Wide field views with SW Esprit 80 Pro

[tonyowens_uk]

Hi. I bought an 80 mm Skywatcher triplet scope a couple of years ago with portable imaging and occasional visual use in mind. Until recently it hasnt had much use. Debugging the imaging side of things is being attended to currently, but I had hoped to come up with a choice of quality eyepieces that allowed widefield sweeping of the Milky Way at one extreme, down to around 160x or so for lunar views while travelling. I have the Skywatcher fleld flattener by the way. So recently I replaced a Televue Panoptic 27 with a Pentax XW30, as I hadnt been happy with the edge of field performance of the Pan with or without the FF fitted. I find the XW30 is not a lot better.

I'm interested in recommendations for oculars that can do justice to the razor sharp imagery that this triplet delivers (evident in the star shapes while imaging). I have no astigmatism or other eyesight defects other than the usual lack of accommodation that is appropriate to a man in his late 50's! I prefer to avoid anything wider than 80 degrees or so (Nagler territory), and I's like to use the scope by day as well as night, so avoidance of 'kidney bean' is also an issue. Mainly, I'm after razor sharp images over 95% of the field and great comfort, with this fast, short FL scope. 

Thanks

Tony Owens

[Louis D]

I would recommend the 30mm APM UFF for edge to edge sharpness and little to no inherent field curvature.  I replaced my 27mm Panoptic with it and have been very happy with that decision.  At very high powers, folks swear by the Vixen HRs and Tak TOEs.  In the middle, the TV Delos, Pentax XWs, and Baader Morpheuses are very good choices.  The TV Delites are another good choice with slightly better correction at a slightly narrower field of view.  There are lots of excellent options out there beyond these as well.

[Don Pensack]

within your requirements, what Louis recommended is a great one.

I have an f/7 triplet as well and found the TeleVue Delites gave superb performance.

I hesitated about a longer focal length, but if you do not wear glasses, the obvious eyepiece is the TeleVue 24mm Panoptic.

If you do wear glasses, the 24mm APM Ultra Flat Field.

[tonyowens_uk]

I have an APM 30mm UFF on backorder with APM. I plan to assess the Pentax XW30 v the APM UFF 30 when I get my hands on one. I'll do this with and without the field flattener fitted to the 80mm APO.

[Don Pensack]

21 hours ago, tonyowens_uk said:

I have an APM 30mm UFF on backorder with APM. I plan to assess the Pentax XW30 v the APM UFF 30 when I get my hands on one. I'll do this with and without the field flattener fitted to the 80mm APO.

I'll be interested in reading your comparison.  I did just that with a 31mm Nagler, 30mm UFF and 30mm XW just 2 months ago.

[Louis D]

3 hours ago, Don Pensack said:

I'll be interested in reading your comparison.  I did just that with a 31mm Nagler, 30mm UFF and 30mm XW just 2 months ago.

Did you post a write-up somewhere?  I recall your recent 30mm UFF write-up on CN.

I would hope at $665 that the 31mm Nagler T5 is pin sharp from edge to edge with no field curvature, no chromatic aberration, and no astigmatism.  My 30mm ES-82 has very noticeable chromatic aberration in the last 10%.  However, I only paid $220 for it years ago, so I'm content to live with it.  It's not apparent in the image below, but it is very noticeable if I let a planet drift from edge to edge during observing.  It is way better than Kasai Super WideVue which looks like a prism starting at 20% out from center.

[Don Pensack]

I didn't want to pre-prejudice your review with my comments.  No posted comparison from me.  I'll wait for your comments.

[tonyowens_uk]

Here is a summary of the testing I carried out on these two oculars a month and a half ago after I received the APM 30mm UFF which was briefly out of stock at APM:

Test of Pentax XW30 v APM UFF30

Date: 25/05/20

 

Setup:

Intes-Micro MN86 Deluxe, collimated, F5.9, flatfield

EQ8, tracking

Visual use with and without glasses

My vision is within 1 diopter of normal, negligible astigmatism, reduced accommodation

Seeing: 7/10, traces of high cloud occasionally, 12 C, not truly dark.

Various sky targets

 

 

Targets

M27 Dumbbell nebula

NGC6960 Veil Nebula area

C1399 asterism (altitude 44 deg)

M8 Lagoon (v low)

Saturn (v low)

Altair (for veiling glare and polish assessment)

 

APM 30 UFF NOTES

545 gms

No chromatic aberration anywhere

Sharp to within a couple of degrees of the edge

Eyecup not as effective as the Pentax at excluding ambient light, but can be folded over quickly to accommodate wearers of glasses.

