You guys seem to be the perfect hardware for a headless astrophotography autoguider
Background: the Earth spins, so the stars in the sky are always moving. If you want to take a photo of something really dark and far away in the night sky, you need to do long-exposure photos but since the stars are moving, you need to move the camera in the opposite direction of the Earth. You can buy a star tracker for this but some star trackers allow you to add a optional secondary camera, an autoguider camera, to move more accurately, you get a sharper image.
Problem being they are $150 for just the camera, plus another $50 for the guide scope, plus you need a laptop to run the software.
I’m playing around with the idea of making all of this cheaper, or at least get rid of the laptop.
Anyways, the algorithm should be very simple. Find a dot, follow the dot by giving the star tracker (or EQ mount) one of four basic signals: left, right, up, down. (it’s controlled via a ST4 cable, just 4 signals, active low, very simple)
Usually during the initial setup, it’ll do a calibration. It locks onto a dot, tells the tracker/mount to go left for a few milliseconds, and see how much it moved and in what direction. This should be easy too.
My options are:
- smartphone with a telephoto lens and a Bluetooth nRF51 doing the ST4 signalling (it sounds cheap but I’d rather still have my phone in my hand all night)
- raspberry pi and HQ camera and a CS telephoto lens (price getting expensive)
- ESP32 cam (where do I get lenses for these? The camera’s quality is usually terrible, dead pixels and such. Plus, I’m not excited about writing image processing in C++)
OpenMV hits a good price, has the super telephoto lens, runs image processing, has GPIOs. Optionally I can add the LCD shield or the Bluetooth shield.
Now I have no idea what the OpenMV camera would actually see when it’s pointed at a star. This is why I’m here on this forum.
My next bit of research revealed that OpenMV is limited to 0.5s of exposure. This should be OK, I think… my 350mm camera lens would see star trails at 2.5s. 0.5s should be fine if I point it at a super bright star like Vega.
The max gain is 32. No idea what that looks like in terms of brightness and noise. I’m honestly not sure how to convert gain to ISO, I know “base ISO” is supposed to be gain of 1, right?
I’m guessing the super telephoto lens is fixed focus at infinity? As long as the star looks round, my idea should work, I just need a point or circle detector algorithm.
Can somebody with the super telephoto lens take a couple of photos of the night sky to share with us? Extra points if you can run the circle detector and provide a plot of XY position frame-to-frame so we can get an idea of the motion noise. (don’t worry, we can filter this noise out, the earth doesn’t change speed)
Has anybody experimented with adding a heat spreader to the bottom of the OpenMV camera sensor PCB?
Thanks, hope you all had a chance to see Comet NEOWISE