[Om_Audio (Clifford)]

I joined the forum just to thank you- no other info on collimation actually gets into the specifics of which screws do what. I got a pair of Zhumell 20X80 that were way out. I got them used but in new cond and was pretty sure I made a $90 mistake until doing some research online. In the end I was ready to start turning screws but really wanted to know what prisms would actually move and in what direction. Anyway- I fixed them in the morning and then by that night out in the Mojave Desert was discovering for myself Jupiter and it's moons and more. Thanks. C

Originally Posted by erick

Here you go:-

http://www.oberwerk.com/support/collimate.htm

http://www.cloudynights.com/item.php?item_id=416

Before you go adjusting anything, do look at the exit pupil and see if it is nice and round or "cat's eyes"? See the Cloudy Nights article.

Woops, I also made a mistake re the adjustment screws. Two are at the eye lens end of the prism, two (at 90 deg to the first) are at the objective lens end of the prism. See the Cloudy Nights photos. Usually, you only ever have to worry about a small tweak of one of the screws near the eye lens end. Your miscollimation sounds more gross.

You can check collimation in daylight, usually on a tripod or resting on a fence/rail/cushion. Find a distant straight left/right line (a gutter is usually a good choice). Set yourself up at 90 deg to it so it goes cleaning left to right across the view. You need to practice holding your head back until you see two separate images, them bring your head forward until they touch each other - do the straight lines in each come together, or is one above the other? You can attempt to adjust any up/down misalignment of the images using one screw (closest to eye lens). If you reach the end of travel (prism stops moving so image stops moving), you'll need to move to the same screw on the other prism. You can even do this is the dark on a bright star/planet. Practice pulling head back until two separate images, then move head forward allowing the images to come together and you'll see if the two images of the star are correct in the up/down direction. Remember, some left/right difference in images is not a problem - your eyes will adjust to that.