Does plate solving replace alignment

[joecoyle]

Hi

I was talking to a friend last night about plate solving.  I've never managed to be successful with it yet, but that's by the by. 

He said he doesn't do star alignments. 

Does plate solving replace the need to run a 2 star align? I would normally run a 2 star align and the all star polar align on the AVX. 

If plate solving does negate alignment (either 2 star or ASPA) what would my new setup procedure be? 

Seems strange to not interact with the hand controller at all  

 

Thanks

Joe

 

 

[Tinker1947]

i have the idea that Plate Solving tells you what you looking at and will align your sensor so images will line up, if the original image the PA was out the the plate solved position to my mind will be out as well.....???

[red dwalf]

i use astro tortilla to plate solve and it works a treat, i use it with eqmod and ascom compatible devices, i haven't used the hand set it years, good polar alignment still helps with guiding so is still important,but what i do is start from parked position, choose a target with stellarium and slew to it, run astro tortilla and it takes an image and plate solves and once solved slews to centre on the target, if your using eqmod, one thing to remember is make sure any saved targets in eqmod is cleared and set it to never save, i`ve found astro tortilla doesn`t work with saved targets in it`s memory.   

[Thalestris24]

Hi

Yeah, platesolving via Astrotortilla or APT replaces star alignment but not polar alignment. Lightt Vortex has a good step by step tutorial for setting up AT. I only use my AVX hand controller as a computer interface

Louise

[joecoyle]

Thanks Louise. I've got APT. So, how do you polar align the mount without running the all star polar align on the AVX? Once I power on, I can't do anything with my hand controller except enter the time then choose an alignment method... I feel I'm missing a step. 

Thanks

Joe

[joecoyle]

So to add a little more: I've just experimented with plate solving / slewing the scope using ASCOM. This is what happened:

1. Enter date / time on hand controller.
2. Brought to the alignment screen.
3. Without doing an initial alignment, neither SGPro or Cartes du Ciel would slew to an object. 
4. As soon as i did a one star align on Vega, then SGPro and CdC slewed the scope in the rough right direction.
5. Plate solved a reference image from AstroBin, solved correctly and then SGPro slewed to the target.

In conclusion, it seems that the mount needs at least one star in its model to orientate itself. So plate solving alone wont replace all the alignment steps.

Would this be an accurate statement?

Cheers

Joe 

[Thalestris24]

Hiya

When I first got the avx I did a single star align. Ever since I've had the hand controller plugged in to the mount so that it keeps its settings via the rtc battery. I just power on, accept the time/date etc and select last alignment. After that I drift align with PHD2 drift align tool. In practice I only do that from time to time as my mount doesn't move. Before I zip through the hand controller menu, but after switching on the mount, I get  Stellarium/Stellariium scope up and running. This is because after last alignment is selected the avx starts tracking and Stellariumscope will throw an error.

I've only used Astrotortilla  to date. I use APT for image capture but haven't got around to trying its platesolving yet.

Louise

[Big Bang!]

I have just entered the world of plate-solving using Sequence Generator Pro - thanks to members of this forum. I have a 10 Micron 1000HPS and have hitherto been using star alignment - either visually using a reticulated eye-piece or visually my imaging camera for centring stars.  I was getting satisfactory results, good enough to go 10 minutes unguided but that is nothing spectacular for mounts that can easily go well over 30 minutes.  I had to learn to plate-solve.  The question became, What software do I use?  Following advice here I went for SGPro combined with PinPoint.  I needed a bit of coaching from ChrisH but within a couple of evening's work plate-solving has become quick,easy and substantially more accurate.

 

I use Stellarium to point to anywhere in the sky (not necessarily at a star). The first three align points take me about 40 seconds and subsequent ones take less than a couple of seconds. SGPro sends each set of align data into the mount and builds the model for you.  I've idea how your rig works but a new model is now about 20 minutes work for me because I no longer have to centre on stars.  

Gus

[chrisshillito]

Platesolving alone is simply a means to find out where you are pointing and does not correct anything. However some tools combine platesolving with iterative goto's that will get you to target by adjusting the next goto to take into account the error between target position and the actual position reported by the plate solve  - alternatively they may issue a sync to the mout driver (which does the same thing) and with EQMOD this can be used to create an aligment model as well ! 

