Mosaic madness
Taking a picture of something big in the night sky like the Andromeda galaxy or the Rosette nebula can be very challenging. If your telescope can’t fit it all in, then your options are to get another telescope or try doing a mosaic that will cover the whole subject. It’s not easy and you will run into many issues so I hope this article will help those of you who are willing to give it a try.
First of all, this is the equipment I am using to do this.
A Skywatcher EQ5 mount fitted with the synscan upgrade allows me to connect to a laptop and control everything from there.
A Skywatcher 200p Newtonian telescope
A Canon 450d for imaging
And an EQ direct cable to bypass the handset that comes with the synscan upgrade and connects directly to the computer.
For the software, I am using the Ascom platform and EQMOD along with APT astrophotography tool and CDC Cartes du Ciel planetarium
Getting APT and CDC working together and making sure your camera is correctly aligned on your telescope is the biggest challenge I faced so let’s trace back my steps as I started off and find out how things progressed.
FIRST ATTEMPT.
Not what I wanted at all, unfortunately, the images were taken at an exposure of 50 seconds each ISO1600 unguided and I took 9 of them just to test out the setting but when they were stitched together in Photoshop nothing matched up so it was back to the drawing board.
Puzzled by why my frames were not matching up I concluded that my camera was not lined up correctly with the RA and Dec coordinates so to put this right you need to do the following.
First, find a bright star in the sky to focus on using live view in your camera and get it lined up in APT using the cross-hair like this. Then line it up so it’s right in the center.
First of all, this is the equipment I am using to do this.
A Skywatcher EQ5 mount fitted with the synscan upgrade allows me to connect to a laptop and control everything from there.
A Skywatcher 200p Newtonian telescope
A Canon 450d for imaging
And an EQ direct cable to bypass the handset that comes with the synscan upgrade and connects directly to the computer.
For the software, I am using the Ascom platform and EQMOD along with APT astrophotography tool and CDC Cartes du Ciel planetarium
Getting APT and CDC working together and making sure your camera is correctly aligned on your telescope is the biggest challenge I faced so let’s trace back my steps as I started off and find out how things progressed.
FIRST ATTEMPT.
Not what I wanted at all, unfortunately, the images were taken at an exposure of 50 seconds each ISO1600 unguided and I took 9 of them just to test out the setting but when they were stitched together in Photoshop nothing matched up so it was back to the drawing board.
Puzzled by why my frames were not matching up I concluded that my camera was not lined up correctly with the RA and Dec coordinates so to put this right you need to do the following.
First, find a bright star in the sky to focus on using live view in your camera and get it lined up in APT using the cross-hair like this. Then line it up so it’s right in the center.
Once it is in the middle of the cross-hair slew the telescope east or west and watch the star. If it goes off the centerline you will need to rotate your camera on your mount to correct this until it follows the horizontal line exactly the same applies to the vertical line in North and South. Once it follows them dead straight then your camera is correctly aligned on your telescope and will match the field of view FOV rectangle in CDC showing where your telescope is pointed.
It also needs to be pointed out that setting your FOV angle in CDC is needed to get your camera correctly aligned using 0 degrees or 90 degrees as shown here in CDCs options for this on number 4 which is my settings for the canon 450d you change it under offset to 0 or 90 this will align your FOV rectangle to lay flat or two be on its side so make sure you match it correctly to what you are seeing when you take a photo of your subject.
So with all that now corrected, I thought all would be well but of course, nothing is easy in this hobby and once again the frames would not match up correctly even though the camera angle had been corrected so it had to be the setting in CDC or APT that were the issue and I was correct. This is how I fixed it and I hope it helps you out if you are having the same problems.
First of all the problem, we had to fix was this.
In CDC the mosaic frames it creates have coordinates that tell APT where to point to in the sky but when I used them APT could not align them to the position of the mosaic panels so it looked like this once the telescope had slewed to there position. Here you can see the area that my telescope has been moved to and in red the actual position of the mosaic frames which is not lining up with my telescope's position.
After much research on this problem I came across the word EPOCH and its associated number J2000? what the hell is that all about I wondered.
Well, it turns out that the EPOCH and its Number J2000 affect the coordinates in APT and CDC and in turn, can mess up your alignment.
It also needs to be pointed out that setting your FOV angle in CDC is needed to get your camera correctly aligned using 0 degrees or 90 degrees as shown here in CDCs options for this on number 4 which is my settings for the canon 450d you change it under offset to 0 or 90 this will align your FOV rectangle to lay flat or two be on its side so make sure you match it correctly to what you are seeing when you take a photo of your subject.
So with all that now corrected, I thought all would be well but of course, nothing is easy in this hobby and once again the frames would not match up correctly even though the camera angle had been corrected so it had to be the setting in CDC or APT that were the issue and I was correct. This is how I fixed it and I hope it helps you out if you are having the same problems.
