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Equipment Discussions >> Eyepieces

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Starman1
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Reged: 06/24/03

Loc: Los Angeles
Re: Pentax XW versus Delos, an informal comparison new [Re: Sarkikos]
      #6036381 - 08/20/13 12:20 PM

Mike,

The human eye doesn't have its peak sensitivity over the entire spectrum.
One of the areas for further research is the spectrum of transmission of eyepieces. Measuring peak transmission at 532nm (green laser) can give you one figure only. A white-light artificial star won't have a uniform spectrum, either, so what does measuring transmission with that light suggest? Does that white light have sufficient output from 400-500nm to be able to give a good spectrum of short wavelength response?

If you look at the Pentax XW transmission spectra here you'll see there is a precipitous roll-off below 450nm.

Does the fact we have our greatest eye sensitivity at 500nm at night, using scotopic vision, mean this will have an effect on what we see or detect?

I don't see much in the way of a red roll-off in the XWs, but people report seeing reds better in the Delos. What does that mean?

The Ethos did the best at f/3.5. Does that mean it is optimized for short f/ratios?

How significant is a measured transmission difference of 0.08 magnitude? And were measurements taken once, or multiple times and averaged? That small a difference says transmission differences won't be easily revealed in the field.

A test like this always brings up additional questions. It is interesting to see how high the Delos scores, though it barely beat the Ethos.


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Sarkikos
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Re: Pentax XW versus Delos, an informal comparison new [Re: Starman1]
      #6036449 - 08/20/13 12:53 PM

Don,

Good questions about light transmission of eyepieces. These are the sort of uncertainties about the light transmission test in the French report which made me question the results. The little bit of jargon that was provided by the article did not impress me. "TRANSMISSION OF LIGHT by projecting the image of an artificial star on the cell with a photometer." Yes ... so what? We need more information than that to determine if the results can be extrapolated to scotopic human eyes. Amateur astronomers are not photometers.

Mike


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Tank
Carpal Tunnel
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Reged: 07/27/09

Loc: Stoney Creek, Ontario, CANADA
Re: Pentax XW versus Delos, an informal comparison new [Re: Sarkikos]
      #6036546 - 08/20/13 01:39 PM

Taste
-Do you like immersive view?
-Do you like seeing Field stop?
-Do you like eye relief?
-Do you like more neutral tone?
-Do you like Heavy big EPs?

These are some questions to be asked too before someone picks these top of the line EPs!
For me nothing beats the XWs yet as a entire Package!
Looked thru the Delos 8,12,14,17.3, Nikon NAV 17.5, Ethos 13, All XWs except for 40mm.
For me the Delos comes close to the XW but the comfort is just not there. Now XWs do have a issues at say 14,20mm FL here I would select a Delos due to FC in newts.
Ethos is just way to immersive for me personally!
Optics are great on all these!


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t.r.
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Re: Pentax XW versus Delos, an informal comparison new [Re: Sarkikos]
      #6036587 - 08/20/13 02:00 PM Attachment (16 downloads)

Quote:

This is the Babylon 10 translation of the French report's test for light transmission:

Quote:

TRANSMISSION OF LIGHT by projecting the image of an artificial star on the cell with a photometer, we have been able to measure the variations of transmission between the different eyepieces. The results obtained are rather good, with very low differences found, at most 0.08 magnitude




Babylon 10 French to English

So should we accept that the Delos 10 and XW 10 have essentially equal light transmission, since they both received a 6/6 on the French report? How does this square with field reports which indicate the Delos have greater light transmission? Personally, I tend to put more weight on field reports from experienced observers rather than lab tests. For instance, would the photometer be sensitive to the same range and peaks of light frequencies that a dark-adapted eye would have in actual field conditions?

Mike




That is the real point. But, there hasn't been enough reports that agree to arrive at a consensus on this. Hence, we are left only with human bias.
Myself and a friend compared the views between the 10 Delos and 10 XW in a TEC 180 FL targeted on comet Garradd and M71. It presented an opportunity to show any contrast/limiting magnitude differences at this scale. There were none. My friend liked the eyecup positioning better on the Delos. I liked the positioning better on the XW. It came down to ergonomics.


