Fabulous XW!

[cs1cjc]

Pentax actually publish technical information on XWs including details of the focal surface curvature (thanks Don Pensack):

Pentax+ / smc PENTAX XO smc PENTAX XW

Pentax+ / smc PENTAX XO smc PENTAX XW

4 focal lengths have positive field curvature (40/30/20/14) and 4 have negative field curvature (10/7/5/3.5). Since newtonians also have positive field curvature (equal to the focal length), the 4 longer ones can provide a bit of edge misfocus in older observers whose eyes no longer accommodate the field curvature. In refractors the field curvature is in the opposite sense (I think, though I have got it wrong before) and generally about 1/3 the focal length so it is the 4 shorter eyepieces that may be a problem in this case.

Many if not most eyepieces have some degree of field curvature and it is only because Pentax have, uniquely so far as I know, published this information that it is possible to do this sort of paper based analysis. Otherwise one has to be at the eyepiece deciding whether the eyepiece is acceptable to ones own eyes.

[John]

Looking at your high power collection now John it appears your Antares 1.6x is also redundant

Possibly, although the barlowed Ethos put up superb views too and it's nice to have that option

I also use the 1.6x barlow for barlowed laser collimation.

[Damo636]

Possibly, although the barlowed Ethos put up superb views too and it's nice to have that option

They sure do..

[PaulC-I]

I don't recall responding to this thread so far so here goes

I've had all the xw lengths (except 40 & 14, please read on)and in my opinion they performed up to level of the best orthos and mono eps I owned. Amazing considering the extra glass involved. Only moved them on as I now exclusively binoview. Although I still have a pair of 20's That will stay with me no matter.

The 14's are the only ones I had not had due to the negative remarks so went for a pair of Denk 14's Which are and heve been reveiwed on CN as bested the XW 14. These pair of Denks have given me the best planetary views to date and are identical in ergonomic use and the cool tack razor image as the XW line

Hope this helps

Paul

[faulksy]

which is the better the pentax xf or the xw ?

[michael.h.f.wilkinson]

The XF 8.5 is outstanding! I do not know how it compares with the XW, except that the latter has 10 deg more FOV (70 rather than 60 for the XF). The focal lengths are different, of course. The XF is really good value for money, at 159 euro. I am planning to replace the Radian 10 by an XW 10, and adding a 7 at the short end. That would give me 10, 8.5, and 7mm for planetary observing in my F/10.

[Doug]

Iv'e also noticed there is a Televue Nagler 12mm T4 for sale on Astro buy and sell

A excellent eyepieces