Focusing Adjustment Not Understood - Forums

Topic starter

27 days ago

I’m using a Focus Cube and N.I.N.A. Autofocus and I’m getting good focus curves. However, the range of steps is getting closer to the Zero point. I know how to fix it. Disconnect the drive, manually move the focused to the midpoint of the focuser range and then reconnect the drive. What I don’t understand is this. Let’s say that perfect focus was at 900 steps. If I manually move the focused to its mid point, let’s say 3000. If I run the auto focus routine won’t the telescope be way out of focus and be unable to reach proper focus? I don’t seem to be able to wrap my head around how this works.

I’d appreciate it if someone would give me an explanation on how this will work.

Hank

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Tony Gondola

Frequent contributor

Exemplary contributor

27 days ago

You would have to be really far off to run out of steps but I suppose it could happen. The thing to do is disconnect the electronic focuser and drive it to the middle of its step range. With the focuser still disconnected, manually bring the scope close to focus. Reconnect the cube and you should be all set.

If nothing in the setup changes you’ll never come close to the travel limits. The only thing that can cause that is if you change the configuration in a way that drastically moves the position of the focal plane, like adding a Barlow. You should not try to drive the focuser to that new position but rather repeat the above steps. Hope that makes sense.

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Mossyback

Topic starter

27 days ago

Thanks Tony, much appreciated.

Tony Gondola

Frequent contributor

Exemplary contributor

27 days ago

No worries, look forward to seeing how it all goes.

Brian Puhl

IOTD Staff

27 days ago

If the focus point is gradually shifting towards zero, then your focuser is slipping. Likely at the collet connecting the focus cube to the focuser.

Some drift is normal due to temperature variations, but if the shift is consistent, then something is wrong.

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Daniel Cimbora

IOTD Staff

27 days ago

Happened routinely on my Tak refractor with both a ZWO add-on focus motor and a Nitecrawler WR35. Eventually I would have to recalibrate the focuser (different routines for each) and it would be back to the nominal “starting” position.

I don’t know why this happened, but I attributed it to a little bit of slip with each refocusing, which gradually caused the focuser to run out of room.

The WR35 is build like a tank and I was surprised to see it happening, albeit less often than with the ZWO/stock focuser.

Interestingly, The CDK14 (S-5 focuser) has not shifted a single tic since I started running it this summer.

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