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kkokkolis
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Reged: 09/23/09

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Re: Pentax XW versus Delos, an informal comparison new [Re: t.r.]
      #6036604 - 08/20/13 02:12 PM

But we know that all these are good and differences of less than 10% are hardly perceivable by human beeings, unless instructed (through behavioral learning) to perceive them, placebo or not.
You say "splitting hairs" and he say "searching fleas in a haystack" here. Since we enjoy it there's nothing wrong,and it is our honest right to know which is the best before we spend our money, but one can enjoy stargazing with Delos, or Ethos, or Pentax XW, or Vixen, or even a Hyperion.
I know you all know it (in fact I learned it here) but I felt the need to express it. This might save me from a new eyepiece shopping spree.


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csrlice12
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Loc: Denver, CO
Re: Pentax XW versus Delos, an informal comparison new [Re: kkokkolis]
      #6036632 - 08/20/13 02:25 PM

"This might save me from a new eyepiece shopping spree."

There's a cure for that...


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kkokkolis
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Loc: Piraeus, Greece
Re: Pentax XW versus Delos, an informal comparison new [Re: csrlice12]
      #6036658 - 08/20/13 02:36 PM

Quote:

"This might save me from a new eyepiece shopping spree."

There's a cure for that...




Spending all my money on an expensive apo?
I suggested that to my wife but she prefers diamond earings.


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csrlice12
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Loc: Denver, CO
Re: Pentax XW versus Delos, an informal comparison new [Re: kkokkolis]
      #6036687 - 08/20/13 02:51 PM

Diamonds make fantastic lenses for eyepieces.......kinda expensive though....

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Pentax XW versus Delos, an informal comparison new [Re: Tank]
      #6036753 - 08/20/13 03:26 PM

Quote:

Taste
-Do you like immersive view?
-Do you like seeing Field stop?
-Do you like eye relief?
-Do you like more neutral tone?
-Do you like Heavy big EPs?




Good questions. I answer:
-Yes, the wider the better. if the eye relief is sufficient, and you have developed the skill of holding the pupil fixed while the head rolls around to look at the edges (say, after several years of using 82 degree eyepieces), who wouldn't prefer a picture window to a pinhole? Especially if it comes with increased sharpness and better star color renditions.
-Don't care. I don't have field stops in my eyes. This is not precluded by having 100-120 degrees. Simply roll your head and look at it. Even in a 70 degree field, if you look left to see the field stop you aren't looking at the field stop on the right side--you can't see the entire field stop with direct vision simultaneously. The difference is that you can move your eye back and forth to see the edges without moving your pupil away from the exit pupil. In a 100+ degree eyepiece, if you tried that you'd occult the exit pupil. You have to hold the pupil steady and roll the head. It's a little different, but it's a skill easily developed.
-Don't care. I observe without glasses. If you have to wear glasses, the widest fields may not be for you. That's really OK when one has to "settle" for the likes of Delos and XW eyepieces. For less.
-I don't know what you're talking about. The objects I view don't show colors. Everything is gray. Is this really an issue for anyone except the Moon viewer? I've noticed that a good yellow filter brights out small details on the Moon incredibly. That's not "neutral". Is complete neutrality always good? And is any eyepiece tinted to the degree of even a light filter, or we talking about the difference in degrees of white? Do you still see any hint of coloration after 10 seconds? That would be unusual.
-My scope handles everything up to 4 lbs easily. It might balk at 6-7 lbs.
I believe that means all eyepieces work just fine, regardless of weight. Balance is always an issue in scopes. Many of the scopes in the '50s and '60s had external sliding weights on the tubes. They were there for a reason. I wish we could get back to that and just stop worrying about the weight of eyepieces. Or learn to construct scopes with relative immunity to the mis-balance caused by various eyepiece weights.

