polar alignment with DSLR question

[graham.hobart]

Most of the time I have my DSLR set up with my scope so I wondered about using drift on an exposure to drift align?
Say, for example a star above me on the meridian (I don't have direct nth or south horizons) or as low in the north as I can get- take a 240sec exposure and keep adjusting RA till no slurring of stars.
So do the same in declination east, -keep adjusting till rounder stars at 240sec
Or would it be hideously slow and drawn out as I would affect the dec everytime I adjusted RA and vice versa?
Just some thoughtage
Graham:question:

[rcheshire]

I use a similar method depending on cloud cover to the South; as follows

10 sec exposure - star drift?

20 secs - star drift ?

40 secs - star drift ?

60 secs - star drift?

If stars drift? correct in azimuth/altitude and take next exposure, 20, 40, 60 as before and so on as required. Generally, round stars at 60 secs means round at 180 secs, or so as a rule with this method.

It's also easier to interpret drift if the camera square; that is the base of the camera is level.

I guess you could start at any exposure time, but the method above very quickly identifies gross error. Not much point starting at 30 seconds only to find trails 10mm long. These would have been evident at 10 seconds.

Tedious to say the least.

Cheers

Rowland

[mswhin63]

I use EQAlign but it does not support DSLR. It uses drift alignment while I can limit it to 240 seconds, I actually leave it for nearly 10 minutes while I do something else. I have found drift alignment to be extremely accurate.

The only program that I know of that provides an automated drift alignment with DSLR is APT (Astro Photography Tool) not sure about any others. It works but I prefer my EQAlign method better.

[graham.hobart]

I use a similar method depending on cloud cover to the South; as follows

10 sec exposure - star drift?

20 secs - star drift ?

40 secs - star drift ?

60 secs - star drift?

Rowland, when you say 'to the South' do you mean you do all your adjustments to the South? I have a house in the way so I would be very high in the South - my roofline is where achenar was last week (sans clouds)
About 45-50 degrees by guestimate..nothing below that but color bond and timber!
Graham:thumbsup:

[rcheshire]

Hi Graham. Sometimes there is cloud to the South and no chance of optical polar alignment, whereas the rest of the sky remains clear. Alignment is performed in the area of sky to be imaged. I can't image near the horizon from my place in any case, consequently, most is near zenith 30 - 40 degrees either side.

The best way is with a proper reticule eyepiece.

[mswhin63]

Graeme this is the primary reason I set-up a guide scope because my house also misses badly South although it still requires some southern stars for more precise alignment but with the guide-scope alignment there is an option for Azmith adjusted accurately. Fortunately for me I have views in some parts of the house that have 30 degree view but my primary position is 40 degrees North, South and 25 degree East. It is really hard to align. West for me at 10 degrees is just plain light pollution and almost unusable.

[graham.hobart]

just had a look at the EQalign and apart from my lack of Spanish it looks good- could not get the link to the SSAG.DDL to work though-has anyone been succesful using an SSAG with this programme and how did they get it to work?
Graham

[mswhin63]

According to the website you need to copy the SSAGIF.DLL file into the EQAlign folder. Can't offer anything more than a webcam.

Just a point, I have been able to get really good polar alignment but have not been able to try guiding so I currently use PHD for that.

Also once you have downloaded EQAlign then do a check for update as there is a version 3 available but not generally.

[DavidTrap]

There's a technique where you move the mount with your keypad (assuming you have one) back and forth in the RA axis. If you have drift, it will create a "V" shaped line. If you wait 10sec at the start, before slewing 20sec forward and 20sec backwards, you will get a bright blob on the V, so you can work out where the line started.

As you correct for drift, the two lines of the V come closer and closer together, before eventually becoming one straight line.

Obviously, the amount of drift demonstrated by this is dependant on your focal length.

It works quite well and only takes ~1minute per exposure.

DT

[graham.hobart]

As you correct for drift, the two lines of the V come closer and closer together, before eventually becoming one straight line.

Obviously, the amount of drift demonstrated by this is dependant on your focal length.


David- I have seen this technique on line but never used it- do you use the meridian RA only or then do the same for DEC in E/W also?

According to the website you need to copy the SSAGIF.DLL file into the EQAlign folder. Can't offer anything more than a webcam.

That's the problem- on the EQalign website (source forge) the link for the SSAGIF.DLL is not working.
Just an aside- Mal, I do have a webcam that I have never used for guiding as I have always used the SSAG- what camera settings would you initially use to make it easier to get guide stars? (Philips Toucam)
Cheers
Graham

[DavidTrap]

You only ever slew in RA. Adjust in azimuth when pointing towards the zenith and altitude when pointing towards the horizon.

