Search the Community
Showing results for tags 'usbst4'.
Found 1 result
Hi, thought I’d share my experience having a go at guiding on a budget. Not much for anyone to learn from it but it demonstrates it’s not complicated. Last year, with astrophotography in mind, I bought a second hand HEQ5 Pro Synscan and a second hand Skywatcher Startravel 120 (it’s 600mm and also came with a few filters and bits). While you get some large and colourful stars in the images I’m more than happy with it to get my astrophotography eye in. Guiding seemed to be the next significant step to take. I’m happy with the polar scope and moving around the sky using the hand controller. So my aim was to keep it simple, just connect camera to laptop and then to scope. Find my target, set it guiding and off I go. My son had an old Celestron Travel Scope 70 telescope (F5.6 400mm and currently £55 on Amazon). So that was the guide scope sorted. It also had its own spotting scope. I then bought a Revelation 0.5x Focal Reducer for £25. So that gave me a more suitable shorter/wider and faster scope at roughly a 200mm/f3. Second came the guide camera. After some searching I settled on an ELP Low Illumination USB Camera Module with the 3.75um Aptina AR0130 1.3MP colour sensor (I couldn’t find a mono version). It seemed a good compromise for £30. I just needed to mount it in a box (I used an ABS enclosure, RS part no. 502-332, 75 x 50 x 27mm) and then fabricate appropriate mounts to make it go into the scope eyepiece. I also added a heat sink and made sure to take any stress and loads off the sensor board. At this point I was just going to use the IR cut filter from the lens that came with the sensor module. You can often just unscrew the ring off the front of the webcam lens and the bits fall out. You can reassembly with only the filter. But it turned out in the bits I had with the used scope was a 1.25” Baader IR blocker filter. So I splashed out £15 on a Webcam to 1.25” Adapter that just screws into the M12 lens mount on the sensor board. That made it painless to screw the filter and reducer on there as well. Then it just slips into the guide scope eyepiece hole. It probably makes for a better aligned sensor than if I made a 1.25” tube assembly on the box myself. Next was the connection from laptop to mount. I briefly looked at making something but in the end I got a ZWO USB-ST4 inline adapter for £35. In addition to being all done and in a nice small aluminium case it also included the USB and ST4 cables needed. To mount the guide scope I used a thin length of metal plate to screw to the telescope rings. I had some 1/4 tripod to DSLR screws that appeared to have the right thread and had the benefit of the being hand screwed and with a coin slot making it easy to assembly. Good solid guide scope mounts don’t seem compatible with a small budget so I used an old swiss arca type camera tripod base plate. I used a wing nut to keep it easy to assemble. I was thinking I could slightly rotate the guide scope left/right if I needed to point it somewhere different to the main target and I’d live with no up/down angle adjustment for now and see how it goes. I contemplated a ball head mount as I had one but it was suggested that it might make it too high and wobbly. For the software I installed ASCOM, PHD2 and the ZWO USB-ST4 drivers. The USB camera had already installed itself OK and all the resolutions, modes and FPS appeared to show up OK in SharpCap. Guiding connections were simple, plug camera USB to laptop and laptop USB to mountST4 via the inline ZWO box. In PHD2 I choose Camera “Windows WDM-style webcam camera” and Mount “ZWO USBST4 (ASCOM)”. It all appears to work OK although I had two minor self-inflicted issues that might be worth sharing. On my first test I couldn’t find any stars. I had tested it during the day on “distant” objects (TV aerials), and pinholes in black card. They focused fine and it all looked OK. But unbeknown to me infinity focus was still enough away from a distant object so that I ran out of focus travel when I went for the stars at night. So without seeing stars I gave up. I tried again a few days later when the moon was out so I had something big to find and it showed it was out of focus even at full limit. But removing a locking ring off the focuser allowed an extra 2-3 mm of inward focus movement to see the stars OK. In fact I might get away with putting it back on now I know where it needs to be. Once seeing a star was all sorted I tried PHD2 for the first time. Initially I couldn’t get it to work. Or to be more specific I didn’t give it time to work. I kept getting a message “Calibration this far from the celestial equator will be error-prone...”. I pointed the scope everywhere and the message kept appearing. In the end I just ignored it and carried on. I took a couple of 2min test shots. Tracking was way way worse than without it! I put it down to something about this error and gave up for the night. So I consulted my astronomy club and they suggested where I should point it. Tried again last Sunday and still the message appeared. Then I noticed the little white text updating in the bottom left corner of the PHD window and I realised it was trying to calibrate even though I had the message. I didn’t appreciate just how long it took to calibrate. After quite a few minutes the graph sprang into life and off it went tracking. My two bad images previously were likely just because I was exposing while it was finishing the calibration. Because of the “error message” I just assumed it hadn’t calibrated right. I tried exposures up to 15 minutes pointing to Andromeda and the stars looked OK to my untrained eye. Set up is a Nikon D7100 DSLR on the 600mm telescope. That probably allows more exposure time than my light polluted town will take! It looks like it tracks keeping within the +/- 1 sec range. So I consider it a success so far. Below is also the first 15min exposure (ISO 200 with Baader Contrast Booster filter). Not the best night for it, bright moon, thin wispy cloud and looking above a street light but I think it demonstrates the guiding is working. Maybe it was not quite as cheap as I initially though it was going to be as I did splash out on the eyepiece mount and USB-ST4 adapters rather than make them (that was £50 of the £105 spent excluding the bits I already had around I used) but I think it was worth it for the extra quality and ease. Anyway I think it will keep me going for a while. I now have no more excuses to avoid actually going out into the cold dark night and using the kit rather than staying inside and just surfing the web and tinkering in the garage instead. John PS sorry for the long read!