Of course, I can see circumstances where one could have different answers. Some of those aren't a matter of taste (e.g. heavy eyepieces) but more a matter of matching eyepieces to the other equipment chosen.


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Scanning4Comets
Markus
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Reged: 12/26/04

Loc: Ontario, Canada
Re: Pentax XW versus Delos, an informal comparison new [Re: Starman1]
      #6036791 - 08/20/13 03:49 PM

I did a comparison between a 14mm Delos and a 14mm ES 100 on NGC-6946 in Cepheus. The 14mm Delos had better transmission as I could see, but the difference was only slight.

The 14mm ES 100 in question used in the comparison was the one that went flying in the air only to hit the ground below and it still worked perfectly.

I have the newer 14mm ES Argon 100 and in just looking through the bottom field lens, it appears to be clearer than my older one. I haven't had the chance to even try it yet and will be waiting for the moon to go away to do so.

In going back to 70 degree fields in eyepieces, it now feels restricted. I'd only grab an XW or two for planets, but I would keep my 14mm ES and 9mm ES 100's because the huge field just covers so much ground and I am basking in the giant FOV. I used to think 100 degree eyepieces were a gimmick, and once I tried them more and more, I am now addicted to them. The 14mm ES 100 is my favorite out of every eyepiece I own.

I've only had the 30mm ES 82 out once and need way more time with that one.....I was impressed with first light in it though. The last view I had with the 30mm ES 82 was just before I packed up at the darker site I go to: The Double Cluster was riding high in the N-E, and I have the view etched in my mind ~ It was really nice !!!!

Getting back on topic here ~ I've used the 6mm Delos and the 7mm XW. I preferred the ergonomics of the 7mm XW over the Delos. However, both are excellent eyepieces in their own right.


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Tank
Carpal Tunnel
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Reged: 07/27/09

Loc: Stoney Creek, Ontario, CANADA
Re: Pentax XW versus Delos, an informal comparison new [Re: Starman1]
      #6036818 - 08/20/13 03:59 PM

Don
Proving my point my answers would be diffent then yours so I would prefer a different high quality of EP
-"Wider the better" is not for me I prefer to see the entire image in one shot therefore the Ethos takes a back seat.
-Seeing the FS easily is a preference of mine which I love having think about it do you like to have pictures without frames again people would answer yes and no to this so its a preference thing.
-I observe with and without glasses and well love the 20mm of ER.
-Neutral tone is more of a color saturation of stars and say color banding on Jupiter you might have a strong preference to a more warm tone therefore the TV products would be a better fit.
-WT im just saying because like you say based on they equipment if you have a GEM you maybe pushing it to the MAX already you want the light weight EP.

I've been observing with a few different individuals and I can say everyone put more stock into a specific attribute in a EP so a individual may see one EP better than another!
Bottom line use what works best for your taste!


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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Pentax XW versus Delos, an informal comparison new [Re: eklf]
      #6037003 - 08/20/13 05:53 PM

Quote:

In light of Televue's perfectly-deserved stellar reputation for continously pushing the envelop on eyepiece designs,I am somewhat surprised (and a tad disappointed) that the Delos series simply equaled what Pentax achieved over a decade ago. This is quite a feat on the part of Pentax.




I agree. I had owned and used several Delos eyepieces before I picked up a 7 and 5 XW. I was surprised that the XW's basically equalled the Delos.


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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Pentax XW versus Delos, an informal comparison new [Re: HaleBopper]
      #6037027 - 08/20/13 06:03 PM

You would have to go with an 11 TV Plossl. How important is eye relief to you? 6mm is not enough for me. https://www.astronomics.com/televue-11mm-polssl-eyepiece_p3303.aspx
I found the large eye lens and long eye relief of the Delos and XW's make doing high power work pleasurable. My eyes don't get tired due to eye strain.


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Rick M.
super member


Reged: 03/16/13

Re: Pentax XW versus Delos, an informal comparison new [Re: GeneT]
      #6037047 - 08/20/13 06:09 PM

Gene, can we assume that Pentax has not made any changes/upgrades to its EP coatings in the last decade?