Little veiling glare apparent on Saturn or Altair

Folded down eyecup a bit more comfortable and suits non-varifocal glasses wearers

 

Pentax 30 XW NOTES

680 gms

Seemed slightly brighter - a little more spectacle

Head positioning to the exit pupil a little easier

Sharpness starts to suffer noticeably from ~60% of the field on, not bad until close to the edge, but noticeable deterioration

Obvious chromatic aberration off-axis on brighter stars

A bit harder to locate the eyeball to the exit pupil perfectly, due to size of barrel end

Little veiling glare apparent on Altair centre-field

A little warmer in colour transmission than the UFF

 

Conclusions

Overall, the UFF performs better due to tighter stars across the entire field and no chromatic aberration. The Pentax is inferior, most likely due to an ageing optical design which does not suit modern astronomical telescopes with image surfaces of low curvature.

I was also able to confirm broadly identical behaviours using a Skywatcher 80mm F5 APO without its focal corrector/flattener fitted, in some quick testing the following night. In view of the poor off-axis performance of the Pentax I didn't bother rigging the APO with the field flattener and retesting. As the direction of image plane curvature is opposite between APO refractors and mirror scopes like the Mak-Newt, it was clear that the Pentax was not going to match the APM ocular regardless of the image curvature sign or magnitude.

[Louis D]

That matches up well with this CN comparison of the edge correction of each.  I've linked the images below:

30mm Pentax XW:

30mm APM Ultra Flat Field:

What I'm wondering is how the Pentax XW 40mm stacks up against the Meade 5000 SWA 40mm that I've been using since the great SWA blowout sale.  I picked it up for $125 and am wondering how much better the $400 Pentax 40mm would be.

[John]

55 minutes ago, Louis D said:

What I'm wondering is how the Pentax XW 40mm stacks up against the Meade 5000 SWA 40mm that I've been using since the great SWA blowout sale.  I picked it up for $125 and am wondering how much better the $400 Pentax 40mm would be.

I wonder how the Aero ED 40 would do compared to the XW 40mm ?

I picked up my Aero 40 (well a clone of it) for peanuts really but it's proved a good performer even with my F/5.3 dobsonian.

Unless someone lends me an XW40 I'm not going to find out. I'm not going to risk $400 for an eyepiece that won't get lot of use.

I feel a little for the folks who paid big prices for the 2 inch XW's during the period when they were out of production. I saw silly prices being asked for the XW 30 and 40 at one time - substantially more than they cost new now.

 

 

 

[tonyowens_uk]

6 hours ago, John said:

I wonder how the Aero ED 40 would do compared to the XW 40mm ?

I picked up my Aero 40 (well a clone of it) for peanuts really but it's proved a good performer even with my F/5.3 dobsonian.

Unless someone lends me an XW40 I'm not going to find out. I'm not going to risk $400 for an eyepiece that won't get lot of use.

I feel a little for the folks who paid big prices for the 2 inch XW's during the period when they were out of production. I saw silly prices being asked for the XW 30 and 40 at one time - substantially more than they cost new now.

 

 

 

As a prominent Western prophet said "the truth will set you free".  Objective eyepiece testing is far from straightforward and in any case is not the only criterion for value of an ocular. I had the chance to return the XW30 I had bought, following my own comparison (using my own preferred equipment). But though I intended to, I have not done so. 20 years ago I remember being blown away by the overall experience of using an XW10 compared with various commercially-available and privately developed high quality oculars - the ease of use, the lack of scatter, the ergonomics, even the smell. That memory was instrumental in my decision to buy a 6 element all-spherical design in 2020. The essential difference between the XW30 and the APM 30UFF (apart from superior tech performance and lower cost of the latter) is 'character'. We humans aren't the cold rational creatures assumed by most economic theory. As I've got older I've come to trust my non-rational judgements more and more...

[John]

3 hours ago, tonyowens_uk said:

As a prominent Western prophet said "the truth will set you free".  Objective eyepiece testing is far from straightforward and in any case is not the only criterion for value of an ocular. I had the chance to return the XW30 I had bought, following my own comparison (using my own preferred equipment). But though I intended to, I have not done so. 20 years ago I remember being blown away by the overall experience of using an XW10 compared with various commercially-available and privately developed high quality oculars - the ease of use, the lack of scatter, the ergonomics, even the smell. That memory was instrumental in my decision to buy a 6 element all-spherical design in 2020. The essential difference between the XW30 and the APM 30UFF (apart from superior tech performance and lower cost of the latter) is 'character'. We humans aren't the cold rational creatures assumed by most economic theory. As I've got older I've come to trust my non-rational judgements more and more...

The Pentax XW's differ in optical design and characteristics across their focal lengths. I too got hooked on them with the 10mm (loaned by First Light Optics). They also loaned me a 30mm XW to compare and review. That was nice but it did not make the impression that the 10mm XW had.

Currently I have the 10, 7, 5 and 3.5 XW's and feel that they are the best of the range for my scopes and preferences