Powermates Barlows and OCA's

Could someone explain the difference between a powermate, a barlow and an OCA. My get feeling is that they are similar but have some differences.

I recently purchased a Stellarvue binoviewer and did not get the adapter with it. I will be using it on my 8"SCT and figured I didn't need one. I also have a WO 66 refractor. Will my current Park 2x barlow work with the refractor or do I need a OCA.
Thanks
Doug Grebe

Hi Doug,

I was hoping someone else would jump on this, but since there has been no response, I will take a stab at it.

A simple Barlow is a single element device that increases magnification. While they amplified the magnification of your telescope, they also played havoc with eye-relief. The two element Barlow was the first to do more than increase magnification without degrading the optics of your telescope. The telenegative Barlow was a three element system. The powermate is a four element system.


The OCA or OCS depending on the manufacture is a multi-element device that was primarily designed to overcome the long light path of the binoviewer by altering the light cone. This can be done with a simple single element Barlow but the magnification quickly becomes too high with that approach. The typical OCA or OCS consists of a combination of Barlow elements and focal reducer elements. This combination controls the level of magnification.

Don Durbin

Doug Grebe said:
Will my current Park 2x barlow work with the refractor or do I need a OCA.

The Parks 2x will likely work, though it will probably be more like
3x or 4x when used with the binoviewer, and that may be more power than
you want. This is where an OCS or OCA would come in handy; it would
give you lower powers.