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A Delos, Pentax XW Comparison

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#1 GeneT

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Posted 15 March 2013 - 10:28 PM

A Delos, Pentax XW Comparison
Recently, I have rethought my needs, and updated my eyepiece collection. I would like to share some thoughts in the area of my decisions I recently made while moving into the ‘high power’ range of eyepieces. For the past two years, I have bought most of the new TeleVue Delos as they were released. I have posted on Cloudy Nights my appreciation for the production quality and outstanding views provided by this new eyepiece line.

I have also read several postings by owners of the Pentax Extra Wide eyepieces saying that these are among the finest eyepieces ever made in their range of specifications. When Cloudy Nights posters ask for their top 10 favorite eyepieces, the Extra Wides often show up in the listings.

It is important for me to have eyepieces that allow me to view while wearing glasses. With minor exceptions, long eye relief is the second or third most important criteria when I consider buying an eyepiece. For this, I need a minimum of 17mm of eye relief; 19 or 20 is even better. Both the Delos and Pentax Extra Wides have 20mm of eye relief, and 72 and 70 AFOV respectively. These are nice criteria for doing high power work.

In the ‘high power’ range, I had purchased the 8, and 6mm Delos eyepieces. I already owned a 4 Radian. I recently found and bought a used 5mm Pentax XO—in my opinion, one of the finest eyepieces ever made. There are no 7 and 5mm Delos eyepieces. Pentax offers a 7 and 5mm Extra Wide, and about a week ago, I purchased both of them. One of my viewing axioms is that I like having eyepiece focal lengths bunched up when moving below 10mm. I now can move in 1mm increments going from an 8, to a 7, to a 6, to a 5.

On Tuesday March 12th and Thursday March 14th, I did some comparison viewing with all four eyepieces. The telescope I used was my 12.5 inch, F5 Portaball. Here are the comparative values of the eyepieces; I did not use a Paracorr:

7mm/218X (Pentax XW)
17X inch
Exit Pupil: 1.5

6mm/254X (Delos)
20X inch
Exit Pupil: 1.3

5mm/305X (Pentax XW, XO)
24X inch
Exit Pupil: 1


I spent about two hours each evening viewing two objects: Jupiter and the Orion’s Trapezium. I viewed in about Mag 4.8 skies about 22 miles from my home. When making eyepiece comparisons I prefer to have Jupiter or Saturn in the equation. I selected the Trapezium because it gave me six stellar points to view—the four main stars, along with E and F.

The seeing was very good Tuesday evening, and excellent Thursday. I made these observations beginning about 9 p.m. central day light savings time. Both Jupiter and the Trapezium were well placed in the sky. I realize the one must extrapolate when comparing a 7 to a 6 and a 6 to a 5. However, experienced viewers learn to make the necessary adjustments to at least get it close. Delos does not make a 7 and Pentax does not make a 6 XW, therefore direct comparisons cannot be made. I also made some comparisons between the Delos 8 and Pentax 7 XW, and other eyepieces. However, my main comparisons are listed below.

Here are my conclusions: Jupiter—
The Pentax 5mm XO yielded noticeably more contrast and clarity on Jupiter than the 5 XW. The word I choose to use here is noticeably. If I were giving the two eyepieces a letter grade, I would give the XW an A and the XO an A+. The 5mm XW did provide excellent views of the planet. With both eyepieces, there was excellent delineation of the belt structure. On Thursday evening, the Great Red Spot was easily seen on the planet’s surface. On and off axis viewing was excellent in both eyepieces.


The Pentax 7mm XW was also an excellent performer on Jupiter. Going back and forth between the Pentax 7 XW and the Delos 6, I was surprised—it was a tie. Both eyepieces gave superb views of the Jupiter. Extrapolating from the 1mm focal length difference, I could not give one an edge over the other. Some people are ‘color’ conscious. It appeared to me that the Pentax eyepieces had just a little bit more of a brownish tone than the Delos. However, for me, that has never been an issue. I will agree that my Radians gave the moon a nice coffee tone, yet this colorization in no way affected the amount of detail I could see on any of the astronomical objects.

