Pentax XW 30mm /40mm in f7 refractor

[CeeDee]

I have an FLT 110 (f7) and FLT 132 (f7) and I cannot decide whether to add a Pentex XW 30mm and 40mm to my eyepiece collection for low power views. I love the the comfortable viewing and the tack-sharp images in the higher mags of XWs but will the exit pupil be too large (I am 64 years old and I know eye pupils don't dilate as well as you get older ). Thus would my eyes 'stop down' the light transmitions from these eye pieces? I would really like to hear from anyone on the forum who has used these particular eye pieces with an f7 refractor.

[Mark at Beaufort]

Hello CeeDee

I know you want a user with Pentax EPs but I have a 4" APO f/7 frac and will be 64 this year. Similar qualifications .

I have used a 26mm Nagler and a 35mm Panoptic on this frac and they both gave an excellent wide field view. I would guess that either the 30 or 40 Pentax would be OK with your age/eyes.

If I had a choice it would be the 30mm - it gives a useful magnification, good FOV and will darken the sky slightly above that of the 40mm.

Hopefully, someone that has these EPs will advise you further. On the other hand you could ask FLO for their opinion as they stock Pentax EPs and William Optics scopes and Steve, James and Martin are very knowledgeable.

Mark

[Ben Ritchie]

I've used the 30mm with an f/8, and it's a terrific eyepiece - my favourite at that focal length, and I think i'd pick it over the 31mm Nagler. I don't think there's likely to be problems with exit pupil on the 30mm.

While the 30mm and 40mm are impressive eyepieces, I don't think i'd have both though, unless money really isn't an issue. With a 4" or 5" refractor the 30mm will show a whole lot of sky, the 40mm will show more but I don't think there would be a great difference in feel between them, apart from a bit of background/exit pupil effects. I've always found that one low-power eyepiece is enough for me, and for real widefield wandering i'd always personally look towards a short focal length refractor - given the 40mm is £435 new you could pick up a nice 80mm and probably still save money...

[John]

I was loaned a 30mm Pentax XW and it was an excellent eyepiece - my scopes at the time were an 8" F/5.9 newtonian and a 4" F/6.5 ED refractor. Personally I preferred the 31mm Nagler because it gives the FoV of a 40mm with a smaller exit pupil and darker background sky. If weight was an issue the 30mm XW (and the 40mm probably) score of course - the Nagler is a real lump !.

My comparison included a Skywatcher Nirvana 28mm (also a lump !) which compared very well optically and costs a lot less of course.

[CeeDee]

Many thanks for your comments lads. Very much appreciated. I managed to compare my new 20mm Pentax XW with my exisiting Panoptic 19mm overr the week end and I have to say although the Pentax is slightly more comfortable to use, the Panoptic just won out in terms of edge-to-edge sharpness. I just wonder how the 30mm XW might compare with the 35mm Panoptic....?

I could be wrong, but my gut feeling is that for wide field viewing probably the Panoptics have it but the Pentax XWs certainly cannot be beaten (as yet) at 14mm and below in my scopes.

[AstroSylv1]

Dear All,

I am actually looking for a Pentax XW 30 mm, and well, since it's been discontinued by Pentax, it's a real hunting nightmare to find one... Anybody has an idea of where to find one ? Any good second one available ?

Thanks

Sylvain

[Astro_Baby]

i bought the last new XW 30 in the UK some time ago. If you are not a total wideview freak you could always consider the Pentax XL which are more reasonably priced and probably more available on the second hand market.

[AstroSylv1]

Thanks for the feedbacl... but since I am viewing on a non-motorized dob, I'd rather go to 70 deg... this is why the XW's are what I am looking for. Besides, the transparency and the sharpeness of the XW's are a must. So, still desperately looking for a last one, in a forgotten drawer, or in a display, or second hand.. whatever :-)

[rowan46]

I think your chances of finding a 30 or 40mm xw are pretty remote. I have seen a handful   of 30's  and 1x40 in the last 3 years on abs. If you want wide  maybe look at the meade or  explore scientific 68 both very good eyepieces

[Tinker1947]

Go for a 31mm Nagler, or a Panoptic the 35mm would be close to the Pentax...

