Automated Focusing, what path to choose?

[Atmos]

Hello everyone,

I know that in the future I do want to go down the path of automated focusing, temperature compensation, so that I can actually get a nights sleep!

The telescope that I am getting in a week or so comes with a United Optics 4" dual speed focuser, being 4" it should be pretty sturdy. There is basically two main ways that I can go moving forward.

1) Keeping the current focuser and attaching a RoboFocus or something of that ilk.
2) Replacing the focuser with a suitable Feathertouch or Moonlite with stepper motor.

Still a little way from getting something, money doesn't grow on any of my trees :( Just looking for some guidance for the future :)

Colin

[rally]

Colin,

So long as the electronic focusser is ASCOM compliant, the various programs that need to use it will be able to do so.

RoboFocus is of course compliant - so its an option.

Try FocusMax - with ASCOM it becomes a powerful tool that is easy to use.

[Slawomir]

Hi Colin,

Automated focus certainly has helped me to collect better quality data. In the past, I would manually readjust focus maybe once or twice a night, but it was not until I got automated focusing sorted that I realised the degree of focus shift with temperature change. Also, with manual focusing, I would need to slew to a bright star, refocus, go back to the target...time consuming and quite labour intensive.

I have been using Moonlite with stepper motor combined with SGP for a few months and have found it to be very reliable and all works very well. I set it to refocus with every one degree change of ambient temperature and SGP very finely and accurately readjusts focus. I also recently added automatic rotator (also from Moonlite) and the whole package works extremely well - no slop/tilt due to gravity at all (have QSI and SX filter wheel and OAG attached to the focuser). In my set-up, both focuser and rotator are controlled via SGP. SGP ensures everything goes smoothly and now I do not need to "intervene" during imaging session or waste time refocusing and slewing around the sky. In sum, while not cheap, Moonlite has been one of my top upgrades and it turned my rather average TS doublet into a neat imaging machine :)

[DavidTrap]

Replacing a 4 inch focuser with Feathertouch or Moonlight is going to be expensive - I've just done it with my TOA-130. Nonetheless, the new feather touch focuser is an incredible piece of machining. I had a Moonlight focuser on another scope, albeit with a Servo motor (not an absolute position Stepper Motor), and wasn't impressed. I much prefer the rack & pinion mechanism of the Feathertouch.

If the stock focuser is satisfactory, a robofocus will be your cheapest option. You can buy a feather touch motor that attaches to a Tak 4 inch focuser - not sure about other brands. Might be worth an email to Wayne at Starlight Instruments - he was helpful with my enquiries.

As for focusing, Focusmax is your best option once you've got an ASCOM compatible focuser. Version 3 is the no-longer supported shareware version, Version 4 is a commercial product (USD$149). Version 3 still works fine for my needs.

DT

[rmuhlack]

A 4" focuser is huge - do moonlite or feathertouch even make a focuser that big? If you're paying a premium for such a large high-end focuser then i reckon fitting an after-market stepper motor to the united optics focuser is the way to go... ;)

[Atmos]

It's your RF3 International on the Classifieds that has kicked this off for me btw :P

[rmuhlack]

i thought it might be... ;) :D

[PRejto]

This winter we have had some shockingly cold nights with very rapidly falling temps in Sydney. I can watch the average FWHM values increase with every sub and sometimes have to refocus every 15-20 minutes. A real pain.. Slewing away to a guide star, focusing, restarting guiding is a huge time waster and is frustrating. Certainly some sort of motorized focuser is required. FocusMax is great. Both old and new versions. But, what I'm excited about is Sharplock and FocusLock (Optec's version) that allows for totally automated focusing based on the astigmatic guide star image in IR as seen through an ONAG. The good news is that Optec is going to release a kit to allow this technology to work on OAG, so ONAG is not required. I have been beta testing this software and it works very well indeed (with my ONAG). I have tested it over a fall of 4 degrees and great focus was easily maintained. Basically you just image and the focus is always good as long as the system was properly set up to start with.

Peter

[gregbradley]

If Optec can do a kit for a MMOAG it would be an amazing accessory.

Greg.

