FocusMax, DC motor focusers - problems

[troypiggo (Troy)]

I have a Moonlite DC motor focuser on my 10" reflector, and use MaxIm DL to image. Been focusing manually with a Bahtinov mask to date, but wanting to avoid having to put the mask on and off between filter changes etc.

Reading the MaxIm manual, they recommend FocusMax for DC motor focusers.

I tried to capture my first V curves the other night by using the wizard. I had done some reading, but most of the tutorials I came across seemed to be for stepper motors, not the DC. I centred a 4th mag star, manually focused on it, then fired up FocusMax and clicked on the first light wizard to start getting V curves.

It took quite a while to run through. Could see it capturing subframes, gradually going out of focus, every so often it would give an error about star off screen or too out of focus (?) and retry. Eventually it looked like it was starting to reel focus back in again, and could see blue circles starting to form a bit of one side of a V for the V curve, but it never seemed to get the other half done and the wizard ended with a message telling me it couldn't complete. (Sorry, I should have screen captured the error messages etc)

Any tips/tricks for this focuser of mine? Is it even possible, or only for steppers? Is it a setting or something I'm doing or not doing? If you need any more info, please ask and I'll try to help you to help me.

[Karls48 (Karl)]

Hi Troy. I have recently build electronic focuser for my 150mm SW refractor using GSO Crayford focuser, Autostar hand controller and ETX 105 focuser motor.
I have spent about four hours trying to get FocusMax to finish V curve, getting same errors you describe. Eventually I got it working. This is how it worked for me.
Manually focus best you can. Selecting right star is probably most difficult. I tried Mag 2 to Mag 6. It did finally worked with Mag 3.4 . I suspect that usable star Magnitude depends on sensitivity of your camera. Centre the star and switch on Autoguiding. Double click on relative position number box – that will reset position to zero. Start the Wizard. When it finally worked it took 61 seconds from start to finish focusing.
I took few images before it clouded over and compared it to previous manually focused images. The focus was better then my best manual focus and if it is going to focus consistently and takes about minute to focus I will be very happy. I could not try is since my first go – it is cloudy all the time

[troypiggo (Troy)]

Thanks mate. Wish I'd read this before I had another go last night.

I found an article for an LX200 that suggested not to do the wizard and walked through doing the curves manually. http://www.rarcher.org/astro/focusmax.html Not all was directly translatable to my mount/focuser combo, but I tried to stick as closely as I could to it. I got some V curves to run this time after much mucking around, but nothing that resembled what I understand to be the ideal "V".

I'm wondering if the issue is the focus position. By manually racking the focuser in and out with FM's "jog" tool, I narrowed down that the full range of steps was about 9900. So fully racked in, let's say that's 0, fully racked out it's 9900. Trouble is the focus position of the camera is around 9600 give or take. Very close to right out. So there's plenty of room in, but not much out.

[DavidTrap (David)]

I had some success with a moonlite DC focuser and Focusmax.

I suggest you move your mirror forward so you're operating in the middle of the focuser's range if that's possible.

I would start by racking the focuser all the way in, then moving out to eg. 5000, then zero the position in Focusmax - this lets it start from a known point. A servo focuser will never be as repeatable as a stepper as there is no feedback as to whether the motor has actually moved in response to the pulse. I had more repeat ability of my results by following this method.

The tutorial about the LX200 microfocuser was what I used as a guide.

DT

DT