40 replies to this topic

[Xrayman]

Hi everyone,

 

I have 10inch GSO dob f5. I recently purchased a Pentax XW10, which is incredible compared to what came with the dob.

I looking at adding my second eyepiece. I'm thinking of a Pentax XW 20 ($390 Aud) or a Panoptic 24 ($520 Aud).

 

The XW10 gives me (125X, 2mm exit, 0.56 TFOV)

 

The XW20 would give  (62.5X, 4mm exit, 1.10 TFOV)

The Pan24 would give (52X, 4.8mm exit, 1.23 TFOV)

 

Its 100% backyard use- Bortle 5, so i'm concerned about pupils not reaching much above 4.5mm

This would be mostly used for star clusters so i'm leaning towards XW20 slightly smaller exit pupil and slightly higher magnification for extra contrast.

Thoughts? Am I splitting hairs?

 

Long term I'm considering adding a 80mm - 400mm FRAC and use the above XW20 or Pan24 for wide views.

XW20 would be (20X, 4mm exit, 3.4 TFOV)

Pan24 would be (16X, 4.8mm, 3.8 TFOV)

 

Thoughts?

 

 

Thankyou in advanced.

 

 

 

Sam

-Sydney, Australia 

 

 

 

 

 

 

 

 

[SeattleScott]

I think you are being a bit conservative with the exit pupil. With Bortle 5 I would be happy with 5-6mm but it is a subjective matter of personal preference.

Your scope has a 2” focuser so that could be an option too, but I will assume you have your reasons for sticking with 1.25”.

The Panoptic is outstanding, although at the time I was comparing it to a 5-element eyepiece at F4 so you have to consider that. But certainly it gets rave reviews, other than unusually high amount of pincushion which can make some feel a little nauseated apparently when panning around looking for targets. I didn’t borrow it long enough for that to be an issue. So the APM 24 UFF would be another option. Reportedly nearly as sharp, with enough eye relief for glasses (if that’s an issue) and no pincushion problem. And cheaper, if that matters.

In general Pentax XWs get rave reviews, but people often avoid the 14 and 20 if they have fast scopes. So based on reputation I would go with Panoptic or APM.

Scott

[RalphMeisterTigerMan]

I guess it all depends on what you will be using them for, I currently have the 24mm Pan, my second one, I use it for my C5+ and love it. I am contemplating on getting the 20mm Pentax smc xw in the near future. The best way for me to get the lowest mag. and widest field in the C5+ is to use the Celestron F/6.3 and the 20mm Pentax. For Nebulae I would get the Televue 1.25" Nebustar Bandmate, I believe those three combined would be a good combination for Nebulae like M27 (the Dumbell) and M42 (the Great Orion Nebula).

 

Because I made the decision to stick with 1.25" accessories, the 24mm Pan is (in my opiinion) the best low-power eyepiece available. 

 

Clear skies!

RalphMeisterTigerMan

[Dave_L]

I think this is going to turn into a landslide vote for the Panoptic. 

[MortonH]

Google Pentax XW 20mm and field curvature.

[Ernest_SPB]

20 mm Pentax builds perfect image in central zone FOV. But in condition of "fast" optics (like Newtons) it shows plenty of field curvature and astigmatism. 24 mm Panoptic has field aberrations 3-4 times less in size. 

[25585]

If you need long eye relief, the Panoptic will fail. Period. The Pentax is great there.

 

An APM 24mm 65° has near-Pentax comfort and performs well at F5.

[Dr Morbius]

I love my Panoptic so my vote goes with my heart.

[Mike W]

24 pan

[John Huntley]

24mm Panoptic or save some bucks and maybe the Explore Scientific 24mm 68 ?

[JayinUT]

I have owned both, and I love my Pentax XW line, but the 24mm Panoptic and the 20mm Pentax XW  got replaced by the 22mmT4 Nagler several years ago and that is the eyepiece I used at this range. If I had to choose between the Pentax 20mm XW or the 24mm Panoptic, I woudl go for the 24mm Panoptic. I also use a Paracorr Type 2.

[BillP]

I had the 24 Pan, then replaced it with the 24 ES68 and used the extra cash for other gear.  I also have the 20 XW.  I reach for and use the 20XW much more than the 24 ES68.  Like the Pan the tighter ER of the 24 ES just makes it not as nice of an experience.  The little extra TFOV is really inconsequential in use too.

