Star hopping down the years

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Grant Privett

I think you will find that the people on here were all beginners once and most did star hopping and remember it well. Some still go that way by choice. I myself didn’t use a GOTO in anger until about 2008 – 37 years since I first had a telescope. While I wanted an LX200 from their introduction onward, mortgages got in the way… An EQ6 eventually proved affordable and is still what I lug outside at night.

My experience suggests that will generally solve any image with more than 10 stars on with an SNR > 5. I’ve seen lots of frames solve with 8 stars – but it may take longer. So, what size webcam sensor are you thinking of then? In a 1sec exposure with a 100mm aperture (£60 from a car boot sale) with an uncooled Lodestar I would expect to image stars down to 12-13th mag which with the 100mm gave an ~30 arc minute field. So what field of view are we thinking for the webcam? Could you post one of his pictures?

Also, the idea of using the main scope was mainly for simplification ie no need for finder scope and the camera used could be used for object imaging.

If you had an alt-az mount set up roughly level or a German equatorial aligned by eye to the pole star, by recursively taking images and adjusting the scope slow motions (as indicated by software) either in alt/azimuth or RA/Dec – you would move toward the correct position even if the scope was not properly aligned. The better aligned the quicker it would succeed, but it would still work in a few iterations (unless your alignments were hugely out – a spirit level for alt/az and the pole star would avoid that).

The lack of blobbiness might be explained by the colour webcam having an integral IR blocker (quite common) but the cost of that is lower camera sensitivity and fewer stars.

Re: eyeballing. You don’t need to know where the telescope is pointing. If you plate solve, the software will know where its pointing from the plate solution for the middle pixel of the image. Thus it can tell you in which direction to move the slow motions. You just need to move in roughly the right direction.

From where I’m standing – beyond using a guide camera instead of a normal Zoom/Skype webcam – the issue isn’t so much the equipment as the software to use it. Its fairly simple though.