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EAF & Celestron Electric focusers fitted onto SCTs - limits on total rotation?

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#1 carolinaskies

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Posted 20 April 2021 - 11:06 AM

Since the EAF has been introduced I've seen various posts about it being adapted to SCTs & Maks.  

As I understand it during calibration the EAF and the Celestron electric focusers should be establishing the endpoint limits of rotation.

Essentially the maximum steps available 'zero' to 'X'.   

Yet I've read a few posts online including on Facebook where users are hitting limits of rotation of the EAF/Celestron focuser supposedly where the are stopping even though the system is out of focus yet was able to achieve focus before. 
This seems odd to me that once the calibration is done properly the unit should easily obtain focus within the range. 

Unless I'm missing something the only mechanical limitation is the telescope focuser itself, rather than the stepper motor which should be able to turn until the limit is reached. 

One explanation I could see is perhaps someone had inadvertently turned the focuser while the unit was off thus the stepper would have an incorrect value for startup position?   Do these units store the stepper position once turned off?  



 



#2 insertnamehere

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Posted 21 April 2021 - 05:14 AM

I have a ZWO EAF on a C8. I use it for astrophotography and at most focus would change maybe 300/500 units over a night of imaging as temperature and angle changed.

 

The EAF has a range or 0 to 64k (16 bits of resolution). That works out to about 11 full turns of the focuser. From memory the C8 focuser full range is 35-40 full turns of the focuser. So the EAF can only cover around 25% of the C8 focus range.

 

It might be possible if you maybe changed to a focal reducer during the night that you could be outside the EAF range if it was centered in the EAF range before the focal reducer. Although I haven't tried this.

 

Chris

 



#3 carolinaskies

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Posted 21 April 2021 - 07:31 PM

I have a ZWO EAF on a C8. I use it for astrophotography and at most focus would change maybe 300/500 units over a night of imaging as temperature and angle changed.

 

The EAF has a range or 0 to 64k (16 bits of resolution). That works out to about 11 full turns of the focuser. From memory the C8 focuser full range is 35-40 full turns of the focuser. So the EAF can only cover around 25% of the C8 focus range.

 

It might be possible if you maybe changed to a focal reducer during the night that you could be outside the EAF range if it was centered in the EAF range before the focal reducer. Although I haven't tried this.

 

Chris

Hmm, I don't think it's that many turns of the C8... I'll have to check.  




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