pipnina

Funny enough I also have those same flat/extraction issues, and given as it's happened on three different scopes I'm starting to think the problem lies elsewhere haha. Probably in my case I need to fully nail the calibration (flatdarks, bias, etc) Software updates have plagued me too, Kstars has had improvements but some releases have been broken and I've had to wrestle the ubuntu package manager to get the old one back! The seller used a much smaller sensor camera, and I suspect this is a big part of why they didn't notice. I did speak to them about it but they seemed fairly sure it worked when they had it, and the pics they sent taken with the scope before I bought it looked ok, in the end maybe it was bad when they sold it, maybe it wasn't! In likelihood it probably was in at least some of the ways described, but it's a bit far gone now to go and complain haha. Thanks for your best wishes also.

2022 was a year of some decent highs and painful lows when it came to my astrophotography ventures. I made the dive from an unmodded DSLR on a handset-only HEQ5 with a 130-PDS, to modding the DSLR, then replacing it with an astrocam and using my laptop to control the setup. Then I broke my PDS (cut the focuser abrrel too short when trying to prevent it from intruding the light path), and replaced it with the horrible TS-PHOTON. That plagued me for 2022's summer and set me back over £900 once I dealt with dovetail bar upgrades and coma corrector upgrades on top of it. Then when I was at peak distress with the PHOTON that would not hold even secondary collimation at this point (took the secondary out to blacken the edges, when it went back in, it wouldn't stay in one spot...) an ad came up in the classifieds here. 130mm f6.6 carbon tube triplet. For 1500 including a 0.79x corrector. In theory that's not just a good deal, but ideal timing for me. Some discussion with the seller and I wind up buying it, and it goes via DHL and turns up at my house a few days later. First night I get to try it, I can't get the corrector to work, massive astigmatism at the edges (later turned out it was my fault, backfocus went down by 6.5mm due to no longer using a M48-T2 adapter). I took the corrector off and realised the focuser was tilted, and not in a small way. And on top of that, the focuser slipped when my ZWO EAF moved back and forth, and even slowly slid out during the night... It needed changing. After bribing the machinist at work with a box of Celebrations and cutting the rear flange off of the telescope to make it accommodate ANY alternative focuser, I was now down £2050 minimum, but I had a 3" R&P with tilt adjustment instead of a rubbish 2" crayford instead. But the images still weren't right. Even dialing in the corrector's backfocus more accurately I realised there was astigmatism on one side and coma on the other, and a bit of coma in the center of the image. The front cell was mis-collimated. After googling and researching and buying an artificial star testing kit, I used my highest power EP to study the center of field star pattern for an afternoon in daylight. I thought then that there was a little astigmatism in the middle still, but hopefully it was improved as the tilt of the cell had now eliminated the off-center rings. Yet the next time I went to image, it was unchanged. Something more drastic is wrong and it's beyond my capacity to correct. If I want to fix it now, I need to send it to a specialist. I contacted the people at FLO and they have forwarded me to Es Reid, who I will be contacting shortly. But they warned me that the *minimum* I would be charged would be £75 per hour, plus the (based on my estimates) £150 needed to post it to and back. Now I am torn. Is it still worth me going through and spending yet more money on this refractor... Or am I just getting trapped in a sunk cost fallacy, and this scope will just cost me more and more money, never being as good as it could have been if I just splashed £3500 on a 120 or 130 triplet straight from FLO which was already checked by Es Reid as part of their running agreements... And saved myself months of stress and DIY and most importantly, NOT IMAGING. I feel like I need this off my chest, just because at this point it's genuinely eating into my life because of the sheer emotional, financial, and time investment I have sunk these last 12 months. Hope all of you are having a better time!

I have been tuning the spacing but since the star shapes are different in each corner it's been hard to get it exact. I will have the chance to test it tonight so hopefully I will know if the tilt is now correct and will be able to dial the spacing in a bit better. A good shout. I have been keeping it outside for a while now as the weather is ok and it is protected from prying eyes. So it should remain decently acclimated to the temperature

The biggest issue as mentioned will be creating the threads. There are a few things that all need to be parallel or concentric in a filter wheel so it might not be easy to print. Given as a good LRGB filter set will set you back at least £400, and a single quality 3 or 5nm narrowband filter will set you back 300-500 (thinking about 36mm size here), I think it's probably not a great place to look for savings sadly. Still, maybe money isn't the point- perhaps it's the challenge and seeing if it's possible regardless. In such a case: off-the-shelf bearings and bright steel rod could make a decently sturdy center for your filter wheel's rotating part with minimum run out. Might be a good starting point?

