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darn close...
Well, it's pretty darn close: after a while you can start becoming really obsessive about "spot-on" - I'd recommend seeing if you can do a star test if you feel like it mbaddah. You'll need a pretty good "seeing" night and I'd suggest start with about 100 mags or so (the rule is double etc that, but I found that helped me get the gist first up.)
Get a star (not a dim one) focussed in your scope and then take it out of focus either side of focus; observing how the star appears to expand into a soft out of focus "disk." If there isn't too much turbulence etc in the atmosphere you should, on carefull obsevation, notice that there should/will be a dark central spot in this disk, which, as you go much further out of focus, develops into an image of your spider assembly. But well before this, in fact at about the time you see the tiny central spot, you'll see a number of "diffraction rings" like tiny black/dark circles (hopefully concentrically) surrounding this central dark spot.
I don't seem to get past seeing 5 of these concentric within each other rings (like an archery or rifle target around the central spot) but they should be, along with the central spot, centred and evenly concentric within your out-of-focus star disk. Bear in mind that these dark rings will be very close to each other and may take some discerning at first. If they're not uniformly concentric then they indicate more collimation tweaking.
Once you get the hang of seeing them, bung up the magnification for a more reliable indicator - but remember, if it's a lousy night you'll most probably have buckley's chance of seeing them! I'm sure there's links on IIS to star-test images and most manuals have something about them in them.
Cheers, Darryl.
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