Polar Alignment with DSLR

[cadams]

I did my first attempt at astrophotography on Monday.  Just a rough and ready practice session to get used to the controls etc.

I secured my Canon 70D camera with 200mm telephoto lens on a Manfrotto ball head attached to the dovetail mount on my Celestron AVX mount.  (No telescope).  I polar aligned the mount by centering (as accurately as I could by eye) Polaris in the viewfinder of the camera.  I went on to take some practice photographs of M31 and the Moon with Venus that came out much as I expected.

I am now ready to move towards more accurate imaging and tracking and I have a question about polar alignment with a DSLR:  It occurred to me that because the DSLR is on a ball head that it will need to be aligned with the mount first before being used as a finder for Polaris and that this could be a difficult task.  Can anyone explain how this can be achieved accurately?

 

 

[BXRO]

Hi I can see what you are trying to achieve, 

How about this for a solution

Fix the camera to the mounting and align It as close as possible to the mounting, perhaps a level and set square needed here.

 

Now polar align using the camera eyepiece, you are now aligninging to the part of your setup that needs to be kept stable 

Use the Dec and Ass controls to set your camera to the target 

Hope this makes sense

 

 

[cjdawson]

Sounds to me like you would benefit from learning a drift alignment technique.

There is the DARV Method. but frankly I've never used this.

There is a piece of software that I'm going to be trying out soon (hopefully tonight) called Alignmaster

http://www.alignmaster.de/

Rather than spending time waiting for drift (as needed in the darv method)  This piece of software does the lifting for you.  Does require more slewing, but it'll help to achieve good polar aligment quicker than with the darv method.

As you can do several iterations of this, it also means that you can get much more accurate faster.

[MarkyD]

Does that mount not have a polar scope?

[ronin]

20 minutes ago, MarkyD said:

Does that mount not have a polar scope?

That was my thought, why use the DSLR at all? Polar align the mount then add the DSLR later. The mount does not need and really should not use a scope or a camera to perform the polar alignment.

[iapa]

32 minutes ago, MarkyD said:

Does that mount not have a polar scope?

Unfortunately, the AVX does not come with a polarscope, it's optional extra

How about, setting the camera as accurately as possible in line with polaris - as mentioned above.

Just 'pretend' your camera is your OTA. Go through the 3 star alignment proves, then the All Star Polar Alingment - allaccessible via the mount hand controller.

 

To improve accuracy, you could add Stellarium and AstroTortilla to the mix.

When you slew to the first star - don't bother trying to see it in the camera; you probably wont.

Go to Stellarium, and select the star that the mount think it is pointing to, and slew to that target.

Use astrotortilla to plate solve and correct the 'pointing' - once it has stopped, return to the mount and just confirm the rough and fine alignment steps

repeat for 2nd and 3rd alignment stars.

Your mount now has a good map of the sky.

Just follow the ASPA steps - again using stellarium/astro tortilla to refine the 'pointing' of the mount to the relevant stars. 

 

[cadams]

Hi, Thanks for all the replies.  From reading them I reckon that my best approach is:

Either

1. use a set square etc and line up the DSLR with the mount or

2. polar align using a polar scope and THEN attach the DSLR and centre Polaris in the viewfinder.  The DSLR would then be aligned with the mount because it is seeing the same thing as the polar scope attached to the mount.

 

[iapa]

Sorry, I wasn't clear

you do both.

1. gets the DSLR line to where the mount is pointing.
2. builds a sky map in the mount. You use the DSLR to that you have lined up with the mount in step 1.

When you follow 2 or three star alignment on the mount, you select a star and slew to it with the hand controller (HC), you then use the controller to centre the star in the eye piece.

What I am suggesting is using some software to centre the star in the middle of the camera view - Astrotortilla can get you to 0.1 arc minutes from centre.

Stellarium - free. Needs USB-Serial adapter, Serial cable for Skywatcher and Celestron mounts to connect to the mount via Ascom driver.

https://www.firstlightoptics.com/celestron-mounts/sky-watcher-synscan-usb-to-serial-rs-232-cable.html and https://www.firstlightoptics.com/celestron-mounts/serial-cable-for-skywatcher-and-celestron-mounts.html c£30 in total

You can control your mount using using the cables from PC to the hand controller.

Once all set up you simple click on the target in and press a couple of keys and it drives the mount to the target.

Astrotortilla - free

This will connect to your camera (via Ascom driver), take a picture, locate the centre, and slew the mount so that the target is in the centre of the picture.

If, instead of looking through the camera view finder to try and centre the target star (or using live view if you have it is better) you take a picture and let the tech sort it out, you will have a good map.

As both application suse Ascom, the both have the same mount information. SO, Stellarium sets the mount to where it thinks it needs to be. Astrotorilla refines that so the mount is where is should be.

TBH you may not necessarily need a really accurate polar alignment if using DSLR and lens as your a likely not doing much more the 10-15 second exposure?

