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RE: Frame & Focus using a 5nm H-a filter



Greetings to the Backyard EOS collective....


I have a question to ask....is there a means within the software to frame & focus using a 5nm Ha filter?


How can I adjust the number of frames that BYE uses from Live View for focusing...

I need to use a larger number.


Looking forward to a response.



The only good photon ....is an old photon


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Well, using a narrowband filter for focusing with LiveView Frame and Focus is very difficult. The LiveView single frame exposures are very short, in order to maintain the maximum frame rate. There is nothing that BYE can do to lengthen them.


You can adjust the number of frames that BYE uses to measure the FWHM focus value by changing the FWHM Average value on the Settings screen. You may want to do that anyway if you have less than perfect seeing.


My suggesting is to get a rough focus using LiveView, without the filter and then take Snap Images to get a fine focus after inserting the Ha filter.  Even with that, you will need a star that shows strongly in Ha or you may need an exposures of several minutes. BYE does support this method of focusing.


DSLR cameras are pretty versatile, but using them for narrowband imaging is very challenging. I tried an Ha clip-in filter in an older Canon and even after a 20 minute exposure the histogram was still plastered against the left hand side of the graph. I haven't used it since.

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As Rick said get a rough focus without the NB filer first.


Then (with your NB filter installed) use the loop feature in the Frame&Focus mode.  Use a high ISO, say 3200 or 6400 and set the exposure to 15 seconds and start snapping pictures (adjust the exposure in 5 seconds increment if you find 15 seconds is not enough).  You may want to set a pause of say 5 to 10 seconds to allow you to adjust focus in between exposures. 


The process should take you anywhere from 2 to 5 minutes to reach focus and I find focusing with a NB filter a lot easier when using a Bahtinov mask as well.

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NB Imaging always stretches the bounds of one's AP Imaging Skills.


Depending on your Rig and Setup, you may a Filterwheel or Filter Slide and be able to switch to a Clear Filter for these Frame&Focus Steps.

But, from the thrust of your question, your setup doesn't allow this - at least not without disassembling part of the Rig (thus ruining your Focus if not your Framing).


So, you'll need to:

1) Before you add the NB Filter, use your Mount's Precision Alignment Routine to establish the most accurate Sky Map that you can.  Slew to the general area of your Target, and Get your Polar Alignment and AutoGuider Calibration and other "Setup Chores" done.  Still before adding the NB Filter, perform your Framing effort.  Use its Bookmark / Sync / Precision Goto feature to "memorize" your Object Framing.  Mark or Note your Camera Orientation.  Make sure that your Tracking is ON, and everything would be "Ready-to-Go" for Focusing and Imaging.

2) Slew to a Very Bright Star within the same quadrant of the Sky (Mag 0-2 stars - Vega, Arcturus, Deneb Altair - not a Planet).  Perform a Rough Focus without the NB Filter.  Mark or Note the Focuser Location.

3) Carefully remove your Camera (without bumping your Mount/Scope) and Add your NB Filter.  Reassemble the Camera to the Scope, and readjust to the Marked Rotation and Focuser Positions.

4) Perform your Focusing Effort on that Bright Star (should still be in Center of your FOV).  Use the High ISO and Long Exposure Settings suggested by Rick and Guylain.  

5) Now, Slew back to your Target - using whatever steps best utilize the Bookmark / Sync / Precision Goto performed above.  Still with High ISO, perform a couple of Test Exposures to confirm your Framing is still acceptable.  When done, remember to reset your ISO.

6) Finally, turn on your AutoGuiding.  Invoke your Imaging Plan.  Sit Back, and examine your Images as they complete.

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