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Lve View and focusing Artemis


Daniel-K
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last night i couldnt get a decent image mainly down to the fact i could not get decent focus.  i was using a 1 sec loop and the stars would show as round but then  id take a 30 sec sub and they where out of focus.

 

what is the best way to focus.

camera is atik 414EX

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Take a three second sub in Bin 1 to average out the seeing. (Too short and the seeing causes the stars to 'boil' in the turbulence.)

Pick a not-too-bright star and draw a box round it.

Double click on the star to bring up the focus window (or open it from the toolbar then click on the star.)

Set the camera to loop in three second unbinned subs and watch the Brightness and Full WIdth Half Max windows. If the brightness reaches 65000 counts you need a fainter star. The FWHM is measuring the width of the star at half its maximum brightness so you want to get that value to be as low as possible.

56c1da728ba0d_FWHMEXPLAINED.thumb.jpg.10

Your other option is to use a Bahtinov mask. I find it quickest to use a B mask and then perfect the focus in FWHM. I also found that on a big, long focal length reflector, FWHM was meaningless and jumped all over the place.

Olly

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14 minutes ago, ollypenrice said:

Take a three second sub in Bin 1 to average out the seeing. (Too short and the seeing causes the stars to 'boil' in the turbulence.)

Pick a not-too-bright star and draw a box round it.

Double click on the star to bring up the focus window (or open it from the toolbar then click on the star.)

Set the camera to loop in three second unbinned subs and watch the Brightness and Full WIdth Half Max windows. If the brightness reaches 65000 counts you need a fainter star. The FWHM is measuring the width of the star at half its maximum brightness so you want to get that value to be as low as possible.

56c1da728ba0d_FWHMEXPLAINED.thumb.jpg.10

Your other option is to use a Bahtinov mask. I find it quickest to use a B mask and then perfect the focus in FWHM. I also found that on a big, long focal length reflector, FWHM was meaningless and jumped all over the place.

Olly

 

thanks Olly MY FL IS ONLY 1370 not that big compared to a SCT i dont think. 

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