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piprees

Is autofocus as good as it sounds?

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Well, I've been hooked for a few years now and over those years I've sorted guiding, processing has progressed to pixinsight and I'm just about getting the hang of CCD with LRGB and narrowband filters together with SGpro. Now, what's come along is Moonlite and/or Lakeside autofocus. It seems on the face of it to be an amazing addition, resulting in pinpoint stars etc. However, at £300-£400 a hit is it really that good. Comments from those that have either will be most welcome. My fear is that, without any experience, it could turn out to be a lot of dosh for possibly very little improvement. How have you guys found it and have you any regrets?

Kind regards,

P.

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Depends if you image remotely really.  I do so it is essential.  I have a few different types (Lakeside, Moonlite and Pegasus) and all are very good.  I'd agree with Gav that the Lakeside is excellent, and probably my choice of the bunch.

If you image next to the rig then naturally it isn't really necessary, but it really is a nice to have, and as you rightly say it will almost certainly give you better focus than doing it by hand, and it will automatically focus between filters if you aren't perfectly par focal, and of course when the temperature changes.

 

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I also use the Lakeside for two different scopes.  It is very accurate - far more so than I could focus manually.  Moreover, it can be programmed to refocus automatically when you want during an imaging run, e.g. if the ambient temperature changes a certain amount, or between filters.

What you do not want are out-of focus subs - as far as I am concerned they are irretrievable.

Chris

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Yes, it is fantastic.  It is amazing to watch and is far more accurate compared to what you could do yourself even with a Bahtinov mask.

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I have Lakeside and Starlight Instruments FeatherTouch. Both are brilliant.

The only thing I would say is that an autofocuser needs highly repeatable movements - so Rack and Pinion is great - a Crayford focuser that doesn't slip is great - but a Crayford focuser that does slip will be a nightmare.

Cheers

Ian

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2 hours ago, ian_bird said:

I have Lakeside and Starlight Instruments FeatherTouch. Both are brilliant.

The only thing I would say is that an autofocuser needs highly repeatable movements - so Rack and Pinion is great - a Crayford focuser that doesn't slip is great - but a Crayford focuser that does slip will be a nightmare.

Cheers

Ian

Yup. If ever I felt like adding three electronic devices and three extra USB connections to our setups (don't hold your breath!) I would only do so with a very non slip focuser. I do have a Moonlite which I think is about as non slip as a ski slope. 

Olly

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I really really hope to find a good autofocuser product that won't cost me a lot, but i don't know if i have to wait or not because i have only ST80, does that autofocuser work on specific scope or it can be universal so i can use it on different scope for same autofocuser unit?

I don't use a Bah. mask and i always trying to depend on my manual focus, i don't know how much i will lose by this way, and i don't know how big/huge difference will be between a very accurate focus and just good focus but not dead on 100%, if there is an example it will help, but please, not a comparison between very accurate focus and not so good focus because this is not a comparison, it will be a joke.

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1 hour ago, TareqPhoto said:

I really really hope to find a good autofocuser product that won't cost me a lot, but i don't know if i have to wait or not because i have only ST80, does that autofocuser work on specific scope or it can be universal so i can use it on different scope for same autofocuser unit?

I don't use a Bah. mask and i always trying to depend on my manual focus, i don't know how much i will lose by this way, and i don't know how big/huge difference will be between a very accurate focus and just good focus but not dead on 100%, if there is an example it will help, but please, not a comparison between very accurate focus and not so good focus because this is not a comparison, it will be a joke.

In my opinion it would not be a good investment to buy an autofocuser for an ST80. You would do far better to improve the scope. Also the ST80 focuser is quite primitive and probably not accurate enough to work under stepper motor control all that reliably.

It is perfectly possible to focus manually. The main advantage of autofocus is being able to leave the scope unattended while you get some sleep. There is a danger of coming to believe that an autofocser is necessary when clearly it isn't. Regular checks using FWHM measurement will keep most scopes nicely in focus. There are some fast astrographs which are notorious for focus drift during temperature change and these will certainly be best under autofocus but I think the idea that we all 'need' it is very strange.

Olly

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I really wouldn't suggest that you buy an autofocuser for your ST 80, it won't improve your images and the money could be much better spent on other equipment that most certainly would improve your images! Hang on to that ST80 to put it to good use further on down the line as a guide 'scope.

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2 hours ago, TareqPhoto said:

I really really hope to find a good autofocuser product that won't cost me a lot, but i don't know if i have to wait or not because i have only ST80, does that autofocuser work on specific scope or it can be universal so i can use it on different scope for same autofocuser unit?