I've done some fiddling with it in daylight and I think I've solved the coma issue in the center. But now that that's solved I think I've introduced astigmatism... or worse, it's there when the cell is properly tilt collimated, meaning the problem lies within the arrangement of the triplet of lenses within... Far beyond my ability. Hopefully this makes it better when imaging however, will report back if it is or isn't 😬

I have my artificial star torch (5 holes, 50 micron, up to 250 micron) and I'm looking at the smallest one in my 6mm eyepiece at a distance of about 13 meters (800mm focal length, 130mm triplet of unknown make and design). As I adjust my focus from intra to extra, I notice that when it's focused it actually looks quite good, intra focal it looks like two strong rings concentric with the white dot in the middle... but the middle isn't well defined. it looks strong, but it also almost looks like three dots split up. Not sure if that's pinching or if it's miscolimation or something else! When I'm extra-focal, I see rings moving into one corner of the outermost ring, which seems like coma (cell misalignment) to me. Should I be basing my adjustments of the tilt of the main cell on the extra focal value? Thanks Here's the best pic I could get down the eyepiece extra-focal, sadly intra focal wasn't possible as getting the phone into position was very hard indeed and the stars were a white-out! And this is what I'm seeing in images (albeit with corrector, but it shows that star shapes are not uniform across the field) I have performed the paper-with-crosshair check over the front of the scope to align the focuser with a laser. And because I have tightened the grub screws holding the focuser that is now rock solid (can't use the rotation feature though now) Should I adjust my cell with this artificial star setup, do I need more magnification, am I reading things right (that extra focal view is showing me the coma error?) Many thanks!

It does produce a cleaner image for sure, but it also does cause some artifacts on stars (they tend to go odd colours) and it means you need to sit there with the phone hitting the shutter button every 4 minutes- deep sky camera lets you take about 30-40 mins worth at a time. That said, I did find a way of controlling my phone from my pc indoors so it might be tolerable if I tried it again. In the end these phones are impressive for jack-of-all-trades devices but I think you'll agree that we mostly image with them from curiosity or necessity and not because we expect greatness!

I have gone down this route, and sadly even if you go through the effort it's not worth it: The camera in the pixel6 (at least the wide angle one, I only have the normal version not the pro) has terrible coma and concentric rings of distortion. It also suffers from internal reflections and has very strong dark noise and hot pixels. Mind this was when I attempted it when night time temps were still 15c, not freezing! The end result is that you hit a brick wall fast, I'll find my attempt that took a lot of working out to get right, and even then it's not as good as I would have liked for I believe 2 hours of data! Edit: Here's what I achieved using the p6 by itself and a star tracker, using deepskycamera app and pixinsight. This used several hundred gigabytes of hard drive space and hours if processing so I think the result is a bit disappointing. Best to stick to the inbuilt 4 minute timer I guess!

It's the wrong time of year right now, as the milky way core is more of a summer-autumn object. I know that usually people refer to the core when they say "Milky Way", but of course everything our human eyes can see without assistance is the milky way (except for the megallanic clouds and andromeda) so really the core would be best specified as the outer milky way is also visible under suitable skies! Based on your location however, visual observations of the milky way structure could be challenging. This is because the brightest part (the core) appears in the south, where you will be staring at london's light pollution! The outer sections of the milky way structure are fainter, and so harder to detect. The outer milky way runs through Cassiopeia down just to the left of Orion. It's not easy to spot but if you can it's quite incredible! In your case I would think you need to drive somewhere dark, but maybe someone more local to you will have better tips and experience to let you know how practical your aims are! I live in deepest darkest devon so the lack of life down here has made astronomical observations a bit easier. I have seen all parts of the milky way visible from the north only a short drive away from my host city. I appreciate I am raletively lucky in this way however. Happy hunting! If you have a modern or higher end phone you might catch the core of the milky way in the summer via the long exposure camera mode? Even when I can't see it directly, the phone seems to be able to with a bit of teasing.

In my case it meant tightening the flathead grubscrews that held the focuser onto the scope. These have always been external screws for me so I could just take a screwdriver to them and tighten them to remove the slop. Only my current focuser is tilt-adjustable though.

