53 replies to this topic

[quercuslobata]

Has anyone compared these two at f5-6? The UFF would have more eye relief, and the field stop on the UWA is wider, but how do the views compare?

 

Reading posts it sounds like 16-18mm in the ~$100 or under category (including dual ED, HD-60, Xcel-lx) is a weak link in just about every line. If you had to pick one 16-18mm eyepiece with at least 60 degrees and a hard budget cutoff of $120 what would it be and why? Assume they all have sufficient eye relief for me.

 

 

 

[KWB]

I have no experience with the 16mm UWA because it doesn't have enough eye relief for my usage, so I couldn't say how these eyepieces compare. I do have the 18mm UFF and will say that it is a well corrected eyepiece, it sharpness and brightness on axis pleases me and it is very eye glass friendly. I like this eyepiece a lot. It works for me. No doubt there are better performing eyepieces in this focal length range but for the $95 I paid for it, I'm not replacing it. It is good enough.

 

[SeattleScott]

My impression is the 18UFF is probably the cheapest pretty well corrected eyepiece around its focal length. It typically sells for more than $100, so more than the others, although you might find it under $100 on the “grey market” ordering direct from China to avoid the middle man.

Scott

[Ernest_SPB]

16 mm UWA has wide AFOV, but correction over field is poor (more or less acceptable in F10 and slower) and too close exit pupil position

 

18 mm UFF is more narrow, but has better correction over field (can be used in relatively fast F6-F7 scopes) and comfortable exit pupil location

[KWB]

I use the 18mm UFF very effectively with my 60mm F/6 refractor. It is my favorite eyepiece with this telescope and provides a 3.25 degree TFOV to darken the sky at 20X using this little refractor. This same eyepiece viewing targets at 50 to 75 meters show me nicely detailed views of a blue jay that lives in a tree on the lot to the west of my house. My eyeglasses and I like this eyepiece.

 

This eyepiece is a keeper.

[cimar]

I prefer the 16mm UWA. I t has a wider AFOV and a distortion similar to TeleVue. The 18mm UFF has a fuzzy field stop and barrel distortion which creates a strom rolling ball effect. Edge sharpness is great.

[cst4]

I prefer the 16 UWA as well.  I had and used both for a while and eventually sold the UFF.  That 16mm has a good bit of field curvature but I still like it.  It's sharp in the middle, bright, comfortable to use, and compact.  So it's a got a good bit going for it.  I actually picked up a second one for a bino pair... the only 82 degree bino pair I own.  The 18 UFF might be flat but has a decent bit of astigmatism... so pick your aberration of choice... I prefer the softness of field curvature over astigmatism.  

[KWB]

The 18 UFF might be flat but has a decent bit of astigmatism... so pick your aberration of choice... I prefer the softness of field curvature over astigmatism.  

What telescope did you use to base this opinion on?

 

One of the reasons why I prefer this eyepiece is it's lack of astigmatism when used with my F/5 and F.6 telescopes. 

[Jon Isaacs]

I have the 16 mm UWA and the 16 mm Type 5 Nagler.  I've been comparing them in my 16 inch F/4.4 with a Paracorr 2.

 

The 16 mm Type 5 is clearly the class of similar focal length  1.25 inch 82° eyepieces. It's very sharp across the entire field. It's short in eye relief.

 

The 16 mm UWA has more eye relief but not the overall field sharpness. But for me, it's sharp enough over a wide enough field that I don't feel like I'm sacrificing much by using the 16 mm UWA.

 

Jon

[cst4]

What telescope did you use to base this opinion on?

 

One of the reasons why I prefer this eyepiece is it's lack of astigmatism when used with my F/5 and F.6 telescopes. 

It's been a couple years at least so hard to say, but I typically use eyepieces in several scopes on several targets over several months before I really form an opinion on performance.  I mostly use a SV 102 Access at F/7 for serious eyepiece comparisons, so it was likely used at some point.  I also use a C6 a lot but it's got enough inherent field curvature and coma that I try to refrain from critiquing eyepieces when using this scope.  Several other scopes have come and gone... only one Newt was F/5, everything else F/6 or slower.  It could have been my sample, or perhaps even just my eyes, but I saw astigmatism approaching the edges in my 18 UFF.

[SeattleScott]

Bench tests show the 18UFF isn’t perfect by any means, but better spot sizes than the 16mm.

