to see the contrast change that is this small in the image. On the other hand - there are several criteria of what the resolving power of telescope is compared to the aperture size. I'm going to use the "strictest" one - sampling rate. We are going to equate MAR of person with the size of a single pixel when critically sampling for given aperture at 400nm of light (lower bound of visible light) - that is absolutely the "worst case" scenario or maximum magnification that we can justify to be able to see all the detail that telescope offers. We can do calculation for 200mm of aperture and it goes like this: Let's say we have F/10 system with 2um pixel size (for critical sampling at 400nm we need F/ratio to be x5 of pixel size). That would make 2000mm FL with 2um pixel size or sampling rate of 206.3 * 2 / 2000 = 0.2063"/px. We need magnification that will turn that angular size into 1' or 60" for 20/20 vision. so we have 60" / 0.2063 = ~x290 That is maximum needed magnification for 200mm of aperture. Similarly for 4" telescope - we get x145 as maximum needed. Other criteria like Dawes limit or Rayleigh criterion give much lower magnifications still. With the change of visual acuity above number changes as well. You will often hear that people use much higher magnifications than this - say x200-x300 for 4" telescope. I can't explain that phenomenon. I do know that I enjoyed magnifications of x1 per mm of aperture (x100 for 4", x200 for 8") since before I knew about above and I probably have slightly better vision than 20/20 - so in my case above theory matches reality.

I'm guessing that selection of materials that you've printed include PLA and possibly PETG. For those materials, stock printers just simply work and if one is not overly keen on getting the last ounce of precision from the printer - they will suffice. Here is an example of what might not be possible with stock printer: Above is a cam shaft that is a part of some crazy design that I recently made. It is 1:324 reduction box with zero backlash and no contact between output and input sections except for bearings. It uses magnetic coupling to do the job. It is part of my effort to create simple / affordable EQ mount that is in EQ5/EQ6 class - yet it will be fraction of the cost with much better performance (I hope). Due to need for precision - above is not single piece but is rather assembly of 5 parts. Otherwise, I'd need to use supports for printing and it would be very difficult to get smooth surfaces where they need to be. Also - assembly with other parts would be impossible. Normal precision of 3d printer is often quoted to be +/- 0.2mm. I don't see why it has to be that low - as most components are capable of higher precision (even 0.4mm nozzle won't suddenly extrude 25% more material to overflow for 0.1mm on each side of the print). With nicely tuned printer one can regularly be in 0.05-0.08mm range. In any case - if you have z axis issues like backlash (due to binding because poor quality control) or perhaps you needed to bring down nozzle for best layer adhesion (manual leveling) - you prints will be always 0.1-0.2mm lower then they should be. This is "within the specs" for 3d printer - yet it is constant error to one side. When you have 5 parts that are on average 0.1-0.2mm shorter - whole assembly will get 0.5-1mm shorter and when you want everything to fit together with ~1mm tolerances that starts to be a problem. I often had to resort to various tricks to get the parts to be of good enough dimensions (mind you - in "everyday use" - like for models or large single printed parts - these dimensional errors are tiny and often imperceptible) - including "baking in" changes to the model itself - which is poor practice if you want to share your design. Before I did mods to my printer, printing 0.75mm pitch threads was hit and miss affair. Now I can be sure that they will work on the first go with my modified printer and what amazed me the most - Bambu Lab P1S did so with very inexperienced person operating it (slicing and all - I just provided the model in FreeCad) 2 days after arriving (It was probably 3rd or 4th print and first custom one / not provided by vendor on SD card). I'm sure most of printers out there work. Some of them even work well out of the box. It is just the question of capability of the printer - for example if it will print nylon, tpu or ASA out of the box (high temps, direct drive, enclosure - perhaps even actively heated, good bed adhesion and so on ...) and the hassle involved to get to result you are after.

Here is a summary of things that I've done to my Ender 3 (I thought about it after I made above post as I never really listed all the things that I've done to it). I started with stock Ender 3 v2 which was about 220e. I added CR touch to it for about 30e. Dual lead screw setup for 35e (AliExpress). I made lack enclosure from two lack tables, acrylic side panels and Klipperized the printer with Banana PI4 for about 180 euro total (two lack tables, banana pi4, custom acrylic side panels, led strip, 12v psu, 12/5v step down converter, some magnets, blower fans for activated charcoal filter ... ). I upgraded to Microswiss all metal hotend with hardened steel nozzle - ~60euro (don't use hardened steel nozzle unless you really need to - regular brass ones are better for regular materials). Another 75euro on linear rails. ~50 for Orbiter v2.0 extruder at least 30-40 euro to some bits & bobs - like: two different sets of bed leveling springs/silicone spacers (trying to get ones that are good), different couplers for z-axis - trying to solve vertical banding issues / backlash and stuff and so on ... Let's sum that up. That is close to 700e. While my machine is printing fine now - it's still not printing at the speeds of P1S and the time and frustration that I had to put in making all the above modifications ... I'm only reluctant to recommend P1S because it's not using open source firmware so you can't easily mod it if need arises. After all of the above - I'm now harboring the feeling that proper way to solve issues is DIY route. Of course - I'm aware that for regular user that does not want to tinker - it is much better to have product that just work, and from what I've seen online - P1S is just such a printer - it works, it's easy to use, you don't really need to fix it in any way. But having said all the above - I just went to see the Ender 3 V3 - and I'm surprised by amount of changes they made - at least to Ender 3 V3 - regular version (not SE and KE). It has most of the things I would change on ender - linear rods instead of V-slot rollers, Core XZ configuration, All metal hotend, Klipper (I don't like it is "creality OS based on klipper" instead of just plain klipper). I'm just wondering how well will it perform out of the box and how much tweaking would it need to run properly.

