testing optics

hi Folks

Just wondering how I go about using double /multiple stars to test the optics of my 90mm F5.5 refractor. I have managed to split castor but I dont know if this is an easy or a hard test. Anybody got any suggestions, as I have not got a clue when it comes to double stars. Thanks

Trevor --

Castor has a separation of 2 arc-seconds, which is a non-trivial split.

However, you should be able to do a bit better yet: the Dawes limit at 90mm is 1.3 arc-seconds. Try 52 Orionis or Pi Aquilae (both 1.4 arc-seconds).

Note that you'll need a lot better seeing than we had tonight (at least in Louth). I was unable to split anything under 1.6 arc-seconds, even with much more aperture.

Cheers,
-- Jeff.

Thanks Jeff.

Would you believe it, it has clouded over here, lovely and clear all day and night and now clouds. I hope it clears for 2 am or so. I must have a go at 52 Orionis the next night its clear. Thanks again.

Trevor,
Try this link, from Cloudy nights

Doubles to test your optics

Castor is a pretty good split, though the difficulty in splitting it is more related to the brightness 1.9 & 2.9 of the stars rather than the Separation 4.3".