Spot sizes at F4 per Ernest:
18 UFF: diffr, 15, 22
16 UWA: under 2, 38, 72
16T5: under 6, 7.5, 7

By comparison, the poorly regarded 30mm GSO Superview, widely considered unusable at F4 but some tolerate it at F6:
Under 5, >30, >70
Basically the same as the 16 UWA. So someone who isn’t fussy about edge correction might find it useful at F6.
Another known commodity, the 38 SWA/40 Swan, considered borderline useful at F5: under 6, >25, >35. Roughly twice as good at the very edge at F4 compared to the 30 Superview or 16 UWA.

Basically, the 18UFF gets respectable scores at F4, so if I had to stay around $100-150 I would go for that. The 16 UWA really just depends on your sensitivity to edge distortion. It won’t be sharp to the edge at F6. Not even close. But edge abberations don’t bother some people much. And they drive others crazy.

If one is willing to pay $100-200 then the 17 Hyperion should be a consideration. I don’t have it (17LVW instead, and would be similar price to a new 17 Hyperion), and Ernest didn’t bench test it, but it has a pretty good reputation.

FWIW a used 17LVW would probably run $150-175 and bench tests at:
2.5, 7, 9
(Still at F4)


Scott

Edited by SeattleScott, 25 January 2023 - 11:41 AM.

[quercuslobata]

Bench tests show the 18UFF isn’t perfect by any means, but better spot sizes than the 16mm.

Spot sizes at F4 per Ernest:
18 UFF: diffr, 15, 22
16 UWA: under 2, 38, 72
16T5: under 6, 7.5, 7

By comparison, the poorly regarded 30mm GSO Superview, widely considered unusable at F4 but some tolerate it at F6:
Under 5, >30, >70
Basically the same as the 16 UWA. So someone who isn’t fussy about edge correction might find it useful at F6.
Another known commodity, the 38 SWA/40 Swan, considered borderline useful at F5: under 6, >25, >35. Roughly twice as good at the very edge at F4 compared to the 30 Superview or 16 UWA.

Basically, the 18UFF gets respectable scores at F4, so if I had to stay around $100-150 I would go for that. The 16 UWA really just depends on your sensitivity to edge distortion. It won’t be sharp to the edge at F6. Not even close. But edge abberations don’t bother some people much. And they drive others crazy.

If one is willing to pay $100-200 then the 17 Hyperion should be a consideration. I don’t have it (17LVW instead, and would be similar price to a new 17 Hyperion), and Ernest didn’t bench test it, but it has a pretty good reputation.

FWIW a used 17LVW would probably run $150-175 and bench tests at:
2.5, 7, 9
(Still at F4)


Scott

Thanks.

 

Is this the table (http://astro-talks.r...p?f=32&t=1483)? I guess I had seen that table but didn't look in the AKA column.

 

Of course one can't expect perfection on a budget. Just curious about what people thought was best in (coach) class. I will take a closer look at the table to compare against things that I know. 

[SeattleScott]

Thanks.

Is this the table (http://astro-talks.r...p?f=32&t=1483)? I guess I had seen that table but didn't look in the AKA column.

Of course one can't expect perfection on a budget. Just curious about what people thought was best in (coach) class. I will take a closer look at the table to compare against things that I know.

Yes that’s the table. I don’t know of anything under $100 that is what I would describe as well corrected, unless you can get the 18 UFF under $100 direct from China or something. I think it is normally $130 in the US. As the table indicates, it isn’t perfect by any means, but pretty good, especially at F6. The 17 Hyperion isn’t too much more at that point, and might be better, or maybe not. Without looking for a 17LVW or 18 Radian in Classifieds, one of those two are probably your best bet if you want good performance for under $200. I just don’t know that there is a good option under $100, unless you go used, or get the 18 UFF direct from China.

Scott

[SeattleScott]

Another way to look at it is value. I don’t consider the 18 Paradigm, 18 Xcel LX, 16 AT UWA, 15/20 Expanse, to be “good values” considering the performance versus the price and specs. You are looking for a relatively budget eyepiece, better than a Plossl but not high end. Which tells me you are after value. Getting the worst performer in the line isn’t generally a good value. You get used to the performance of the better ones in the series and the weak one will just annoy you. Maybe it’s ok at F8, F10, F12. But F6 is moderately fast. So if you are really after value, as opposed to “I literally only have $80 in my bank account so I just have to pick the best of these weak performers,” then you probably want to step up to the $100-200 price range, or you will probably just end up replacing it later. Spending $65-100 on an eyepiece that doesn’t perform well at F6 and you will just end up replacing later isn’t a good value. At least that’s the way I see it. Based on bench tests, the 18 UFF is the cheapest that performs pretty well. Now it is interesting that some seem to prefer the 16 UWA, at least in slower scopes. And granted I don’t personally own it, and perhaps Ernest got a poor sample (although there are plenty of critical reviews of the 16 UWA). But just based on the bench test and what I have read about the 16 UWA, I would avoid it at F6.

