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Budget autofocusing for telescopes.

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#1 Nikonist800

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Posted 17 March 2019 - 08:44 AM

Hi.

 

I have a Skywatcher 80ed DS Pro and are looking to buy the Skywatcher Auto-Focus System for telescopes and a HitecAstro DC Controller.

 

HitecAstro-DC-Focus-Controller-500x375.jpg
Skywatcher-Auto-Focus-System-for-telescopes.jpg

 

I will use either Astrophotography Tool or Sequence Generator Pro and I will need to get autofocus to work from within the program.

How does the HitecAstro DC Controller work? confused1.gif

 

For example, can you get Sequence Generator Pro to completely focus between filter changes automatically or can you "learn" the programs where the focus is for each individual filter?

On the forum, people say that the Skywatcher Auto focus is not a stepper motor but a DC motor. According to all, these astrophotography programs cannot set autofocus with DC motors.

 

How do I go about solving this issue. crazy.gif  

Please shine some light on this.

 

Thank you guys. flowerred.gif

 

 



#2 bobzeq25

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Posted 17 March 2019 - 09:23 AM

Here's some light, but not a cheap solution.  I don't know of one.

 

It's tough to get a DC motor to autofocus because it will move more in one direction (when the weight of the camera drags it down) than the other, with the same inputs in both directions.  There is no magic cure.  Autofocus depends on calibration by moving the focuser precise specified distances and measuring the width of stars.  The "precise specified distances" is what requires a stepper motor.  As stated on the HitecAstro website in bold letters.

 

"It should be clearly noted that all DC motors are NOT capable of repeated absolute positioning."

 

The cheapest autofocus is to DIY a setup with a stepper motor and your own electronics.  Not an easy project.

 

The bottom line is that autofocus is not cheap.  It can be programmed to automatically compensate for filter changes.


Edited by bobzeq25, 17 March 2019 - 09:33 AM.

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#3 ajaymandke

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Posted 17 March 2019 - 09:31 AM

I am considering this myself - DIY Arduino ASCOM focuser..

https://sourceforge....focuserpro2diy/

 

Ajay



#4 Nikonist800

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Posted 17 March 2019 - 09:53 AM

Here's some light, but not a cheap solution.  I don't know of one.

 

It's tough to get a DC motor to autofocus because it will move more in one direction (when the weight of the camera drags it down) than the other, with the same inputs in both directions.  There is no magic cure.  Autofocus depends on calibration by moving the focuser precise specified distances and measuring the width of stars.  The "precise specified distances" is what requires a stepper motor.  As stated on the HitecAstro website in bold letters.

 

"It should be clearly noted that all DC motors are NOT capable of repeated absolute positioning."

 

The cheapest autofocus is to DIY a setup with a stepper motor and your own electronics.  Not an easy project.

 

The bottom line is that autofocus is not cheap.  It can be programmed to automatically compensate for filter changes.

It sounds very complicated and expensive with autofocus.
However, it seems that many have made this combination work well with eg APT and SGp.

 

What I am pensive about is how the DC controller works.
Is it by making a small adjustment using contrast recognition from eg SGp, or do you set the focus manually for each individual filter and save the data that causes SGp "automatically" to go to that value when the filter wheel changed filter?

 

I get that neither Stepper motors nor DC motors can easily maintain continuous focus, but that is not what I am looking for.

I assumed that "repeated absolute positioning" means that.

 

Sorry but my English is not that good ... bawling.gif



#5 bobzeq25

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Posted 17 March 2019 - 10:20 AM

It sounds very complicated and expensive with autofocus.
However, it seems that many have made this combination work well with eg APT and SGp.

 

What I am pensive about is how the DC controller works.
Is it by making a small adjustment using contrast recognition from eg SGp, or do you set the focus manually for each individual filter and save the data that causes SGp "automatically" to go to that value when the filter wheel changed filter?

 

I get that neither Stepper motors nor DC motors can easily maintain continuous focus, but that is not what I am looking for.

I assumed that "repeated absolute positioning" means that.

 

Sorry but my English is not that good ... bawling.gif

It _is_ complicated and expensive.  A great deal in astrophotography is both.  Patience is a requirement.

 

Big suggestion.  I suggest avoiding autofocus when starting out.  There's just too much to learn when starting out.  One example is the camera calibration frames; bias, flats, darks.  They are more important.  See my post in your other thread.

 

And, you can better setup autofocus _after_ you've learned to do it manually.  I suggest a Bahtinov mask, it provides positive indication visually that you're in focus.

 

Yes, SGP can automatically adjust for filter changes.  It doesn't use contrast (astrophotography has surprisingly little relationship to terrestrial photography), it uses star width.


Edited by bobzeq25, 17 March 2019 - 10:26 AM.


#6 Nikonist800

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Posted 17 March 2019 - 11:01 AM

It _is_ complicated and expensive.  A great deal in astrophotography is both.  Patience is a requirement.

 

Big suggestion.  I suggest avoiding autofocus when starting out.  There's just too much to learn when starting out.  One example is the camera calibration frames; bias, flats, darks.  They are more important.  See my post in your other thread.

