Pentax 3.5 XW

[Timebandit]

Hello there. I have just acquired a lovely pentax 3.5 xw. It was a bit of a debate whether to purchase a delos which was for sale or the Pentax. The Pentax won , mostly because I have got pentax xw already and optically find them first class. I do like televues and rate them very highly. But they do seem to be getting harder to justify some of the price requested. And the Pentax from my use of them seem optically as sharp as you are going to get unless you dip into the pot of the ZAO or TMB supermono. The Pentax has the field of view of around 70 d which I like, and nice eye relief of around  the 20mm mark.  The eyepiece is for high power use on my Ed apo refractor and is pushing the limits at around 260 x magnification. But on a good clear night then the views of splitting stars and high power lunar ,planetary use should be possible and interesting. It is also going to be tried in the dob . I have heard the 500 x lunar magnification possible and this eyepiece in my dob will give around the 450mark, and with a 1/10 mirror it will be an interesting experiment how the dob reacts to such a high magnification on the lunar landscape. Therefore I do look forward to a nice clear steady atmospheric night to put the frac and the dob to the test with this very capable eyepiece ,

 

 

 

 

 

I hope you approve of the Pentax as an addition to the eyepiece case☺

[John]

I do approve

Steve (FLO) was pursuading me to try XW's years ago but it took me a while to come around to them. Once I did (Steve loaned me the 10mm) I could see what he was talking about - they ousted my much loved Nagler T6's (although the latter are excellent too) !

I use the 3.5mm in my refractors more than in my 12" dob but it does occasionally get some use in the big scope when the target / seeing will support 454x !

I find it and the 5mm XW fantastic lunar eyepieces and they seem to show details that other eyepieces just hint at.

 

[mikeDnight]

I love Pentax XW's and think the 3.5 and the 5mm to be some of the finest eyepieces available, having the purity of a quality orthoscopic but with much better field and eye relief. I also think the 10mm and 20mm are terrific on the deep sky giving a very comfortable field and offering superb contrast and definition. Over the summer i bought a second hand 14mm XW but havent had time to try it out yet. Though ive read mixed reviews about the 14mm im sure ill find good reason to fall in love with it despite any shortcomings. 

Congratulations on your acquisition of that wonderful 3.5mm. I think its one of the best if not the best high power eyepiece on the market, only beaten by using two eyes.

Mike 

[Timebandit]

On 30/09/2016 at 17:47, John said:

I do approve

Steve (FLO) was pursuading me to try XW's years ago but it took me a while to come around to them. Once I did (Steve loaned me the 10mm) I could see what he was talking about - they ousted my much loved Nagler T6's (although the latter are excellent too) !

I use the 3.5mm in my refractors more than in my 12" dob but it does occasionally get some use in the big scope when the target / seeing will support 454x !

I find it and the 5mm XW fantastic lunar eyepieces and they seem to show details that other eyepieces just hint at.

 

 

Thanks John. It's nice to know that someone with so much more experience than me also rates these eyepieces highly. Steve from FLO Obviously gave you the heads up when loaned you the 10mm to gain your interest, and judging from your eyepiece case you are obviously very happy with them .

I first noticed the XW being talked about by the astronomy site on the other side of the pond(CN) . And as those chaps in the US do really seen to like the televues and defend them quite strongly at times, when I heard opinions of the visual sharpness xw equal or better than numerous of the televues then it certainly got my interest. And also with SGL members also rating them highly, when some used came up I put my toe into the water with the Pentax XW and I must say was very impressed and rate these eyepieces as superb . I have had my best view to date of Saturn with the Pentax, so that speaks for itself .

The 3.5 mm I got primary for the frac apo but will try it in the dob at 450x should be very interesting on a clear night on the lunar landscape.

I presently have the xw 3.5 , 7 and 10 all first class in my opinion and when compared to the cost of something like the delos then they seem sensible price. As you can probably notice the 5xw is missing from my collection, so a 5mm will have to be in my sights in the near future I suspect☺

 

 

23 hours ago, mikeDnight said:

I love Pentax XW's and think the 3.5 and the 5mm to be some of the finest eyepieces available, having the purity of a quality orthoscopic but with much better field and eye relief. I also think the 10mm and 20mm are terrific on the deep sky giving a very comfortable field and offering superb contrast and definition. Over the summer i bought a second hand 14mm XW but havent had time to try it out yet. Though ive read mixed reviews about the 14mm im sure ill find good reason to fall in love with it despite any shortcomings. 

Congratulations on your acquisition of that wonderful 3.5mm. I think its one of the best if not the best high power eyepiece on the market, only beaten by using two eyes.

Mike 

 

High Mike, I like the fact that you feel the 3.5 and 5mm xw to be some of the finest eyepieces available. I agree optically they are super and with the extra field and eye relief than you get over the normal Ortho. You get top Ortho visual performance with the xw IMO, but with the comfort of lovely eye relief and such a nice field of view at around 70d .A 5mm will have to be in my sights I suspect and hopefully in the not to distant future.?

