Focus Max.

[TheDecepticon]

I am interested in running Focus Max with my setup.
I'm having a bit of trouble getting the V curve set up going. I can see what it is doing, but half way through it seems to loose the star and fails. Is there a trick to it or is there a way to do it manually?
Can it be used between exposures to check focus slip or is that sort of thing restricted to units such as Robofocus, which I am also interested in, but I will have to wait a while for that, narrow band filters first!!:)

[Bolts_Tweed]

gday - Do it manually. Roughly focus and select endpoints option. the variation of the endpoints from the focus position will depend on your set up. You can limit it to say 250 or 300 steps either side. So if you are focused at say 3500 steps set the V curve to run from the endpoints of 3200 to 3800. Run a first V curve at say 20 step increments. When finished click on focus and it should focus using the first curve - then use (from memory - im at work) midpoint (or offset) its the other option from endpoints . the midpoint will be set to the last focus point and you set how far from that midpoint you want to run the curve - again dont go too far from focus it might not find the star - I generally use about 300 steps. Repeat the whole procedure at finer steps until the mean slopes agree as well as you can get them (you can delete your first rough curves once you build upo a few better ones). The variation (I forget whats it is called) should also be at a minimum - it is reported beside the two v curve slopes. You may need 10 to 12 good cruves for intial system calibration.

If it is getting lost in the middle of the run - that is where your focus should be best - shouldnt lose it there - it sometimes get lost a long way from focus but not at focus.. Either the scope is drifting off the star - I guide during the process or you are not starting at good focus. If you start a long way from focus this can sometimes happen. You can jog the focuser and focus manually prior to running the V curve using teh Jog tab.

You can efinately use it between exposures - My televue is a bit touchy with temperature variation and in summer I focus every exposure or every second exposure - takes about 40 to 50 seconds to focus with focus max.

I have had similar problems with a SC buit I know someone else who uses it succesfully with Meade ACF. I use it on refractors and it is fantastic - perfect focus every image.

mark

[TheDecepticon]

Ok, so I am using Focus Max because I have a normal DC motor not a stepper motor, and MaxIm suggests this software for normal DC motors. The steps you are talking about, how does it know what is a step if it has no absolute positioning or encoders? Are you using a stepper or a normal DC motor?
Thanks.

[Bassnut]

Thats was I was wondering sort of, are you actually useing an auto focuser, or totally manual, Im confused. If manual, I cant see all this is worth the bother?.

[TheDecepticon]

Ok, thanks for your help.:thumbsup:

[Bassnut]

"a normal DC motor" is a servo if there is encoder feedback, a stepper control assumes set steps, doesnt *need* encoders. A DC motor without feedback is well, not what focus max can use, it has no idea what the motor is doing.

[Bolts_Tweed]

Gday Mate -

Moonlite hi res stepper controlled focuser and a Moonlite controller. The controller takes Maxim out of the loop - computer (focus max) talks to the controller and the controller steps the motor - there is no other software involved.

I dont know about dc focus control through Maxim however the operation should be similar. In my case - focus max tells the focuser to move 'x' steps thru the controller (thse steps are the x axis of the V curve - obviously I suppose). With a DC motor it should be pulse the dc motor for 't' duration to move the fosuer 'x' distance - I imagine thats what Maxim does - just that it must be linear for a given load - if it pulses for say 20 millseconds it must move it the same distance every 20 millsecond pulse (similar to a stepper controlled ystem). These pulse durations or focuser movement distance also will form the x axis of the V curve and it measures 1/2FD ( the y xis of the V curve) at each step (or pulse).

It then just does a linear regression (I assume linear but some form of regression) on each side of the V curve, works out the x axis intercepts and the idea is to get them as close to each other as possible - ie the 2 lines meet in the middle at the smallest possible 1/2FD. So the basic operation should be the same

What I dont know (have never used) is the communication between Maxim and the DC motor but the basic operation of FocusMax should be the same using pulses instead of steps.

If the problem is with FocusMax I can probably help but if the problem is with communication and control via Maxim it may ned someone familiar with it. I have it on this computer and will read thru it.

Damn i am curious now - when you open the V curve window (not the wizard) under the endpoints check button it says intital then final then the next box down says step increment - is that the same as yours? If it is diferent it must run a different set up for a DC motor.

It'd be good to get it going - it works brilliantly - I will have a read of Maxim docs and see I can fathom it.

Mark

[Bolts_Tweed]

Good point Fred - if its a straight dc motor youre wasting your time I think. Dont Shoestring (FC-USB or something?) make a communication box between the computer and dc motor for this type of application - say a Skywatcher focuser?
M

[Bolts_Tweed]

This may help

http://www.store.shoestringastronomy.com/products_fc.htm

M

[AlexN]

Mark & Fred - I used a Shoestring FCUSB with a Moonlite DC motorized crayford on my C11 SCT with FocusMAX with good results. It also worked well with CCDSoft's @focus2.

This also worked with a JMI Motofocus unit..