Phobos 226

Hi Sam, I was faced with a very similar position and budget as you last year and thought I'd pass on a little of my journey as well as what I would do differently in retrospect. As of today I have a Skywatcher 130PDS which is an extremely well regarded compact imaging newtonian mounted on an EQ5 that I "tuned' myself using a few different guides and converted from manual to fully Goto using the open source OnStep system. I've been working on a little blog site that explains the process I went through to get it all working and you can see my recent results on Astrobin. All that being said with the benefit of hindsight I would look at perhaps a slightly more compact and lighter scope with the EQ5 for astrophotography as I'm really pushing it with the 130PDS. I will likely be upgrading to an EQ6 or similar quite soon to better cope with the weight and give me tighter guiding which averages 1.4 to 0.9 arc seconds RMS depending on the night. I will then likely put a smaller, shorter focal length and lightweight refractor on the OnStep EQ5 which it should be better suited for. If I were going into it again with the EQ5 as my only option I would still pursue OnStep as it has clear benefits as an overall system than the stock EQ5 Synscan system and even some off the shelf Goto mounts owing to the active and open source nature of its development. The caveats here are is it requires some DIY knowledge and a bit of a delve into electronics as well. I would also probably look at a shorter basic refractor as a starting point, something well regarded for imaging at a budget like a 72ED or similar at ~half the weight versus the 130PDS with mandatory tube rings which add almost half the weight of the OTA on top. Another option if you're just starting and already have some lenses for your DSLR is have a look for a fast prime lens on the second hand market and mount the DSLR to the EQ5 directly with a basic dovetail/saddle and you might not even need to guide under 2-3 minutes if you're lucky. The benefits of shorter focal lengths let you tackle bigger targets like nebulae and a full shot of Andromeda as well as being more tolerant to coarse guiding which you get with the EQ5 no matter how hard you tune it as it's just made cheaper and lacks things like a proper DEC axis bearing, instead relying on teflon washers over a proper bearing. Of course the safest and likely most sensible option is to save up for an HEQ5 or EQ6 class mount or hope you get lucky on the second hand market (difficult in these COVID19 times) and work your way up with the mount capacity already in hand as most of the work in taking good astrophotos is down to the mount alone and I'm sure many others have ended up in a situation where they feel 'undermounted' and wishing they had more payload capacity from the beginning. You can always upgrade incrementally as budget allows but spending once on a mount is something that will be a net benefit overall and your future self will thank you for it. The question is do you want a challenge and to learn something new as you go on your astrophotography journey, or do you want to avoid the hassles and get to decent and reliable imaging ASAP? I certainly know far more about how mounts, worm drives, gear reductions, periodic error, soldering, stepper motors and microcontrollers than I did a year ago that's for sure and I look at it as an invaluable learning experience that taught me so many new things and skills I never would have had the confidence to even attempt not so long ago. Since then I've build my own regulated power distribution hub, electronic focuser, peltier cooler for my DSLR, light box for taking flat images, a DIY dew shield from a yoga mat and even removed the IR filter from my 400D to make it 'Astro-modified' for better Ha response. Hopefully that's some help to you as somebody who had similar thoughts and was in a similar position as you almost exactly a year ago! Just remember this is a what can be done and not in any way what should be done; I'm not suggesting you follow the same path as me unless you intend to get the same experiences and challenges out of it! Just be aware that you'll probably be like me and looking at cooled mono cameras, bigger mounts and more OTAs on your shopping list as the bug bites you down the line... But I don't think that's a rare phenomenon in this world as many would agree.

Having just set up one of the 0.4A 27:1 Nema 17's from stepperonline I've found it works perfectly with a DSLR and I could turn the current setting on my LV8729 right down low so everything is virtually silent while still managing more weight than I have available to add to the focuser right now. I'm happy this is future proof for whatever weight I want to add. With a direct coupling to the coarse shaft on the focuser (don't use the fine focus) on my Skywatcher Crayford I can full-step for 2.2 microns of accuracy on my f5 130PDS, which is plenty enough inside the Critical Focus Zone. As for the backlash, yes it's there but not nearly as bad as I had anticipated and it can be compensated for in software/firmware. Having absolute positional accuracy (provided no missed steps) with full-stepping, the reduction in power requirements, less heat from fully energised coils and the huge amounts of torque in reserve is an acceptable compromise for me. So there's another +1 for the 27:1 from me, if it's of any help.