[alan potts]

Cee Dee,

I don't know what sort of size my old eyes stop down to as you say, I'm 58 and the other day was told I had the eyes of a younger man, so maybe I should give them back. I use the 35mm Panoptic all the time in many of my scopes, it is a great eyepiece and I would say your biggest issue is not with the Exit Pupil but with the Light Polution. If you have too much in the way of LP you will have washed out views in which case the shorter focal lengths of the Pentax and others will darken the sky somewhat.

Alan

[estwing]

Holy thread revival batman!

[AstroSylv1]

Indeed, quite a revival... this is due to my hunting of THE eyepiece :-) thanks all for your inputs.. I'll keep looking for one, no rush, I am patient, and my eyepiece collection is only made of 3 focal length, and it's ok with me so far... the hunting of that Pentax eyepiece is more of a hobby or a Graal to find than a real absolute need... I have a Pano 24, Delos 10 and Delos 4.5, and it covers all I need to far... I used to have a XW 5 mm that I miss actually, the image was as perfect as the Delos 4.5, but the eyecup was easier to use than the Delos' one. Anyway, thanks all for your comments, my hunting is not over... I have time 

[estwing]

Happy hunting!

[rwilkey]

Hi Cee Dee, I think the 30mm or the 31mm hit the sweet spot for low power use, though looking at what ep's you already use, esp. in fracs, I can't see that you need to urgently fill that gap, what with the 32mm Panoptic etc?

[AstroSylv1]

Found one, got it, tried it, love it ! I told my kids it would part of their heritage :-D

[AstroSylv1]

After two nights of testing it against a genuine TMB Paragon 30 mm, it confirms that the XW is still ahead of its peers... A little less contrast than the TMB, but more comfortable and better corrected on the edges...

[AstroSylv1]

Same applies to the TMB Paragon 40 mm compare to the Pentax XW40 I have been lended.

[YKSE]

After two nights of testing it against a genuine TMB Paragon 30 mm, it confirms that the XW is still ahead of its peers... A little less contrast than the TMB, but more comfortable and better corrected on the edges...

Same applies to the TMB Paragon 40 mm compare to the Pentax XW40 I have been lended.

That's really a high praisae of TMB Paragons considering the price differences. Do you see any differences in edge correction of 30mm and 40mm?

[nicoscy]

I am also interested to hear about the Paragons in terms of edge correction.

How do they handle astigmatism at f7?

[John]

I believe the Skywatcher Aero ED's, the Astro Tech Titan II's and the TSED 2" range have the same optics that the TMB Paragon used ?

I'd be surprised if they were as well corrected at the edge of field in a slowish scope as the Pentax XW 30 / 40 is   

[Astro_Baby]

Problem with the Pentax XW is they are probably as rare as hens teeth.  Sorry but as far as I know I bought the last new one in the UK some time ago.

Its been used once only and was rather nice   but unfortunately I cant say more than that not having used it much.  It was vert flat in the field and had very good correction at F5 and was also very comfy to use.  Thats about the limit of what I could say - it was hardly an exhaustive test

[AstroSylv1]

I tried all 4 eyepieces (XW 30 and 40, and TMB Paragon 30 and 40) on my SW 100ED Pro, the golden color one. It's at f/d 9. In terms of edge correction, both XW easily win the contest : the Paragons show a lot of astigmatism, so much that it was difficult for me to really claim if the true FoV was the same in both XW line as the TMB line... If you stick on axis, TMB Paragons show a little better contrast, but off axis, the XW show way better correction. I didn't try on my Dob.

[YKSE]

 the Paragons show a lot of astigmatism, so much that it was difficult for me to really claim if the true FoV was the same in both XW line as the TMB line

Can you quantify "a lot of"? Is it 20% or 60% from the edge? Do you see any field curvature in any of the 4 eyepieces?

[AstroSylv1]

I would say the very extreme edge, like the last 10 % of the TMB, typical astigmatism on the edge to me... and no, no field curvature on my 100ED with any of the 4 eyepieces, which is surprising, reading all the comments of the FC of the Pentax on different forums... Never had to change the focus position between on axis and off axis... or maybe the eyepieces have a field curvature compensating the one of my refractor ? I wouldn't know...