[Paul Haese]

Getting a Robofocus unit (assuming the spindle of your focusor fits the unit) and then using Focusmax is my recommendation. Though it all depends on weight being lifted. If you plan on lifting a very heavy payload then you will need to consider a FT focusor, FLI focusor or Belliphone focusor. For the average load though a rack and pinion focusor which is very beefy ought to work well.

I refocus after each sub with the FSQ. I have the programme slew to the zenith focus and then head back to the target. It takes about 5 minutes each time. I lose over the course of a night the equivalent of two 20 minute subs with imaging time. Worth it in my opinion. I don't image below 36 degrees, so I am only looking for high quality subs.

With the RC I focus once every hour. It does not change much during that time.

Focusing once or twice a night is not nearly enough for telescopes with a very shallow CFZ. Even a slight shift will result in an out of focus subs from that point on. I also recommend not using temperature compensation as it can be a little unreliable especially with regard to CFZ.

[Shiraz]

Also have a look at Sequence Generator Pro - the focuser routine uses multiple stars where you are pointing. It does not need to slew elsewhere, so no upset to guiding or realigning the field. I have a moonlite stepper and focusing takes about a minute for broadband and a couple for NB and, at f4, refocus is needed 10-20 times a night, depending on temperature. SGP will drive any ASCOM focuser and, with sequencing, plate solving, focusing and smart recovery, can pretty much automate your system.

Hardware wise, SharpSky is nice for adding to an existing focuser - includes temperature tracking refocus and dew heater control.

[DavidTrap]

Feather touch do make them this big. Things of beauty with a price tag to match unfortunately... There was slop in the stock 2.7inch focuser on my Tak - it's gone now. I also needed a larger focuser for the big flattener.

DT

[rustigsmed]

hmmm SGP sounds like it is pretty good. not having to slew the mount sound like a timesaver. additionally for some reason I always assumed that 'auto'focus products required a lot of user calibration :question:
might be time to upgrade from backyard eos.

[Paul Haese]

Focusmax you can focus in the field you are imaging in, I just choose to focus at the zenith to get sharper focus control. It is not a matter of having to do that. :)

[Paul Haese]

I had a 3" R&P and it was very smooth and precise. Like you say, a thing of beauty. I had to give it up to fit all the equipment into my back focus otherwise I would still have it.

[Shiraz]

no calibration at all. You have to play with a few obvious parameters for fine tuning, particularly for NB, but it should work straight out of the box as is - bit like phd for total lack of setup complexity. Only downside is a slightly idiosyncratic interface - SGP has it's own strong logic, but until you get used to it, you will find yourself muttering "now where the *6%$ did they put that".

[rustigsmed]

thanks Ray, i'm definitely going to get onto this for sure :thumbsup: a minute or two extra time is well worth it.
$US99 seems reasonable too.

cheers

Russ

[codemonkey]

I might just hijack your thread with a newbie question if you don't mind, Colin.

Do you actually need a controller if you plan to automate focus using SGP (or some other software solution)? Is the controller only for manual control, or does it serve another purpose?

[Shiraz]

Your main software (eg SGP) will send out a command along the line of "move to 1256" or whatever and the controller will read that command and generate the electrical pulses required to move the stepper in the focuser to get it to the desired position. you need a controller to interface between the software and whatever hardware you have

[Slawomir]

Hi Russell,

I am using SGP and you only need to manually focus once - SGP takes it from there. You do not need to calibrate anything, and as it has been said before, the scope remains on the target while refocusing, and if there is any drift during focusing routine, SGP will put it back on track after focusing routine. With NB filters, it takes about 2-3 minutes to adjust focus.

[codemonkey]

Thanks Ray :-)

[Atmos]

Well it looks like I am going to HAVE to buy FocusMax over the coming days. Bought a RoboFocus from a fellow ISS member so I am hoping that arrives some time next week. Going to have to figure out how to get everything attached correctly when it all arrives.
It sounds like FocusMax is going to do a better job than Maxim DL at doing the whole automated focusing thing.

Thanks everyone for the wealth of information.

[rustigsmed]

thanks Slawomir, I'm kind of embarrassed i didn't look into this more, earlier on! It sounds so much easier!! :thumbsup:

Russ