Focusmax - V curve question

[Skipper Billy]

I ran a full set of V curves last night and each curve had the bottom of the V to the left of centre.

The next run started off with the new centre but ended up left again - this happened every time

The start position for the middle was 6000 ish and ended after 20 runs at 4000 ish.

It seems to focus OK but does this indicate something slipping ???

[Davey-T]

I get the same thing, off centre to the left, focus seems OK though, you could have a look on CDWare forum.

Dave

[Skipper Billy]

Thanks Dave - I had a look on CCDWare forum and its not just me that has this issue - some people have even run out of range resulting in Focusmax stopping because it thinks it cant move any more.

I have pinged Ron at Moonlite a quick email for his advice. If I get a result I will post it here as it might be of use to others with a similar issue.

All the best.

[Skipper Billy]

The attached document might be useful for people suffering the same issue with a Moonlite.

MoonLite focuser adjustments.docx

[cfpendock]

Surely the bottom of the v-curve depends on the start and finish position when running the v-curve?  In any case I thought that the important thing was the slope obtained from the v-curve,  rather than the position of the bottom of the v-curve?

I have to say that I have no problem focussing using Focusmax, either using my Tak 106, or my CPC1100 which uses a Moonlight focuser, but I have certainly observed out-of-centre intercepts on the v-curves.

I don't know if this helps - just someone else's experience.

Chris

[Skipper Billy]

Thanks Chris,

My problem was that each successive run had a different position of what it defined as critical focus and it was considerable - about 900 points on each run and was rapidly heading for a point where it couldn't focus.

It seems that on each step the drawtube slips a little. I am going to try increasing the drawtube pressure a little to see if it helps.

Its holding an Atik EFW2 and an Atik 460EX and I was using a star near the zenith so all the weight was pulling almost vertically downwards.

[Davey-T]

Did you include a backlash value, and step size ?

What software are you using to capture ?

The motor should hold the position regardless of the tensioner, mine is just tightened enough to stop it undoing itself and falling out in the dark.

Dave

[Skipper Billy]

13 minutes ago, Davey-T said:

Did you include a backlash value, and step size ?

What software are you using to capture ?

The motor should hold the position regardless of the tensioner, mine is just tightened enough to stop it undoing itself and falling out in the dark.

Thanks Dave

No backlash value entered but I have it focusing 'inwards' in the belief that wil do away with backlash ????

Maxim DL5

I made the adjustments suggested by Ron at Moonlite and I am currently runninga  fresh batch of V curves and the PI difference is now around 0.2 to 0.3 down from the 30 - 40 I was getting yesterday and the V shapes are all bang in the middle and HFD values down into the 2's even in poor seeing.

Just taken a quick test sub and the stars are round and very tightly focused - hopefully this has sorted it - the two tension coarse adjustment grub screws were actually loose !

 

[Davey-T]

This is what should happen, it's FMax3 but similar to FMax4.

Peter as Lakeside recommends backlash value of 20. it's not critical.

Dave

[Davey-T]

The HFD should stop around 40, yours is going up to sixty, if it goes too far it losses the star completely.

You may need to enter settings in Maxim for scope focal length etc, will check as it's awhile since I set mine up.

Dave

[Skipper Billy]

Thanks Dave - I will have a watch at that whilst I am watching it draw pretty patterns !!!

Thanks again.

David