Old 17-05-2010, 03:14 PM
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Automated Focusing

I am looking for recommendations re automating focus on my 127 ED Triplet, I could fit a robofocus to the current focuser or purchase a complete new moonlight unit. I do not have a large heavy CCD at present but I do have ambitions - an I think the focuser could move with me to a future scope if I choose the right one....

The reason I am interested in doing this is the need to make (small) focus adjustments to get best focus with each of the individual LRGB or Ha-Oiii filters in the automated sequences I use. It would be great to be able to focus each filter once and then have the unit be able to return to the correct spot automatically thereafter so I really need something robust that stays accurate after many cycles, even better if these focus positions can be found automatically also.

At present I tend to use LRGB or Ha-Oiii in loops to ensure that I have some useable data in the event clouds roll in rather than 16xL then 16xR etc.

What is recommended - L focus, R focus, G focus, B focus seems a little heavy on the focuser so perhaps some compromise is usual?

Any views or experiances (eg is temp compensation required) with automated focusing pros/cons and recommendations are welcome...
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Old 17-05-2010, 04:31 PM
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Bassnut (Fred)
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There are several temp compensated focusers out there, the Optec TCF-S I have springs to mind, but the robofocus has temp options. I dont use the temp function, its a ***** to calibrate, but it maybe worth it on a refractor. SCT focus is less critical.

Maxim DL has a filter focus offset function, so you only focus each filter once, enter the difference focus count in the filter set up, and thereafter you only focus on one filter and the offset is applied automatically to the others as you use them. Saves a lot of time.
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Old 17-05-2010, 05:59 PM
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John the moonlite stepper with moonlite controller works well in Maxim along with focus max. Temp compensation is built in (unlike the ceris option) and all focusing is very repeatable. Very robust and precise units for AP. As Fred says, setting up the temp compensation is a right pain in the backside.

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Old 20-05-2010, 01:33 PM
jase (Jason)
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Robofocus is repeatable and works to give the level of automation required to operate remotely. Coupled to FocusMax, you'll hit the critical focus zone of your imaging system time again.

Temp control is a waste of time. If you've got the right tools to automate focusing, the focus routine will be quick and efficient thus it is easier to simply refocus every so often. Fred highlights focus offsets which I'm also an advocate for. Other than refocusing between filter changes, focus offsets are the next best alternative. Save time allowing time for data acquisition...which can only be a good thing. Simply use the luminance/clear filter as the reference and calculate from there. These can be configured in most data acquisition tools such as MaximDL. Make sure you average your results over several runs to improve the accuracy of the offset calculation.
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Old 21-05-2010, 06:26 AM
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Thanks Guys, great info!
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