Could be the front cell or the focuser aren't quite done up tight? I've had that issues before...

Something about this reminds me of a very old post here, I think by @ollypenrice looking for some sort of "andromeda shelf" that was not confirmed at the time but someone had claimed to detect. Could this be the object in question?

Personally I've based my opinions around printing materials on this guy's tests: He tends to do a variety of tests that show tensile, impact, and other kinds of strength. So in general I feel it's good enough for us amateurs!

I found it rather hard to design a newt in the online newt calculator tools that had good illumination across a good FOV, plus by removing the 90 degree light path turn you make it easier to baffle the tube and remove stray light from entering from the side of the focuser. It's also just something interesting to work on regardless haha. A fair few correctors work with f3 mirrors which would be quite a good setup, something like a 10" or 12" F3 mirror and camera style focuser might be a bit better regardless of not exactly being a RASA. But if I find like you did that it's not all that, I won't have spent much money to find out!

For now, I think I can only print with PLA anyhow as ABS requires a warmed containment for the printer to avoid warping, and PETG/Nylon etc filaments require hotends that run much hotter than my Ender3 can handle (above 235c I think is unsafe as the hotend has PTFE tubing running all the way up to the nozzle, which fumes up and can even burn above 240c) PLA+ seems "stronger" than normal PLA, but only because normal PLA is very brittle, while PLA+ tends to accept a lot more bend. I think tests do show normal PLA to take more force before total failure however. I expect creep to be the big problem here. A test part I made for a catflap cover has warped and all I did was leave a plate on top of it. I am thinking that steel spiders might be a necessity, but the holder for the focuser seems rock solid even with this PLA+ so I don't expect to need to change that material. I am planning on making the spiders out of plastic first, and attaching them to the focuser holder and seeing what weight they handle. I may put some weight on them and wait a few days, see if they move... I also plan on making them quite tall, as I think they can be any depth without impacting the image... Not 100% sure about that though. I always assumed only the thickness impacted diffraction. I guess eventually i'll find out!

I had been thinking of this for a while, but until I got my 3D printer it was a bit of a non-starter. Learning the ins and outs of printing and using FreeCAD has been quite challenging, but last night the first "finished-looking" prototype for the focuser-holder for my newtonian conversion came off of the build plate! And it fits very nicely. My next step is to design the way to support it. EsunPLA+ may not be strong enough to support several kilograms of camera and focuser, so I may have to look into a hybrid approach with sheet steel vanes fixed into the PLA supports... Work ongoing! For now, i'm happy I managed to design and produce a working holder for the focuser. While I could have bought a 2" rotating focuser as suggested by @vlaiv, which would reduce the obstruction and weight, I wanted to see what the minimum conversion cost would be for someone who already has a printer, so replacing the focuser isn't my intention at this time. I intend to post more updates in this thread as my project progresses. And eventually find out if it's a worthwhile re-configuration for newt imagers! So far this setup gives a central obstruction of 95~ mm diameter. Which is about 2-3mm more than the obstruction created in the RASA8's optical train. Perhaps I will work on a way of removing the focuser adjustment knob and replacing it with a printed part that can be slid on and off the shaft so it need not interfere with images... Thoughts welcome!

Thing is, my 24mm I think has LESS relief than my shorter EPs! Both the Vixen SLV and Stellalyra UWA have 20mm whereas I think the maxvision is around 17 or 18. Yet the shorter lengths feel harder to use somehow.

I don't know if it's just me, but I've noticed that even the medium-to-high quality EPs I have seem to be rather challenging to observe through. For instance, my vixen SLV 10mm and stellalyra uwa 6mm both seem very hard to get a proper look through. I find as I get closer to the eyepiece, the field of view widens, but by the time I get close enough for it to widen to above say 40 degrees afov, the edges blacken as if I am now too close? For my maxvision 24mm/82deg EP, I find it's quite hard to see the edge of the afov too, but I can definitely see much more of the afov in that EP despite not having as much eye relief as the 10mm and 6mm, it also lets me move my eye around much more than the other two, which seem very fussy about my eyes pointing straight forward all the time. Could it just be that the small exit pupil makes them more challenging, the EPs genuinely aren't as good as I thought they were (mismatched expectations) or maybe the clouds have gotten me too far out of practice haha. Am I alone here with this struggle? I'm not a newbie by any means but I do seem to be struggling.

