The gear used to take this is found here
LRGB 300 seconds each sub @ -20 ℃, 2×2 bin, 8 subs per filter. Processed in PixInsight (for which I’ve still have my L’s on).
This was taken from Govetts Leap, Prince George Lookout, it was so windy the tripod kept wanting to blow over. It is a 20 second, ISO 6400 shot, taken with a Sony a7s 24mm F4 lens, using an iOptron SkyTracker. That’s the LMC down the bottom in the trees.
Post playing in lightroom
Every Astronomer needs at least one star trails photo. This one from the back yard. Taken on a Sony a7S, 24mm lens, F4, exposure 15 sec @ ISO 400. 2 1/2 hours of elapsed time, no moon. Processing with StarTrails.
So I finally gave up and brought a new scope, a Planewave CDK20 with a fused Silca mirror and an IRF 90 Focsuer/Rotator. I put the same old FLI Proline 16803 but it failed with a chip error within a month of operation, a new one is on the way. Below is the scope installed.
It’s installed at iTelescope.Net at Siding Springs, Coonabarabran, NSW, Australia where the 3.9m AAT is. The guys have been unbelievably helpful, not just with the install but with all the new things that can take a little while to sort. There are a thousand thing that happen slightly differently when you are doing remote hosting of your scope. These guys have it all down pat. Setup of new filters, flat frames, etc.
My first image was M46 and friends. Isnt it a cute planetary? I finally have round stars. No more Rila Fast problems, yeah!
I cant wait to take additional images. I was doing 1 hour subs of Sharpless 308 when my FLI Proline failed (attempting to copy one of the masters Mike Berthon-Jones). Another month to wait until the new camera turns up.
My ATC-02 had a problem. The red light was on but it would talk to the PC. The baffles would open and close using the buttons on the scope but nothing else. The Officina Stellare crew where great, and after awhile its repaired and operational. Temperature controlled mirrors, fans, baffle control all at the touch of a button again. First light was last night after only getting it back the day before (not sure what happened to the usual astronomy curse). Its a pleasure to use.
Its been a while, a very frustrating while. So much so that I had almost given up ever getting the collimation complete. Persistence is apparently the key.
I learnt two things.
1) the secondary mirror has 4 small hex bolts that adjust the shape of the stars. They can be set to distort the image. Moving these a small amount can bring the star into round. The problem with this is that if the primary mirror is not adjusted correctly as well its a move this, check, move that check back and forward. All of this on a defocused star (both sides of focus) smack in the middle of the image. Do no deviate even a little from the center, plus or minus 10 pixels in my case was enough to distort it.
2) Move the tip tilt plate out about 0.5mm all round and confirm the spacing with a feeler gauge. Make sure you know how the screws line up with the image, put your hand in front of the telescope so that its in the same relative position as the screw but at the front of the scope, take a picture and document where each screw lines up. Move the rotator so that the screws are aligned to with the image so that the triangle they form has one side lined up with a rectangle of the CCD image. When the stars look like horse shoes on the edges do up the screw, when they look like diamonds or triangles undo the screws. Movements are very small, 1/4 turns at a time. Start with the most out of shape stars.
Alignment of the tip tilt screws and the image.
The tricky bit is knowing when the primary mirror alignment stops and tip tilt should start. On my Proline 16803 image the horseshoe stars where only about (note the ABOUT) two/three times as long they where wide. 1/4 – 1/2 turn made these very close to round in the corners. Just refocus after each adjustment.
This is of course after the distortion correction above.
These scopes are a bugger to collimate and I will not be buying another one. Longer exposures will have to do.
Still the tech support form the Officina Stellare guys was very good and the final result is actually quite pleasing. Not perfect but close.
Final image, combined, stretched.
The Rila is a new scope for me, mine’s a 400mm f3.75. I’ve previously collimated an SCT and of course my refractors haven’t require any changes since I’ve brought them.
I’ve got to say the manual from OS looked like it was designed for an RC but the guys in their support are really helpful and know what they are doing. Cris at Astronomy Alive was a God send, not only putting me in touch with the OS guys but also other amateurs who have had to work through similar configurations.
