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Getting a Denk to focus on a Newt

Started by georgepn, 02/27/2007 08:14AM
Posted 02/27/2007 08:14AM Opening Post
My astro club has a Denk bino that was originally intended for SCTs. It has two 2” lenses: one being what I call a “Barlow” and the second being a Star-sweeper. I’ve borrowed it to use on my Obsession 20” F/5 Dob, but can’t get it to focus with any configuration of these lenses, or without them. What do I need to buy from Denkmeier to get to focus without cutting the truss poles on my Dob?

George N
Posted 02/27/2007 09:14AM #1
Hi George,

You may already have what you need to come to focus in your DOB.

The OCA or OCS is normally a combination of a Barlow and a Focal reducer lens. The Barlow goes in front of the focal reducer. (i.e. closer to the telescope objective) One rule is that the focal reducer cannot overpower the Barlow. Another variable in this is the distance between the Barlow and the focal reducer.

Your StarSweeper module is a focal reducer. Try plugging that into a Barlow and then put it in your DOB. You may need to slide the StarSweeper away from the Barlow to get your DOB to focus.

I did a little write-up about building your own OCA a while back. You can find it here.

Good luck,
Don Durbin