Understanding Pentax XL and XW eyepieces

Posted by Greg Nowell 06/23/2009 07:00AM

This is a pictorial essay on Pentax XW and XL eyepieces. Disassemble at your own risk! I hope you find this article useful.

Before the pictorial presentation, a few comments: There's no point in getting the 14mm and 20mm focal lengths on your fast dobs. They just won't work. The short focal lengths, 3.5mm to 10mm, and the long focal lengths, 30 to 40mm, will do fine on fasters telescopes. At f/6.5 and longer, you are "in the zone" for the full range of Pentax eyepieces.

To get eyepieces that do better than the short focal length XWs on planets, you are looking at alternatives such as the Zeiss Abbe Orthoscopics, and even then, you may not be sure, most of the time, on most nights, that you're besting the XW. You will find the ergonomics of the super-pricey planetary alternatives inferior to the XWs.

Pentax eyepieces are engineered with a different aesthetic priority in comparison to Naglers and even wider field eyepieces: the aesthetic assumes that you want the field where you can see it, and eliminates kidney bean and other distractions. If you like this aesthetic than XWs are for you; if you prefer "space walk," then you are going to be looking at Televue alternatives.

In terms of light transmission, Pentax XW eyepieces are at 96% which does not leave much room at the top for the competition, whether multi-element or "simple glass."

So far as I know the Pentax eyepiece series have made their way into amateur astronomy entirely on reputation. I have never seen them advertised except as part of the general offerings on multi-page spreads from major vendors. There are no "Pentax on oyster shell ads," which is too bad, because the Televue ads were quite clever.

The XL eyepieces are no longer in production, and their prices on the used market seem to have stabilized at about 90% of their former new prices.

The used market for XW eyepieces is distorted by retail pricing practices that have the sanction of the U.S. Supreme Court, which voided a certain section of the Sherman Antitrust Act in June 2007. The vote was 5-4. The result it is legal for manufacturers not to let retailers listed prices that are below the manufacturers' minimum. The prices advertised on web sites for XWs (and many other consumer goods) are not the "real" prices that vendors will actually sell them for. To get the real price, you must actually make a phone call. There's no way around this. Eyepieces that list at $330 will typically sell "on the phone" for $290. The 30 and 40mm XWs will typically sell "on the phone" for about $490, as opposed to $540 listed on web sites.

This pricing confusion has been transferred into the used market. Many of the people selling a 10mm XW, for example, are unaware that the "telephone price" is $290 because they paid substantially more. They thus list used for $270 or $275 and think they are giving a good break on the price. They often find buyers who are also unaware of the "telephone price." But the truth is that at $275 one might as well buy a new one at the "phone price" of $290.

Photo No.1