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Old 06-06-2018, 12:59 AM
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Astrofriend (Lars)
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Astrofriend is offline
Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 185
Hi Jameson, thanks for your reply

If your telescope is a f/7 I get about +/- 30 microns or 60 micron overall for the visual wavelength. I will say att least 10 micron move per step or down to 5 micron. The blue wavelength is more critical. My setup is about 2 micron and it's also a f/7 telescope, APO TS130. That's the theory, practicaly there are a lot of limtiations, the seeing, not perfect optics and other things. Earlier I had problem with slip in the friction coupling in the focuser, I hope that problem is solved now.

In the calculations I setup it up to calucalte for the full draw tube length. When I change field flatterner it change the focuser position. 25 to 35 mm in one case and 45 to 65 mm in another case. Of my 100 mm draw tube lengt I can use about 85 mm with the choosen gear ratio.

You can read more about my focuser project here:

The temperature drift is heavy when everything working perfect, the telescope is sharp and it's easy to see when it's out of focus. About one degree change and the temperature compensating kicks in.

The motor focuser and later temperature compensation is by far my most important changes of the setup.

There is a back lash compensation built in the driver for focuser, I think it work relative good. But of course better with no backlash. I use USB-focus driver and ATP to control the focuser. Setup with 1/2 micro step, no more! More and the stepper motor loss a lot of torque and the precission will be bad.

I have updated my homepage now, corrected some information and added more.


Last edited by Astrofriend; 06-06-2018 at 07:26 AM.
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