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Compared with XWs and others, I can see the difference, the warmer tone in the older Televue Plossls/Radian/Panoptic/Nagler series. But not in the later series, Ethos & Delos, which have 'toned' down.

To me, this is almost an undeniable fact, since many others have reported seeing the warmer tone.

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I have two pairs of binocs I mostly use for birding: My Swarovskis are a little "warm," i.e., yellow; my Leicas are a little "cool," i.e., blue.
Bill

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Wouldn't the coffee/yellow tint be much easier to see on bright extended objects such as bright planets and the Moon rather than pointicular objects - stars - or dim extended objects such as galaxies and nebulae?

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I could have added Venus and the moon... Jupiter and Mars are quite colorful. Stars are quite bright in a large scope, I would think if there were a tint, it would be apparent.

Jon

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So... you also looked at Venus and the Moon on the same night through the Televue eyepieces and did not notice a coffee/yellow tint? Which TV eyepieces? From what I've read in this thread, the Ethos, Delos and maybe some other late model Televues do not have the coffee/yellow tint.

Mike

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So I "upgraded" my Ethos with the Delos. I can't wait until I get the 4.5, 8 and 12mm Delos in my case. The rest of my gently used Ethos will be on AMart coming this fall.

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Now you've gone and done it! There goes the Ethos sales and there won't be a Delos on the shelf to be had!!!

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So I "upgraded" my Ethos with the Delos. I can't wait until I get the 4.5, 8 and 12mm Delos in my case. The rest of my gently used Ethos will be on AMart coming this fall.

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Now you've gone and done it! There goes the Ethos sales and there won't be a Delos on the shelf to be had!!!

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The TeleVue rep with us saw the difference and Al knows that there is a difference. But the tradeoff is field of view for transmission. Given my type of observing, I'll take the transmission and contrast.

Again looking at bright objects with a little scope, the difference is very hard to discern.

We used a 32", a 28" and a 36" at the field and Lowrey's 48" at his observatory. I personally use a 22" and 30". I can see the difference in my 22", but not as profound as what I see in larger scopes during TSP.

I'll still use my ZAO-II's as my main eyepieces.

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So... you also looked at Venus and the Moon on the same night through the Televue eyepieces and did not notice a coffee/yellow tint? Which TV eyepieces?

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Wouldn't the coffee/yellow tint be much easier to see on bright extended objects such as bright planets and the Moon rather than pointicular objects - stars - or dim extended objects such as galaxies and nebulae?

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But the tradeoff [between Ethos and Delos] is field of view for transmission. Given my type of observing, I'll take the transmission and contrast.

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7) Ergo, the differences being described are more in the realm of "personal preference" and not "accuracy" or "flatness of spectral transmission".

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But the tradeoff [between Ethos and Delos] is field of view for transmission. Given my type of observing, I'll take the transmission and contrast.

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Query: The field stop aperture of an eyepiece is a critical limiting factor in the total flux of light input that can enter the eyepiece, and therefore also on the total transmission of light through the eyepiece. Across the board, the Delos EPs have substantially smaller field stops than do the closest equivalent focal-length Ethos, for example the 6mm Delos has a field stop of 7.6mm, while the 6mm Ethos has a field stop of 10.4mm, or almost 37% greater diameter field stop aperture.

Granted, there are a variety of other factors between the entry of the light into the eyepiece through the field stop and its exit through the eyelens that can influence transmission, such as any losses at internal lens interfaces or coatings, or different-size eyelens apertures (given an equal amount of total light transmitted through two different eyepieces, the one with the larger eyelens must spread that energy out over a larger area).

Nevertheless, 37% is a HUGE initial transmission advantage for the 6mm Ethos that the 6mm Delos has to make up during internal throughput via other factors. Televue does not give comparative specs on their chart for eyelens diameter, but rather only for barrel diameter (dimension D on the chart), but that would at least allow a roughly comparable substitute comparison: the 6mm Delos has a barrel diameter of 2.2in, vs the 6mm Ethos at 2.1mm...hmmm, little difference there. Perhaps someone possessing both eyepieces could give a direct eyelens aperture size comparison.

Alvin's argument is that somehow the differential in better transmission he perceives in the Delos is due to a disadvantageous transmission efficiency tradeoff necessary to achieve a 100 deg AFOV in the Ethos vs a 70 deg AFOV in the Delos. Perhaps so...in fact it's quite plausibly so given that the end result is only a relatively very small advantage to the Delos (but worthwhile for the sorts of exotic targets Alvin often pursues). The differential field-stop line of reasoning also doesn't address what the sources for any differential in contrast might be between the two eyepieces (again, 6mm Ethos vs 6mm Delos).

