On Thursday, May 21, 2015 at 12:13:28 AM UTC-7, RichA wrote:
On Wednesday, 20 May 2015 11:59:00 UTC-4, palsing wrote:
On Wednesday, May 20, 2015 at 3:51:20 AM UTC-7, wrote:
On Wednesday, May 20, 2015 at 12:23:52 AM UTC-4, palsing wrote:

Whatever, these guys are terrific planetary eyepieces...

Are you damning them with faint praise?

Not at all, these guys are highly regarded by many folks who like to observe the planets, planetary nebulae or double stars, especially at high powers, even though they have a very restricted 32-degree field-of-view when compared to most modern eyepieces. See this...

http://www.cloudynights.com/documents/tmb.pdf

... and check out the chart on the last 2 pages... and this review...

http://ejamison.net/equipment_reviews3.html

... and there are many others to be found, too.

So fantastic...they stopped making them due to lack of demand. But, if anyone is interested and you know a good machinist, you can always have barrels made and buy 10/20 scratch/dig triplet lenses from a good supplier and get something similar to the monocentrics.

I believe the main reason they stopped was because the designer and manufacturer, Thomas M Back, passed away suddenly in 2007. Keep in mind also that these are very specialized eyepieces and not very popular with the general amateur observing population, due to their very narrow field of view. Still, there are a lot of experienced observers who swear by them for high magnification views of small and dim objects, as they pass more light than just about any other eyepiece design.

\Paul A