Scott

[PJBilotta]

The 15-18mm eyepiece slot is a really tough one to fill because there simply aren't many options that are both affordable and well corrected. Let's see, I tried the 17 Hyperion, 18 UFF, 16 UWA, 16 ES 68, 15 Luminos and half a dozen others. I finally bit the bullet and got the 17.5 Morpheus and it checks all the boxes. Initially, it was far more than I wanted to spend ($190 used at the time), but it has proven to be worth the additional investment.

If I had to pick the best of all the others I tried, I'd have to say the 18 UFF is probably the best option.

[ihf]

Yes that’s the table. I don’t know of anything under $100 that is what I would describe as well corrected, unless you can get the 18 UFF under $100 direct from China or something. I think it is normally $130 in the US.

The 18mm SVBONY SV190 Ultra Flat Field Eyepiece (B08Z2ZW7MK) is identical and costs USD 96 on Amazon and sometimes on sale for USD 60-ish. The 10mm SVBONY SV190 (B08Z3SS7CK) costs regularly USD 55 but has right now a 50% off coupon[1]. Now the 10mm is not as good as the 18mm, and the 9mm Paradigm should probably be prefered to the 10mm UFF by many users... But the 18mm can be a great and unique deal.

 

[1] Amazon/Ebay SVBONY pricing can be mysterious and is worth checking periodically.

[Jon Isaacs]

By comparison, the poorly regarded 30mm GSO Superview, widely considered unusable at F4 but some tolerate it at F6:
Under 5, >30, >70

Basically the same as the 16 UWA. So someone who isn’t fussy about edge correction might find it useful at F6.

 

 

I have both eyepieces. At F/5, they are very different. 

 

It's really important to look through an eyepiece to understand it's issues.. 

 

With the 16 mm UWA at F4.7 with a Paracorr. (F/4.06 without) I'm seeing primarily what seems to be field curvature with some off-axis astigmatism. The field curvature can be  reduced by balancing center and edge defocus. The curvature seems to be closer in center, opposite of a refractor.  In my 90 mm F/5.5 refractor, it's not at all bad.

 

Balancing field curvature is quite effective since the curvature is a second power function of the off-axis distance. You reduce the edge defocus to 1/4 of what it was while increasing the center defocus to 1/4 the edge defocus.

 

The 16 mm UWA seems to be quite sensitive to focal ratio. The difference between last night at F/5.07 in the 16 inch and F/4.67 in the the 12.5 inch are very apparent.

 

With the 30 mm SuperView, it's primarily off-axis astigmatism which you're stuck with. 

 

Right now it's 2 am. It's 43°F with the wind averaging 24 mph with gusts to 30 mph. You've motivated me to go back our and enjoy the Comet C2022 E3 in my 12.5 inch F/4.06 (F/4.67 with the Paracorr) and the 90 mm F/5.5 Svbony achromat. 

 

So far this evening, the 16 mm Type 5 Nagler has been in the case, I'm using the 16 mm UWA. It's really quite decent. To my eye, much better than Ernest's F/4 numbers would suggest.

 

What are your experiences with the 16 mm UWA? With the 30 mm Superview.

 

Jon

[quercuslobata]

I guess the table of bench tests is a valuable resource, but also probably need to remember that comparing different eyepieces based on the values will depend on among sample variation too.

 

I also appreciate the perspective of needing to look through them to know for sure as choices seem to be really personal. I have really limited time, so usually catching 20-30 minutes of observing when I can, but I can see the value of observing with a club or at a start party. Maybe someday for me.

 

I don't know enough yet to be able to name the aberrations that bother me, but I think I am somewhat sensitive to edge performance. I had an 18mm HD-60 but thought it was pretty poor at the edge (again I couldn't say why), especially in an f5 ST80, but it was a while ago and I was new and probably sold it too quickly before learning more about why I didn't like it. I have a 32mm Q70 clone and it definitely has edge issues of some kind even at f7.