Plate solving with a tool like astrotortilla doesn't replace alignment beause it is alignment, you just don't know you're doing it.

Chris.

[Thalestris24]

50 minutes ago, Big Bang! said:

I have just entered the world of plate-solving using Sequence Generator Pro - thanks to members of this forum. I have a 10 Micron 1000HPS and have hitherto been using star alignment - either visually using a reticulated eye-piece or visually my imaging camera for centring stars.  I was getting satisfactory results, good enough to go 10 minutes unguided but that is nothing spectacular for mounts that can easily go well over 30 minutes.  I had to learn to plate-solve.  The question became, What software do I use?  Following advice here I went for SGPro combined with PinPoint.  I needed a bit of coaching from ChrisH but within a couple of evening's work plate-solving has become quick,easy and substantially more accurate.

 

I use Stellarium to point to anywhere in the sky (not necessarily at a star). The first three align points take me about 40 seconds and subsequent ones take less than a couple of seconds. SGPro sends each set of align data into the mount and builds the model for you.  I've idea how your rig works but a new model is now about 20 minutes work for me because I no longer have to centre on stars.  

Gus

Hi

With plate solving you don't need a model though having one can reduce the number of plate solves you do. On the other hand it might only take 10 secs to plate solve a target. PA still needs to be good to prevent field rotation and drift with long exposures especially if unguided. I suppose it has to be spot-on for unguided imaging.

Louise

[Big Bang!]

Hi Louise,

Using plate-solving I have recently got my PA down 0' 24"  whereas before I had difficulty getting below about 1' 15" - so it has definitely improved things.  To date I have not had noticeable field rotation at 15 minutes unguided - I expect to eventually get to 30 minutes unguided with this mount as I improve my modelling.

I am very new to this and in my very brief experience I have found that once SGPro has built a basic model into the mount subsequent images usually solve within 2 seconds.  This enables a very comprehensive model to be built in very shot order and I understand this is the key to long unguided exposures.  If the mount doesn't have a model then presumably you have to guide in order to to track accurately?  

 

Gus

[Thalestris24]

Hi

Guiding is to correct small errors in PA and mechanical (tracking) errors. High end mounts can track accurately for quite long periods e.g. maybe 30mins, without guiding. Platesolving makes for accurate goto by calculating and correcting positional errors.

Louise

[saac]

Louise,  probably a bit of a silly question, and apologies to Joe for side tracking the thread, but does guiding in any way correct for any misalignment in polar alignment?  From your post above I would guess not but I just wanted to get my head around this as it's one of the next hurdles for me.

 

Jim

[Thalestris24]

41 minutes ago, saac said:

Louise,  probably a bit of a silly question, and apologies to Joe for side tracking the thread, but does guiding in any way correct for any misalignment in polar alignment?  From your post above I would guess not but I just wanted to get my head around this as it's one of the next hurdles for me.

 

Jim

Hi

It should correct the small errors caused by slight polar misalignment. These small errors can be used to some advantage by telling the guiding software to correct errors in DEC in one direction only i.e. against the drift in DEC caused by misalignment. What constitutes a 'small error' will effectively be dictated by your scope focal length.

Louise

[saac]

Thanks Louise, I had always wondered just exactly what guiding could compensate for in any error in polar alignment.  I'm just getting familiar with my AZEQ6 at the moment and guiding will be the next step for me.  I guess spending time refining polar alignment would mean there is less reliance on correction from other parts of the system.  So much to learn.

 

Jim

[Thalestris24]

9 minutes ago, saac said:

Thanks Louise, I had always wondered just exactly what guiding could compensate for in any error in polar alignment.  I'm just getting familiar with my AZEQ6 at the moment and guiding will be the next step for me.  I guess spending time refining polar alignment would mean there is less reliance on correction from other parts of the system.  So much to learn.

 

Jim

Hi Jim

I think with any typical mount you'll get periodic error, at least, and guiding will compensate for that. PA error will vary with what part of the sky you're pointing at but will be 'amplified' by scopes with a long focal length. A short refractor is probably the easiest scope to image with

Louise