How to focus camera lenses robotically?

[ollypenrice]

Hi All,

We are setting up a Samyang 135 with a ZWO focus motor for unattended robotic imaging. Has anyone done this? The problem is that the lens can't be driven a long way past the infinity stop in order to build a vee curve, whereas it can on a telescope. We'd be grateful for any pointers on how to go about this, with what software, etc.

Thanks,

Olly, Paul and Peter.

[vlaiv]

One way of doing that is to slightly tweak sensor distance so that infinity focus is no longer at infinity position of the focusing ring but somewhere closer - that way there will be some distance past infinity focus for automatic focus to work.

[Adreneline]

44 minutes ago, ollypenrice said:

Hi All,

We are setting up a Samyang 135 with a ZWO focus motor for unattended robotic imaging. Has anyone done this? The problem is that the lens can't be driven a long way past the infinity stop in order to build a vee curve, whereas it can on a telescope. We'd be grateful for any pointers on how to go about this, with what software, etc.

Thanks,

Olly, Paul and Peter.

There are lots of examples on the Samyang thread, mine included with lots of photos etc. HTH

Edited December 21, 2022 by Adreneline

[Adreneline]

8 minutes ago, Adreneline said:

There are lots of examples on the Samyang thread, mine included with lots of photos etc. HTH

I found it helps if the spacing is exactly right and you accurately measure the backlash in the gear/pulley system; once the backlash is determined you can set the min and max steps with confidence and ascertain a limit position, all in the software.

NINA did the job perfectly but it's a lot easier with an ASIair.

HTH

[ollypenrice]

1 hour ago, vlaiv said:

One way of doing that is to slightly tweak sensor distance so that infinity focus is no longer at infinity position of the focusing ring but somewhere closer - that way there will be some distance past infinity focus for automatic focus to work.

Thanks Vlad. We'd considered this but we want to use the lens wide open at F2 so we wonder if we really have any room to look for more extra-focal distance without introducing off-axis distortions. We can experiment, of course, because we have an adjustable back-focus gadget.

Olly

[vlaiv]

4 minutes ago, ollypenrice said:

Thanks Vlad. We'd considered this but we want to use the lens wide open at F2 so we wonder if we really have any room to look for more extra-focal distance without introducing off-axis distortions. We can experiment, of course, because we have an adjustable back-focus gadget.

Olly

If you make worm / worm wheel arrangement - then you will have extremely precise control over focus position.

One whole revolution of stepper motor will be - just "one tooth" of the focusing ring

That can give you enough motion for V shaped curve to work with minimal motion past infinity focus ...

Edited December 21, 2022 by vlaiv

[ollypenrice]

8 minutes ago, vlaiv said:

If you make worm / worm wheel arrangement - then you will have extremely precise control over focus position.

One whole revolution of stepper motor will be - just "one tooth" of the focusing ring

That can give you enough motion for V shaped curve to work with minimal motion past infinity focus ...

Ouch! We are using a (very crappy!) toothed belt system and hoping to get it to work. I can imagine designing and building a much finer adjustment system but I am hoping not to have to!!

lly

[vlaiv]

1 minute ago, ollypenrice said:

Ouch! We are using a (very crappy!) toothed belt system and hoping to get it to work. I can imagine designing and building a much finer adjustment system but I am hoping not to have to!!

lly

It is fairly easy to do it you have access to 3d printer.

I'm slowly starting to push the idea that 3d printer is as essential to astro amateurs as is barlow lens or T2 extension

 

[ollypenrice]

14 minutes ago, vlaiv said:

It is fairly easy to do it you have access to 3d printer.

I'm slowly starting to push the idea that 3d printer is as essential to astro amateurs as is barlow lens or T2 extension

 

My chances of getting a 3D printer to work are... zilch!

I could make a fine focus out of proper materials, though: wood and metal. I just don't want to!!!

lly

[Phillyo]

Hi Olly, 

I use the Samyang 135mm lens and was having the same issue as you, being unable to get much past infinity to get a good v curve. I did a little bit of surgical work to remove the hard stop and now it works perfectly. There's a video explaining how to do it, it's a really easy 5 min job. I'll see if I can find it and post the link below. 

Hope that helps. 

Phil

 

[ollypenrice]

On 23/12/2022 at 09:58, Phillyo said:

Hi Olly, 

I use the Samyang 135mm lens and was having the same issue as you, being unable to get much past infinity to get a good v curve. I did a little bit of surgical work to remove the hard stop and now it works perfectly. There's a video explaining how to do it, it's a really easy 5 min job. I'll see if I can find it and post the link below. 

Hope that helps. 

Phil

 

Thanks Phil. That looks like a very convincing solution. I'll put it to the team!

Olly

[Alien 13]

That infinity focus mod looks good but I would be tempted to either modify the slot in the existing removed part or manufacture another part so that a hard stop still exists.

Alan