[RikM]

I have the XW's from 5mm through to 20mm and love them. When I eventually get a quality 100-120mm refractor I will surely get a 3.5mm XW to go with it.

[mikeDnight]

I had my first opportunity last night to try out my 14mm XW that I bought second hand over the summer. I noticed the Pleiades was on view and although it wasn't high, i set the scope up on its AZ4, inserted the 14mm XW and WOW! I wasn't dark adapted and the scope was warm yet the nebulosity was the first thing that struck me. It wasn't just visible around the brighter stars but the whole cluster was swaithed in a wraith like mesh which was easily visible. The Pentax XW's are a perfect match for my small refractor and although the 14mm has received mixed reviews, i found no fault with it. To get an idea of the real field I aimed the scope at M31. The nebulous arms of the galaxy extended beyond the field but the two companions were still well within the field and were very obvious. The double cluster was beautiful with its orange and red stars standing out against their glittering backdrop. The whole session lasted no more than 15 minutes but the memory of it will remain with me forever.

Mike. 

[John]

Great result from the 14 XW Mike

 

[BGazing]

how is the field curvature in pentax xws? i know people mention 20mm as the one which adds to the curvature of the telescope, how about the others?

[mikeDnight]

8 minutes ago, BGazing said:

how is the field curvature in pentax xws? i know people mention 20mm as the one which adds to the curvature of the telescope, how about the others?

Field curvature in the XWs has never been a problem for me at least. The 20 mm is an excellent eyepiece for dso's and star fields, having great contrast and purity, and is currently my lowest power eyepiece. I'd never part with it! The 31mm Nagler is far worse in respect to field curvature but even then FC only an issue when observing terrestrially. 

Mike

[Ricochet]

5 hours ago, mikeDnight said:

Field curvature in the XWs has never been a problem for me at least. The 20 mm is an excellent eyepiece for dso's and star fields, having great contrast and purity, and is currently my lowest power eyepiece. I'd never part with it! The 31mm Nagler is far worse in respect to field curvature but even then FC only an issue when observing terrestrially. 

Mike

Are you confusing field curvature (different focus point at centre and edge of field) with pincushion distortion (straight lines appear curved)? I find FC more objectionable than PC for astronomical observation but probably the opposite terrestrially. 

5 hours ago, BGazing said:

how is the field curvature in pentax xws? i know people mention 20mm as the one which adds to the curvature of the telescope, how about the others?

These diagrams can give an idea of how they compare to each other. Notice that the longer focal lengths curve in one direction and the shorter focal lengths in the other so that one set adds to the FC of the telescope and the other cancels. 

[BGazing]

Thanks! This is the first time I see something like this released by a manufacturer (or recorded by someone else). Looks like the shorter lengnths cancel the curvature out (the typical one), and I see why 20mm is singled out in reviews...

[mikeDnight]

12 hours ago, Ricochet said:

Are you confusing field curvature (different focus point at centre and edge of field) with pincushion distortion (straight lines appear curved)? I find FC more objectionable than PC for astronomical observation but probably the opposite terrestrially. 

These diagrams can give an idea of how they compare to each other. Notice that the longer focal lengths curve in one direction and the shorter focal lengths in the other so that one set adds to the FC of the telescope and the other cancels. 

Nice graphs! I think however you've got the definition of field curvature and pin cushion the wrong way round. Field curvature causes a linear feature to appear curved and pin cushion leads stellar points to have a slightly different focus.

Mike

[Ricochet]

20 hours ago, mikeDnight said:

Nice graphs! I think however you've got the definition of field curvature and pin cushion the wrong way round. Field curvature causes a linear feature to appear curved and pin cushion leads stellar points to have a slightly different focus.

Mike

Sorry, Mike, but it is you who has got the definitions the wrong way around.

Quote

Petzval field curvature, named for Joseph Petzval,[1] describes the optical aberration in which a flat object normal to the optical axis (or a non-flat object past the hyperfocal distance) cannot be brought properly into focus on a flat image plane

Quote

In pincushion distortion, image magnification increases with the distance from the optical axis. The visible effect is that lines that do not go through the centre of the image are bowed inwards, towards the centre of the image, like a pincushion.

As you have both the 10mm and 14mm XWs would you be able to do me a favour and measure the height of each, with the eyecup extended, but excluding the nosepiece  (i.e. the amount that each eyepiece extends out of the focuser) and the widths at the widest point? Thanks. 

[John]

For what it's worth, I've read reports on another forum that the 3.5mm and 5mm XW's have now ceased production. They don't appear now on the Ricoh / Pentax UK website:

http://www.ricoh-imaging.co.uk/en/eyepieces.html

 

[mikeDnight]

6 hours ago, Ricochet said:

Sorry, Mike, but it is you who has got the definitions the wrong way around.

As you have both the 10mm and 14mm XWs would you be able to do me a favour and measure the height of each, with the eyecup extended, but excluding the nosepiece  (i.e. the amount that each eyepiece extends out of the focuser) and the widths at the widest point? Thanks. 

Well that's a rum do! All these years I thought I knew what field curvature and pin cushion was. Never mind!

