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Narrowband: do you use a focus star?

1 month 3 weeks ago
MikeCEM60
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Narrowband: do you use a focus star? #61300
Seem like with my setup i have to run autofocus for each NB filter. Tried multiple strategies (full field/ donut/ subframe)(exposure times) but too often, with autofocus failing often after 20+ minutes, the scheduler aborts...

I would think a slew to a designated bright star would allow for much shorter exposure, and get more reliable results...

Would be interested in your thoughts/ strategy

Thanks,
Mike

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1 month 3 weeks ago
airscott
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Narrowband: do you use a focus star? #61303
Standard practice is to autofocus ONLY with L filter and then use measured filter offsets for all other filters (both board and narrowband).

But results depend A LOT on the composition of the image frame. There are some very difficult targets with few good stars in the frame, especially when imaging small fields in star-poor parts of the skies (ie, many galaxies).

It would be GREAT to have a simple option to specify a slew to a focus star as part of the autofocus system, tied to the scheduler so it's only triggered occasionally.

As long as we have reliable behavior in the "align" module, there's really no penalty for this hourly slew-and-return.

We can engineer this behavior by careful and tedious composition of sequences and schedules, but it's prone to error and logic gotchas.
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1 month 3 weeks ago
xsnrg
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Narrowband: do you use a focus star? #61324

airscott wrote: Standard practice is to autofocus ONLY with L filter and then use measured filter offsets for all other filters (both board and narrowband).


I've tried doing this, but for whatever reason, maybe even the flex in the filter disk or something as odd, I have better luck auto-focusing on filter change.

If the autofocus routine uses the offset as a starting point for the auto-focus run, that would be wonderful though.

Jim

12" pier with HDX110 using EQMod
ASI 1600 mono/color mains with ASI290MM in off-axis
ASI filter wheel
Moonlite focusers for the sharpening
AT115EDT w/.8x for the light
Fedora Linux, 100% INDI
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1 month 3 weeks ago
DerPit
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Narrowband: do you use a focus star? #61355

xsnrg wrote: If the autofocus routine uses the offset as a starting point for the auto-focus run, that would be wonderful though.


Hmm, but it's doing that, isn't it? At least for me, the offset is applied as soon as the filter changes. Then the AF is triggered, starting from that setting.
(I have AF on filter change set for all filters, and the respective relative offsets in the table).

As for NB, it might help to use near-by BB filters. I.e., for me the focus for Hα and R is basically identical. I don't have OIII, but could imagine its focus would be very similar to G? (At least if the filters are from the same manufacturer and have the same thickness). Then do a 'fake' BB exposure to trigger AF (AF on filter change set), then switch to NB (set same offset, no AF on change).

I myself do AF on Hα, but I do have a 6nm one. That is enough to get sufficient signal in 8s exposures (ASI1600 at unity gain).

openSUSE Tumbleweed KStars git INDI git
GPDX+EQMOD, CEM60EC, ASI1600+EFW+EAF+ASI290 mini
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1 month 3 weeks ago 1 month 3 weeks ago by xsnrg. Reason: added the actual focuser settings too
xsnrg
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Narrowband: do you use a focus star? #61361

DerPit wrote:

xsnrg wrote: If the autofocus routine uses the offset as a starting point for the auto-focus run, that would be wonderful though.


Hmm, but it's doing that, isn't it? At least for me, the offset is applied as soon as the filter changes. Then the AF is triggered, starting from that setting.
(I have AF on filter change set for all filters, and the respective relative offsets in the table).

As for NB, it <em>might</em> help to use near-by BB filters. I.e., for me the focus for Hα and R is basically identical. I don't have OIII, but could imagine its focus would be very similar to G? (At least if the filters are from the same manufacturer and have the same thickness). Then do a 'fake' BB exposure to trigger AF (AF on filter change set), then switch to NB (set same offset, no AF on change).

I myself do AF on Hα, but I do have a 6nm one. That is enough to get sufficient signal in 8s exposures (ASI1600 at unity gain).


It may very well be using the offset then. To be honest, I focus on every filter, so had not bothered to check closely. I am using an ASI1600MM as well, though at 75 gain for captures. I crank it up to 300 gain for auto-focus so that I can still do shorter subs and speed focus along a bit. My filters are all Astrodon finally, and supposed to be para-focal. I say supposed to be, because they are not, and they are off far enough to be very visibly noticeable. I will attach me settings for reference. The process tab has the new SEP Profile options that I have not played with yet.


12" pier with HDX110 using EQMod
ASI 1600 mono/color mains with ASI290MM in off-axis
ASI filter wheel
Moonlite focusers for the sharpening
AT115EDT w/.8x for the light
Fedora Linux, 100% INDI
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