Something I noted was that PHD would fail to calibrate if too close to the north pole. Because 60 seconds of RA movement covers a far smaller star movement at +80deg DEC than 60 seconds of RA movement at +60deg DEC. What was your target?

My small 130PDS did very nicely (with the exception of its known design flaws, primarily the focuser tube protrusion). But of course this is a fairly small scope compared to what you're thinking of, it still did nicely on small-ish galaxies: I also used a scope more in the realm of your considerations: A TS-PHOTON 200/800. That made nice images... When behaving. It also seemed to suffer more from not producing a flat background, maybe the tube walls were not black enough or somesuch. It also NEVER kept collimation, it required modifications to be usable at all for imaging as the collimation shifted just by changing where the mount was pointing... I also never got it to dial in perfectly, all of my images with the scope have some coma or astigmatism somewhere. The images I *did* get, I was mostly happy with. It wasn't easy to gather them though! My advice: If buying a smaller newt, go cheap and do things like put flocking material on the inside of the tube and blacken the secondary edges. If buying a bigger newt (i.e. larger than 150mm) you need a more expensive model to have any ease of use. For some reason the step up from a 5/6" mirror to 8" increases the hassle involved massively unless the scope is better mechanically designed. Good luck!

That's pretty shocking! I bought an A3 paper sized £35 panel from amazon intended for artists to illuminate their paper/canvas. It isn't perfectly smooth but has allowed me to take good flat frames, on my DSLR it was spotless, leading me to think irregularities with my flat calibration are more to do with my astrocam or telescope optics rather than the flat panel. How "proper" astro companies can sell something that is less relaiable than a random cheap amazon purchase, for 5 times as much is beyond me...

I suppose in PI you might do background extraction before the fit? I don't know, I tried it but maybe some small residual gradients were left (the scope was a bit dodgy in that regard)

I've noticed it can be a bit dodgy though- assuming it's valid for use in mosaic images. I could often get two images to linear fit together, but quite often when you stretched the merged linear-fitted images, one would get a black background before the other anyway... It also couldn't handle one of my panels that accidentally had 768 offset instead of 0 (before i knew what offset to actually use). Linear fit just could not correct that and i got my python-coding friend to make a script to just subtract 768 from each pixel of a fits file, which did work. Sadlly the mosaic was impossible for me to complete regardless as I couldn't balance each panel's brightness... Not sure why linear fit wasn't working. I even tried the DNA linear fit script too I believe.

Orion Optics make the CT8, which is f4.5, carbon tube and still cheaper than the vixen, I have hard of people getting good results with these, but I am not an orion optics connoisseur so sadly I can't give first-hand impressions 😕 I have looked for the vixen and it seems like it could be out to cost you about £1600-1700 already, so the Orion option is most likely cheaper. The TS I can see is probably more expensive as you say however, but from what I hear the TS ONTC scopes and the Orion AGs are about as good as it gets for newtonian imagers. IMO it's a choice between the vixen, which you know will have excellent optics and rigidity but also have very very chunky diffraction spikes, against the more expensive TS ONTC and the cheaper Orion CT. I might be missing a brand somewhere but afaik mid-high end newtonians are actually not easy to find, but the budget/low-end market is flooded. Also: In theory the wynne corrector will work with any newtonian, as they all have parabolic mirrors, and as such are all the same shape, if the diameter and f ratio are the same.

I have looked at it myself before and seen a lot of people complain about the super-strong diffraction spikes (you can see in the pics of the scope that those spider supports are very thick!). But if you like strong spikes you might consider that a positive. I think vixen are quite highly regarded so the optics are likely very good. However: I don't have much more knowledge about them sadly as it's not a popular model! I do know that the TS carbon tube scopes are highly regarded for imaging: https://www.teleskop-express.de/shop/product_info.php/info/p6119_TS-Optics-8--f-4-ONTC-Carbon-Tube-Newtonian-telescope---fully-customizable.html A bit expensive though, but I don't know how it compares in price to the vixen. I would personally avoid reflector greater than 6" unless they're of a premium (vixen, TS ONTC, etc) as my own experience shows they do not hold collimation at all. My 8" TS PHOTON was atrocious, but my cheaper built 130PDS was rock solid, for example. Hope you find the one that's right for you, and I hope this helps!