[Astrofriend]

A lot of people use this equipment when they polaralign:

http://www.qhyccd.com/PoleMaster.html

 

But then you must have a computer with you also.

 

Maybe easier if you can get a polarscope and align it accurate to the RA axis of your mount. A 200 mm lens need high precision align to the polarstar, and the polarstar is a bit off the correct point where you should align your RA axis to, it's the Earth rotation axis you align to. In a polarscope you have circles where you should put your polaris star. It depends also on time and place where you are. I have an App in my mobilephone to find the correct position of polaris and where to put in on the circle. You find links to software and apps I use here on my homepage:

http://astrofriend.eu/astronomy/equipment/astronomy-equipment.html#part06

 

I hope you find a solution for it in someway!

 

/Lars

[Owmuchonomy]

On 4 January 2017 at 11:49, cadams said:

Hi, Thanks for all the replies.  From reading them I reckon that my best approach is:

Either

1. use a set square etc and line up the DSLR with the mount or

2. polar align using a polar scope and THEN attach the DSLR and centre Polaris in the viewfinder.  The DSLR would then be aligned with the mount because it is seeing the same thing as the polar scope attached to the mount.

 

Well, just be aware that for polar alignment it is the mount you are aligning, not the item attached to it. In any case, correct polar alignment will have you positioned about 40' from Polaris. If you are thinking of investing To help you with this excercise you could do worse than look to purchase the SW Star Adventurer package to use.

[wornish]

On 04/01/2017 at 10:17, cadams said:

I did my first attempt at astrophotography on Monday.  Just a rough and ready practice session to get used to the controls etc.

I secured my Canon 70D camera with 200mm telephoto lens on a Manfrotto ball head attached to the dovetail mount on my Celestron AVX mount.  (No telescope).  I polar aligned the mount by centering (as accurately as I could by eye) Polaris in the viewfinder of the camera.  I went on to take some practice photographs of M31 and the Moon with Venus that came out much as I expected.

I am now ready to move towards more accurate imaging and tracking and I have a question about polar alignment with a DSLR:  It occurred to me that because the DSLR is on a ball head that it will need to be aligned with the mount first before being used as a finder for Polaris and that this could be a difficult task.  Can anyone explain how this can be achieved accurately?

 

 

The polar scope for your mount is approx £30 probably save you a lot of frustration going forward if you can get one.  

Without accurate polar alignment you will certainly suffer from elongated stars or worse.

[Randalloverby]

On ‎1‎/‎4‎/‎2017 at 05:17, cadams said:

I did my first attempt at astrophotography on Monday.  Just a rough and ready practice session to get used to the controls etc.

I secured my Canon 70D camera with 200mm telephoto lens on a Manfrotto ball head attached to the dovetail mount on my Celestron AVX mount.  (No telescope).  I polar aligned the mount by centering (as accurately as I could by eye) Polaris in the viewfinder of the camera.  I went on to take some practice photographs of M31 and the Moon with Venus that came out much as I expected.

I am now ready to move towards more accurate imaging and tracking and I have a question about polar alignment with a DSLR:  It occurred to me that because the DSLR is on a ball head that it will need to be aligned with the mount first before being used as a finder for Polaris and that this could be a difficult task.  Can anyone explain how this can be achieved accurately?

 

 

Do you have any pics of the setup, I was thinking about doing the same thing with the AVX ?

[cadams]

I have another idea that might be useful.  I think that unless the camera axis is aligned with the mount then simply having a mount that is Polar Aligned will be of no use.  The camera must be Polar Aligned as well and this will only be true if the camera and mount are aligned first.  This, I imagine, isn't an issue with a telescope because it is fixed at two points on the mount and these will already have been lined up.  It is an issue with a camera that is free to swivel on a ball head.  

I have thought of a possible iterative method to check alignment- any comments on whether this will work appreciated:

1. Align camera to the mount by eye as accurately as possible and tighten the ball head.

2.  Polar align as best as possible with the camera viewfinder on Polaris.  I'm aware that using Polaris is only an approximation but it is the principle that I am interested in.

3. Swing the camera in R.A. and if Polaris stays still then the camera is aligned with the mount.  If Polaris moves in the viewfinder then the camera is not aligned with the mount (It will be skewed from the mount's axis).   In this case readjust the ball head and polar align again until Polaris stays still when the camera is rotated in R.A.  (The direction of any movement of Polaris in the viewfinder should indicate the direction that the camera is misaligned from the mount).

[RayD]

Does your AVX not have a Polar Alignment menu in the handset?  Mine does and it works ok.  If not you may need to update firmware.  You can then use BYEOS or similar to view the image with cross hairs to centre.

Ideally you need to polar align your mount first, then the 1, 2, all star alignment will factor for the cone error, which is how far out your camera alignment is from your mount.

[MARS1960]

On 1/4/2017 at 10:17, cadams said:

I did my first attempt at astrophotography on Monday.  Just a rough and ready practice session to get used to the controls etc.

