Thanks Andrew.
I have quite a stock of PD products, including their straps (and bags, and pouches, and clip-mounts)
Brilliant company
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This guy is an amazing documentary photgrapher would be well worth a visit to see the full exhibition.
I have just joined a local camera club to hopefully re engage some creativity that I might have left. I now have some basic post processing skills and able (sometimes) able to make a silk purse out of a sows ear. Here is some of my mostly reworked stuff that I plan to show
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Tonight’s club competition entry is themed decisive moment - This is one of my entries
taken 34 years ago!
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Could you try and be a tiny bit less good-at-stuff! 
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Delighted -My efforts to day have given me a working and nearly finished Star Tracker for my camera - My first effort at this was a total failure and I nearly gave up - This curved rod method of drive is looking very positive.
Unusually my calculations appear fairly accurate and over two hours 5v to the motor has moved me 28 degrees instead of a required 30 degrees - Just some small voltage adjustments are required to fix that.
Next stage is to point the finder on the pole star and try it out - A clear night is needed.
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You’re a clever fucker, Andy, I’ll give you that 
PS: if you get a chance, bang it on to Jupiter - it’s approaching its closest to us for a while over the next few days - near the moon in the sky tonight, too.
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Very neat. I’m not sure how the motor drive raises the platform on the curved rod but nice work.
Forgive me for being simple but doesn’t the pole star appear to stay put & everything else appear to revolve around it?
Is it a threaded curved rod? Is that a thing?
As for the alignment, consider the camera pointed in line with the finder - it’s going to just point at the pole star all the time. If you then point the camera at a different thing in the sky, then as long as you’re aligned with the pole star and the rotation plane is exactly perpendicular to that (which I think should be achieved by setting the angle to earth - is that the declension?) then it should track that point around the sky, as long as you have the speed right.
I guess you would still need software to build up the image from the many individual photos, which would correct for small alignment issues, but this system means that you can have several hours’ work of photos, rather than just a few minutes.
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Yes. The camera will photograph Polaris and a few of the things around it. The better the tracker is working, the more the long-exposure images of the things around Polaris will come out like points rather than streaks. Or, if you take two separate images rather than one long exposure one, the less any of the things around Polaris will move between shots.
I had to bend the threaded rod myself and it’s not perfect - Neither is the pressed in nut on the large pulley wheel. I may have another go at these later but for now it’s good enough to prove the process and see if it produces something 1/2 decent.
The plan as you guess is to load it into a free app (DeepSkyStacker) this should align and stack the multiple images. Then it will need some further colour adjustment in gimp.
One minor difficulty is that I need to get on my roof to see the pole star from home to align the unit or go out in the car.
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As long as you use a curved nut.
I assume you’re thinking of declination? Andy’s mount will track Right Ascension. Tracking in declination isn’t really required.
The tracker should allow for long exposures ( a few mins). This is more important for deep sky stuff as you’ll be using long focal lengths. For wide angle milky way type photography you can even go untracked if using short exposure (say 300/focal length). You can still stack to reduce noise.
Had my first go at astro a few weeks ago. I now realise it’s really hard and takes a lot of time and patience.
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I know others have explained it, but here’s my attempt.
1/ Point the centre line of the door hinge on my unit at the pole star ( The actual point to aim for is not exactly directly at the star, but quite close to it)
2/ Then point the camera any direction/stars that you want.
3/ Set the motor running to change angle of the tracker by 15 degrees every 2 hours (again not exactly but close) Theory is that if you do this 100% then all the stars will be effectively stationary.
4/ Carefully focus the lens (not trivial)
5/ Take a series of images - Lens wide open and exposure time around 20 - 250 seconds ish
6/ Align and stack images in online app export completed stack
7/ Faff around in photoshop or similar
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One tip I learned was to use a laser pointer through the scope to get a rough alignment on Polaris. Once it’s actually visible in the scope then you can get a fine alignment.
How are you going to compensate for the motor running at different speeds in different temperatures? I would expect it to vary a bit between a warm indoors and a cold outside.
I cheated and bought a tracking mount. I’m glad I did, because I’ve discovered that the other bits are hard enough without worrying about the mount and gettung that working right.
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My spotter Scope is a red dot one and I have downloaded Polaris view on my phone - It shows that the polar centre at the moment is 1/2 way out at 1PM O’clock.
Fine alignment is going to be a real pain because I have ball type camera mount.
Once I get a few results and If I find I really like this type of photography I might also buy a pucker mount that will easily cope with a 135mm lens.
Measuring any speed changes of my motor is going to be difficult and another days problem - I suppose you have a goto type mount?
I bought an iOptron Skyguider as they’re relatively cheap and well regarded. It has an Alt-Az base for the fine alignment.
Getting everything rigid enough and making sure you don’t accidentally knock it out of alignment is a challenge, especially when trying to mount a 600mm lens.
Good luck with that - 600mm is quite extreme.
For 300mm lenses I was looking at the fornax lightrack 11 and wondering if I could reverse engineer it? I’m not sure my design will cope even with my 150 mm Sigma - Once you have it set up with declination it all feels wobbly.