Here's how I get the PA with video - If I run my occultation timing device over the video stream (I use a GSTAR-EX), then I can registax align it over a number - ie a non-moving object to give the 'streak' when i stop the scope drives - I've enclosed an example I took a few weeks back. There are plenty of software packages that can overlay an image on top - webcamMax for eg. I'm sure there must be an easier method but it works for me.
I didn't do such a good job - I needed to have turned up the gain a little to get a more saturated path, but it is enough to get a reading.
The interesting thing is that my PA seems to be much closer to 90 degrees than it is predicted to be, and your estimated PA is spot-on.
If you get another chance to make a measurement, then it would be very valuable - one of my colleagues at the AAQ could make something useful from it...
Great work Dennis.
>snip
If you get another chance to make a measurement, then it would be very valuable - one of my colleagues at the AAQ could make something useful from it...
Jonathan
Hi Jonathan
You’ve made easy work of splitting the Pup – well done! The GStarEX certainly seems a very versatile and capable imaging device.
I don’t follow a rigorous observing or imaging program, I’m more of a space tourist so I don’t calibrate or pre-configure my system to a baseline set up and orientation to allow me to make measurements as you do.
However, I’ll certainly give this one another go and orient the DMK aligned to the NSEW axis more rigorously, so I am better able to take some measurements. All I need now are some, well, clear skies!
As a comparison against the Mewlon 180 F12, here is a stacked image of Sirius taken through the Celestron C9.25 F10 with essentially the same set up; a TeleVue x4 PowerMate and DMK31, albeit in seeing judged to be slightly inferior, estimated at 6 to 7/10 on 7th Feb 2009.
What was really surprising, were the patterns of diffraction spikes in an SCT that only has a central obstruction, no spider vanes????
The spikes are rather odd for an SCT.. I would have thought it would give normal round stars with a slight airy disc... ?? Oh well.. In any case, this is a good comparison, the C9.25 was still able to very clearly split the pup from sirius, although I think due to the seeing, the Mewlon image has come up trumps.. Its always good to be able to do these sorts of comparisons..
Well, dogged persistence has paid off. I cracked it visually a few nights back, and was surprised at the distance they are apart. Dim though that secondary, dim I say.
With the x4 PowerMate, when I defocus Sirius just inside and then outside of focus, I see nice concentric rings either side, once the tube currents have died down.
I’ll confess up front that I’m no optics genius, but I once saw a photo of pinched optics in a book and I think the diffraction patterns were more like rounded triangles?
Well, dogged persistence has paid off. I cracked it visually a few nights back, and was surprised at the distance they are apart. Dim though that secondary, dim I say.
Hi Gary
Well done mate! You must be riding the wave of recent Kiwi successes.
I am curious to know: is that the true diameter of Sirius you are seeing, or would it actually be say 70% that size and the atmospherics etc are 'fuzzying' its light image up bigger?
Sirius A is grossly over exposed in order to bring out the much fainter Pup, Sirius B. If I set the optimum settings for Sirius A alone, it would look something more like the following example of Eta Orion, where you can see the Airy pattern.
I would probably have to expose at around 1/1000 to 1/2000 sec to avoid Sirius A from saturating and “blobbing out” to the extent it did.
On March 6th, I had another go at Sirius A and B with the intent of trying to make a composite of the pair, without the A component being “blown” out. I used a Celestron C9.25, Televue x4 Powermate and DMK31AF04 CCD camera, working at F40 and an effective focal length of 9400mm.
To record both A and B in the same frame, I used an exposure of 1/15 sec, which grossly over exposed the much brighter A component, but revealed the fainter Pup.
To record A as a more pleasing “dot” I reduced the exposure to 1/4000 sec which means that B was not recorded as it was too faint for such a short exposure.
I then made a composite of A (1/4000 sec) and B (1/15 sec) to more realistically show the separation between these components. I measured the distance between A and B at around 76 pixels. With an approximate image scale of 0.1 arcsec/pixel, this gives a separation of 7.6 arcsecs.
Finally, I included a single frame from the 1250 frame AVI to show what a raw, unprocessed image looks like.