 

I appreciate everyone's input. This is more of a snowy weather pondering type situation than an urgent decision. This is a second set that I want to be inexpensive enough my kids could use it without me worrying to much about it, but good enough that they (and I) want to use them. Much of the set are HD-60's (used) so I may be leaning towards the UFF (used or otherwise cheaper) to keep the eye relief longer. I don't wear glasses, but I like the idea of having an eyeglass friendly set just in case.

[quercuslobata]

Maybe getting off topic, but I was also wondering if aberrations scale linearly with f ratio (such that one can interpolate f6 as being around the mean of f4 and f10 in the table)? Does it depend on the type of aberration?

 

I imagine these are difficult questions to answer, but asking just in case.

[Jon Isaacs]

Maybe getting off topic, but I was also wondering if aberrations scale linearly with f ratio (such that one can interpolate f6 as being around the mean of f4 and f10 in the table)? Does it depend on the type of aberration?

 

I imagine these are difficult questions to answer, but asking just in case.

 

There are some generalizations one can make but it depends in part on the exact aberration. 

 

I've not used the 18 mm UFF, I imagine it's quite sharp across the field of view, similar to the 30 mm UFF which I do have.

 

But I'm struggling with reconciling  Ernest's numbers for the 16 mm UWA with what I'm seeing in the eyepiece. It's not the 16 mm Type 5 Nagler, an eyepiece I own and use a great deal but very few eyepieces are that good, 82° or otherwise... But it's a decent eyepiece and I'd probably choose it over a better corrected 65° eyepiece. 

 

Jon

[SeattleScott]

Maybe getting off topic, but I was also wondering if aberrations scale linearly with f ratio (such that one can interpolate f6 as being around the mean of f4 and f10 in the table)? Does it depend on the type of aberration?

I imagine these are difficult questions to answer, but asking just in case.

Generally the abberations should scale somewhat linearly. Jon suggested the 16 UWA might not be as linear and might hold up better at mid F ratios before tanking more at F4, hard to say. Unlike Jon I don’t get cheap eyepieces that can’t compete with what I (or even my kid) already own just to report out to others so I can’t say from personal experience. Do keep in mind that Jon was using a coma corrector that costs about as much as an 8” Dob, and generally wouldn’t be considered needed at F6, and the coma corrector has a reputation for reducing the effects of field curvature. So his experience with the 16 UWA might not line up with yours, although he was operating at F5 not F6. Personally I am picky about edge correction so I will just avoid eyepieces known for bad edge correction. I could care less about EOFB. You just have to understand your preference.

Jon is right that you can tame the tield curvature a bit by shifting the focus slightly. You give up a little contrast in the center but the edge performance improves. So you can make a wider view look decent at least. Ernest’s bench tests showed the 16 UWA besting the Nagler in the center so clearly there wasn’t any effort made to balance the focus and improve edge correction. Also to some extent the eye/brain can accommodate some degree of FC, which could contribute to the opinions on the 16 UWA generally ranging from it’s decent to its just plain bad.

[Tangerman]

If you go down the column in Ernest's table to the Williams Optics UWAN rather than the TS UWAN, the numbers for the 16mm UWA are better, with 4, 20, and 55. I haven't used the 16mm UWA, but I have used the GSO 30mm Superview, and I was having trouble believing the 16mm UWA, which from subjective reviews I've read isn't the best but isn't the worst, would be as bad as the GSO Superview, which many people do describe as one of the worst for edge correction. 

[Lagrange]

There are some generalizations one can make but it depends in part on the exact aberration. 

 

I've not used the 18 mm UFF, I imagine it's quite sharp across the field of view, similar to the 30 mm UFF which I do have.

 

But I'm struggling with reconciling  Ernest's numbers for the 16 mm UWA with what I'm seeing in the eyepiece. It's not the 16 mm Type 5 Nagler, an eyepiece I own and use a great deal but very few eyepieces are that good, 82° or otherwise... But it's a decent eyepiece and I'd probably choose it over a better corrected 65° eyepiece. 

 

Jon

 

If you've ever tried the 24mm UFF then it should be similar since it's a scaled version of the same design (as is the 15mm UFF).

 

The 30mm seems to be the pick of the bunch but it benefits from a slightly wider AFOV and an extra element in the design which presumably helps give it an edge.

Edited by Lagrange, 26 January 2023 - 10:55 AM.