The Trapezium—
The Pentax 5mm XO yielded just a tad more granularity in the stellar components compared to the
5 XW. However, the differences on the stellar points were not as marked between the two eyepieces as were the clarity and contrast in the views of Jupiter. The Trapezium’s four main stars were tack sharp in both eyepieces, as were E and F. On and off axis views were excellent. I am not sure of the reasons why the 5 XO did not provide a more significant difference when compared to the 5 XW. However, I remember reading that the Pentax 5 XO was designed to be a first rate planetary eyepiece. It truly is. One conclusion I drew from this is that when doing work on stellar objects, the Pentax 5 XW will get most of the use in that range—the 70 AFOV and 20mm of eye relief makes viewing much less challenging.

The Pentax 7mm and Delos 6 also were outstanding performers on the Trapezium. All the stellar points, to include E and F, were nice and sharp, on and off axis.

Some final thoughts:
If you own the Pentax XW’s, would I recommend that you sell them, for the new Delos? Definitely not! I was really surprised that the Pentax XW’s provided as good a views as the new Delos. The XW’s came on the scene about 10 years ago. Along the way, did Pentax improve the polish, coatings, and possibly make some improvement tweaks to their lens configurations for their more current rendings? I don’t know. Is the XW of 10 years ago as good as the current ones? I don’t know. Maybe someone else can answer that through some A B comparisons.

I was surprised how these comparisons came out. I thought that the Delos would be noticeably better than the XW’s. After all, the Delos emerged from the design methodology learned from the excellent Ethos series. The Delos drew on the lessons learned over the past 10 years when the XW’s emerged. What I thought I would be doing was to make these comparisons, and that the Delos would be the clear winner. I then was going to sell my Pentax 7 and 5 XW’s. No way—I am keeping them both!

If you own neither the Pentax XW’s or the Delos, and would like to pick up some with these characteristics (they are very similar), which ones? You could just flip a coin—and you will be a winner either way. They are both excellent eyepiece series. You could calculate and decide if, in the high power range, a Pentax 7 and 5 combination, or a Delos 8 and 6 combination, or possible a Delos 4.5 or 3.5, would best serve your telescope type, and your viewing habits. If you want a new Pentax XW, I would check with various venders to see if they have the one you want. There is some question of Pentax plans to continue the XW’s. The Pentax XW’s are dribbling in by ones and twos. There is plenty of product in the Delos line. Does one need a 7, 6, and 5mm eyepiece? (I also own a 4 Radian.) Probably not. However, as I noted above, when moving through the high power ranges, I like to have shorter stops between eyepieces. In the wide angle range, I make wider sweeps—going from a 31 Nagler to a 22 Nagler, to a 14 Delos. As we all know, seeing dictates how much magnification we can use, as does collimation and mirror cool down. But, when the gods align, one can keep moving to more and more magnification. This become important when doing double star work, and when seeing planetary detail, and other objects. I rarely use the Radian 4—so that is the shortest mm eyepiece I own.

Lastly—I recommend you beg, borrow or steal (no—just kidding; never steal :grin:) a Pentax 5mm XO if you want to max the potential for seeing planetary detail.
GeneT

#2 Stephen S

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Posted 15 March 2013 - 10:57 PM

Thank you for sharing this info. This is consistent with what I've read in other posts and with my own brief experience.

I really like TeleVue stuff. I have the full set of 1.25" Pentax XWs. I seriously considered making the change. I purchased a 10mm Delos to see if I might want to make the change. After comparing the Delos head to head with my 10mm XW, I had a tough time calling one a winner over the other.

I like (am used to) the ergonomics of the XWs. I've already have a full set of XWs and they are cheaper. I'm sticking with the XWs for now. That said, I'm thrilled to see that TeleVue has come up with a comparable line of eyepieces. Great time to be in the hobby!

Still hoping for a high quality, wide FOV zoom eyepiece that has long eye relief. Were such an item to appear in the market, I'd be one of the first in line to order. Until then, I will gladly pack my XWs as my go to grab and go eyepieces.

Thanks! Steve S

#3 mgwhittle

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Posted 15 March 2013 - 11:12 PM

I notice you didn't do any comparison of light throughput of the Delos versus the Pentax. From what I keep reading, that is an important strength of the Delos line. Maybe a follow up test on that?

