Plate Solving w/ Narrowband filters


#1

I was reading in a book (The New CCD Astrophotography) that plate solving cannot be performed when imaging with narrowband filters. Huh?? I have a Starlight Xpress AO unit, OAG with mini filter wheel, and Trius SX-694 camera. The OAG has a pick-off prism in front of the filters, and I guide with a Lodestar 2X, using PHD2. I use either SGP or IP for image capture. Is it true that I cannot plate solve with SGP if I am using Hubble Palette filters? One other question…will my Moonlite auto-focus work with narrowband filters, or do I need to go strickly by using a Bahtinov mask? I am not sure how I am going to achieve focus with the guide camera in front of the filters. Thanks in advance for any help and suggestions.
Byron Labadie
Astronomy Club of Tulsa


#2

No, you can solve with any filter. Narrowband filters will just take a lot longer to solve with because they are much more restrictive in the data they allow to be captured. This is why we recommend that yoiu perform all solve operations with a LUM filter. LUM will typically solve well in most areas with 5-7s of exposure, whereas NB filters will require around 45s or more.

Again, this is something we don’t recommend. Your AF frames will need to be well integrated and AF will take a long time. This is why we recommend focusing with LUM and using known filter offsets between focus with LUM and focus with various NB filters.


#3

LUM as in Luminance? I don’t plate solve with my RGB filters either? I
still want to use my Narrowband set, can you point me to the direction I need
to learn how to plate solve using either LRBG or the three primary
narrowband filters? Sorry for my ignorance, forgive me. I will inquire with Astrodon
about NB filter offsets from LUM, once I figure out what LUM is.


#4

Yes.

Yes, you can plate solve or auto focus very easily with any broadband filter. It’s just NB that will give you grief.

Here is info on auto focus including info on overriding NB filters to use LUM instead:

http://mainsequencesoftware.com/Content/SGPHelp/AutoFocus.html

Once you do this, you will need to correct for the difference in focus between LUM and the NB filter you are using for imaging:

http://mainsequencesoftware.com/Content/SGPHelp/AutoAdjustFocusPerFilter.html

They probably won’t be able to help you much. True focus offsets are a property of the entire imaging train. This is likely an exercise you will need to conduct manually (at least one time… and then record the results in an equipment profile).


#5

Your time and help is much appreciated, thank you!
Byron


#6

I plate solve with narrowband filters (Baader and Astrodon) without any issues at all. The exposure needs to be longer of course to get more light to the sensor. Other than that they work flawlessly. This through a MN190 and WO ZZ6SD using an Atik 460EX and previously a QHY IMG2Pro. I now use Platesolve2 but Elbrus was just as reliable.

Works for me anyway.


#7

Good to know! Thank you!


#8

Same here. I have an STF8300M with the SBIG FW and I auto focus through my 3nm Astrodon NB filters all the time. It does take a bit longer, but as you said it works quite well. Now for plate solving, I always use my LUM filter. :smile:


#9

If I’m shooting mainly NB all night then generally will autofocus through the NB filter rather than offsets/LUM for best focus. Depends how temp sensitive your rig is too and how much time you think you’ll lose.

If shooting 20min or longer subs, I definitely don’t want to find out my LUM offset needs tweaking.


#10

Thank you for sharing.
Wasting a entire night with out of focus images would be bad. Something has
gone wrong in the night to all of us, I just like to keep those nights to
a minimum if at all possible. The more I learn, the better prepared I will
be.
Byron

In a message dated 2/26/2016 9:00:59 P.M. Central America Standard T,
forums@mainsequencesoftware.com writes:

 _RobF_ (http://forum.mainsequencesoftware.com/users/robf)

February 27
If I’m shooting mainly NB all night then generally will autofocus through
the NB filter rather than offsets/LUM for best focus. Depends how temp
sensitive your rig is too and how much time you think you’ll lose.
If shooting 20min or longer subs, I definitely don’t want to find out my
LUM offset needs tweaking.


#11

Yeah … I got a bit lost there. I focus (well you have to don’t you?) and plate solve through NB filters without any issues at all.

:slight_smile:


#12

If you’re using auto focus I’d always recommend using offsets for focus - it’s just much quicker and saves valuable imaging time.

As long as you find the focus point for each filter relative to luminance (and this needs to be calculated in fairly stable temperatures) you’ll always achieve excellent focus through offsets. I promise you won’t want to do it any other way once sorted. 9 x 5s for an auto focus run is so much more efficient than 9 x 45s!!!

Kit


www.mainsequencesoftware.com