 

And, you can better setup autofocus _after_ you've learned to do it manually.  I suggest a Bahtinov mask, it provides positive indication visually that you're in focus.

 

Yes, SGP can automatically adjust for filter changes.  It doesn't use contrast (astrophotography has surprisingly little relationship to terrestrial photography), it uses star width.

I actually bought a bahtinov mask.
The idea of autofocus for me is to put the focus with the bahtinov from start, but to avoid having to go out into the cold and change the focus manually every time the filter wheel has changed the filter.
From what I understand, it can be difficult to set the focus when having the Ha filter mounted.

Therefore, it would be great to have a preset value stored in the program for that specific filter and to get the program to make these small adjustments based on what filter is currently infront of the sensor.

 

So if it is possible to get e.g SGp to make the corrections based on each narrowband filter then it would be the dream.

I don't care about having to focus with the bahtinov mask from the start.

 

You are absolutely right when you recommend investing in one thing at a time and learning it properly.
However, I have already spent huge amounts of money on everything else so I might as well spend some on autofocus right away, get everything mounted and start learning the equipment as a whole.

Unfortunately, this is just the way I work. bawling.gif lol.gif



#7 Noah4x4

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Posted 17 March 2019 - 11:12 AM

I dont know the HiTec Astro focuser kit, but would make this general observation;

 

SG Pro's autofocus is superb with a top quality focusser like (say) a Microtouch MKIT20 controller and Feathertouch Microfocuser that is very precise and fast. It also offers control over individual frames and automatic temperature adjustment (albeit that isn't always perfect). Autofocus takes a bit of patience to determine your best settings, but works really well if paired with a high enough quality device.

 

However, attempt this with much low budget solutions and I suspect that you may be disappointed with the results and ultimately may end up wasting money when you discover you need to further upgrade to the kit that you really need to accomplish autofocus. Other motors and controllers can be terribly slow and too imprecise to improve upon less sophisticated (but sound) methodologies (see next paragraph). But to be fair, unless somebody with the Hitec Astro kit + SG Pro comments  this is just my $0.02 generic opinion.

 

If budget is an issue, a simple motorised focusser (to reduce vibration) and Bahtinov Mask and/or FWHM software tool (like that in Atik Infinity camera software) should give you pleasing results, and in my experience, be content with that or invest in top dollar gear, albeit SG Pro itself will deliver many other benefits to justify its purchase (such as filter change). Frankly, autofocus is only needed for the longer range of longer exposures/stacks (albeit a filter change can impact) and there are many more challenges than focus. A better investment might possibly be in mount (albeit I don't know your mount). Hence, what you propose might be a sensible budget compromise if you temper your ambitions to simple motofocus. But who knows, the HiTec Astro device might even work fine with SG Pro  autofocus, but you perhaps need a user of this combination to confirm that it does else accept that there might be limitations. All I can confirm is in my experience other low budget solutions don't deliver.


Edited by Noah4x4, 17 March 2019 - 11:21 AM.


#8 bobzeq25

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Posted 17 March 2019 - 11:18 AM

Have you imaged anything at all yet?  Nothing will help more than having some experience.

 

I suggest starting with just black and white images using the Ha filter.  They can be pretty nice, sample below.  Sharper version here (the forum limits image size).

 

https://www.astrobin...1497/B/?nc=user

 

The problem is that suitable Ha targets are a bit scarce right now.  An alternative is do do black and white with a simple UV-IR blocking filter.

 

Imaging using O(III) and, moreso S(II) flters is very challenging.  The signals are much weaker than Ha.  The processing is quite complex, you have to "map" the various filters to new colors, since Ha and S(III) are both red.  That makes the stars look funny, some people accept that, some work on the stars separately.

 

Get some experience with your new setup, as simply as possible.  No one has ever found doing this well easy.

 

Minor point re: "huge amounts of money".  You do realize Rista's lens cost $10,000?  That he now uses it on a $5000 mount?

 

The setup that took the image below was about $7000, total.  CEM60 mount. Stellarvue SV70T with reducer/flattener, Atik 460EXM camera, Astronomik 6nm Ha fliter.  60mm guidescope, 174 mono guide camera.  Polemaster for polar alignment.  Intel NUC for managing the data collection, remotely connected to my desktop indoors.

 

And about 4 years of experience.  <grin>

 

CED214 v2.jpg


Edited by bobzeq25, 17 March 2019 - 11:32 AM.

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#9 Nikonist800

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Posted 17 March 2019 - 11:35 AM

Have you imaged anything at all yet?  Nothing will help more than having some experience.

 

I suggest starting with just black and white images using the Ha filter.  They can be pretty nice, sample below.  Sharper version here (the forum limits image size).

 

https://www.astrobin...1497/B/?nc=user

 

The problem is that suitable Ha targets are a bit scarce right now.  An alternative is do do black and white with a simple UV-IR blocking filter.

 

Imaging using O(III) and, moreso S(II) flters is very challenging.  The signals are much weaker than Ha.  The processing is quite complex, you have to "map" the various filters to new colors, since Ha and S(III) are both red.  That makes the stars look funny, some people accept that, some work on the stars separately.