NEVERTHELESS, if the differences Alvin claims exist (and who am I to doubt his perceptions, given his observing experience and accomplishments)... the factors outlined above invite a better explanation of why any claimed differences in transmission should exist based on the AFOV difference. Where the 37% differential advantage in input light flux for the 6mm Ethos gets internally dissipated relative to the Delos is a lot to explain.

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The field stop, combined with the telescope's focal length, determines the true field, with the outer portion of the field stop defining the outer edge of the field of view. Now it's true that an eyepiece with a larger field stop will transmit more light, but only because it is looking at a larger area of the sky or Moon or whatever is being viewed. From the viewpoint of how much total light you get from all the objects in view, then you could say a larger field stop means more light.

Field stop size, however, has absolutely no relation to the brightness of any object in view. The field stop simply blocks light from objects outside your field of view. If you are looking at M13, it is going to have the same brightness in a narrow field eyepiece as it will have in a wide field eyepiece (same telescope, of course, and ignoring differences in actual eyepiece transmission).

I do think there are some perceptual differences when comparing eyepieces of differing apparent fields.

Clear skies, Alan

Edited by Alan French (05/01/12 04:12 PM)

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But the tradeoff [between Ethos and Delos] is field of view for transmission. Given my type of observing, I'll take the transmission and contrast.

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Query: The field stop aperture of an eyepiece is a critical limiting factor in the total flux of light input that can enter the eyepiece, and therefore also on the total transmission of light through the eyepiece. Across the board, the Delos EPs have substantially smaller field stops than do the closest equivalent focal-length Ethos, for example the 6mm Delos has a field stop of 7.6mm, while the 6mm Ethos has a field stop of 10.4mm, or almost 37% greater diameter field stop aperture.

Granted, there are a variety of other factors between the entry of the light into the eyepiece through the field stop and its exit through the eyelens that can influence transmission, such as any losses at internal lens interfaces or coatings, or different-size eyelens apertures (given an equal amount of total light transmitted through two different eyepieces, the one with the larger eyelens must spread that energy out over a larger area).

Nevertheless, 37% is a HUGE initial transmission advantage for the 6mm Ethos that the 6mm Delos has to make up during internal throughput via other factors. Televue does not give comparative specs on their chart for eyelens diameter, but rather only for barrel diameter (dimension D on the chart), but that would at least allow a roughly comparable substitute comparison: the 6mm Delos has a barrel diameter of 2.2in, vs the 6mm Ethos at 2.1mm...hmmm, little difference there. Perhaps someone possessing both eyepieces could give a direct eyelens aperture size comparison.

Alvin's argument is that somehow the differential in better transmission he perceives in the Delos is due to a disadvantageous transmission efficiency tradeoff necessary to achieve a 100 deg AFOV in the Ethos vs a 70 deg AFOV in the Delos. Perhaps so...in fact it's quite plausibly so given that the end result is only a relatively very small advantage to the Delos (but worthwhile for the sorts of exotic targets Alvin often pursues). The differential field-stop line of reasoning also doesn't address what the sources for any differential in contrast might be between the two eyepieces (again, 6mm Ethos vs 6mm Delos).

NEVERTHELESS, if the differences Alvin claims exist (and who am I to doubt his perceptions, given his observing experience and accomplishments)... the factors outlined above invite a better explanation of why any claimed differences in transmission should exist based on the AFOV difference. Where the 37% differential advantage in input light flux for the 6mm Ethos gets internally dissipated relative to the Delos is a lot to explain.

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Chris,
The obvious answer would be based on the assumption the Delos has a smaller number of elements. But, given the high transmission of the Pentax XW eyepieces (averaging 8 elements), and the tests on-line that show that the number of elements and transmission is somewhat loosely related (some high-element count eyepieces have better transmission than some low element count eyepieces), the difference would appear to be part physical, part physiological, and part psychological:

The physical side would be in the nature of optical quality, transmission percentage, spectrum of transmission, exit pupil produced, etc. Since Ethos and Delos are both using state-of-the-art coatings, I wouldn't really expect any difference here that could be measured by anything except a machine in a lab.