 

I think you should be considering instead the APM 24 UFF vs. 20 XW vs. 17.5 Morpheus as they all have very comfortable ER (the latter since your exit pupil is a concern).  The Morpheus will give you 1.05 degrees instead of the 1.10 from the XW.  When I bring out that eyepiece, it then gets used more than the 20XW as the view is superlatively transparent and high contrast.  It is a phenomenal performer.

 

BTW, a 400m focal length rerfractor is going to have A LOT of FC from the objective and no eyepiece is going to fix that.  So just be prepared.  500mm is much more tolerable.  600-700mm best.

Edited by BillP, 20 February 2021 - 04:27 PM.

[f18dad]

Listen to the wisdom, and experience, of BillP, or get an APM 20mm XW/100 IMHO.

Edited by f18dad, 20 February 2021 - 09:00 PM.

[Tank]

The 20 xw will give a better presentation but optically the 24 pan will be better in fast scopes
Had both tough decision beto the two
But i prefer many others over these

[faackanders2]

If your dob only has a 1.25" focuser or you think in the intermediate term you may buy binoviewers, I would get the 24mm 68AFOV Panoptics for widest view in a 1.25" focuser.  If your dob has a 2" focuser and you do not believe you will ever get a binoviewer, then you can go either way, or buy an eyepiece where you have the biggest gap with eyepiece focal ratio,

[25585]

Not much difference between 65° & 68°! APMs have no undercuts.

[Mirzam]

In my f/4 dob, the XW 20 displayed out of focus stars in the outer 1/3 of the field when the central field was perfectly focused.  This seems to be an issue mainly with the xw20 and xw14 designs when paired with fast reflective optics.  I have all the other shorter focal length XWs and they perform well.

 

JimC

[f74265a]

I skipped the 20xw bc of its well documented reputation for field curvature in my refractor and went for the 24 pan instead which works very well

[John Huntley]

I skipped the 20xw bc of its well documented reputation for field curvature in my refractor and went for the 24 pan instead which works very well

So did I. I also skipped the 14mm XW in favour of the 14mm Delos for similar reasons and with similar results. The 14 and 17.3 Delos reach focus closer to where the shorter XW's do as well.

[f74265a]

The 14 and 17.3 Delos are indeed nearly parfocal with the shorter fl XWs which I too find convenient.

[Xrayman]

Wow,

 

Thanks for all the replies. I had no idea about the 20XW having FC problems.

I was so amazed by the 10XW I didn't bother looking into it. I'll probably go for the 24 PAN.

 

I should have clarified, I don't need glasses, and yes I do want to stick with 1 &1/4"  to keep prices down for filters.

 

One more follow up question, its probably a silly one. Long term, if I get a small refractor to use with the PAN 24 for wider views,

why would an F6/F7 have less FC then the F5? I thought it would perform as well as the f5 dob?

 

Thanks again.

[areyoukiddingme]

It's the focal length of refractors that is the issue. When I had a 6" F8 refractor, the 20XW (and 14 for that matter) worked great. I really had to look for field curvature. In my short 80mm F6, there's plenty of field curvature, both from the scope and the eyepiece. You'll see your short refractors FC using the Panoptic too.

 

I use the 20XW in my F5 reflector, and without coma corrector it is quite bad. But with coma corrector, things are improved, but not perfect.

 

I'd expect the 24 Pan to work very well in refractors and reflectors (I have a 27 Panoptic which does that).

[MortonH]

Field curvature depends on focal LENGTH, not focal ratio. There is both positive and negative field curvature, with refractors having the opposite sign of reflectors (can't remember which is which). Eyepieces can also have positive or negative FC.  The combination of a particular eyepiece with a particular scope can be good or bad depending on how their FC 'adds up'. In some combos they cancel each other out and you get a nice flat field.

 

This thread has some interesting info:

 

https://www.cloudyni...ield-curvature/

[csrlice12]

Have both....guess I'm a glutton for punishment having to use such inferior gear....

[SeattleScott]

I’m not really seeing much if any FC with either one. Maybe some with the ES (I suppose inherent FC from the scope will be more obvious with wider AFOV). I see some RD, especially with the ES as expected. The ES has wider AFOV so it will have more RD. Plus the XWs are designed with spotting scope use in mind, so they don’t have as much RD. Better for terrestrial observing that way.

It is interesting, because everyone knows a F5 refractor has field curvature, and everyone knows the 20XW has field curvature. But that is a really sharp looking field stop to me. I almost wonder if the FC in the XW might be opposite and be canceling out the FC in the refractor? The XWs were made with spotting scopes in mind so it might not be a huge leap to think they might have designed in some FC in order to cancel out the FC in a typical F6 spotting scope.

Scott