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themos

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Everything posted by themos

  1. Surprised that I noticed the Great Conjuction 11 years ago!
  2. Just be careful with the worm holder, I've had mine break in bits.
  3. Hello, If you have a camera and a laptop, you can use my PhotoPolarAlign method described here, it's been tested in Southern Hemisphere and can give Polar Alignment accurate to a few arcminutes in about 15 minutes.
  4. Sorry Olly, as I understand it it's not about saturating your chip with orange glow. The general rule for a single exposure is expose until your read noise is not the limiting factor. That happens earlier in the exposure for low-read-noise cameras (modern CMOS, for instance). So what other noise sources are there that we should think about? There's dark noise which is what you get even with the shutter closed. And there's shot noise, which is the uneven dribble of photons from light polluted "background" sky. The more light pollution there is, the more photons come from it and the associated
  5. I should add that the method I used in PPA also appears in SharpCap http://www.sharpcap.co.uk/sharpcap/features/polar-alignment so if you like the extra bells and whistles you might like to give that a try.
  6. I think it would be great for someone to add this, but I wouldn't be using it myself. Given that hardly anybody has a mount with motorised elevation/azimuth controls of the polar axis, the PPA process will always involve a human being iterating moves and closing in on the error. People with observatories can take their time and people that set up every night can use a piggy-back camera (even a compact camera will produce good enough stars in 10 seconds or so).
  7. I am sorry, that's not it! The first couple of images will fix the pixel position of the polar axis no matter what orientations you used. The requirement for the second image to be horizontal is to translate the x/y correction that is calculated (which is merely along the long side and short side of the sensor) to the left/right and up/down instructions needed for the person doing the mount correction.
  8. Hello Steve, I've avoided using the reflector at prime focus because 1) the image scale is a bit excessive for the purpose ,2) reflector images have the wrong parity which messes up the move instructions and 3) it's more tricky to know what horizontal is. Best way of making the mapping from arcminutes to screw turns is to solve images (with PPA!). I guess I would do the first couple to get the polar axis, then give a full turn to raise the polar axis and do an improvement solve, then note the new error (the Up/Down move instruction). Repeat for Left/Right. For this to work, you must
  9. It should be ok, I guess you will need to experiment. But you don't have to slew, you can just undo the RA clutch and swing the axis manually. Atsrotracs can't do that but your CG-5 should be able to do it.
  10. My Stellarium (0.17.0) says, when I click on Polaris, RA/Dec (on date): 2h55m07.03s/+89d20m23.7s. So that is nearly 40mins off the current NCP.
  11. Hello, I've added your ideas in the GitHub Issues. I am not sure when I will find time to add these but they are there in case anyone is tempted to implement them and do a pull request. Polaris was at ~44 minutes in J2000 but not now! PPA does adjust for the wandering of the Earth's axis (precession).
  12. Hello, After trying to make USB shutter control cable for an EOS 20D and failing (soldering skills and eyesight failing) I am asking the community to help me finish this. I already have an FTDI USB to TTL cable for the job and I have converted the 20D shutter control to 2.5mm female audio jack. The circuit needed is like this one except it will be driven by the GREEN/BLACK wires of the FTDI cable instead of the pin-7/pin-5 of the serial port in the diagram. If you can help, please get in touch. Themos
  13. They second one has just disappeared from the website!
  14. They've arrived! I got the one advertised as damaged case but I can't see any damage! I will give a further report later.
  15. Hello, whenever I have verified the PHD GuideLogs after a session, I find an estimated PA error that's quite similar to what PhotoPolarAlign (same method that Robin has put in SharpCap) measured. I use PHDLab for analysing PHD GuideLog files. A couple of things to check: It could be that PHD's Drift Align procedure is not as robust as PHDLab's analysis (remember that PHDLab can see the entire session, not just 10 minutes, and tell how much Dec correction was applied). The other thing is refraction. If you are imaging fairly low in the sky, there will be significant and varying refraction
  16. Hello, I am using a non-LiveView Canon EOS 20D camera with a Canon 200mm f/2.8LII lens. To focus it, I need to take one exposure after another as there is no Live View feed, either on-camera or through USB cable. I put the lens in MF-mode and use the focusing ring of the lens. The actual focusing is done by an internal motor and the focusing ring is not mechanically driving the focusing mechanism but senses which direction the user wants instead. It is my impression that moving the focusing ring is only effective when the shutter button is half-pressed. This is because I tried to change
  17. Isn't this IC 59 and IC 63? https://apod.nasa.gov/apod/ap111103.html
  18. If you insulate the front end of the laser (where the laser diode itself is) it will not be affected by the cold so much.
  19. First thing to do is to figure out how far from focus you are. You need two numbers: the focal length of your scope and the distance to the farthest object you CAN focus.
  20. Hello, If you have the stomach for it, you can hack an inch or so off the bottom of the tube and reattach the mirror cell. Perhaps you will lose some light as the secondary will be closer to the primary and may have been sized to the limit, but you are doing astrophotography so you can always get more light by increasing exposure length. I've done this with a cheap f/8 Newtonian.
  21. The Pacman Nebula in Cassiopeia (NGC 281). Captured with APT, Canon DSLR, Baader coma corrector, Hα filter, .25m f/4 reflector, at ISO800, 19x600sec exposures. Guided with PHD2, finderscope, Atik16ic. Registered and stacked in Iris, processed in PixInsight, no calibration frames. The last 5 exposures were taken in a sky with no naked-eye stars visible (due to thickening high cloud) and the first 6 were badly focused! So definitely a session to learn from...
  22. Thanks! I know there's no getting around the extra shutter control cable needed for >30 second bulb exposures. I was hoping that I could still use it with a Windows 10 (64-bit) system, but apparently not.
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