Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

Using SharpCap's Polar Alignment feature
bbbigca
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Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#1

Post by bbbigca »

Hi all,

I have been using my Celeron Evolution 8 mount with a wedge, manually aligning with its handset or its PC software CPWI. I am interested in using SharpCap's Polar Alignment (SCPA) feature to automate my alignment, vs. buying Celestron's StarSense Autoalign.

What I am puzzled about, is how SharpCap's alignment would work in conjunction with Celestron's own alignment...? In other words, would Celestron's CPWI be aware of SCPA's alignment settings, so that I can then use CPWI to slew to a target? Would I be able to Save and Load alignment in CPWI after SCPA?

My question is due to my ignorance around where the alignment data is kept in memory. I would think that it would be logical to store alignment data in the mount itself, but I get the impression that the settings get saved to the software that performs the alignment (i.e. handset, or CPWI), and they aren't interoperable?

Please help me better understand - much appreciated!
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#2

Post by admin »

Hi,

so there are two types of alignment going on here – firstly polar alignment gets your RA axis aligned properly with the Earth's rotation. Secondly there is what we might call a star alignment stage which is where your mount learns the mapping between RA and declination coordinates in the sky and the same coordinates in its own movements.

SharpCap takes over the first stage – getting the polar axis lined up. I presume that you can just skip that stage in the CPWI software and move on to the star alignment stage which SharpCap wouldn't be involved in. Note that the measurements that are made in the star alignment stage on many mounts will allow the software to compensate (at least in part) for any problems with the polar alignment or with cone error. My experience is that while that works to a degree, having the polar alignment just right and any cone error eliminated does help lead to better accuracy in go to movements.

Maybe someone who also uses the CPWI software and SharpCap's polar alignment will be able to comment further.

Cheers, Robin
bbbigca
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#3

Post by bbbigca »

Hi Robin,

Thanks for your prompt feedback. Yes, I realize polar alignment isn't going to do what I'm trying to do. That said, I am also finding that there are software that will allow me to also automate star alignment e.g. KStars (https://rasc-vancouver.com/2020/01/10/p ... alignment/). I imagine SharpCap could be updated to also support automated star alignment in the future?
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#4

Post by tmyers »

I am curious as to how any software program is going to adjust your Altitude and Azimuth knobs for you. They may tell you which direction and how far in Minutes and Seconds it has to be moved, but can't turn the knobs for you. Adjusting the Alt and Az is the only way to physically Polar align.
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#5

Post by admin »

Hi folks,

I must admit that I haven't got any plans to add functionality for the star alignment into SharpCap – that is usually fairly well handled by other software applications or even hand controllers, whereas with polar alignment it was a real struggle to find software that was both accurate and usable in the days before the SharpCap polar alignment functionality.

@Tim - I suppose you could imagine the altitude and azimuth adjustments being motorised – I'm not sure that there are any mounds where this is actually available as a feature though. Once you get to the point where that sort of feature makes sense as the best thing to add to amount you are properly at the price point where most people are going to be building observatories anyway.

Cheers, Robin
bbbigca
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#6

Post by bbbigca »

admin wrote: Tue Aug 18, 2020 6:00 pm I must admit that I haven't got any plans to add functionality for the star alignment into SharpCap – that is usually fairly well handled by other software applications or even hand controllers, whereas with polar alignment it was a real struggle to find software that was both accurate and usable in the days before the SharpCap polar alignment functionality.
Most star alignment requires manually locating/centering stars, which is PIA when you have an AP-only setup (that especially lacks absolute encoders). Since SharpCap's PA feature requires/uses a ~200mm scope+camera anyway, it would be great to also re-use that hardware for automated star alignment. Wouldn't it be a small extension of the Plate Solving feature (https://www.sharpcap.co.uk/sharpcap/fea ... te-solving)?
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#7

Post by admin »

Hi,

not really – the polar alignment feature in SharpCap is very much focused about dealing with stars near the celestial pole and makes a number of assumptions in the mathematics that are only valid if you don't stray too far away from the pole. Additionally, only caring about things within about 5° of the pole means that the star database doesn't need to be very large.

I think the sort of automated steps that you are wanting to run could be easily handled by the sequencing tool that will be available in the next version of SharpCap – basically you could have a sequence where SharpCap would go to each coordinate in a pre-determined list and once the GOTO was complete it would do a plate solve (using something like Astap or AstroTortilla) and then synchronise the mount to the solved coordinates. I think that would have the effect that you're looking for.

Cheers, Robin
go4launch
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#8

Post by go4launch »

This response is a little late for the original question, but just in case anyone else is using Celestron CPWI with a wedge and is interested in using SharpCap to perform a polar alignment, here is the process I used:

1) Level mount and point the wedge toward Polaris. I use the altitude screw as a pointer to get as close to North as possible.
2) Start CPWI and connect to the hand controller
3) Make sure lat/long and local time are set properly. Make sure the "Wedge Enabled" checkbox is checked.
4) Click on "Manual Alignment" and follow the directions to set the scope parallel to the plate facing due south. Use the index markers on the arm to make sure the scope is parallel to the plate.
5) Click on "Ready" once scope is point south and parallel to the plate. Then click on "Finished". Then click "Exit"
6) In the Celestron menu, click on Mount-->Disable Tracking
7) Now adjust the scope back to the Meridian by clicking on Mount-->Slew Controls and using the left/right arrow only to adjust until Right Ascension (RA J2000) exactly equals Local Sidereal Time (LST). You will need to set the slew rate to 1 or 2 for the final tuning to get timing offset between LST and RA to <1 second.
8) Now using only the up/down arrow keys, adjust the mount altitude until the Altitude readout exactly equals your latitude. Again, you will need to use a slew rate setting of 1-2 for the final adjustment to set altitude to <1 second of your latitude.
9) Start Sharpcap Polar alignment and follow the instructions
10) When instructed to rotate the mount 90 degrees in RA, use the CPWI slew control right arrow key to rotate approximately 90 degrees
11) Sharpcap will then prove and azimuth and altitude offset. Use the wedge azimuth and altitude screws to perform this final adjustment
12) Once you have an "Excellent" indication from Sharpcap, lock the wedge altitude and azimuth screws

You are now polar aligned. You just need one more tweak to make sure the mount is properly aligned in Right Ascension.

13) On the CPWI Menu select Mount-->Enable Tracking
14) On the CPWI Menu select Alignment-->Add Reference(s)
15) Select a star nearby the object you intend to observe/image and Click "Go To"
16) Use the slew control to place the star in the center of your eyepiece, or camera image
17) On CPWI click on "Centered" then click on "Finished"

You are now fully aligned. I find this process to be much faster than using the CPWI All Star Polar Align (ASPA), and also much more accurate. Using ASPA I tend to get drift during my imaging sessions, but using Sharpcap, I see almost no star drift during an imaging session.

Clear Skies!
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#9

Post by admin »

Thanks for sharing - glad to hear it worked well!

cheers,

Robin
StarManFlorida
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Re: Newbie very puzzled about how SharpCap Polar Alignment would work with Celestron CPWI

#10

Post by StarManFlorida »

To go4launch... Which hand controller are you using for your post #8 ?
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