Telescope Reviews: How big is a star..in pixels??

I struggled with focus early on, tried a few different software packages, all of which focus on metrics like FWHM etc, and never had a 'good' result from it. Then one day I stumbled on a different method, that actually works really well for me.

Like you, I am on the island, and, we have a great view of the northern sky from here. I use this technique with both the Nikon D-50 and the Canon 300D. I always start by aiming at the alcor/mizar pair. Looking thru the viewfinder, it's relatively simple to get focus in the ballpark on this widely spaced pair. Once I'm close thru the viewfinder, I switch to the 'shoot/download/analyze' method. I'm using motor focus on the scope, so I can make very fine adjustments, semi-repeatable.

For the second stage of the focus, I completely ignore star brightness, and any metrics like FWHM etc, but instead concentrate on mizar, it's a double. Set the camera to jpg fine for faster downloads, and use 2 second exposures, then adjust focus to cleanly split the mizar double. That gets us 'real close', and when that double is cleanly split, you will see another star (mag 7) starting to show up between alcor and mizar. You may have to bump exposure time up a little to see it. Once that one shows in the frame, use it to further fine tune focus, maximizing its brightness. When you get 'really close', it may start saturating and you need to shorten exposure again, back down to 1 or two seconds.

Once I've got that nailed, I slew onto my final target, and take a 10 or 20 second exposure to validate my framing. To finalize focus on my final framed position, I like to use at least 15 second exposures, home in on some very dim background stars that _just_ show up in the frame, then make fine focus adjustments to once again maximize the brightness on those dim stars. Using specific numbers with the 127mm mak and the 300D, when I'm 'close' to focus, I will be able to clearly distinguish mag 9 or 10 stars on a 15 second exposure. When focus is right on the money, mag 11 and 12 stars will start popping out, which were not visible on the earlier shots.

Using the nikon camera, it's sometimes tough to find software that actually works and 'helps', but, there is stuff out there that can be quite useful. Here is a technique you can try, and you will be quite surprised at how well it works. Start Deep Sky Stacker Live, then as you take focus shots, download them immediately into the folder DSS Live is monitoring. Watch the statistics on the frames as they get absorbed by the program, ignore FWHM initially, and just look at star count. Using shorter exposures (10 to 30 seconds), the star count will start to jump up dramatically as you get very close to focus. I use jpg with the canon 300 for focussing because it's usb 1 and VERY slow to download (62 seconds for a raw image), but the nikon we just use raw all the time, it's usb2 and downloads are snappy.

Where are you located on the island ? We are in Duncan, and will have a new mount to try out just as soon as this weather system finishes moving through. If we got together for an evening with a clear sky, I think we can get you repeatably focussing that system 'dead on' with just a couple hours of 'playing'. Are you going to be at the Rascals star party end of the month on the malahat ? We will be there, easy to spot us, his and hers astrophotogrpahy setups. His = EQ6-Pro with skywatcher telescopes mounted sid by side, Hers = HEQ5-Pro with a Williams Optics Zenithstar 80 hosting a Nikon D-50+300mm lens piggyback. A year ago we couldn't get anything focussed repeatably, today, we can set up, polar align, and focus both systems in about half an hour. Up until now, 'hers' has been on the NEQ3, but, the HEQ5 should arrive today or tomorrow

And yes, I'll plead guilty to inviting in 2 weeks of cloudy weather by purchasing new gear, at least I had the foresight to time it on a full moon cycle