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EAF + telelens issue

ZWO EAF ZWO ASIAIR Plus Auto-Focusing Troubleshooting
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Federica Panzarella avatar
Federica Panzarella avatar
Hello everybody,
I recently bought the ZWO EAF and a support to use it on my canon 70-200 f/2.8 L.
I have problems in reaching the perfect focus.
First of all I manually set it, then I run the focus feature on my Asiair Plus but I never get a V-shaped curve nor a perfect focus point.

and this is the result
while I would like to reach this result instead

can someone please help me?
Maybe there’s someone that use it with my same Canon lens or with Samyang/Rokinon.
Thank you in advance!
Bronco Oostermeyer avatar
Bronco Oostermeyer avatar
I would increase the step size (considerably).
HubSky avatar
HubSky avatar
Yes, increase step size.  The EAF takes 5,760 steps for one rotation and your graph is only about 1,500 steps.   Increase until you start getting a good U curve which will make the autofocus routine appropriately accurate.
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HubSky avatar
HubSky avatar
Sorry, it just hit me you're using a terrestrial lens.  You may not be able to use an autofocus routine with such a lens.  The autofocus routine has to be able to get sufficiently out of focus on both sides of the focus point for it to plot a good curve.  Some lenses have very little, if any, focus travel left past its infinity focus point.  If that's the case then the autofocus routine won't be able to get enough outside focus to do its job.  When you focus manually, check to see how much you can turn the focus ring beyond infinity.  It's also possible you may not realize that the EAF motor is stalling if the lens has hit its stop point when it starts the autofocus routine.
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Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
I use the EAF with a Samyang 135, I didn't need to do any modifications to it (although I have now). I didn't increase the step size from my normal 20-30. I did however manually set the zero and max travel values in the settings. Maybe switching it to reverse mode could help as well? Not sure what software you use, I use the Asiair so I can't comment on anything else.
GoldTop57 avatar
GoldTop57 avatar
I agree with step size adjustment as others have mentioned above - see this thread from the ZWO forum: https://bbs.zwoastro.com/d/12849-eaf-focus-issue


Good luck!
Steven Bellavia avatar
Steven Bellavia avatar
Is the lens auto-focus or manual?

If itt has a built-in motor for focusing, you might want to consider an Astromechanics adapter.  

https://astromechanics.org/

And if you really want to use the EAF, then check the infinite focus, as was mentioned.  You need sufficient room past infinite focus for the EAF to work.

Increasing the step size might help too, though the focus curve you presented does not seem to indicate that is the issue.
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Michael avatar
Michael avatar
I am having the same problem with my Rokinon 135 mm lens using the ASIAIR.  It was working well until the temps dipped below 0 F, and was no longer able to focus.  I removed the hard focus stop to be able to focus past infinity, but unfortunately I have had no opportunity to try this (fix?) out due to bad weather and severe cold.
Concise
Federica Panzarella avatar
Federica Panzarella avatar
Sorry, it just hit me you're using a terrestrial lens.  You may not be able to use an autofocus routine with such a lens.  The autofocus routine has to be able to get sufficiently out of focus on both sides of the focus point for it to plot a good curve.  Some lenses have very little, if any, focus travel left past its infinity focus point.  If that's the case then the autofocus routine won't be able to get enough outside focus to do its job.  When you focus manually, check to see how much you can turn the focus ring beyond infinity.  It's also possible you may not realize that the EAF motor is stalling if the lens has hit its stop point when it starts the autofocus routine.

Thank you for your reply!
But I’m wondering, if it’s not possible to use the EAF with terrestrial lens, with would be many adapters be available like this one I got? https://minenko.org/photastro/universal-on-ota-mounting-kit/
Federica Panzarella avatar
Federica Panzarella avatar
Steven Bellavia:
Is the lens auto-focus or manual?

If itt has a built-in motor for focusing, you might want to consider an Astromechanics adapter.  

https://astromechanics.org/

And if you really want to use the EAF, then check the infinite focus, as was mentioned.  You need sufficient room past infinite focus for the EAF to work.

Increasing the step size might help too, though the focus curve you presented does not seem to indicate that is the issue.

Hello and thank you for your reply! My lens is set to manual. Sadly I don’t have an astro camera yet but I use a Canon reflex so I don’t think I would need another adapter for the focus… I will try to increase the step size and see what happens!
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HubSky avatar
HubSky avatar
Federica Panzarella:
Sorry, it just hit me you're using a terrestrial lens.  You may not be able to use an autofocus routine with such a lens.  The autofocus routine has to be able to get sufficiently out of focus on both sides of the focus point for it to plot a good curve.  Some lenses have very little, if any, focus travel left past its infinity focus point.  If that's the case then the autofocus routine won't be able to get enough outside focus to do its job.  When you focus manually, check to see how much you can turn the focus ring beyond infinity.  It's also possible you may not realize that the EAF motor is stalling if the lens has hit its stop point when it starts the autofocus routine.

Thank you for your reply!
But I’m wondering, if it’s not possible to use the EAF with terrestrial lens, with would be many adapters be available like this one I got? https://minenko.org/photastro/universal-on-ota-mounting-kit/

I didn't mean to imply that it's not possible, only that it may not.  You have to check your lens to make that determination.  If it's an issue, some will adjust the stop point or remove the stop if it's possible and within their skillset.
Aleix Roig avatar
Aleix Roig avatar
Federica Panzarella:

Thank you for your reply!
But I’m wondering, if it’s not possible to use the EAF with terrestrial lens, with would be many adapters be available like this one I got? https://minenko.org/photastro/universal-on-ota-mounting-kit/

Great link. I’m considering a KIT for camera lenses and this one looks great and very solid.
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