I don't use a Bah. mask and i always trying to depend on my manual focus, i don't know how much i will lose by this way, and i don't know how big/huge difference will be between a very accurate focus and just good focus but not dead on 100%, if there is an example it will help, but please, not a comparison between very accurate focus and not so good focus because this is not a comparison, it will be a joke.

You usually have to either get a kit for the scope in question, or adapt the relevant motor to the scope (I tend to use a bit of metal and bend/drill as needed).

If you have the skill to do so (soldering, and a bit of computer knowledge) you could build an Arduino based focuser for much less than a commercial product would cost. I've done so for my widefield lenses and scopes - cost about 35 quid or so. See https://sourceforge.net/projects/sglfocuser/.

Regarding the Bahtinov mask, I think if you have a motor to control the focuser, you can get just as good results with the mask manually moving the motor in and out. Moving it by hand is much harder - you won't be able to make as fine a movement.

 

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Totally agree with Olly and Steve.  The investment specifically for the ST80 probably wouldn't be justifiable, although you can use the focuser on another OTA and just get/make a new bracket and connector.

With regards to examples, it literally would be as you note which is out of focus images with stars appearing slightly "fuzzy" rather than pin sharp.  Whilst there is nothing at all to say you can't get excellent focus manually, the ability to move in microns which the focus motor allows may provide a more repeatable result.

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I have a crayford Moonlite motorised focuser on my SCT.  It is great for push button focusing using a bahtinov mask but no so good for automatic focusing since I think there must be some slippage when moving the focus but inwards, this makes use of focus max impossible.  I have a rack and pinion focuser on my FSQ and this is fine with focus max provided the small amount of backlash is adjusted for.  On my Skywatcher MN190 I have the original, and much derided, single speed crayford and I find this works brilliantly with a Bahtinov mask.  So I have plenty of experience using automated focusing, electronic focusing under manual control and also fully manual.

The benefits of electric focusing have been well discussed already and for remote use it is essential.  However, like much expensive astro kit, users who have made the purchase tend to exaggerate the benefits.  In real world use I don't feel the focus I achieve manually is any worse than achieved with an automated focuser.

There is also a learning curve and the usual IT gremlins, another link in the chain of things to spoil your nights imaging!

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I have three autofocusers one each for the three scopes I own. One is a rack & pinion focuser and is very reliable to use with auto focus. The other two are crayford focusers, one I use auto focus but I keep my beady eyes on the focus routine - Just in case. The other I use FWHM. A repeatable focuser is a prerequisite to consistent auto focussing. 

Steve

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If you are imaging only (and therefore need just a small range of movement at the drawtube) it is easy to make a tangent arm microfocuser like this.

microfocus%203-L.jpg

This is actually my favourite manual focuser for imaging and I have a standard Tak and a Feathertouch in use as well. I like it because the smallest turn you ever need to make is about half a turn. (It is 'micro' as in micro!) It also holds the focuser in position as well so there is no need for a lockscrew and no possibility of slippage. I have it in mind to make an improved version which does away with the spring by pulling on the arm as well as pushing but this one works so well that I never get round to it. Highly recommended and it cost about 10 pence!

Olly

 

Edited by ollypenrice
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Well, i think i will pass that autofocuser for ST80 then, i just asked as i thought maybe i can just move the autufocuser motor from one scope to another without more changes or adding something.

I upgraded my ST80 focuser to 2" CrayFord focuser to make it clear, it has dual speed, the black knob is really something else, and yes, i now do better focusing manually, but just wanted for precise or more accurate, but sounds if i will buy another scope anyway then better i wait and buy autofocus motor for new scope.

How much sharp or focused the stars need to be? i asked  above if tiny focus change may cause big or huge difference overall, or if it is not that much important anyway.

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3 hours ago, TareqPhoto said:

 

How much sharp or focused the stars need to be? i asked  above if tiny focus change may cause big or huge difference overall, or if it is not that much important anyway.

They need to be as sharp as you can possibly make them. This is very important. But the fact remains that you can get them sharp without robotic focus. Note that with an ST80 'sharp' depends on the wavelength you are interested in becaue the ST80 cannot bring all colours to the same focus at the same time.

Olly

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True, then i will suffer a bit and use a Canon lens instead of ST80, the lens is better than ST80 and in same class as APO scopes, just the focus ring on one lens is bad, not sure if i will be able to focus using the ring of the lens, sounds all signs telling me to go and buy an APO triplet as soon as possible.

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