Let me know if you have any questions on the DeLites.

 

Thanks very much for an excellent review Bill. Must have been quite an effort to put these eyepieces thru their paces. I had skimmed the article on another forum site a few days ago, but couldn't find that link again. Glad I found the original article here and can review it throughly again this weekend.

Harry D.

 

Actually not so hard when eyepieces perform this good!

 

I especially appreciate the comparisons you have done with the other eyepieces in the review. Places things in perspective and makes points and observations much more meaningful.

Oh, and the layout of the page is A+. Love the organization, captions, introduction, etc. as in a proper article. And the pics are just making me drool! Great job again and thanks for sharing.

Harry D.

 

Thanks Harry. AstronomyConnect gets all the credit for the layout, captions, intro, etc. They have a great editor! Heck...they have an editor!!

 

I just sold my last Radian, a 4mm. Looking forward to trying out the DeLights but will wait 'til a 4 or 5mm comes to market.
Bill, when you get a chance, I hope you'll do a comparo with a similar f.l. Nagler T-6. I always enjoy your reviews - thnx!

 

Unfortunately, sold all my T6s a long long time ago. Referred the Meade 5000 UWAs for their planetary performance over the T6s. Then switched those out for the ES82s. Then switched those out for the XWs. Plan to possibly "supplement" my XWs with a 4-5-6 series of DeLites if they end up offering those three focal lengths.

 

Bill, can you recall what you preferred about the Meade 5000 UWAs over the Nagler T-6s?

 

Tone was a little cooler. Also on-axis planetary performance was a little crisper. So those two things clinched it for me. I felt the ES82s and the Meade UWAs were on-par for the most part, maybe a gnat's hair split better to the Meades on planetary.

 

Thanks Bill for the reply. I'm looking to replace my shortest f.l. T-6s with the DeLights when they eventually become available, or maybe a comparable Morpheus. (What's plural for Morpheus - Morpheuses or Morpheui?) Your reviews carry a lot of weight with me.

 

Hi Bill,

Thank you for writing such a thorough review! You mentioned that you often use Tak LE EPs (7.5 and 5mm?). How do these EPs compare to DeLite performance in your experience?

 

I enjoy my Tak LEs for multiple reasons, but they are definitely not as crisp and precise as the DeLites. But I like them because they are very small, their build quality is IMO the best in the industry, and their slightly larger 52 degree AFOV is actually pleasingly better when viewing than a standard Plossl. So if one uses standard Plossls and wants a more premium feel and a slightly enhances AFOV, then they are the ticket

 

Appreciate the thorough review! Good detail and photos. Nicely written, too. Thanks for taking the time on it!

Had two nit-picks, however!

1. "While the larger 70º AFOV of the Pentax XW was obvious, the DeLite's 62º AFOV was still appealing and I did not feel I was losing anything with the smaller AFOV of the DeLite."

Well, you were losing one thing--about 8 degrees across! Which is a loss of nearly 25% of the field of view!! (62^2 / 70^2). In contrast, it's only a loss of 14% vs. the XL series.

2. That photograph of the bricks certainly looks like there's LOTS of rectilinear distortion!!

In fact, the bricks don't look straight anywhere!

-------------------------------------------
Just read more closely! Have a third nit.

3. You were using the DeLites in a 10" f/4.7 dob, but with a Televue Paracorr!

That's a whole different ball game, changing the focal length some, but more important, flattening the field. Already, I've read threads elsewhere in which people are citing your review as claiming excellent performance even down to f/4.7, but ignoring your use of the ParaCorr.

While you were good about mentioning the ParaCorr, you also wrote,

"Off-axis performance was excellent and as good at f/4.7 as it was at f/8, with perfect star points and detailed planetary views visible right to the field stop."

Probably should be tweaked to "as good at f/4.7 with a ParaCorr as it was at f/8"

So, the question would be: How do these do at naked f/4.7?!

------------------------------------------

Back again with one final question.

4. How does these do on galaxies (e.g., M31, M33, M81/82) and bright nebula (e.g., M42 or M8)?

I noticed your test objects didn't include galaxies or bright nebula! In my own extensive comparisons of Radians with Pentaxes, I found that the transmission was often better on the Pentaxes. The Radians often did better on DSOs where stars were involved, and particularly globular clusters such as M13 or M22.

 

Good questions....

On the differing AFOVs, as I said, I did not "feel" like I was losing anything at all. So this is a qualitative reaction saying that while yes the field was smaller, from a practical standpoint in the observation the smaller FOV was really of no consequence. It is all a matter of taste and perspective how we each react to AFOV sizes.

For most eyepieces, RD is a fact of life. TeleVue employs RD as a way to keep a sharp star point in the far off-axis. If you don't accept the RD, then you have to live with AMD, Astigmatism, etc. In comparing the RD shown in that pic to other wide fields, it was on-par, so nothing dramatic. Most Plossls show good amounts of RD also FWIW.