I didn't, but I've not been running the official Raspbian release for some time as I switched to Ubuntu Mate with Stellarmate OS and then KDE with their latest update. I never encountered any overheating or throttling problems with this case however and it stays very cool compared to running it with no fan and heatsink out on the bench/desk. I've seen a lot of recommendations for the FLIRC case though, which has a plastic bottom shield to help out the WiFi and an all aluminium core that acts as one giant heatsink that sits directly on the chip. As it's going to be in the cool night air I imagine this would be perfectly fine as well, as we're not running them stuffed away inside some entertainment centre or under a TV etc. I'll probably switch to a FLIRC case in a little while as I do like the look of the finish and it's not too expensive.

It was one of these by John Sinclair but I bought it direct from his eBay store as I don't have a printer myself. The 4 can get rather hot, especially with the warm nights we had over the summer in the UK South East this year.

Had a busy weekend, here are some quick phone images that I only just got around to! I just got my power distribution box finished and mounted this evening and you can see it underneath the RPI4. I've got the platform mounted in a 'wing' style at the moment as I moved my guidescope back a bit a more. The weight imbalance here is only about 200g which isn't too bad opposed to mounting it directly over the centre axis of the OTA. The platform has two mounting points with 1/4 inch UNC bolts that thread directly into the 33.5cm dovetail which had those holes pre-tapped. I added my own holes to the dovetail threaded directly into my scope rings using the same UNC threaded bolts. This is on a 130PDS and the rings that came with it as standard from Skywatcher, so they may be smaller on the SW 80ED I'm not sure, but the principle remains the same. Using an OAG you can mount the plate/platform directly over the centre of the tube so you can be a bit more flexible in your layout than me trying to get around the limited space I've got left on my setup here. Either way I'm happy with my new power box!

I just did something similar with my RPI4, USB hub and my in-progress power distribution box. I mounted a long (cheap) 35cm Skywatcher dovetail onto the top of my tube rings and made a platform bolted to it from rigid 5mm thick matte black Perspex which then has my bits mounted using strips of 3M Dual Lock so I can swap parts around if I need them or not/shift the balance etc. Of course you can bolt things to it as well, but it's cheap, lightweight and easy to work with. If you wanted it more rigid then I would get some aluminium plate in place of the acrylic and bolt through as has been suggested, but with no cameras directly coupled to it I see no issues in a little flex for a distribution box on the top of the tube. P.S The RPI4 4GB is a dream running KStars, I can run everything locally on Pi now and just remote in from my 4K TV at native resolution. Works flawlessly and I'm sure you'll be happy with it too!

If you're up for a project, I and many others have done full conversions of EQ5 mounts with precision steppers and pulleys using the excellent OnStep project. Total costs can be very low for a full conversion of an EQ5 at around £60-100 for the electronics, about £20-30 for the motors and another £20 for belts and pulleys. The only tricky parts are figuring out a mounting system (I used standard Nema 17 metal brackets that I drilled adjustable holes into to allow the belts and pulleys to be tensioned correctly) and potentially a bit of soldering depending on the 'kit' or controller you base the project on. You will also need to add a guide scope and camera if you want to get into guided images, but even without one some people have been able to use the 'Full Dual Axis Compensation' on OnStep with 6-9 star alignment to achieve up to 3min unguided subs on various mounts. I'm not 100% sure on the numbers on an EQ5 though as I have always guided with this setup, but even that can be achieved fairly cheaply with a converted finder and an old webcam or second hand ASI120MC/MM. I use a cheap 50mm guidescope from Svbony I got for about £50 on ebay. Overall you can end up with a system that can compete an off the shelf mount albeit with a lower weight capacity for photography, but still just about adequate for a 130PDS and DSLR which is exactly what I am using on mine right now. Of course you'll get a fair amount of dropped frames compared to a higher end solution, but as a rough guide my one of my tests was 40x300s exposures on M33 using my old 400D. Currently I'm fine turning my guiding accuracy and getting everything pin sharp, my best results so far have been a total guiding error of 1.1" RMS seen in this quick and dirty process of 17x300s test on M27 from 2019/09/06. Hope this helps open up another option for you to consider!