Star adventurer Pro - alignment

[SStanford]

Hi all, 

I have what might be a silly question regarding alignment of the start adventurer:

Are you able to align the mount without being in sight of Polaris? 

I'm weighing up my mount options and was curious if this is possible. Most of my AP will be done from my balcony and unfortunately the North star isn't visible at all from this point. 

S. 

[Davey-T]

If you've got a south and east view you can drift align or use the DARV system pointing south.

Dave

D.A.R.V (Drift Alignment by Robert Vice) - Articles - Articles - Articles - Cloudy Nights

[SStanford]

47 minutes ago, Davey-T said:

If you've got a south and east view you can drift align or use the DARV system pointing south.

Dave

D.A.R.V (Drift Alignment by Robert Vice) - Articles - Articles - Articles - Cloudy Nights

That's great, thanks! 

Unfortunately I'm only able to make 30 second exposures with my dslr so it seems go-to is my only option. 

[Davey-T]

7 minutes ago, SStanford said:

That's great, thanks! 

Unfortunately I'm only able to make 30 second exposures with my dslr so it seems go-to is my only option. 

Something like the SW Star Adventurer should work fine with a DSLR using DARV to align it, doing a three star GoTo alignment might prove tricky depending on your view.

Which DSLR have you got ?

Dave

Edited November 29, 2020 by Davey-T

[SStanford]

30 minutes ago, Davey-T said:

Something like the SW Star Adventurer should work fine with a DSLR using DARV to align it, doing a three star GoTo alignment might prove tricky depending on your view.

Which DSLR have you got ?

Dave

I have a Canon 450d.

Yes, I'm a little stuck as I need a mount but I'm not sure if splashing out on a HEQ5 would be best if I'll struggle to align properly. 

I asked a similar question in an earlier post and was relieved to hear its possible to align without Polaris using 2/3 star with go-to. 

[Davey-T]

37 minutes ago, SStanford said:

I asked a similar question in an earlier post and was relieved to hear its possible to align without Polaris using 2/3 star with go-to.

You can use the Canon Utilities for longer exposures or an intervalometer

Depends on the choice of stars you get, some mounts are very limited and don't give you the option to choose ones you can actually see.

Dave

Edited November 29, 2020 by Davey-T

[SStanford]

15 minutes ago, Davey-T said:

You can use the Canon Utilities for longer exposures or an intervalometer

Depends on the choice of stars you get, some mounts are very limited and don't give you the option to choose ones you can actually see.

Dave

Thanks Dave, 

Do you know if the EQ3 Pro offers a comprehensive range of stars to choose from? 

I'll be limited to a selection in South to East. 

[Davey-T]

1 hour ago, SStanford said:

Thanks Dave, 

Do you know if the EQ3 Pro offers a comprehensive range of stars to choose from? 

I'll be limited to a selection in South to East. 

Sorry no idea, may be an online manual.

Dave

[Seelive]

I assume all the SW EQ goto synscan mounts have the same data base that includes over 200 alignment stars. Obviously not all of them will above your horizon at any particular time and if you've only got a limited area of the sky available it can taken some time to scroll through the list to find 2 that are visible to you (if you've only got a limited sky view then I wouldn't even consider 3 star alignment!) But are you confusing mount alignment with polar alignment? They are not the same thing and for astrophotography polar alignment is the critical thing, the goto mount alignment just helps to find objects easier (and relies upon having a reasonable polar alignment to start with).

[SStanford]

6 hours ago, Seelive said:

I assume all the SW EQ goto synscan mounts have the same data base that includes over 200 alignment stars. Obviously not all of them will above your horizon at any particular time and if you've only got a limited area of the sky available it can taken some time to scroll through the list to find 2 that are visible to you (if you've only got a limited sky view then I wouldn't even consider 3 star alignment!) But are you confusing mount alignment with polar alignment? They are not the same thing and for astrophotography polar alignment is the critical thing, the goto mount alignment just helps to find objects easier (and relies upon having a reasonable polar alignment to start with).

With a limited sky view, what would you recommend instead of 3 star alignment? 

So without polar alignment, astro photography is useless using 2/3 star alignment, even if you're using a wide view scope? 

[SStanford]

Sorry to bump the topic!

Having done a little more reasearch, I'm wondering if the following combined would provide alignment good enough for widefield AP on a EQ3 pro?