[Jon Isaacs]

Generally the abberations should scale somewhat linearly. Jon suggested the 16 UWA might not be as linear and might hold up better at mid F ratios before tanking more at F4, hard to say. Unlike Jon I don’t get cheap eyepieces that can’t compete with what I (or even my kid) already own just to report out to others so I can’t say from personal experience. Do keep in mind that Jon was using a coma corrector that costs about as much as an 8” Dob, and generally wouldn’t be considered needed at F6, and the coma corrector has a reputation for reducing the effects of field curvature. So his experience with the 16 UWA might not line up with yours, although he was operating at F5 not F6. Personally I am picky about edge correction so I will just avoid eyepieces known for bad edge correction. I could care less about EOFB. You just have to understand your preference.

Jon is right that you can tame the tield curvature a bit by shifting the focus slightly. You give up a little contrast in the center but the edge performance improves. So you can make a wider view look decent at least. Ernest’s bench tests showed the 16 UWA besting the Nagler in the center so clearly there wasn’t any effort made to balance the focus and improve edge correction. Also to some extent the eye/brain can accommodate some degree of FC, which could contribute to the opinions on the 16 UWA generally ranging from it’s decent to its just plain bad.

 

 

 

I can be extremely picky about edge correction and arguably own the sharpest eyepieces manufactured. I also own and use the best coma corrector available as well as a refractor that is fully corrected for field curvature as well as the other aberrations. My eyes are free of astigmatism even at large exit pupils so I am pretty confident in what I see as the eyepiece's aberrations.

 

A coma corrector does not corrector coma in the eyepiece nor does it correct field curvature in the eyepiece. What it does do is correct the coma and field curvature of the mirror so the field curvature and coma seen in the eyepiece are those of the eyepiece and not the mirror or objective, in the case of a field flattener.

 

I do not consider $100 "cheap" and I buy eyepieces like the 16 mm UWA to use. In the case of the 16 mm UWA, I traded a finder for a new eyepiece shipped from Astronomics. My hope was to use it in my 50 mm F/4 StellarVue finder as the finder's eyepiece. It would have provided something like a 6.3° field at 12.5 x. Unfortunately, the barrel is too long so it won't come to focus. 

 

It does focus in my 50 mm F/5 Astro-Tech finder and would provide a 5.0° field at 16x, so if I can figure out how to install cross hairs, it still maybe still viable. I did try it and it's actually quite nice though I did not give it the full test.

 

When I discuss an eyepiece, I like to have some actual experience with it. I don't discuss Delos and Delites or Morpheus's because I have no experience with them. People are spending money on eyepieces based on what they read here so I want to be confident in what I'm posting.

 

Relying on the numbers only gets you so far and as Tangerman discovered, the numbers for the UWAN are significantly better than the numbers you found ,

 

Your numbers: 16 UWA: under 2, 38, 72

 

Tangerman : 16 mm UWA: 16 UWAN: 4, 20, and 55.

 

Those make much more sense to me. The very edge is not so pretty but in an 82° eyepiece, it's not staring you in the face the way it is with a 65° eyepiece. The rest of the field is pretty good.

 

I believe that if you'd ever actually looked through a 30 mm GSO Superview as well as a 16 mm UWA, you never would have suggested they were similar. Likewise with the Expanse eyepieces, this eyepiece seems better than the 9 mm Expanse by quite a bit.

 

Jon

[SeattleScott]

yes the numbers for the old UWAN are better, perhaps sample variation? Still not nearly as good as the 18UFF. It would be one thing in a SCT but in a moderately fast scope, especially if one finds the edge issues of the 18 Xcel LX annoying, the 18UFF seems the much safer bet. With the 16 UWAN the edge issues are there, they just aren't staring you in the face as you say, but they are still there. Which will annoy some, while others will just tune it out and use it more like a 70 AFOV eyepiece. At which point there isn't much difference between it and the 65 AFOV 18UFF. We can debate how bad the 16 UWA is or isn't, but the consensus from personal reviews and bench tests is that it isn't on par with the 18, so especially if one has been annoyed by a "weak link" in the Xcel LX series, they wouldn't be advised to purchase the "weak link" in the UWA series. 

 

There is value to both personal experience reviews and bench tests. The bench tests don't test for everything. They are simply one data point. And there could be sample variation. But at least they are objective, as opposed to someone saying an eyepiece is good on axis, the edge issues don't distract them, etc. What doesn't distract one person might drive another person batty. There are those who happily use 40 Swans at F5 and others who would consider the 40 Swan paperweight (or perhaps counterweight?) at that F ratio. So personal experience is good, but adding in objective bench test data is useful also. People can take both into account.