This evening there was a lull in my usual lunar occultation work and I turned my C14 onto Sirius. Now my C14 has always suffered from a slight haze on the inside of the corrector plate, and I have never plucked up the courage to remove and clean it like I did my old C8. Further the alignment of the secondary is tweaked to approximately correct to give good star images but is not perfect and in/out of focus images at high power will testify. So what I am saying is the optics are not perfectly clean nor perfectly aligned. Conditions were relatively steady. So I first of all inserted a standard (40 to 60 degree field) 8mm – 24mm zoom eyepiece. At 24mm (X163) the pup was very difficult to see close to the brilliant image of Sirius. It was easier to zoom in to the 8mm focal length (X489) when it stood out so plainly with black sky all around that I was wondering whether I was looking at the correct star. Zoomed out back to X163, (now knowing precisely where to look), I was able to spot it, by moving my eye around the eye lens a little, to cause the rays emanating from nearby Sirius to avoid this area and so reveal the ‘pup’ very close to Sirius. Re-inserting my standard 25mm eyepiece (X156), I managed to repeat this operation.
Now my views on this are, short of using an occulting bar: Firstly, if using a Newtonian, check that the spikes from the diagonal support will not be in the way.
Secondly, ensure that the conditions are sufficiently good to obtain a sharp and relatively stable star image.
Thirdly, don’t muck around with a low magnification. Go straight to 400 or 500 so that the pup will be a reasonable angular distance from Sirius. Only when thus located, scale back and check out the lowest magnification that you can reasonably see it. I would suspect this to be around X150 or a tad less. There is no point trying to initially pick it up at a low magnification!
As I reported earlier in this thread, these results tonight were very similar to those with my 150mm refractor last March, except that the refractor produced a much fainter image and a whole lot of colour from chromatic aberration.
I will try 150mm refractor with the 112 mm aperture stop to see if I can still pick up the pup.
Now I must confess, that tonight I did not play fair at all. Not only was I using the C14, but you probably don’t want to know the altitude of Sirius at around 11hrs 30min when I observed it. I will tell you anyway… around 65 degrees!
So whatever I have recommended should be taken with a grain of salt when you factor in its altitude from your site.