DT

[mswhin63]

I use a regular (electrically) unmodified vAgent from www.liquiddigital.com.au camera that I have had for a couple of years now, Guiding software using frame stacking to give fainter stars to work, generally on PHD I set the slider to 80% and the time to 2-3 seconds. EQAlign I leave it mostly default as I only use it for polar alignment at the moment, sometimes though I set it to "SUM" x 2 or 3 to stack. I will be trying to work out later this year why it doesn't guide for me.

I use EQMOD pulse-guiding though as I have not built the ST4 guide package as yet.

[bartman]

Hi David, ( and Graham)
Just to double check....( I havnt done this method before, but have read about it, and this has now sparked my curiosity again) ...when you say 'zenith' does it have to be the zenith or can it be anywhere between the southern horizon and zenith along the meridian?
And for Alt anywhere above the horizon directly E or W (Keeping it as low as possible of course)?
Ive worked out which way to turn the mount for Az..... gotta put my thinking cap on for Alt now:D
Cheers in advance!
Bartman

[mswhin63]

I imaged last night to clarify something, EQAlign uses a different type of polar alignment method but similar to Drift alignment. Drift alignment shuts down the motors and makes a comparison to the projected path whereas EQAlign uses PEC data from the normal mount control without guiding.

2 Screen shots:

1 - East or West stars for ALT adjustment
2 - Meridian not Zenith for AZ adjustment. (Think some programs work zenith only)

Last night as for the past couple of weeks it has worked really well for me where all other methods have failed almost completely. Only Alignmaster stands a chance but the elevation is still an issue.

I am only imaging starting from today when I go out to ASWA event as tomorrow is my official Uni busy period. I can take some screen shots when i go there maybe.

[jenchris]

I use APT - with the cross hairs and x10 live view.
set it on a star in the east to change alt and one at zenith to do E/W.
it takes about 20 mins to get VERY close (well inside PHD tolerance.)

[Visionoz]

How about this? http://www.astrophotoinsight.com/node/568

HTH
Cheers
Bill

[bartman]

Thanks Bill that was the article I read a while ago but never tried. However.....sorry for my naivety( is that the nice word for 'stupid repetitive question'?) that tute still indicates to me that you need the scope to be in the "park" mode position..... ie pointing to Octans. I cant see Octans from my backyard, so my question still remains : can I pick a star ( for instance tonight canopus is at the right height- for me- at about 20:30 WST on the meridian due-ish south) which means moving dec and ra?
I think I might have thought of the answer, but I'll eagerly await a contradiction to the " read what it says in the tute" response :P:D;):thumbsup:
Cause that would help......:thanx:
Bartman

[DavidTrap]

You need to be aim as close as you can to the point where the meridian and celestial equator intersect (ie 0 deg declination). Your point in the east/west should be on the celestial equator, and within 20-30 degrees of the horizon (or as low as you can go).

That was the article I was thinking of. I think the first line is misleading - point due south and 0deg dec - remember this was written in the norther on hemisphere, in Australia you are pointing ~30 degrees north of the zenith.

DT

[graham.hobart]

Even with the SSAG.ddl in the same folder as EQAlign, I still can't get it to recognise my SSAG, will recognise the webcam though.
Anyone had any success with EQalign and an SSAG?
Graham

[Peter.M]

When I am going to use my SSAG to drift align I generally use PHD. Just calibrate it on a star at the meridian, in the options turn off guiding and then watch the declination in the graph.

If it drifts either way make adjustments to azimuth. Do the same for a star low to the east or west and adjust the altitude. This way if you are pretty far off you will see instantly and can correct and you wont have to wait for the exposure to end.

[Peter.M]

The alternative that I have is alignmaster which I find to be excelent if I can see the stars it wants to use.

For instance at the moment around 930pm I can use Acrux and Miaplacidus. Before this time Acrux is behind a house and I am unable to use alignmaster.

[mswhin63]

Hi Peter,

I like the idea of PHD doing all of it but I found EQAlign is great that there is no need to look at it. Just set it and 10 minute later come back and it shows where to position the scope and where to make the adjustments. Actually I also watch the graph as well to see if it is way out and cut the time down to a couple of minute for the first time.

If you can't get EQAlign to work then maybe PHD would be a good solution. Try and contact the developer. The program still being developed because version 3.0.x is only a recent version.

[Visionoz]

Hi Bart

For polar alignment (to adjust the azimuth) it is usually done on a star pretty close to the junction where the celestial equator meets the meridian and particularly in our case we have to point Northwards since we are in the SH (so any reference to point to Octans would be from someone who is in the NH) - and to correct for the latitude we pick a star in the east or west about 20-30 degrees above the horizon and pretty close to DEC 0 ie close to the celestial equator

I do PA by the drift method (takes about 30mins) or by using Alignmaster and then cross-check by drift-aligning which takes even lesser time - ie if there is no drift after 10mins I'm good to go :thumbsup:

BTW do you have Holden car plates that is an acronym of your name? Thought 'twas you I was behind in Midland ;)

Cheers
Bill