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INDI Library v1.9.6 Released (21 May 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

stupid question on DC focuser / stepper and autofocus

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I am a bit confused regarding the autofocus module.

I own a HitecAstro DC focus which is has a "relative" motor (??) does that prevent me from using autofocus ? I do not understand the relation between the "autofocus module" method and needing to have a stepper motor... Could someone help me clarify this ? I think I am mixing a couple of concept there ;)
"Some people are so poor, all they have is money"
SW Black Diamond 80ED | SW150MAK | Newton SW 200/1000 | Orion 50mm Guider with Helical Focuser |Sirius EQ-G Rowan Belt Mode
Canon 1000D moded | ZWO ASI185MC | Baader Mark III Zoom
INDI | Stellarmate on RPI3B+ | Stellarium | Pixinsight
4 years 11 months ago #17634

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Hi!
First you don't need a stepper to focus. I own two setups using Orion Accufocus and being driven by Arduino + Moonlite Driver by emulation.
Basically the firmware they have emulate steps just like a stepper. (Check my signature). In fact, just seeing the Hitec Control Panel, your focuser
controller does exactly the same.

The use of steppers is common because generally they are more precise and repeateable (you can repeat the same position every time).
My focusers have DC relative motors too. They always start at the same position (5000), they don't even save the last position. They focus at current position without any problems.

I use autofocus with my Atik 420 and Canon 550D with a high degree of confidence. Sure, steppers would give more accuracy but in my
opinion you can get away fairly easy with DC motors. All in all you just have to find out the best settings for your focuser/motor combination.

Also you must have a suitable INDI driver, if you don't have one, adapt an existing driver.

As said, that's my experience. Other may diverge from this point of view.
(PT) SC@ROS Observatory
TS 6" F4 Newt / Nikon D5500 / GPU CC / Datyson T7M / Arduino Moonlite DC Clone- HEQ5 Pro
Orion 120ST / Explore Scientific 80APO / TSAPO102Q Sextuplet / G2-8300FW5 / ES FF 2" / ASI120MM - Arduino Moonlite DC Clone - Vixen GPD2
www.flickr.com/photos/139335144@N03/
The following user(s) said Thank You: Robert Woodcock
Last edit: 4 years 11 months ago by nMAC.
4 years 11 months ago #17635

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Thanks for your answer :)

I went through the documentation (should have done that first!... RTFM as they say) and you are correct about DC focuser being supported.

"While Ekos Focus Module support relative focusers, it is highly recommended to use absolute focusers."

and the documentation lists the difference between the types of focuser:

- Absolute: Absolute Position Focusers such as RoboFocus, MoonLite..etc
- Relative: Relative Position Focusers
- Simple Focusers: DC/PWM focusers with no position feedback

There is a little catch for DC focuser : "For absolute and relative focusers, the step size is in units of ticks and for simple DC focusers, the step size is in milliseconds"

Right now, I focus manually using a bathinov mask, so, if I understand correctly, I could use the autofocus module and rely on the Half-Flux-Radius (HFR) method and ditch the bathinov mask ? I plan to set the focuser to an already "close to focus" position and let the autofocus module refine the focus. Does that make sens ?
"Some people are so poor, all they have is money"
SW Black Diamond 80ED | SW150MAK | Newton SW 200/1000 | Orion 50mm Guider with Helical Focuser |Sirius EQ-G Rowan Belt Mode
Canon 1000D moded | ZWO ASI185MC | Baader Mark III Zoom
INDI | Stellarmate on RPI3B+ | Stellarium | Pixinsight
Last edit: 4 years 11 months ago by Yannic Delisle.
4 years 11 months ago #17636

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Yes it does make sense, thats exactly how I do it and it works very well.

You also can choose various focus algorithms in the autofocus windows, it's a matter of trying them and see wich suits best.
(PT) SC@ROS Observatory
TS 6" F4 Newt / Nikon D5500 / GPU CC / Datyson T7M / Arduino Moonlite DC Clone- HEQ5 Pro
Orion 120ST / Explore Scientific 80APO / TSAPO102Q Sextuplet / G2-8300FW5 / ES FF 2" / ASI120MM - Arduino Moonlite DC Clone - Vixen GPD2
www.flickr.com/photos/139335144@N03/
The following user(s) said Thank You: Yannic Delisle
Last edit: 4 years 11 months ago by nMAC.
4 years 11 months ago #17638

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Hello

I did some tests and you are right, the autofocus was working with my DC focuser. The only issue I had was that the movement of the focuser were way to long, moving an inch inward and outward each time so I could never get it to focus properly.

I would guess that this has to do with the value I use in the setup of the driver. Could you tell me which value you use to see if I am way off ? This would help me clarify a bit what value I should put in "ticks" and "steps"
"Some people are so poor, all they have is money"
SW Black Diamond 80ED | SW150MAK | Newton SW 200/1000 | Orion 50mm Guider with Helical Focuser |Sirius EQ-G Rowan Belt Mode
Canon 1000D moded | ZWO ASI185MC | Baader Mark III Zoom
INDI | Stellarmate on RPI3B+ | Stellarium | Pixinsight
4 years 11 months ago #17759

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Hi,

well in my case I used 100ms ticks to emulate (in arduino firmware) a step and so I choose steps.
In you case you must select ticks, because It's a different driver and uses timmings.
Try with 50/100ms (miliseconds) or less and keep increasing until you find a reasonable value.
Try to focus a bright star and find a step value that really changes the focus. If the value is too small you won't see any difference at all.
(PT) SC@ROS Observatory
TS 6" F4 Newt / Nikon D5500 / GPU CC / Datyson T7M / Arduino Moonlite DC Clone- HEQ5 Pro
Orion 120ST / Explore Scientific 80APO / TSAPO102Q Sextuplet / G2-8300FW5 / ES FF 2" / ASI120MM - Arduino Moonlite DC Clone - Vixen GPD2
www.flickr.com/photos/139335144@N03/
The following user(s) said Thank You: Yannic Delisle
Last edit: 4 years 11 months ago by nMAC.
4 years 11 months ago #17760

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