On the Paracorr issue, it is very predictable what any eyepiece will show when using a Newt at that short under f/5 focal ratio...the outer 50% of the FOV will show the mirror's coma, and that will overwhelm anything else. The f/5 to f/6 range is the gray zone where a Paracorr might or might not be needed for many folks. However, under f/5 and the coma is just too much and you will be looking at deformed stars in the off-axis, especially for longer focal length eyepieces. While I understand that some folks do not use a Paracorr even in something like the Orion XT10 (I did not either for a long time), the truth of the matter is that once you do you wonder why it took so long as the views are as they should be with the mirror's coma corrected so the eyepiece can behave as it capable. So bottom line IMO is that in a sub f/5 Newt, not using a coma corrector is really using the scope in a way that is largely not recommended. And like I detailed here, how the view will look is very predictable without a Paracorr...50% of the off-axis will show coma deformed star points.

 

Bill, appreciate your thoughtful reply! I was partly teasing on my two nit-picks--hence, the smiley face!

1. I knew you meant that it didn't *feel* like you were losing anything -- but such a difference in field of view is strikingly obvious! I've had both Radians and Pentax XLs in my kit-- and the difference even between 60 degrees and 65 degrees is quite clear... More than that, many, if not most, people find the exit pupil eye opening more comfortable and expansive in the Pentax than in the Radian, especially if they are eyeglass wearers.

I'll bet that most observers would be instantly struck by the difference in both the FOV and the visual feel of an XW vs. a DeLite!

My main reason that nit-pick is that we (not you, but us) forget that, while 70 degrees vs. 62 doesn't sound like that big a difference, one has to square them to get the visual FOV difference. And, it's a large loss; the DeLite losing a whopping 25% of the FOV! It's similar to the way beginners (not you) don't understand that a 6" and 8" telescope differ greatly in mirror area (28 sq in vs. 50) (or, just compare their squares--36 vs. 64) with the 8" thus having nearly twice the light gathering power of the 6"!

2. As to the rectilinear distortion, again it was meant as a friendly nit of your bold declarations!

You wrote,

"they should be able to maintain relatively little rectilinear distortion"​

and that, like the Takahashi eyepieces, you found

"the far off-axis rectilinear distortion of the DeLites to be minimal". ​

What cracked me up, though, was the seemingly hyperbolic comment that the

"bowing of the horizontal lines formed by the rows of shingles is very minimal and well controlled."​

The photo, though, shows it to be anything but minimal, but quite striking!

I'm a veteran amateur, so I know about the optical trade-offs in eyepiece design, and that there is typically greater rectilinear distortion in the Televue eyepiece so that they correct more for other optical distortions. I saw it in the 22mm Panoptic and chose the 21mm Pentax XL over it, even though it is plagued by field curvature in its outer reaches.

It's impressive that the DeLites are comparable in RD to that in high-end orthos (which was your main point), although seeing a photo of the orthos' RD and the bricks for comparison would have been good.

Bottom line: it was your describing the bowing as "very minimal" that made me laugh out loud, especially when I thought about how a novice or even a veteran observer would react when reading that and then seeing the photo!

----------------------------------------

3. As to the ParaCorr... Been there, done that and was unimpressed. I've owned and used both the Televue 2" and'the rare 1.25" models... The improvement, for me, was marginal even at f/4.5 and not worth the hassle of the extra piece of kit, balance issues, etc. I sold them and added a Pentax 10mm XW and another Radian to my case. Clearly, observers differ greatly in how much coma bothers them!

Many observers, especially the more budget-minded or novices who buy f/5 and below scopes won't have the funds, experience, or willingness to spend $300-450 on a ParaCorr... and, if they did, would probably buy pricier eyepieces than the DeLites (unless it's an eye relief question).

So, it would still be interesting to learn about how the DeLites do at a straight up f/4.7.

By the way, I found the Radians superb in a high-end 12.5" f/5-- without ParaCorr-- but whether that would be true of the DeLites at f/4.5 or f/4.7 or f/5 would be good to know!

-----------------------------------------

4. Last, but not least by any means, was my final question. It's the other real question besides #3.

How do these do on galaxies (e.g., M31, M33, M81/82) and bright nebula (e.g., M42 or M8)?

As I mentioned, I noticed your test objects didn't include galaxies or bright nebula! In my own extensive comparisons of Radians with Pentaxes, I found that the transmission was often better on the Pentaxes, with them doing better on galaxies and nebulae, while the Radians often fared better on DSOs where stars were involved, particularly globular clusters such as M13 or M22, but also bright nebula entangled with stars.

I'm wondering what you've found as to the DeLites on those objects, especially compared to the Pentaxes.

Thanks again for your incredibly informative and helpful eview. I've posted at length because I think an exchange and different viewpoints are always helpful to readers.

 

Yes, we all have our own perspectives...like on RD. I personally do not like it. But again, comparatively to other eyepieces that have it, the amount of bowing was not prominent in the DeLites. If the pic I had in the review showed the entire AFOV then would be more apparent as to how controlled it was. At any rate, it was not showing anything excessive and some less than what I consider typical.

