Q-Day!

[montewilson (Monte)]

Welcoem to the FSQ club Andrew. I have a venerable but excellent FSQ. Probably the earliest one in Australia S/N 18. I love it. Tak is addictive stuff. Be prepared. Are you going to get a Tak mount? I have an EM-200. It is probably only bettered by a larger Tak mount or Paramount for performance but is still portable.

I agree with all Jase has offered WRT Robofocus. Its a valuable tool. I didn't use that pissy bracket they send with the kit. I made one out of a piece of aluminium bar. I just can't imagine there wouldn't be some tortional play in their bracket. Others may disagree and I may not need the extra strength of mine but I sleep better knowing it can't be an issue.

I have the small step value set to one. I used to set it to 4 but I found with the backlash in the gears the perfect focus point was often jumped over between steps.

I know Jase has got FocusMax working well and I plan to do the same soon. Software Bisque claim to have a similar system working with CCD Soft that I will try. FocusMax is not as easy for me as I don't have MaximDL.

Keep us informed of developments!

[montewilson (Monte)]

Hey Jase - I have a RoboFocus question. Does the temp comp happen even during exposures? I see there is a manual and auto setting. The auto can be set to make changes (when required) every set period. If that happens during a shot surely this will ruin the shot. How do you have yours running?

[jase (Jason)]

You don’t need MaximDL to use FocusMax! It can be used independently or integrated into CCDSoft (just as it can be with MaximDL).

Wow, that’s keen. In my opinion, a microstep size of 1 is way too small. It would take the focuser way too long to move. Ultimately, such as size does not improve the focusing accuracy and would significantly slow down any automated focusing routines performed by FocusMax or @Focus. Typically a microstep size of 3 or 4 will give you the .0005” (0.0127mm) resolution per step (this can slightly vary per stepper motor hence the 3 or 4 value). The FSQ in its native focal length (530mm) and ratio (F/5) has a CFZ of 55 microns or .0021” (0.0533mm) so the focuser must hit focus within 4 steps assuming the 0.0127mm equates to 12.70 micron (12.7 x 4 = 50.3 micron) – this is not hard to achieve for the stepper or software assuming you’ve built a good v-curve model in FocusMax (not sure of the equivalent in @Focus). As a guide the size should be 15%-20% of the CFZ, so a step size between 8 to 11 micron is acceptable. Don’t get confused by microsteps and steps. A microstep is one pulse of the stepper. What you are defining how many pulses make a single step.

With a microstep size of 4, FocusMax repeatedly hits the FSQ CFZ within ~70 seconds (acquirestar, calculate position, step through HFD calculations, then move to the best focus position into the CFZ) – too easy!

Backlash can be an issue, but this is focuser specific. I haven’t experienced such issues with the new Tak 1:10 MEF (micro edge focuser) used on the FSQ-ED. I have told FocusMax that the final movement to the CFZ must be on the “in” side of focus, thus the weight of the camera is pulling on down on the focuser. Perhaps the FSQ-N is slightly different.

Temperature compensation is considered passive focusing. Once you’ve calibrated the temp slope (temp x = focus position y) you must determine a dead zone. The dead zone defines what is an acceptable temperature change before the focusing position is changed – based on the slope value. You don’t want the focuser to be changing constantly if the temp changes by a small factor such as .01 of a degree. Hence the dead zone is important. You can set a correction rate to determine how often the temperature is checked – 5 minutes is normally sufficient. It is possible to change focus during a sub exposure without ill effect. If your temp slope is not accurate you may experience soft focus if you slightly miss the CFZ. The biggest issue I experienced with this method was vibration, so I prefer to configure the corrections to be made between sub exposures.

Having stated all this, I don’t use temp compensation at the moment – may get back to it soon. I’m presently using active focusing, that is, automatically refocusing every x minutes. So for example, if I’m collecting 15min subs for luminance data and the refocus interval is 30 minutes, the set up will take two subs before the auto focus routine kicks in and establishes focus again, then automatically continues with data acquisition (as the autofocus routine doesn’t take long, I don’t lose much time and can be assured I’ve hit the CFZ again). I’ve also saved time with filter offsets. My LRGB filters are parfocal, but the 10nm Ha filter isn’t. So when the Ha filter is selected, the focuser automatically shifts a defined number of steps to reach precise focus using this filter. No need to perform the initial focus – though the filter would be refocused anyway by the refocus interval (30 mins).

EDIT: Don't believe that temperature compensation is the ultimate in focusing. There are numerous other factors (not only temperature) that can cause focus drift. Something as simple as seeing conditions will affect focus (especially if your arcsec/pixel is small). Hence, I feel the most accurate method is periodic refocusing between subs (active focusing).

Hope this helps.
Cheers

[Comet Hunter]

Cheers Monte.

At this stage the G11 is front runner - I'm open to suggestions/discussion though. What I'd like to do is de-fork the SCT and mount both side by side. The weight of both OTA's combined is ~20Kg + accessories. I know this is really pushing the G11 for ideal imaging but I'm hoping fine tuning will help minimise the adverse effects the extra weight and bulk brings with it. As I mentioned last night, Titan/AP would be better suited but the G11 is already pushing the limit. Next time though....

I agree the bracket, as provided, does leave a bit of doubt. A custom made fitting with a stronger material would be ideal. Once everything is mounted I might see about attaching a custom bracket to the dovetail - this would remove screwing around trying to get the correct angle with the finder mount while keeping the focuser square with the shaft etc.

Wow Jase, thanks for that! I was under the impression Focusmax required Maxim as well. Installing now to have a play.

[jase (Jason)]

Distributed as part of the ASCOM package is the FocusAPI plug-in for CCDSoft. There are some basic instructions provided to get FocusMax integrated. The plug-in enables CCDSoft to communicate with an ASCOM focuser, by translating the FocusAPI calls from CCDSoft into ASCOM equivalent calls.

Bisque's @focus 2 capabilities I believe are now comparable with FocusMax. @focus 1 was rather lame. FocusMax is still evolving (as is @focus) as per my previous post (FMx 3.4.1 released). I don't think either have the edge on the other. Depends on your preference and ultimately whether the software gets your camera's focal plane into the CFZ every time.

If you're scared of ASCOM and prefer to stick with proprietary code such as that developed by Software Bisque. You are stuck with @Focus 1/2 for automated focusing. I'm not saying that's a bad thing, but I feel its important to have a choice. ASCOM opens up a wealth of device support.

[montewilson (Monte)]

You're right Jase @focus1 left a lot to be desired. I only got it to work once!

I know I could get Fmx to work with CCDSoft but I am not as technically gifted as you! I looked into it and beat a hasty retreat. I guess that marks me out for mediocraty because AP is full of similar challenges.

WRT the focuser on the Q, mine is quite coarse and yours has the benefit of many years of evolution. We may find there is a significant difference between them.

OK on what you said with the focuser progy and setting it up to work between exposures. I will go and harras the guys on the Bisque help forum to see what they know.

Andrew! If you want to do more than 20kg forget the EM-200 you would need an EM-400 but alas, they have stratospheric prices. A GM-11 would be a fine alternative. Don't forget a great mount will bring the best in any scope, a bad mount will bring out the worst.