First of all the problem, we had to fix was this.
In CDC the mosaic frames it creates have coordinates that tell APT where to point to in the sky but when I used them APT could not align them to the position of the mosaic panels so it looked like this once the telescope had slewed to there position. Here you can see the area that my telescope has been moved to and in red the actual position of the mosaic frames which is not lining up with my telescope's position.
After much research on this problem I came across the word EPOCH and its associated number J2000? what the hell is that all about I wondered.
Well, it turns out that the EPOCH and its Number J2000 affect the coordinates in APT and CDC and in turn, can mess up your alignment.
So what is an EPOCH and J2000?
(Due to the wobble in the Earth’s orbit the RA and Dec positions of the Stars appears to change. The older star atlases used Epoch 1950 for their positions, newer atlases use Epoch 2000.)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time.
For example, orbital elements, especially osculating elements for minor planets, are routinely given with reference to two dates: first, relative to a recent epoch for all of the elements: but some of the data are dependent on a chosen coordinate system, and then it is usual to specify the coordinate system of a standard epoch which often is not the same as the epoch of the data. An example is as follows: For minor planet (5145) Pholus, orbital elements have been given including the following data:[4]
Epoch 2010 Jan. 4.0 TT . . . = JDT 2455200.5
M 72.00071 . . . . . . . .(2000.0)
n. 0.01076162 .. . . . Peri . 354.75938
a 20.3181594 . . . . . Node . 119.42656
e. 0.5715321 . . . . . Incl .. 24.66109
where the epoch is expressed in terms of Terrestrial Time, with an equivalent Julian date. Four of the elements are independent of any particular coordinate system: M is mean anomaly (deg), n: mean daily motion (deg/d), a: size of semi-major axis (AU), e: eccentricity (dimensionless). But the argument of perihelion, longitude of the ascending node and the inclination are all coordinate-dependent, and are specified relative to the reference frame of the equinox and ecliptic of another date "2000.0", otherwise known as J2000, i.e. January 1.5, 2000 (12h on January 1) or JD 2451545.0.[5]
Ok, that's the nerdy stuff out of the way so now we need to tell CDC and APT and EQMOD what are Epoch settings are so that they are both singing from the same hymn sheet!
Correcting the setting in CDC APT and EQMOD
1. Go to the general settings panel and set it to Force J2000 and make sure you are using Alt/Az coordinates in the chart settings.
In APT make sure that the JNow button is not used.
Leave this JNow tab not highlighted so it does not convert J2000 to JNow as you have told CDC to use J200.
And lastly, in EQMOD in the driver set up, you will need to change it to J2000 under Ascom options
Right then that's all the setting put in and in part two of Mosaic Madness, I will continue with my progress and let you know how I get on. PHEW!
(Due to the wobble in the Earth’s orbit the RA and Dec positions of the Stars appears to change. The older star atlases used Epoch 1950 for their positions, newer atlases use Epoch 2000.)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time.
For example, orbital elements, especially osculating elements for minor planets, are routinely given with reference to two dates: first, relative to a recent epoch for all of the elements: but some of the data are dependent on a chosen coordinate system, and then it is usual to specify the coordinate system of a standard epoch which often is not the same as the epoch of the data. An example is as follows: For minor planet (5145) Pholus, orbital elements have been given including the following data:[4]
Epoch 2010 Jan. 4.0 TT . . . = JDT 2455200.5
M 72.00071 . . . . . . . .(2000.0)
n. 0.01076162 .. . . . Peri . 354.75938
a 20.3181594 . . . . . Node . 119.42656
e. 0.5715321 . . . . . Incl .. 24.66109
where the epoch is expressed in terms of Terrestrial Time, with an equivalent Julian date. Four of the elements are independent of any particular coordinate system: M is mean anomaly (deg), n: mean daily motion (deg/d), a: size of semi-major axis (AU), e: eccentricity (dimensionless). But the argument of perihelion, longitude of the ascending node and the inclination are all coordinate-dependent, and are specified relative to the reference frame of the equinox and ecliptic of another date "2000.0", otherwise known as J2000, i.e. January 1.5, 2000 (12h on January 1) or JD 2451545.0.[5]
Ok, that's the nerdy stuff out of the way so now we need to tell CDC and APT and EQMOD what are Epoch settings are so that they are both singing from the same hymn sheet!
Correcting the setting in CDC APT and EQMOD
1. Go to the general settings panel and set it to Force J2000 and make sure you are using Alt/Az coordinates in the chart settings.
In APT make sure that the JNow button is not used.
Leave this JNow tab not highlighted so it does not convert J2000 to JNow as you have told CDC to use J200.
And lastly, in EQMOD in the driver set up, you will need to change it to J2000 under Ascom options
Right then that's all the setting put in and in part two of Mosaic Madness, I will continue with my progress and let you know how I get on. PHEW!
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