On the AFOV differences, sure they were different. In the end not anything to write home about from an observational perspective and target framing for me. Will others perhaps react differently? Sure. Some will think it is a lot more...others will think it is negligible. Can't predict what others will think...however I can relay how the difference impressed me or did not impress me...which is the purpose of my review. So just to inform folks how *I* reacted to the eyepieces. And I react, like most others I speak to, which is that it is the linear difference rather than the area difference that is most overt. So in that respect, the XW is 13% larger. FWIW I think most people read reviews incorrectly -- they are not cold bench test results, but instead are one human's reaction to an experience. So that context needs to always be remembered and factored relative to our own likes and dislikes.

We will just have to disagree on the fast mirror issue. The way to best test the DeLite at f/4.7 would be to do it in a refractor or some other design that does not generate coma. Sure there are lots of folks that do not use Paracorrs in instruments, but that does not negate what they will be looking at...coma It will easily overwhelm any other aberrations there. So I already know from experience that in a Newt that fast or faster, about 1/2 the AFOV will show aberrated star points from the coma. My personal opinion is that fast Newts, if sold without a coma corrector, are really incomplete instruments not quite finished. So my advice is that if you are < f/5, factor the coma corrector in as a required accessory...like an eyepiece is a required accessory, unless you like observing coma (LOL).

Finally...on the galaxies or faint nebula I did no observations (M42, M31 I consider in the same class as M57 which I did observe in the review). I am not a faint fuzzy hunter. That being the case I can't offer too many insights as I do not regularly observe them. And again, the article is based on what my reactions were to what I observed (i.e., not trying to be everything for everyone). I can extrapolate some though I feel...and would not expect their performance to be of any consequential difference, like we see from folks commenting on the Delos vs. XW. Six of one, half dozen of the other. So will probably be a flip of a coin. But never know until the faint fuzzy hunters out there get some, compare, and let us know what they see!

And anyway...for those considering XWs or DeLites which overall do I think are best? No contest...the Morpheus ... More AFOV...sharp across the FOV...reasonable price...great eye relief and exit pupil behavior.

 

I read Bill's review and one that appeared in the Sky At Night magazine and have bought the three. Both had good reviews.

I have a colleague coming over the pond to the UK next week and he is bringing them with him.

That is a massive saving for me as the $ price number equals what we pay in £'s here in the UK.

BTW Bill I have a copy of your book and it is well used for background and reference.

 

I have used all 3 DeLites with a 4" f/7 triplet refractor and in a 12.5" f/5 dob with a Paracorr.
In both scopes, the DeLites impress with astoundingly good contrast. I have seen (and own) other eyepieces equally as sharp, but none with this level of contrast.
In the dob, the galaxy detail visible at 261x (the 7mm DeLite) was exemplary. I saw no loss of detail compared to my reference eyepieces.

It should be noted here, for those not familiar with the ideas:
Coma is a radial aberration and the size of the comatic star image increases linearly with distance from center, i.e. the star image is twice as wide at 2 times the distance from center.
So a 62° eyepiece will display less coma than a 70° eyepiece of the same focal length which will display less coma than a 100° eyepiece of the same focal length.
Double the power with a barlow or use an identical eyepiece with half the focal length, and the field is 1/2 the size, so the linear size of the comatic stars at the edge will be 1/2 as big. But the doubling of magnification means the apparent (what you see) size of the comatic star will be the same (2 x 1/2 = 1).
So the appearance of coma, assuming a flat field, is related to the apparent field of the eyepiece, not the focal length.
If you don't like coma and don't want to see it, but don't want to use a coma corrector, use narrow field of view eyepieces.
If you want to use 100° to 120° eyepieces, and not see coma, expect to use a coma corrector.
In a way, coma correctors made the 100° revolution possible for newtonian scopes.

So the DeLites will show less coma in the field in an f/4.7 scope without a coma corrector than the Delos, XWs, Ethos, Naglers, etc. simply because the fields are narrower.
But, I might add with emphasis, if you are paying this amount of money for a high-resolution eyepiece with superbly small spot sizes everywhere in the field, and doing high resolution viewing of the Moon, the planets, and double stars, avoiding the use of a coma corrector at f/4.7 will simply reduce the eyepieces to an average performer everywhere except the central 10% of the field. In a newtonian, the coma-free field (where coma is smaller than the Airy disc) is 0.005mm x the f/ratio³. At f/4.7, that's 0.52mm.
Even a 2mm 62° eyepiece has a field stop 4 times that wide.
I'm just sayin', if you want to see sharp images from side-to-side, and your scope is f/4.7, you may need to stick to orthos or something equivalently narrow, and even then, the edge will show coma.

Don Pensack
Los Angeles

 

FWIW, I used to be one of those never-use-a-paracorr fellows with my f/4.7 dob. What cured me of that was switching to refractors. Once I appreciated the coma-free fields for a while, when I started taking the Dob out again I *had* to use the Paracorr otherwise things looked like yuk. So it sits in the focuser always now.

Good point too if paying this much for eyepieces, worth seeing them up to their potential so just get a Paracorr!