I secured my Canon 70D camera with 200mm telephoto lens on a Manfrotto ball head attached to the dovetail mount on my Celestron AVX mount.  (No telescope).  I polar aligned the mount by centering (as accurately as I could by eye) Polaris in the viewfinder of the camera.  I went on to take some practice photographs of M31 and the Moon with Venus that came out much as I expected.

I am now ready to move towards more accurate imaging and tracking and I have a question about polar alignment with a DSLR:  It occurred to me that because the DSLR is on a ball head that it will need to be aligned with the mount first before being used as a finder for Polaris and that this could be a difficult task.  Can anyone explain how this can be achieved accurately?

 

 

As mentioned you don't polar align with a DSLR, you polar align your mount, save yourself a lot of wasted clear skies and poor subs and get a polar scope would be my advice.

[Freddie]

or just use DARV as was suggested earlier.

[cadams]

4 minutes ago, MARS1960 said:

As mentioned you don't polar align with a DSLR, you polar align your mount, save yourself a lot of wasted clear skies and poor subs and get a polar scope would be my advice.

I agree with this and I definitely will follow the advice given here (many thanks for this by the way) and buy a polar scope.  But even if I Polar Align the mount it will be a waste of time if the camera is pointing skew whiff and this is what I was trying to find a technique to avoid.

[MARS1960]

1 minute ago, cadams said:

I agree with this and I definitely will follow the advice given here (many thanks for this by the way) and buy a polar scope.  But even if I Polar Align the mount it will be a waste of time if the camera is pointing skew whiff and this is what I was trying to find a technique to avoid.

The camera only needs to be attached to the mount,  it wont need polar aligning, if your mount is polar aligned all you need to do then is carry out the usual star alignment and the star you used for alignment will be in the FOV.

I always do this with either camera or scope and i can get 5min subs no trailing without guiding. 

[RayD]

5 minutes ago, cadams said:

I agree with this and I definitely will follow the advice given here (many thanks for this by the way) and buy a polar scope.  But even if I Polar Align the mount it will be a waste of time if the camera is pointing skew whiff and this is what I was trying to find a technique to avoid.

That's where your star alignment comes in as it allows for the cone error, which is the misalignment between your camera and mount, but you need to be polar aligned first.

[wornish]

8 minutes ago, cadams said:

I agree with this and I definitely will follow the advice given here (many thanks for this by the way) and buy a polar scope.  But even if I Polar Align the mount it will be a waste of time if the camera is pointing skew whiff and this is what I was trying to find a technique to avoid.

It doesn't make any difference what your camera is pointing at as long as the mount is polar aligned.  The star that you are looking at in the viewfinder will stay in the same position as the mount rotates, it is compensating for the earths rotation.  

Thats the reason people use equatorial mounts for astrophotography.

[RayD]

4 minutes ago, wornish said:

It doesn't make any difference what your camera is pointing at as long as the mount is polar aligned.  The star that you are looking at in the viewfinder will stay in the same position as the mount rotates, it is compensating for the earths rotation.  

Thats the reason people use equatorial mounts for astrophotography.

It does if he wants to use the GOTO function of the AVX which is why he will need to do a star alignment so the camera is essentially pointing at the star the mount thinks it is.

[wornish]

7 minutes ago, RayD said:

It does if he wants to use the GOTO function of the AVX which is why he will need to so a star alignment so the camera is essentially pointing at the star the mount thinks it is.

That is true, but you can't even start until your mount is polar aligned.  All he needs to do is make sure Polaris is visible in the viewfinder when he is polar aligned. Then follow the mounts alignment routine and ensure he centres the first star in the camera viewfinder and so on.

If you manually target a star just adjusting the camera on the ball mount then it wont move if your polar aligned.

[cadams]

2 minutes ago, RayD said:

It does if he wants to use the GOTO function of the AVX which is why he will need to do a star alignment so the camera is essentially pointing at the star the mount thinks it is.

Yes and that is the reason that I want to ensure the mount aligns with the camera.  This whole discussion has helped me (very much a beginner at the start of a learning curve) understand a lot more about how to set up and Polar Align so thanks.  I think I now have several methods to try out next time the sky clears. I'll probably have more questions about other aspects (image processing for example) as time goes on.  Thanks again

[RayD]

Just now, wornish said:

That is true, but you can't even start until your mount is polar aligned.  All he needs to do is make sure Polaris is visible in the viewfinder when he is polar aligned. Then follow the mounts alignment routine and ensure he centres the first star in the camera viewfinder and so on.

If you manually target a star then it wont move if your polar aligned.

Yes I agree, and said before he needs to polar align first, but he was trying to do this just using the DSLR and the AVX actually has quite a good polar alignment function.

[MARS1960]

Best of luck, just remember, dont waste valuable time trying to polar align your camera, once the mount is aligned just attach the camera, as long its pointing roughly north (which it should be anyway) then all will be good.