#4 Scanning4Comets

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Posted 16 March 2013 - 12:11 AM

Nice report Gene! Very thoroughly executed and a real enjoyable read.

:waytogo:

Cheers,

#5 dcoyle

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Posted 16 March 2013 - 12:19 AM

Thanks for writing that up, Gene.

Do you take your glasses off for the 5.1 XO? I find the eye relief tight without glasses. I ask because if you do, that could account for some of the enhanced contrast effect.

Dan

#6 Roswell_UDSO

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Posted 16 March 2013 - 08:08 AM

Nice write-up - Thanks.

#7 t.r.

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Posted 16 March 2013 - 09:13 AM

Gene, I have followed your process of inquiring and acquiring these eyepieces from the onset. If anyone is objective, I think it is you. Great report on your findings and not surprising to me. LLegee and myself compared the proto-type, first 10 Delos to my 10XW awhile ago in a TEC180FL and AP130GT and posted our findings here which mirror yours. We observed comet Garradd near M71 and Jupiter for a variety of detail. I however, found the Delos warmer than the XW, while Luke saw no difference in tone. We'll chalk that up to individual eyesight and color perception which is known to vary highly in individuals to say the least. But, for the most part, I think the data points are in agreement that no difference can be seen in these eyepieces. Thanks for the write-up and continue to compare and contrast that lineup! ;)

#8 Damo636

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Posted 16 March 2013 - 09:34 AM

Great write up Gene :waytogo:

#9 catboat

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Posted 16 March 2013 - 10:23 AM

Thanks, Gene. That's a clear, thoughtful, and very useful review.

#10 Sarkikos

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Posted 16 March 2013 - 10:40 AM

Lastly—I recommend you beg, borrow or steal (no—just kidding; never steal :grin:) a Pentax 5mm XO if you want to max the potential for seeing planetary detail.
GeneT


+ 1 :waytogo: The Pentax XO 2.5 is not too shabby, either.

If you liked the XW 5 and 7, maybe you should think about the XW 3.5. It's my favorite eyepiece for high-power views of planets or doubles when I want more FOV for my Dob than the XO's will provide. I had a great look at Saturn last weekend through the XW 3.5. Nice detail and color in the rings and globe.

So far the XW's have seemed neutral-toned to my eyes. If the Delos are cooler than the XW's, than the Delos must truly be ice-cold!

:grin:
Mike

#11 MRNUTTY

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Posted 16 March 2013 - 10:48 AM

I found exactly the same non-differences between XW's and the Delos. I also like to have small increments in FL especially under 10, where I want 1mm, ans closer under 5mm.

I would be interested in a XW to Nagler comparison, if there is one, across the whole range. I know of a few like the 31nag vs 30XW.

#12 Rich V.

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Posted 16 March 2013 - 11:05 AM

Gene, nice report. Did you notice a difference in "ease of view"?

I borrowed a 10mm Delos from TV's John Rhodes last year at GSSP. I felt it gave great views; very similar to my Pentax eyepieces with one exception--finding the perfect eyepoint wasn't quite as easy for me compared to the Pentax.

Putting my eye up to my Pentax EPs, the full FOV just naturally pops into place, with the old XLs just a bit easier than the XWs. The Delos reminded me a bit of my Ethos eyepieces; it's "perfect" eye position was a bit finicky to find; less so than the Ethos, though.

I know we all have our personal preferences in how an eyepiece "feels" to us and I'm wondering if you noticed any difference in this regard.

Rich

#13 JayinUT

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Posted 16 March 2013 - 11:30 AM

Gene,

I really enjoyed reading your post. Well written and fun. Both are great eyepieces. Thanks for the write up and again, well done and a pleasure to read.

#14 Kutno

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Posted 16 March 2013 - 12:38 PM

Thank you, Gene, for your writeup.

Just curious: You indicate you have an 8mm Delos; but did not throw that unit into the mix. If you ever intend to do one, I would be interested to learn the results of a similar comparison between that Delos and the 7mm XW.

#15 coutleef

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Posted 16 March 2013 - 02:53 PM

Thanks for the nice review and comparison.

