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Old 21-02-2012, 10:35 PM
Carl
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Auto focusing system

Hi all
I have a new Skywatcher Black Diamond ed120 and i want to get a simple auto focusing system that will allow me to focus even more accurately than using my hands on 10:1 focuser.

I also do not want to spend the equivelent of the GDP of a small country.

I'm currently succesfully focusing by hand using Nebulosity2 and simply want to continue using that software via a hand controller so i do not vibrate the focuser and gain more minute control over the focusing. The last thing i want to do is have to spend my evenings getting my head around another peice of software instead of taking photo's.

Any suggestions appreciated
Carl Rainer
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  #2  
Old 22-02-2012, 04:01 AM
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OzRob (Rob)
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I have found the Robofocus unit coupled with FocusMax a good system. Once it is set up and a few things learnt it is reliable. If you get into it further down the track it allows for unattended automatic focusing.
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Old 22-02-2012, 05:55 AM
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Carl, although auto focusing systems have there place i have always just focused through my past imaging system by eye alone with 95% spot on accuracy, after a while of practice it just falls into place and most of my images were pretty sharp.

Leon
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Old 22-02-2012, 08:05 AM
Poita (Peter)
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I love my optec TCF, it is bulletproof.
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Old 22-02-2012, 09:02 AM
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Carl

I presume you mean a motorized focuser as autofocusers are quite different
You could get one of these to add on to the micro focus shaft, but do check with them if it'll suit your focuser
http://www.bintel.com.au/Accessories...oductview.aspx

Autofocusers from what I understand require ascom control and the software would measure fwhm and adjust till optimum.

The optec tcf does look very good, but I'm guessing is quite expensive as well

Cheers
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Old 22-02-2012, 01:01 PM
Mighty_oz (Marcus)
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Quote:
Originally Posted by Poita View Post
I love my optec TCF, it is bulletproof.
Wish mine was, one day the temp device is working the next it's not, but i have to say that with focusmax it works well, often 60 or so and the stars are focused, do a couple images refocus. When it all works it's a dream.
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Old 22-02-2012, 07:27 PM
Poita (Peter)
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I'd get it checked out then, mine has literally never failed once.
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Old 22-02-2012, 08:08 PM
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mplanet62 (Michael)
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I feel like I've missed something. Autofocus for telescope? Ideal focusing is easy with Bahtinow mask - cheap and effective. If DSLR has live view (even better on computer screen) it's like a toy, too simple. And, with prime focus photography all system needs to be focused once for all session. So what's the point to make simple things complex?
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Old 22-02-2012, 08:39 PM
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Originally Posted by mplanet62 View Post
I feel like I've missed something. Autofocus for telescope? Ideal focusing is easy with Bahtinow mask - cheap and effective. If DSLR has live view (even better on computer screen) it's like a toy, too simple. And, with prime focus photography all system needs to be focused once for all session. So what's the point to make simple things complex?
if only it were that simple.

Focus changes on telescope throughout the night as temperature drop and mirrors/lenses stabilise. So depending on scope you need to refocus every 3 - 6 degree temp drop.

Also when imaging not all filters are parfocal so you need to adjust focus for each of your filters.

Automated focus makes this very easy to do and also enables unattened imaging as you can use scripts via automation software to tell your focuser to refocus every hour or if temp drops more than x degrees or when filters are change etc....

if using hand a bhatinov mask however is the ticket

Last edited by cventer; 22-02-2012 at 11:47 PM.
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Old 22-02-2012, 09:09 PM
Carl
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focuser

Thanks every one
Christ it's a big learning curve. Just come in from setting up the scope, focused by hand using Nebulosity HFR 1.45. Not bad.

So Is the Robofocuser alos an auto focuser if you use the right software?

Regards
carl
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Old 22-02-2012, 11:49 PM
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Thanks every one
Christ it's a big learning curve. Just come in from setting up the scope, focused by hand using Nebulosity HFR 1.45. Not bad.

So Is the Robofocuser alos an auto focuser if you use the right software?

Regards
carl
Carl Robofocus comes with a focus control box that connects to the PC. It also comes with software and is ASCOM compliant so any software that can control a focuser via Ascom can use robofocus.
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Old 24-02-2012, 08:47 PM
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Carl, I got the Skywatcher autofocuser for Christmas and while I haven't used it yet in anger I have set it up though and it looks like it'll do the job I need. It does say it supports the ED models so you should be right but if you decide to get one I'd double check.

It's simple to set up and easy too control too so it's worth considering.

