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Expose BYE as an ASCOM focuser driver


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I like to use my Canon lenses as wide field APO lenses, but unless I'm shooting the moon, nothing is bright enough for the Canon's autofocus to work. If BYE could expose an ASCOM focuser interface, it could act as a communications translator between the various astronomical autofocus routines out there, and my canon camera with canon lenses.

The 3rd party AF apps work fine when my canon body is connected to a telescope focuser, but there is nothing that lets me do AF when I'm using my Canon lenses on the same body...

Thanks for listening!

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There are two issues with your request:

1) The Canon SDK only allows BYE to control the lens only when LiveView is active.

2) Autofocus software requires an absolute focuser. This is necessary to create a V-curve of focuser position versus star size. If an ASCOM focuser driver could be created to adjust a Canon EF lens, it would be a relative focuser where the focuser does not have an absolute position, but only accepts movement amounts.

You said "The 3rd party AF apps work fine when my canon body is connected to a telescope focuser, but there is nothing that lets me do AF when I'm using my Canon lenses on the same body...". I have a question and a commnet about that statement.

How do you connect your Canon camera to a telescope focuser? This does not seem possible.

Perhaps the reason that "there is nothing that lets me do AF when I'm using my Canon lenses on the same body..." is because it is not possible.

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Hi, Rick, a

8 hours ago, astroman133 said:

There are two issues with your request:

1) The Canon SDK only allows BYE to control the lens only when LiveView is active.

2) Autofocus software requires an absolute focuser. This is necessary to create a V-curve of focuser position versus star size. If an ASCOM focuser driver could be created to adjust a Canon EF lens, it would be a relative focuser where the focuser does not have an absolute position, but only accepts movement amounts.

You said "The 3rd party AF apps work fine when my canon body is connected to a telescope focuser, but there is nothing that lets me do AF when I'm using my Canon lenses on the same body...". I have a question and a commnet about that statement.

How do you connect your Canon camera to a telescope focuser? This does not seem possible.

Perhaps the reason that "there is nothing that lets me do AF when I'm using my Canon lenses on the same body..." is because it is not possible.

In order:

I did not realize that the Canon SDK only allowed focus control in LiveView; that does make it more difficult, though you could still work around it by taking an image, then switching to live view, moving the focus position, drop back out of LV, shoot another image, and repeat the cycle as needed. In addition, there is no hard reason that you would need to construct a V-curve for autofocus, and in fact Voyager, which does a much better job focusing than SGP does, does not. Instead, it does a statistical curve fit, but not even that is absolutely required. You could do it much more simply with relative movements by tracking the movement steps, and once your focus metric (HFD, FWHM, StdDev, etc) starts getting worse, move back to the position where it was best. You could of course do curve-fitting calculations or construct a v-curve with relative movements if desired, but that is not absolutely necessary.

As for your question, I connect the camera to a telescope focuser with a T-ring, just like everybody else does, and then the software controls the focuser. I assume you thought I meant that the camera was *controlling* the focuser, but no, that's not what I meant. It could certainly be done if you wanted to reverse-engineer the canon lens communication protocol and make a physical adapter and some electronics to translate between the canon focus commands and the focuser's commands, but that would be a huge effort.

 

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Yeah, I guess that the Canon engineers thought that it would not be useful to adjust focus when you cannot see the change that you are making.

I thought that you meant some type of controlling connection between the focuser and the camera. Duh!

Also, there is no guarantee that there even is a "Canon lens communication protocol". it could be that the camera drives the lens via analog voltage levels, like an ST-4 connection.

I am not saying that what you are requesting is not useful. But my guess is that it would be a major rewrite of BYE/BYN. With current versions it is not possible to switch from Imaging to Frame & Focus when a capture plan is active. A couple of years ago I suggested an enhancement that would allow the user to pause the capture plan between exposures, switch to F&F, re-focus, go back to Imaging and resume the capture plan.

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Well, maybe by the time I retire in a few years, I'll have my head around VB.NET well enough to tackle that project myself (just made a post about that over on the ASCOM dev group). Of course, I'll need to learn the Canon SDK at the same time...

Always something new to learn!

 

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