How to Calibrate Out the Backlash

beachbum

I've been searching the forum looking for a procedure as to how to adjust out the backlash. Is there a set procedure someplace that you know of here?

I checked the ZWO EAF PDF instructions, and it shows how to measure it, but not how to correct it. Not sure where to set the Steps...I have a backlash of right at 100 steps.

Thanks,

Rodney

WalterT

From what I understand once you measure it and entered the value into the EAF menu it will be taken into account anytime you make an adjustment. You can test this out. Move the focuser in one direction by something like 500 steps, then have it move in the opposite direction by 80 steps. If you see the knob move than it is being compensated, otherwise it would not move at all since your backlash would be bigger than the 80 steps. The AF routine also compensates for backslash by building the focus curve in one direction only and then overshooting it when going back to find fine focus point (as explained somewhere else here by Chen).

beachbum

WalterT

Okay got it...I played with it earlier this morning going back and forth with it. I adjusted the steps to where it moved almost immediately in both directions without a delay. Guess that is how then. Understanding that it does depend on everyone's application...How old their equipment is, etc..Ended up setting it about 50 steps...

Thanks!

Rod

WalterT

beachbum Great. I'm not sure if I'm misunderstanding your reply. It sounds like to estimated your backslash and got pretty close to it. If that's the case you will want to measure it more precisely and read below, otherwise glad it worked out for you.

You can measure your backslash by moving your focuser out a large amount in one direction, say 500-1000 steps. Then set your "Slow" movement to something like 5 or 10 steps. Then start moving it back in the opposite direction one "Slow" movement at a time all while keeping a very close eye on your fine focus knob and keeping track of how many movements it takes until you see the knob move for the first time. Then just multiply the number of movements by the slow step size and that should be your precise backslash.

beachbum

WalterT

Yeah, I read in the ZWO manual where it recommended doing it ever 5 steps...I used 10, but I can sure do the 5...The more precise the better I like it! I taped a toothpick on the focus knob, so I could see it move. When it does start to move it is very slight, then the next click it goes all the way where you set it.

Now I'm just hoping that next time out it will focus okay...Looking for that 'U' or 'V' pattern...Before those dots were all over the place, and I didn't have a clue what that meant...

WalterT

That’s great. Glad you got it sorted out.

beachbum Before those dots were all over the place

Yeah this happened to me too with my SCT, nothing I could do about it, so I had to add a Moonlite focuser to the back.