With my 150PL on the eq3-2 the shake is terrible for manual focus so this will get rid of the need to touch the thing. Especially useful when using the webcam.
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Old 24-02-2012, 10:27 PM
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I've recently realised there's motorised focusers and there's motorised focusers. The SW one is a DC motor. I have a Moonlite DC motor. While it'll work and all that, you may be disappointed if you want to try to use it with FocusMax and "autofocusing". I tried night after night to get it to calibrate and get reliable V curves. No dice. While I've read that guys have persisted and got it working, I decided that I was spending more time mucking around with calibrating it that I would if I were to focus manually with a Bahtinov mask.

If you want that next level of automation like using FocusMax, save yourself a world of frustration and go straight for a stepper motor type focuser. The difference with them is that they know where the focuser is positioned. ie they're "absolute" focusers. DC motors have no way of knowing what position they're in, ie "relative" focusers.
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Old 24-02-2012, 11:16 PM
Carl
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Focusing systems

THis is a very interesting point you make Troy and it is very true. I suppose that is why a robofocuser will set you back $500 and the Skywatcher $90. However is you are interested got to astronomyorg.co.uk also hitecastro.co.uk
There is a unit which called DCfocus controller. You connect the skywatcher motor up to this then it is connected to your computer. While it is not a stepper motor it is recieving rave reviews. Apparently you control the whole thing from your computer and can focus with very minute steps and accuracy.
Skywatcher moter and hand controller $90
DCfocus $99
You need nothing else. Sirius optics have just been appointed distributor in Australia. I sent a couple of questions to the UK manufacturer and got a reply within a day.
It's not as good as JMI, Moonlite ar robofocuser but affordable if you are on a budget, fortunately for me I'm not. I just have to way up the overkill factor. I am only using a Skywatcher ed120 black Diamond there is a limit to what you canm expect to or need to achieve.
All good food for thought, especially with a good Aussie dollar.

Cheers and Thank's
Carl
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Old 25-02-2012, 06:58 AM
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I have a FCUSB controller for mine. I think the end result is the same, though. The Hitecastro is just a controller, it doesn't make the motor any smarter. It's still relative and doesn't know its actual position.
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Old 25-02-2012, 08:31 AM
rally
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Troy,

The Robofocus and others that use the same/similar motor/gearbox hardware - (eg Cercis Astro) doesnt know its absolute position.
There is no feedback system - ie no rotary encoders on the output.

The controller relies on the fact that the stepper motor has in fact stepped when its been asked to.
If it has stepped, then the step is accurate and all is well, but if the load is too great or there is some interference then its possible that the controller tells the motor to step, but it it doesnt actually make the step because the motor is stalled with the load and then you will have some problems as the controller now thinks it has made the step and the controllers positional information is now wrong.
If that occurs repeatedly on every focus cycle, the focus position incrementally gets worse each time.

This can occur with very heavy loads at/near Zenith when the focus system gearing is not high enough to overcome this maximum load position or worse yet even slips.
You can adjust the motor power as an option, but that only helps so much.

If you are having problems keep this in mind.

Also bear in mind that these systems usually rely on the same effect to calibrate their "home" position, so they make a very large move in one direction to close up your focuser till it reaches a hard stop, the motor still keeps going, but there is no movement.
If the hard stop position is actually more like a soft stop (ie its somehow flexible or changing) then the the focusing system may be unreliable.

Cheers

Rally
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Old 27-02-2012, 11:15 AM
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Quote:
Originally Posted by rally View Post
Troy,

The Robofocus and others that use the same/similar motor/gearbox hardware - (eg Cercis Astro) doesnt know its absolute position.
There is no feedback system - ie no rotary encoders on the output.

The controller relies on the fact that the stepper motor has in fact stepped when its been asked to.
If it has stepped, then the step is accurate and all is well, but if the load is too great or there is some interference then its possible that the controller tells the motor to step, but it it doesnt actually make the step because the motor is stalled with the load and then you will have some problems as the controller now thinks it has made the step and the controllers positional information is now wrong.
If that occurs repeatedly on every focus cycle, the focus position incrementally gets worse each time.

This can occur with very heavy loads at/near Zenith when the focus system gearing is not high enough to overcome this maximum load position or worse yet even slips.
You can adjust the motor power as an option, but that only helps so much.

If you are having problems keep this in mind.

Also bear in mind that these systems usually rely on the same effect to calibrate their "home" position, so they make a very large move in one direction to close up your focuser till it reaches a hard stop, the motor still keeps going, but there is no movement.
If the hard stop position is actually more like a soft stop (ie its somehow flexible or changing) then the the focusing system may be unreliable.

Cheers

Rally
I believe that there is a more powerful motor available now for the Robofocus if you have a lot of weight.
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