 

Get some experience with your new setup, as simply as possible.  No one has ever found doing this well easy.

 

Minor point re: "huge amounts of money".  You do realize Rista's lens cost $10,000?  That he now uses it on a $5000 mount?

 

The setup that took the image below was about $7000, total.  CEM60 mount. Stellarvue SV70T with reducer/flattener, Atik 460EXM camera, Astronomik 6nm Ha fliter.  60mm guidescope, 174 mono guide camera.  Polemaster for polar alignment.  Intel NUC for managing the data collection, remotely connected to my desktop indoors.

 

And about 4 years of experience.  <grin>

 

attachicon.gif CED214 v2.jpg

I did not mean that MY "huge amount of expenses" applies to all people, but on an individual basis it is for me, no matter how much money Rista´s equipment costs.

I´m at about 6K right now.
I find that images from the same imagetrain as I have, show impressive evidence of what to expect in the future when I get used to everything.


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#10 WadeH237

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Posted 17 March 2019 - 02:27 PM

Here are a few comments:

 

There are at least a few ways that software does autofocus.  None of them that I am aware of focus the way that you would do it manually.  In other words, they don't adjust focus until it looks right and then stop.

 

One method is used by FocusMax (and possibly others).  It works by sampling a number of focuser distances and compares it to the width of a star.  It does this repeatedly to characterize the focuser's behavior with that optics.  When it comes time to actually focus, the software actually determines focus by sampling an out of focus star.  It uses the pre-computed characterization to move from that out of focus position, to correct focus.

 

Another method is used by SGP (and possibly others).  It works by starting at an out of focus position, and then moves through focus, sampling the aggregate width of all the stars in the field periodically.  After it's moved to a position out of focus on the other side, it computes where the ideal focus would be and then moves directly there.

 

As you may note, both of these schemes finish up by moving from an out-of-focus position, to a calculated best focus position.  The methods vary, but they have that in common.  Because of this, a focuser without good repeatability is next to useless for automatic focus (and I have tried it; it's not fun).

 

To answer the question about filters, there are two ways of dealing with them, and all of the software that I've used supports it.  You have a choice of always focusing through the filter you are using, or you can always focus through the same filter (ie. the luminance filter) and then using a predetermined offset to apply to the filter you are going to use.  To determine the offsets, you do a one-time operation where you do many focus runs through each filter to determine the number of focus counts that each uses.  From that, you can do simple subtraction from whichever filter you want to use as the reference.  Again, without repeatability, this doesn't work.

 

Finally, I strongly suggest that you get really good at manual focus, so that it's second nature, before trying to automate it to work when you are not there.  I give the same advice for automating any part of imaging.

 

I hope that this helps to fill in the explanation.


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#11 Charlie B

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Posted 17 March 2019 - 03:15 PM

Hi.

 

I have a Skywatcher 80ed DS Pro and are looking to buy the Skywatcher Auto-Focus System for telescopes and a HitecAstro DC Controller.

 

attachicon.gif HitecAstro-DC-Focus-Controller-500x375.jpg
attachicon.gif Skywatcher-Auto-Focus-System-for-telescopes.jpg

 

I will use either Astrophotography Tool or Sequence Generator Pro and I will need to get autofocus to work from within the program.

How does the HitecAstro DC Controller work? confused1.gif

 

For example, can you get Sequence Generator Pro to completely focus between filter changes automatically or can you "learn" the programs where the focus is for each individual filter?

On the forum, people say that the Skywatcher Auto focus is not a stepper motor but a DC motor. According to all, these astrophotography programs cannot set autofocus with DC motors.

 

How do I go about solving this issue. crazy.gif  

Please shine some light on this.

 

Thank you guys. flowerred.gif

Look at Pegasus Astro's FocusCube (https://pegasusastro...ucts/focuscube/).  $310 and adapts to most focusers. It is compatible with SGP.

 

Regards,

 

Charlie B.



#12 Nikonist800

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Posted 17 March 2019 - 03:21 PM

Answer from the seller regarding my needs and what their DC controller can deliver.
...

Given that the difference between filters is usually quite small, I did not think a DC motor will be accurate enough to duplicate this on a consistent basis. The issue with DC motors is that it is much harder to reproduce the exact position of the motor shaft time and time again. I do believe that you will not be entirely happy with the performance of a DC motor, given that your ambitions include reproducing the very small variances between filter positions.
...

Conclusion.

I will listen to you now. I give up!! Haha **** it! I'll set the focus with my Bahtinov mask before shooting and between each filter change manually. I will not be in such a hurry anyway as I am set to shoot for 3-4 hours per night anyway.

Thanks again for your insight into this topic and that you all give such incredibly nice feedback. Thanks again. Sincerely, Andreas
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#13 OldManSky

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Posted 17 March 2019 - 06:24 PM

There's one aspect to the hardware you originally wanted to use that is a show-stopper right from the get-go:

 

It doesn't have any way to connect to a computer (and be controlled by it).

It only has the push-buttons.

 

So this is a non-started.  Even if it was a stepper motor.


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