After reading several threads on delos versus pentax i had come to the conclusion that pentax users would find the pentax sligthly better and delos users would find the delos slightly better. Meaning that these EPs were equivalent.

You demonstrated great objectivity as you are a delos user and found both equivalent

I must admit as a pentax user that the variety and selection of FL of the delos is superior to that of the pentax however.

#16 Mike B

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Posted 16 March 2013 - 03:17 PM

Thanks, Gene, for a fine write-up! Enjoyed reading it very much :jump:

Having recently jumped into the fray with a 10mm XW, i've been wrestling with the thot of trying the 7xw- but felt the mags produced might render it less useful for my situation. Your efforts have helped me focus on the possibility of an 8mm Delos as a "perfect" higher-mag compliment to the 10xw in my scope.
:waytogo:

#17 Tank

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Posted 16 March 2013 - 03:22 PM

From what ive experienced i think if you like more the immersive feeing the delos might be a better pick if you like the more the seeing the FOV easier a bit backed out and framed the XW is for you.
So far what ive seen i like the XW but its just what i like others may have a different take.

#18 GeneT

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Posted 16 March 2013 - 03:34 PM

I notice you didn't do any comparison of light throughput of the Delos versus the Pentax. From what I keep reading, that is an important strength of the Delos line. Maybe a follow up test on that?


Good question. I don't pursue very often dim fuzzies that task the limits of my mirror. This would be an important question for those who do.

#19 GeneT

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Posted 16 March 2013 - 03:38 PM

Do you take your glasses off for the 5.1 XO?


Yes I do. Also, I am careful not to blink too often because the XO's short eye relief causes it to get dirty easily. My XO does not come out at star parties or outreach events.

I should have reported that I tested all these eyepieces both while wearing glasses (except the XO) and with my glasses off. In other words, I went from the XO to the XW back and forth with glasses off.

#20 GeneT

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Posted 16 March 2013 - 03:41 PM

I however, found the Delos warmer than the XW, while Luke saw no difference in tone. We'll chalk that up to individual eyesight and color perception which is known to vary highly in individuals to say the least.


I agree. Years ago when I joined the Air Force, a doctor told me that about 15 percent of those who would like to become pilots could not because they could not pass the color blindness part of the eye exam. Even those who can pass, we will see and process color differently.

#21 GeneT

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Posted 16 March 2013 - 03:42 PM

maybe you should think about the XW 3.5


I would--but I rarely use my Radian 4 and decided not to invest in a new eyepiece in that range.

#22 GeneT

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Posted 16 March 2013 - 03:45 PM

I borrowed a 10mm Delos from TV's John Rhodes last year at GSSP. I felt it gave great views; very similar to my Pentax eyepieces with one exception--finding the perfect eyepoint wasn't quite as easy for me compared to the Pentax.


I found both eyepiece series easy for me to find the exact place to place my eye to obtain the best view--both while wearing glasses and with them off.

#23 GeneT

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Posted 16 March 2013 - 03:48 PM

Just curious: You indicate you have an 8mm Delos; but did not throw that unit into the mix.


I did throw the 8 Delos into the mix. I did some back and forth between it and the Pentax 7 XW. As with the 7, the Delos 8 performed superbly. However, I decided for this writeup to focus more in the high power ranges going from the 7 to the 6 to the 5's. I agree that in most cases, an 8 does live in the high power range.

#24 GeneT

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Posted 16 March 2013 - 03:51 PM

I must admit as a pentax user that the variety and selection of FL of the delos is superior to that of the pentax however.


The Delos followed the Pentax XW's. Maybe they built that into the equation to be more competitive regarding their focal length offerings. However, I also wondered why Pentax went from a 10 to a 7 in their XW series. Why not a 10 to an 8?

#25 Rich V.

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Posted 16 March 2013 - 04:46 PM

Thanks, Gene.

I also wondered why Pentax went from a 10 to a 7 in their XW series. Why not a 10 to an 8?


Then there'd be too big a gap between the 8 and the 5! ;)

It seems Pentax was content to closely duplicate their XL series focal lengths and leave it at that. The 28mm 1-1/4" XL was replaced with the 30mm 2" XW to keep a common AFOV; a step in the right direction. The focal lengths follow a progression of approx. 70% FL increments.

Rich






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