The Rila has a number of possible adjustments.
1. The adjustment of the spider that holds the secondary mirror
2. The adjustment of the collimation screws on the secondary
3. The adjustment of the collimation screws on the primary
4. The adjustment of the tip/tilt adaptor that attaches the imaging train to the back of the scope.
So all up its 13 degrees of freedom. Be prepared to spend some time.
First of all if your collimation is out the cause is most likely your tip/tilt adaptor. Play with this first. Check out your corners.
The equipment setup:
I had a replacement collar (the red bit connecting the focuser to the scope) sent out from Italy so I could attach the collimator and the tip/tilt was very different. I should have marked where everything was first. Next time.
Don’t bother to remove the primary baffle, it makes no difference. Don’t bother using the laser with circles because the rings cannot be seen because of the size of the secondary. See photo below.
But the rings are clearly visible on the secondary.
OK, the steps:
1. Measure the distance from the secondary mirror holder to the external octagon. It should be possible to get the four equally spaced measurements from any section to the secondary within 0.5 mm. I used a vernier calliper all measured up to 140.72mm.
2. Loosen the locking screws on the primary mirror. Screw down the collimation screws on the primary and secondary mirrors so they are fully done up, but not super tight.
3. Put the laser in the back of the scope with the provided collimator bracket and adjust the secondary until the laser hits the center of the circles in the secondary.
4. Use the Tak collimation scope and put the dot in the center of the secondary mirror circles. The Tak doco is pretty good on this. However you cannot see the spiders and you cannot see the reflection of the edge of the primary mirror. You can see the shadow of the secondary but it should like up pretty well because of step 1. The tak causes an additional shadow which you can see around the outside of the secondary mirror shadow. Ignore it. Mine was not quite a circle and I discovered it move when I rotated the Tak anyway. When you have the Tak at the right focus you can see the central dot and what looks like diffraction rings around it. using these you can get a very accurate positioning of the dot inside the secondary circles, adjust the secondary’s collimation screws to ensure the dot is in the center. Just beware that this is still mechanical alignment.
5. Pull off the collimation adaptor and put your imaging rig back on, defocus so you can see the diffraction rings clearly, bigger stars say >20 pixels across is fine, we can make them smaller later, start taking say 2 second frames with your imaging rig and put the star smack in the center (ok plus or minus 20 pixels is fine) and make sure your tracking is working well. Point it at a not to bright a star say mag 5 and check out the star shape. This is typically what you do with SCTs but here you are playing with the primary mirror collimation screws only. You will need to back each of them off say 1/2 a turn to start with so you have some room to adjust. The basic idea is to move the star, using the screws. The star should move in the direction of the squished diffraction rings. The idea is to get a nice circle. Equally spaced diffraction rings on each side. You will need to play to determine which screw moves which angle and if tightening or loosening moves the star so that the diffraction rings spread out or move closer together. This is standard collimation stuff and there are lots of examples on the net about how to do this. You will need to do this with a star that is well out of focus, and then closer to focus. The closer you get the smaller the movements need to be. This star has to be kept in the center of the image all the time so be prepared to move your scope after each adjustment. This is in my opinion the longest and most frustrating step. Ignore the star shapes on the edges of the frame. Take longer shots up to about 30 seconds to see how you alignment goes as you get closer to focus. This means you end up with something like this, one sub 1200 seconds, Ha, stretch only, nothing else:
The central stars are pretty close but check out the corners! The top left and top right are miles out, with the bottom left OK – but not brilliant – and the bottom right almost as good as the top right.
6. The final stage is to make sure the stars are the right shape across the entire image. You do this by making very small adjustments to the tip/tilt plate that attaches your imaging train to the scope. Mine is a red collar with small hex grub screws. undo the larger grub screws a very small amount and try tightening the smaller grub screws fractions of a turn. Check out the edges of you image while you make these adjustments so you can see if the star shapes in the corners are headed in the right direction.
Good luck its taken me days.
This is M20 & M21 in narrowband, Hubble palette.
This is NGC6357 in narrowband, Hubble palette.