Quote:
Originally Posted by Jethro777
What do you guys think? If you were to invest in something (why not, I'll save for something!) what should it be? A star tracker like the iOptron or Vixen Polarie? A proper mount?
Love to hear your thoughts!
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I do most of my AP with DSLR from regular tripod, no trackers, no barndoor mounts etc. Its definitely doable and can take a bit of fiddling to fine tune. First I suggest ignoring your lenses unless you want to use for wide angle shots, instead find a good quality fast (f2.8) lens around 150-200mm. Prime not zoom. And work around this being your astro setup.
First do tests with manual settings (its all manual setting really) adjusting just f-stop to find your combos optimimal sharp sweet spot with stars (with a f2.8 lens f4 tends to be much sharper, but an f4 lens it'll be more f5.6/6.3. Once you find that you have one manual setting to stay put on. Next use the "500 rule" as a guidline. divide 500 by the focal length of the lens to get your starting test exposure time. eg 150mm lens is 500/150 = 3.333s call it 3 sec. now set exposure time to 3sec and point at night sky (pick random direction each time as linear rates change and take a test shot each time and zoom in on the pics to see the stars should be more round than little streaks, adjust shutter speed one increment on your camera and repeat until the stars are a good roundness and not streaking . It'll be close to the initial 500 rule value. Note the stars will distort anyway in a camera lens but the more they start to streak the harder it becomes to align and stack images. So you've now got the second manual setting value you need, th third and final is ISO, set your camera with the first two values and take shots at each iso setting until the images are obviously too noisy on the lcd. decide which are starting to get too noisy to work with. Too much noise and again aligning is problematic. as you work you improve your workflow in time so can revise iso to try to capture fainter nebulosity by capturing a lot more shots. but basically those three settings you can lock off on the camera and are about the limit of the gear combo for capture.
use a remote trigger or intervalometer to take say batches of 100 shots, after that you'll need to reframe your camera as the stars will have moved. I take about 500 shots in batches of 100 which pretty much fills one memory card and drains one battery. when you register/align the images the movement and rotation is taken care of and stacking a lot of shots takes care of the iso noise giving you a good snr integrated image to start stretching etc.
next purchase should be a tracking mount, like an EQ6. something good that will last and can take a scope when budget allows. you will need to find a suitable dovetail plate for the mount that lets you attach a camera to it. You then use live view etc to do star alignment of the mount so it can track and slew to nonvisible targets. This means you can retest your maximum shutter speed to maintain round stars and iso too for cleaner subs. this will open up a whole lot more shooting opportunities for you. every mount has limitations and if you aren't precise with alignment, especially cheap travel options like polarie you are often limitied to little better than a static tripod anyway. A quality mount will give you the chance to go for longer telephoto lenses as well as scope OTA and imaging cam options. If you skimp on the mount it will be less stable and less flexible for options in the long run, best to save and wait until you can get the right long term mount rather than a quick disappointing stopgap.