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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Pentax XW versus Delos, an informal comparison new [Re: Sarkikos]
      #6037053 - 08/20/13 06:12 PM

Quote:

This is the Babylon 10 translation of the French report's test for light transmission:

Quote:

TRANSMISSION OF LIGHT by projecting the image of an artificial star on the cell with a photometer, we have been able to measure the variations of transmission between the different eyepieces. The results obtained are rather good, with very low differences found, at most 0.08 magnitude




Babylon 10 French to English

So should we accept that the Delos 10 and XW 10 have essentially equal light transmission, since they both received a 6/6 on the French report? How does this square with field reports which indicate the Delos have greater light transmission? Personally, I tend to put more weight on field reports from experienced observers rather than lab tests. For instance, would the photometer be sensitive to the same range and peaks of light frequencies that a dark-adapted eye would have in actual field conditions? Mike




I always go with my own viewing tests and trust what I see. I also respect the results of carefully conducted lab tests. I am buying a few small glass, high throughput eyepieces to see if I can tell any differences. I am looking forward to BillP's book and his thoughts on this matter.


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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Pentax XW versus Delos, an informal comparison new [Re: Starman1]
      #6037067 - 08/20/13 06:18 PM

I can't get Google translate to work on this. http://www.cieletespace.fr/files/InstrumentTest/201306__6_oculaires_10mm.pdfDoes
Does anyone have a direct link for this article in English?


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dscarpa
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Re: Pentax XW versus Delos, an informal comparison new [Re: coutleef]
      #6037082 - 08/20/13 06:28 PM

For nighttime use your impression of the T6s vs the Delos and XWs mirror my own. My three T6s are as good which is to say very good for HA however and see a lot of use in my Lunt 60. I've recently bought more than a few simple glass eyepieces with a 5 XO being the most recent and am comparing them to the widefields for day and night. David

Edited by dscarpa (08/20/13 06:33 PM)


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Jeff Morgan
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Reged: 09/28/03

Loc: Prescott, AZ
Re: Pentax XW versus Delos, an informal comparison new [Re: Starman1]
      #6037089 - 08/20/13 06:33 PM

Quote:


-Yes, the wider the better. if the eye relief is sufficient, and you have developed the skill of holding the pupil fixed while the head rolls around to look at the edges (say, after several years of using 82 degree eyepieces), who wouldn't prefer a picture window to a pinhole? Especially if it comes with increased sharpness and better star color renditions.




Quote:

-I don't know what you're talking about. The objects I view don't show colors. Everything is gray.




OK, so color is rendered better, or not there at all?

But about this pinhole business. The smallest AFOV in a production eyepiece is about 40 degrees (30 degree on a special order Monocentric from Markus at APM). Even the relatively small Monocentric AFOV is comparable to the AFOV most us experience sitting in their customary seat watching our lovely big screen TVs. If you don't believe it grab a tape measure and do the math.

AFOV is of course purely a personal preference, 70 degrees appears to be a very popular place to be. Wide fields without unusual and un-ergonomic head or neck contortions in the dark.


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Jeff Morgan
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Re: Pentax XW versus Delos, an informal comparison new [Re: GeneT]
      #6037099 - 08/20/13 06:39 PM

Quote:

I always go with my own viewing tests and trust what I see. I also respect the results of carefully conducted lab tests. I am buying a few small glass, high throughput eyepieces to see if I can tell any differences.




Yes, that is always the ultimate test because you buy equipment with your money, not the Lab's money.

It is amazing how we all seem to react differently to different scope and eyepiece combinations.


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JustaBoy
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Re: Pentax XW versus Delos, an informal comparison new [Re: Jeff Morgan]
      #6037178 - 08/20/13 07:21 PM

*AFOV is of course purely a personal preference, 70 degrees appears to be a very popular place to be. Wide fields without unusual and un-ergonomic head or neck contortions in the dark.*

Very well said, Jeff - Thanks for this!


Don - I know that you are correct in what you say, you're just not correct for all of us:-)

Thank you,
-Chuck


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