GraemeH

Hi James, I bought one of these https://plater.manufacturer.globalsources.com/si/6008852269094/pdtl/Mini-PC/1162987701/Mini-PC.htm in 2017 (bought from Amazon but it's no longer available there) to test the concept. More recently I added one of these https://www.amazon.co.uk/gp/product/B07FXDW41T/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 for my other mount. Performance wise they are very similar. I slightly prefer the first one just because of its slightly smaller size, but the second one has more RAM and a slightly faster processor which I think is the reason that it's slightly faster for plate solving. Graeme

I have 2 mini PCs - one on each of my two mounts. They run APT, PHD2, ASCOM and associated mount and focuser drivers, Sharpcap and Stellarium without coming under much stress. I have them set up to attach to my home WiFi and access them through Windows Remote Desktop from indoors. They are set to save images from my DSLRs to my OneDrive folder, so I can check the subs on my main PC without affecting anything during capture. I previously tried using a USB device server instead of a mini PC, and whilst it worked for the connection to the mount and my DSLR, I couldn't get anything from my guide camera (QHY5Lii). I suspect the device server simply wasn't able to cope with the bandwidth required for the guide camera. I find it extremely convenient to be able to head straight indoors after completing polar alignment and then get on with capturing images from my warm comfortable sofa. I realise that might make me something of a lazy imager, but I can't see the attraction of spending hours outside in sub zero temperatures.

+1 for going down the DIY route. I made one of these https://sourceforge.net/projects/arduinoascomfocuserpro2diy/ for my EdgeHD8 without really having a high level of soldering skill. The instructions are excellent and Robert is responsive to questions on the sourceforge forum. I think mine cost around £40, including buying loads more than I actually needed (I found it cost around the same to buy some components by the 100 as it does to buy 3 or 4) so when I make another for another scope it will cost even less.

Taking some sky flats in preparation for an evening of imaging.

Just in case anyone else has similar thoughts about this I thought I'd confirm my results. I have been able to get focus on my QHY5Lii with the 0.5x reducer screwed to the C mount extension supplied with the camera. I suspect with other OAG designs this may not be possible because of the need to move the camera closer to the prism, but with the Celestron OAG I had enough room. Platesolving an image from the guide camera has given me an effective focal length of 1141mm with my Edge HD8 (my imaging camera shows an effective focal length of 2140mm with this scope), so the reducer is giving me ~0.53x. The wider FOV on the guide camera is great for picking up more stars for guiding.

I was the very grateful recipient of a Skywatcher ED72 at Christmas, and bought an OVL flattener to go with it. I want to use it for imaging with a full frame dslr, so would like to use my m48 t-ring to minimise vignetting. The flattener comes with a thread adapter on the camera side which is m42, and my rough and ready measurement of the thread on the body of the adapter suggested it was m54, so I bought an m54 to m48 adapter. It didn't fit - the adapter is a tiny bit too small on the female side. I guess it might be m55 on the flattener, but I don't want to just keep guessing and buying the wrong thing. Does anyone know exactly the thread measurement on the body of the OVL flattener, and if there is anywhere that I can buy a thread adapter to take it to m48? Thanks, Graeme

Thank you vlaiv - I think that's clear now. If I understand correctly, then in order to keep the optimum backfocus distance to my imaging camera, I'd have to be able to position the guide camera much closer to the prism turret in the OAG. I think this could be possible with the Celestron OAG. I currently have a 6mm T spacer, then T-C adapter to attach the QHY5Lii to the guide port - I could remove these and insert the camera body into the 1.25" holder part of the OAG to push the camera sensor closer to the prism with the reducer in place. The diagrams certainly help with understanding.

Thanks vlaiv - you've given me a couple of things to think about. I think I probably can improve the focus on my guide camera. It's well enough focussed for reasonable guiding, but I do think it could be improved a little which may allow me to pick up fainter stars. I'm already set up with the prism on the long side of my sensor (full frame DSLR), but I might be able to push it in a tiny further in to the light path. I already use 2x2 binning for guiding, and do use the ASCOM driver at 12 bit. I mostly use 3s guide exposures but there's no reason I couldn't try going a bit longer to see if it helps. The one part of your reply that confused me a little was your comment about back focus effects on the imaging sensor - what I was proposing was to put the reducer between the prism and the guide camera so this should have no effect on my imaging camera in my mind. I do understand what you mean about being limited by how much light can be picked up by the prism though. My prism is 12.5mm, and the QHY5Lii chip is 4.8mm x 3.6mm but I haven't tried yet to calculate the size of chip that could be illuminated by that size of prism.

