Focusing-Positive (Outward)

[jhopkins]

Please help. This is more complicated than I ever imagined. I have an ASCOM focuser (ZWO EAF) on 500mm refractor
and a DSLR. I’m trying to eventually be able to autofocus using ‘Autofocus Refocusing’ in SharpCap.

In the manual it says ‘the focuser was moving in the positive (outward) direction.’ Does that mean that the camera is moving away from the telescope? In which case, because of the weight of the camera and with the issue of backlash in the focus motor and the camera always being lower than the telescope, should I be approaching correct focus from the negative (inward) direction? Or not?

And would I use the EAF Hand Controller to do my first focusing routine, apparently as a basis for using the ‘one click’ focus routine from there on out? And with the hand controller I’m not even sure how to tell if I’m moving it ‘in’ or ‘out’.

[admin]

Hi,

the only real way to be sure which direction the focuser moves for higher (or lower) values is to use the software to move the focuser (say from 20000 to 25000) and watch to see what happens. This is because when you mount the focus motor on your telescope, the direction of movement will depend on whether you mount it in place of the left or right focus knob. Again, the same trick with the handset will help reveal which button moves in which direction...

You *may* be able to reverse the movement in the setup for the ZWO ASCOM driver if you would prefer the movement directions to be the other way around - SharpCap used to have an option for reversing the buttons, but it turned out that it wasn't possible to fully deal with the problem of reversing the direction in all parts of SharpCap, so that has been removed.

It's probably good practice to approach focus in the direction that is moving the camera up against gravity, but the really important thing is to use one of the backlash compensation options in the SharpCap focuser settings to deal with any backlash in the focuser. The overshoot option is the simplest - when SharpCap needs to move the focuser in the direction opposite to the preferred direction, it will overshoot and then move back to eliminate any backlash.

Hope this helps,

Robin

[jhopkins]

Thank you, Robin, for such a quick reply. I've been using SharpCap for three years and love it for polar aligning but I want to use it for other procedures, too.

The focuser and refractor are new to me, coming from a 300mm camera lense, so I feel like a school kid learning the basics. I think I'm supposed to go to focus assistant and then to multi-star FWHM and move the focuser with my EAF hand controller to find the best focus by watching the colored bars come up. And then find the numbers that correspond to the focuser position somewhere in the program. But I'm not sure what to do with them yet. Maybe to find out if I should start the auto routine in a positive or negative direction? In your example 20000 went to 25000. Is that a positive/negative direction or an in/out?

Once I finally get this I want to learn plate solving which so far I also haven't been able to get to work. But one thing at a time.

Thank you so much for your help.

[admin]

Hi,

so, ideally, you don't touch the hand controller and do both the movement of the focuser and the measurement of the quality of focus from within SharpCap. This will let SharpCap build up a graph of quality of focus against different focuser positions - either guiding you to best focus or finding it automatically. You would probably be best starting with this section of the documentation if you haven't already looked at it : https://docs.sharpcap.co.uk/4.1/#Which% ... %20Used%3F

You can also find quite a few videos on youtube either walking through the procedure or just using it as part of an observing session to help you see it in action.

In regards to the positive/negative/in/out - the example I gave of going from 20000 to 25000 is moving in the positive direction (increasing number), but it could be in or out - depending on the mechanical arrangement of the focus motor relative to the focuser.

cheers,

Robin

[jhopkins]

Thank you again, Robin. Just knowing not to use the hand controller is a huge step forward for me. I have read through pretty much all of the instructions at least once but they're difficult to understand sitting at home when I don't have the program working in front of me. So I'm just waiting until the next time the weather allows me to get up the mountain to my astro site so I can try again. Thank you again.

[admin]

Hi,

If you have your setup with you, testing the focus routines on a fairly distant terrestrial object (tree, roofline, etc) during daytime is a great way to get to know how everything works without without needing to wait for clear skies and while you can see what you are doing! The 'contrast detection' focus measurement routines should happily find focus on terrestrial objects.

cheers,

Robin

[jhopkins]

Yes, thank you for that suggestion. I may be going up tomorrow night.

[jhopkins]

Well, my truck was broken into early this morning. Stole my whole rig. So it'll be quite a while before I get back to you, Robin. Thank you

[admin]

Oh no

I'm so sorry to hear that - must be devastating for you.

Robin