 - Rough Polar aligment as outlined by @Terrierist here: https://stargazerslounge.com/topic/323882-polar-alignment-during-the-day-polaris-not-visible-in-northern-hemisphere/

 - 2/3 star aligment

 - Guidescope/cam connected to EQ3 to reduce tracking error

I'm thinking that a loadout like this with a much smaller, dedicated AP scope (Redcat?) will allow at least 30s/1m subs?

I've had a look at drift alignment as an option as Polaris is out of sight; looking at various vdeos this seems to require state of the art kit/much clearer skies than those offered by Harrow!

Let me know your thoughts.

[Davey-T]

When Imaging I don't bother with star aligning, just sync on a bright star near to the target.

You can use PHD to drift align just get a star in the cross hairs and see which way it drifts, with guiding switched off obviously 😄

Dave

[Seelive]

To quote my SynScan manual for 3-star alignment of EQ mounts "Preconditions: The skies of both sides of the meridian are clear of obstructions." So if you only have access to the sky between E and S I would suggest 2-star alignment. You should be able to select 2 alignment  stars to the E of the meridian.

Once star aligned, SynScan will tell you the polar alignment error so you could make adjustments at that point and repeat the process or do the same using PHD to drift align.

If you are guiding then, even if your polar alignment is poor, the guide software will keep the guide star in the same place. Unfortunately, any polar misalignment will cause all the other stars to appear to rotate around it. The amount of rotation is determined by the polar alignment error and the exposure time so short exposure times will negate large polar alignment errors as will short focal lengths. Their have been a couple of papers published in the Journal of the BAA that have dealt with estimating the expected field rotation based upon the polar alignment error. A very old one (1989) based upon using film (rather than digital sensors) can be found here:

http://adsabs.harvard.edu/full/1989JBAA...99...19H

But an internet search for "astrophotography field rotation due to polar alignment" should give more up to date information. 

[SStanford]

1 hour ago, Davey-T said:

When Imaging I don't bother with star aligning, just sync on a bright star near to the target.

You can use PHD to drift align just get a star in the cross hairs and see which way it drifts, with guiding switched off obviously 😄

Dave

Apologies for my ignorance, quite new to this! When you say sync to a bright star is this one star alignment? 

53 minutes ago, Seelive said:

To quote my SynScan manual for 3-star alignment of EQ mounts "Preconditions: The skies of both sides of the meridian are clear of obstructions." So if you only have access to the sky between E and S I would suggest 2-star alignment. You should be able to select 2 alignment  stars to the E of the meridian.

Once star aligned, SynScan will tell you the polar alignment error so you could make adjustments at that point and repeat the process or do the same using PHD to drift align.

If you are guiding then, even if your polar alignment is poor, the guide software will keep the guide star in the same place. Unfortunately, any polar misalignment will cause all the other stars to appear to rotate around it. The amount of rotation is determined by the polar alignment error and the exposure time so short exposure times will negate large polar alignment errors as will short focal lengths. Their have been a couple of papers published in the Journal of the BAA that have dealt with estimating the expected field rotation based upon the polar alignment error. A very old one (1989) based upon using film (rather than digital sensors) can be found here:

http://adsabs.harvard.edu/full/1989JBAA...99...19H

But an internet search for "astrophotography field rotation due to polar alignment" should give more up to date information. 

This is really useful, thank you. Field rotation error is another new area to explore! 

Can you suggest a guide scope and camera that would work well with eq3 pro/redcat (wide field) scope and dslr? Weight limit is my main concern.

Thanks again. 

[Davey-T]

34 minutes ago, SStanford said:

Apologies for my ignorance, quite new to this! When you say sync to a bright star is this one star alignment? 

Basically yes but you get to choose your own star.

I use this but probably cheaper options

ZWO Mini Finder-Guider & ASI120MM-Mini Bundle | First Light Optics

Dave

 

 

[Seelive]

1 hour ago, SStanford said:

Can you suggest a guide scope and camera that would work well with eq3 pro/redcat (wide field) scope and dslr? Weight limit is my main concern.

Thanks again. 

The combination suggested by Davey-T would certainly be capable of guiding a 250mm scope with a Canon 450D (and as he says, slightly cheaper options are available).

[SStanford]

Thanks chaps, very helpful.