Aligning camera in RA and Dec

[kirkster501]

Hello all, please would someone kindly advise how to align camera in RA and Dec?  Olly has suggested this is good imaging practice, but I confess I am not sure why or how?  I take my framing sub at the beginning of the imaging run to get the subject the way I like it.  So how, from that image, can I orientate the camera in said RA/Dec???  What is my reference to do that from the acquired sub?

Thanks,

[Freddie]

You can't do both. If you align your cam to get the framing you are happy with then that is the alignment you will stick with. If you want to align the cam with RA and DEC, align roughly by eye and then with the cam set on a couple of secs exposure, move the mount in RA. Look at the sub and adjust the cam until you have a horizontal line. Repeat for DEC until you have a vertical line.

[Jessun]

I simply turn the camera as best as I can to align it. Then I pick a bright star and expose whilst slewing. The trail will tell me how to adjust.

I always have North up. No reason for it whatsoever, just my way of doing it - it just matches my mental picture of the targets I suppose. This means that my M31 is often said to be up side down... You can't win!

/Jesper

[ollypenrice]

Dead easy, Steve. Have the camera running on a bright star. Open the crosshairs on your capture screen and put the star in the middle. Now slew slowly on whatever is the long side of the chip (which could be RA or Dec depending on Landscape/Portrait orientation.) Unless you're already orthogonal the star will now be above or below the line of the crosshair so you rotate the camera so that the star is back on the the line.  Now 'slide' the star along the crosshair by slewing the other way to the opposite side to confirm it's remaining on the crosshair. Give the camera a final tweak of rotation if necessary. It takes two minutes at most.

Olly

Oops, beaten to it! As Freddies says, you can't have both optimal framing and orthogonal alignment but I find I hardly ever need to move from orthogonality.

Edited April 22, 2017 by ollypenrice

[CraigT82]

As to the why.... I believe it makes sense in that it makes diagnosing tracking errors easier if you know which way things are moving in your image 

Edited April 22, 2017 by CraigT82

[Davey-T]

If you want perfection you can plate solve it in Maxim and it will tell you how far out you are, usually just do it by eye myself.

Dave

[ollypenrice]

1 minute ago, CraigT82 said:

As to the why.... I believe it makes sense in that it makes diagnosing tracking errors easier if you know which way things are moving in your image 

That's true. The other reason is that it makes the image more repeatable if you want to come back to it for more data in the future. It takes ages to recover an arbitrary camera angle when framing. And then there are mosaics. I once tried to do a mosaic with an arbitrary angle optimized to the target. Never again!!!

Olly

[SteveA]

1 hour ago, ollypenrice said:

That's true. The other reason is that it makes the image more repeatable if you want to come back to it for more data in the future. It takes ages to recover an arbitrary camera angle when framing. And then there are mosaics. I once tried to do a mosaic with an arbitrary angle optimized to the target. Never again!!!

Olly

Why on earth didn't I think of this? It's the simplest of solutions and I have always struggled when returning to a target to get a similar orientation.....?. I'll be making this part of my process from now on...thanks.

Edited April 22, 2017 by SteveA

[ollypenrice]

7 minutes ago, SteveA said:

Why on earth didn't I think of this? It's the simplest of solutions and I have always struggled when returning to a target to get a similar orientation.....?. I'll be making this part of my process from now on...thanks.

It was a while before the penny dropped with me, too.

Olly

[kirkster501]

Many thanks guys, I understand.  I will have a go next time we get a clear night.

[Quatermass]

Doing a mosaic will soon have you scratching your head if your camera is not aligned to RA and Dec even though the mosaic frames look good in your software they will come out all wrong if your camera is not aligned like this. The first picture is how my 4 shots came out when I stacked them all up the second picture shows the actually frames in CDC super imposed over the final image. You can see that if I had aligned my camera to ra and dec it would have lined up ok but because my camera was not lined up with RA and DEC my mosaic came out all screwy.  Testing to see if your in line with RA and Dec as listed above is good practice for sure especially if you want to avoid this nightmare. The camera needs to be at 0 or 90 degree angle to start but you must test it out by focusing on a bright star and while doing the exposure move in ra and get that lined up straight I use Astrophotography Tool or backyard EOS both good programs. And also make sure that you have a good size overlap on your mosaic frames to crop off dark edges caused by gradients. OR avoid going insane by not doing mosaics in the first place.

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