What's your budget? Having started with Ender 3, which was at the time sensible offer, I'm reluctant to recommend it at this time. I've heavily modded mine to get it to print the way I want it. Overall cost of all modifications is higher then much more serious printer. Now, this is just my opinion on the subject, but I'd recommend getting a printer that will be capable of printing advanced materials like ASA - which means enclosure, good heated bed and all metal hotend. Also, if you want 3d printer for astronomy - then you probably don't want to tinker too much with it. Such style printer that will be much much better that one would be this: https://eu.store.bambulab.com/products/a1?variant=47554015691100 On the other hand, if you want to print advanced materials - get this one (it comes with enclosure): https://eu.store.bambulab.com/products/p1s?variant=47422304289116 Although I haven't personally worked with Bambu labs printers - I recommended one to a friend of mine (P1S model) and he is very happy with it. Two days after receiving it - he was able to print M63/M48 adapter that I designed for him - without any previous knowledge of how 3d printing works (except watching few videos on youtube).

It's a pity you did not choose to go with curved spider wanes to avoid diffraction spikes - these come "for free" with 3d printing

I usually don't like nylon because it creeps a lot, but for this application it will be well suited (one might even say it's a bit overkill - but it will work great). Looking forward to hearing if this design aperture mask improves contrast.

What material did you choose for that print? PLA in black color might not be best suited for solar applications - if there is no enough air flow (at least some light breeze) to keep it sufficiently cool.

That's not M1 but nice image anyway (hint: )

To me it looks like one of screws that holds focuser attached to the OTA, but I'm not sure (and that sort of seems logical as you need such screws but they are not listed on diagram).

To further expand: https://en.wikipedia.org/wiki/Solar_eclipse (it has nice info on both lunar and solar apparent size depending on current orbital position and how they relate)

Right. Position A - better if there is street lamp near by (although if scope is properly baffled and dew shield has mat black paint on the inside - difference will be minimal if at all visible). No difference between two positions as far as view goes when there are no street lights involved. Sources at infinity don't really care if mask is a bit away from the lens. This is strictly not true for very wide field use, where edge of the field stars / objects won't hit center of the lens if aperture mask is further away - but for normal use and few degrees of distance from optical axis - everything is the same (here is diagram to explain this last bit): If incoming light rays are at very high angle and aperture mask is further away - you might end up using edge of the lens rather than center - red arrows in above diagram. For few degrees - this is generally negligible effect (you can calculate the offset - as it is sin(angle) * distance - so for 2 degrees of axis, or 4 degrees of FOV in total and 20cm of distance of aperture mask - offset would be 6.9mm from center)

When focused at infinity - I think there is zero difference between the two. There might be slight difference in what you suggest - but only if you have significant source of light that is in front of telescope - but not directly - so that light is able to hit interior of dew shield.

I don't think meridian flip un-glitched the software I'm more inclined that meridian flip un-glitched dodgy power connector for 12V to camera cooling. Without it - peltier won't work and although software might think it is cooling the camera - without power it won't.

It is very easy for an achromatic refractor to reproduce images obtained with Seestar50 - even cheap achromatic refractor. With achromatic refractors - there is something called CA index - or index of chromatic aberration - which is a number obtained by dividing F/ratio of the lens with aperture in inches. 50mm is 2" and telescope needs to be F/10 or slower to show virtually no CA. In fact - if we take very cheap and common 80/900 refractor and put 50mm aperture mask on it - we will get F/18 instrument with 2" of aperture. I think that sharpness of such arrangement will beat seestar in terms of performance (if we speak of sharpness and contrast). Even very fast ST80 will come very close to be color free and very sharp without any filters if we put 2" aperture mask. Most people with SkyWatcher version (not sure if other versions have this feature) can actually try this by removing small central cap of the lens cover:

I've been saying that 3d printer is probably one of highest value accessories in this hobby - for anyone with even slightest DIY ambition. Astronomy buddy of mine just got himself a Bambu P1S and one of his first prints was M48 / M63 adapter to attach camera and reducer to focuser on his 6" RC. He intended it for prototype only - to verify correct spacing and that he'll be able to achieve the focus, but after seeing the quality of the print (I helped a bit with modelling and slicer settings) - he now thinks he'll be just using 3d printed version.

That is a trick question, and like dear friend of mine once said - "I don't answer trick questions"

I think you are right! Same thing is mentioned in the answer that I linked.

I don't know much about this, but from what I've gathered, rated voltage of stepper is not important as it is used. This I've gathered from 3d printing forums as steppers are used to move the mechanics of 3d printers. In any case, stepper can be driven in two different ways, if I'm not mistaken, and most modern stepper drivers are current drivers. They just pump enough current (depending on settings) to get the motor running. I think that max voltage has something to do with holding torque in that case - if you want more holding torque (or is it max speed?) - you need to provide higher voltage. Some stepper drivers work with 48V - and you can use those drivers with 3.5V motors for example. With current drivers - you really don't care about declared voltage. See this answer for more details: https://electronics.stackexchange.com/questions/200324/how-to-interpret-the-stepper-motor-voltage-requirement

You can use something like torch - one that focuses to tight beam to illuminate the ball bearing from the side. Use very small ball bearing to get small reflection.