Autofocus EAF to max position

Markus

Today I installed my new corrector that moved my focus point 5 mm outwards. After manually focussing the zwo EAF via the move buttons in ASIAIR Pro, the autofocus function moves the OAZ always to max position. Switching everything off, reconnecting nothing helps.

When Autofocus starts at pos 1940 (manual focus), it makes the first picture and then moves to max position 2800 makes the next pictures and tells me he can’t move anymore. I started at different positions within +/- 200 around the manual focus position… no change in behaviour.

My focus area is quite short as I have only 2 cm focus way at my Octoplus OAZ, but I had this behaviour never before.
All parameters are as they had been before.
Any idea what is wrong?

Markus

w7ay

Markus Autofocus starts at pos 1940 (manual focus), it makes the first picture and then moves to max position 2800 makes the next pictures and tells me he can’t move anymore.

This may actually be the normal behavior ("normal" for ASIAIR, that is), Markus, depending on what you have set as the autofocusing step size in the (EAF) Focuser Setting window.

To get their focuser curve, the ASIAIR starts at an EAF setting far enough larger, so as to get an HFD of over 7 or 8 (I don't know the actual limit).

If, after moving to 2800, it is insufficient to get a large HFD, it then cannot proceed.

Change your EAF Max Step to something much larger than 2800. Try 5000 or 7000, for example. You can then look at where ASIAIR starts at, and in the future, if you want a small max step, reduce the max step to a delta a little more that the ASIAIR needs.

Your corrector may need a larger draw tube travel to get stars to show up with HFD of over 8.

Chen

Markus

Thx Chen, never had the feeling that he needs as much distance from focus, but as you mention the better optical quality and sharper stars may be the reason. So my maximum travel way of 2cm will make it tricky. I will try.

Thx again

w7ay

Markus So my maximum travel way of 2cm will make it tricky

Marcus,

If moving the EAF steps from 1940 to 2800 actually moves the drawtube by 2cm, then you are right; that should be more than enough to defocus a star by more than 8 HFD.

HFD of 10 for a 3 µm sensor is about 30 µm. With a f/7 telescope for example, that would correspond to around 210 µm (0.21mm) of drawtube change.

What is the EAF scale for your focuser? With the 1x shaft of my rack and pinion focusers, I am getting around 4 µm of drawtube travel for each EAF step, so 860 EAF steps (from 1940 to 2800, for example) will only move my drawtubes by about 3mm, well under 2 cm.

See if you can double check to see how much your drawtube really moved between EAF step of 1940 and 2800.

I usually move by 10000 EAF steps, and measure my drawtube using a pair of calipers. The linearity of the EAF is not too terrible, so I can just divide the drawtube change by 10000. See this linearity measurement that I did last year.

https://bbs.astronomy-imaging-camera.com/d/12562-5v-eaf-linearity-and-backlash

Chen

Markus

Hi Chen,
I made a short check and at least I saw that I limited my possible way of 2 cm too much. My EAF scale is about 4 micros, makes 5000 steps for 20mm. The range min/max I used between 0 and 2800 is only about half of the possible way of my draw tube. The 860 steps are about 3.5 mm movement.

First I will calibrate EAF and draw tube again, setting zero point and max step to use most of the possible 20mm. Without extension rings I should have about 6.8 mm from focus point to draw tube limit, I think this should be enough way for the Asiair. My FF DSLR has 5 micro pixel and I use a f4,5 10” system.

After I have done my homework I will tell about the result, whenever there is a little bit of clear sky again, which seems not to be within the next two weeks.

Thanks a lot, Markus

Markus

Yesterday before a storm came, sky cleared and I could test. Everything worked fine. I set the limits to max possible range for my draw tube and I used a 12mm extension, to move the focus point to a smaller position within the range.
Although the focus is now at about position 400 and is quite near to zero, it seems to be more important to have a wider range extrafocal than intrafocal. Somewhere I read that you need about a range of 900 steps extrafocal, for the autofocus algorith of the Asiair to work.

thanks for the help
Markus