The heights of the 14mm and 10mm XW bodies but not including the chrome barrel, and with the eyecup fully extended are 14mm = 3.2", 10mm = 3.6". Their widths are 2 3/8" which is slightly wider than the advertised width of 2.25". 

Mike 

 

[F15Rules]

I have the earlier Pentax XL versions in 5.2mm and 10.5mm, both are superb. I did have XWs in 14mm and 20mm but got major kidney beaning/blackouts in the 14mm and severe curvature in the 20mm. I replaced the 14mm with  Morpheus which has a 76deg fov (now one of my favourite eps), and didn't replace the 20mm as my ES24mm is so good with much less FC. That said, and being budget limited at present I've just ordered 7mm and 18mm Xcel LX's to fill the gaps (see my signature for full ep line up).

When funds do permit I would love to get an XW 7mm and maybe a Delos or Delete in 17 or 18mm range. I know all the XWs at 10mm or less are superb.

Will be interesting to see how the 60 degree Xcel LX's stand up against my Pentax (65deg) and Morpheus (76 deg) units...I've read good things about their bang per buck performance:-).

Dave

[YKSE]

1 hour ago, F15Rules said:

Will be interesting to see how the 60 degree Xcel LX's stand up against my Pentax (65deg) and Morpheus (76 deg) units...I've read good things about their bang per buck performance:-).

Dave

My wild guess is that you'll be more impressed with 7mm Xcel-LX than 18mm

[F15Rules]

43 minutes ago, YKSE said:

My wild guess is that you'll be more impressed with 7mm Xcel-LX than 18mm

That's interesting...have you read reports to that effect, or used them yourself?

Dave

[YKSE]

50 minutes ago, F15Rules said:

That's interesting...have you read reports to that effect, or used them yourself?

Dave

I read some optical bench tests, should be interesting to know how it compares to what our eyes see

[Ricochet]

4 hours ago, mikeDnight said:

Well that's a rum do! All these years I thought I knew what field curvature and pin cushion was. Never mind!

The heights of the 14mm and 10mm XW bodies but not including the chrome barrel, and with the eyecup fully extended are 14mm = 3.2", 10mm = 3.6". Their widths are 2 3/8" which is slightly wider than the advertised width of 2.25". 

Mike 

 

Thanks, Mike. That means that my spotting scope stay on case might zip up with the 14 but probably not the 10.

[Pig]

The 3.5mm XW is a fantastic eyepiece Simon and you will not regret choosing this over the Delos, I am sure you will get some high numbers in terms of magnification without a problem

[Sunshine]

This looks to be an old thread but, I am a little excited while waiting for my 3.5 XW from a local scope shop where it was selling on consignment. This will be my second XW as I have the 14mm which has proven to be a great eyepiece, no complaints with my frac.

[Louis D]

I find my 3.5mm XW to be every bit as sharp and easy to use across the field as my 5.2mm XL.  I'm not as fond of my 7mm XW which exhibits a bit of edge issues on bright stars.  I also really liked my 14mm XL for years until my aging eyes could no longer accommodate its field curvature.  I ended up swapping it for a 14mm Morpheus.  Similar field curvature, but quite a bit wider (78 vs. 65 degrees), so the field curvature tends to start further out.  However, I find myself using my 12mm ES-92 more often than either 14mm.  It is phenomenal in every respect.

Enjoy using your new to you 3.5mm XW.

[Timebandit]

On 30/09/2016 at 17:26, Timebandit said:

Hello there. I have just acquired a lovely pentax 3.5 xw. It was a bit of a debate whether to purchase a delos which was for sale or the Pentax. The Pentax won , mostly because I have got pentax xw already and optically find them first class. I do like televues and rate them very highly. But they do seem to be getting harder to justify some of the price requested. And the Pentax from my use of them seem optically as sharp as you are going to get unless you dip into the pot of the ZAO or TMB supermono. The Pentax has the field of view of around 70 d which I like, and nice eye relief of around  the 20mm mark.  The eyepiece is for high power use on my Ed apo refractor and is pushing the limits at around 260 x magnification. But on a good clear night then the views of splitting stars and high power lunar ,planetary use should be possible and interesting. It is also going to be tried in the dob . I have heard the 500 x lunar magnification possible and this eyepiece in my dob will give around the 450mark, and with a 1/10 mirror it will be an interesting experiment how the dob reacts to such a high magnification on the lunar landscape. Therefore I do look forward to a nice clear steady atmospheric night to put the frac and the dob to the test with this very capable eyepiece ,

 

 

 

 

 

I hope you approve of the Pentax as an addition to the eyepiece case☺

 

 

Woow , getting on for 4 years now . where does time go ?

XW  Still as good as ever and is still in the eyepiece case . A keeper 

 

 

 

[John]

I have the Pentax XW's in the 10, 7, 5 and 3.5 focal lengths. I went for the Delos in 14 and 17.3mm because of the field curvature that Louis mentioned with the XW 14 and 20m although I've alse read that many folks don't have a problem with those.

I find that I use the 5mm and 7mm XW's the most, the 3.5mm occasionally and the 10mm rarely but they are all very good performers.