Thanks Doug - I've fixed the URL. In terms of separate guide scope, I'm pretty convinced by the many threads on here on the subject that suggest long focal lengths really need off-axis guiding to perform well. I don't think I want to introduce the complication of differential flexure. My preferred targets are generally galaxies, but I'm still very much a beginner and trying to understand how to tackle lots of different objects. Dave - unless someone indicates that there's no way to make the reducer work, I may just give it a try anyway. It's only around £20, so a much more financially sensible option than a Lodestar if I can make it work. Thanks for taking the time to reply though.

I occasionally have difficulty in locating a guide star using my Edge HD 8 with an OAG and QHY5Liic - my limiting magnitude for guide stars seems to be between around 10 and 10.5, and the very narrow field of view when imaging at f10 means that I sometimes can't find one that gives good framing of my target object. If I were to attach a 1.25" focal reducer (e.g. https://www.telescopehouse.com/revelation-0-5x-focal-reducer-1-25.html ) to my guiding camera, would this work to increase the FOV of my guider or does the prism size in the OAG mean that this wouldn't work? Hoping some of the experts here can tell me if my thinking is fundamentally flawed.

Exactly right

I use exactly that MiniPC Steve. I have it attached to my HEQ5 mount using some self adhesive velcro strips and attach my DSLR, guide camera and autofocus controller using coiled USB cables to the MiniPC. The coiled cables help to ensure that nothing gets tangled as the mount slews around the sky. The HEQ5 connects by bluetooth using a BT-EQDIRECT adapter to EQMOD. The MiniPC connects to my home wifi, so I can control everything from indoors over Remote Desktop on my Win10 laptop. As others have indicated, it's only the host PC that requires Win10 Pro for Remote Desktop, and that's what's on the MiniPC. My Win10 Home laptop connects easily. The MiniPC is running EQMOD, PHD2, APT and Stellarium, and with my setup I usually get blind plate solves (via PointCraft in APT using ASPS) in around 90 seconds, and near solves in about 20 seconds (PlateSolve2, again via PointCraft in APT). I think the best aspect of this setup is that once I have my polar alignment completed and guiding running, I can start an imaging plan in APT and then it doesn't even matter if the MiniPC loses either its wifi connection to my home network or the Remote Desktop connection to my laptop - the plan will continue regardless. I can then just reconnect the laptop remotely when it recovers. The MiniPC, the mount and my DSLR are all run from mains power from a weatherproof mains extension reel with RCD protection. Hope some of this information is helpful. Graeme

I've certainly felt very frustrated in the last few weeks at the weather, particularly because having just started trying to learn how to make my first forays into DSO imaging, and feeling like I'm making quite good progress, I really want to spend all the time I can continuing to learn and to correct my earlier mistakes. What I have gained in that time is some useful practice in image processing, aided immeasurably by the many generous members here who are happy to share their knowledge and experience. In summary, the frustration is real but it's never reached the point of regretting a single penny that I've spent on astro gear. Graeme

Mark, I just wanted to say a huge thank you for sharing this method. I am still taking my first baby-steps in astroimaging, and it's only because of people like yourself and others on here who are always happy to share tips and give advice that I've been able to start creating some images that I'm very happy with. The attached image of the central part of M33 was processed by following your guidance. Graeme

I had another shot at processing my data using some of the techniques described in astrobackyard.com, but not strictly following a specific workflow. The more I play around with this, the more I realise I need to learn.

Wow! I don't mind at all - you've shown me that I have good data to work with and that it's worth investing the time in learning how to process it properly. I'm still a real novice at this.

My first real attempt at a DSO. M101 from 21/9/17. Until now, I've restricted myself to nice easy moon images that are nice to look at but the satisfaction of grabbing my first DSO is huge. 18x120s, no darks, flats or bias. Canon 6D unmodded at prime focus on Edge HD8 unguided. I know it's not the best, but I'm really pleased with it as a starting point.