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This good stuff, but in the end i recommend running autofocus on filter change . Your are not likely optimally focused anyway due to falling temperature!
Hi! Really interesting information. I run one filter (or no filter) on an OSC camera. When discussing with my sales rep they informed me to deal with the filter offset via shims that I’ve placed on the camera, behind the spacer. They indicated the filter would require a chance to back focus. This effectively pushes my camera sensor back by the amount of offset specified by the filter manufacturer. I do not have offsets defined (Ekos). Once my OAG camera is focused I generally do not need to touch it. Autofocus is working fine with filter and shims. Removing filter (filter drawer, not automated) and shims does require an OAG refocus. Would you recommend that I begin using software offset configuration or is what I’m currently doing equivalent? Did they give me bad info? My results have been good so I have not pursued any changes. Thank you, Cheers!
Great question! They did not necessarily give you bad info :) First, could you share some more information about your equipment? Do you have some kind of flattener or reducer? If you don't have a flattener or a reducer, you shouldn't have to worry about back focus. If you do have a flattener or a reducer, back focus is important to get right. But in my experience, in most cases, it is not critical to get back focus absolutely perfect. Being within 1mm of the ideal value is probably fine for most people (there are notable exceptions, mostly with super fast telescopes...) Once you've achieved good back focus, you don't need to mess with your shims. Which is why I strongly recommend that you look into filter offsets, and applying them via software, even if you use a manual filter wheel or a filter drawer. Hope this helps!
@@darkskygeek thanks so much for the reply! I run a field flattener (55mm back focus) -> OAG -> filter drawer with a duo-narrowband at 1.85mm filter thickness -> standard ZWO camera spacer-> .9mm shim stack -> camera. So my shim offset to backspacing is + .9mm. .9mm was derived from .5 filter thickness of 1.85mm rounded to as close as I could get. I would be happy to ditch the shims as I feel they’ve introduced a small amount of tilt. I will set it up in software and remove the shins.
Good but better to just keep it simple, run a single filter per night and adopt a slow burn multi-night project mentality. Ha one night, Sii another night and Oiii when the moon is down. KISS. These targets only really begin to look a cut above the rest at around 25+ hours total integration time anyway.
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