The physiological side would be that there is some evidence that shielding the eye from peripheral light may improve sensitivity on the central axis. In that way, a somewhat narrower field of view might, by making a larger "blacked out" periphery, make fainter targets more detectable. I would like to see more tests in a lab on that, but it would explain why many people see fainter targets in narrower field eyepieces, for instance, when the light transmission difference is beneath the brain's ability to see it.

The psychological side of it would be in how the viewer relates to the larger eye lens, greater eye relief, and just relaxing comfort of using the eyepiece. I have often heard comments about the Pentax XWs concerning how being in a very relaxed condition, visually, allowed for easier use and more study of the target. The Delos might just be a bit more comfortable to use, leading to a longer and more comfortable examination of a target--hence, more details seen.

One thing that occurs to me is the quality of the individual sample. Though there is very little variation between eyepieces of the same brand, model, and focal length, there is some. I have seen this myself when comparing 3 of the same eyepiece in the same scope on the same night on the same target. Production quality (in all its aspects) is most certainly a bell-shaped curve. The best eyepieces have an exceedingly narrow bell, but some golden-eyed individuals can see the difference--especially when eyepieces are on opposite sides of that bell-shaped curve. Alvin may have gotten some perfect examples of the design. That that can have an effect is seen in star images for sure. But can it be seen on other targets? Maybe.

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7) Ergo, the differences being described are more in the realm of "personal preference" and not "accuracy" or "flatness of spectral transmission".

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I agree 100%. That does not mean that personal preferences aren't important to those that express them.

Whether the "coffee stain" tint that I see in some TV eyepieces (especially the Plossls) or the "neutral" tint that most Pentax EPs have is more accurate, I don't care. I do know that I prefer the Pentax tints. Some of the more recent TV designs have a much more Pentax like tint ... I don't know what the transmission curves are actually like. I suspect what happens at the extreme red & violet ends of the visible spectrum is relatively unimportant as the eye has very poor sensitivity out there - especially at the violet end, for those of us who are getting long in tooth & grey in hair (or bald) and still have our natural corneas.

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A relevant point. If the individual is getting older, and his lenses (in the eye, that is) are yellower, perhaps a more minor roll-off in the blue has a greater effect?
In which case older individuals would see more "tinting".
I remember when the late Walter Scott Houston reported on the effects of his having cataract surgery that he said (paraphrasing) that the world was so much more blue! Stars appeared bluer in the telescope and he saw planetary nebulae as blue now that he had formerly seen as green.

If the eyepiece rolls off the blue a tiny bit, it could be the "straw that broke the camel's back", producing a visible tint where a younger individual might see none.

Interesting.

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But the tradeoff [between Ethos and Delos] is field of view for transmission. Given my type of observing, I'll take the transmission and contrast.

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Query: The field stop aperture of an eyepiece is a critical limiting factor in the total flux of light input that can enter the eyepiece, and therefore also on the total transmission of light through the eyepiece. Across the board, the Delos EPs have substantially smaller field stops than do the closest equivalent focal-length Ethos, for example the 6mm Delos has a field stop of 7.6mm, while the 6mm Ethos has a field stop of 10.4mm, or almost 37% greater diameter field stop aperture.

Granted, there are a variety of other factors between the entry of the light into the eyepiece through the field stop and its exit through the eyelens that can influence transmission, such as any losses at internal lens interfaces or coatings, or different-size eyelens apertures (given an equal amount of total light transmitted through two different eyepieces, the one with the larger eyelens must spread that energy out over a larger area).

Nevertheless, 37% is a HUGE initial transmission advantage for the 6mm Ethos that the 6mm Delos has to make up during internal throughput via other factors. Televue does not give comparative specs on their chart for eyelens diameter, but rather only for barrel diameter (dimension D on the chart), but that would at least allow a roughly comparable substitute comparison: the 6mm Delos has a barrel diameter of 2.2in, vs the 6mm Ethos at 2.1mm...hmmm, little difference there. Perhaps someone possessing both eyepieces could give a direct eyelens aperture size comparison.

Alvin's argument is that somehow the differential in better transmission he perceives in the Delos is due to a disadvantageous transmission efficiency tradeoff necessary to achieve a 100 deg AFOV in the Ethos vs a 70 deg AFOV in the Delos. Perhaps so...in fact it's quite plausibly so given that the end result is only a relatively very small advantage to the Delos (but worthwhile for the sorts of exotic targets Alvin often pursues). The differential field-stop line of reasoning also doesn't address what the sources for any differential in contrast might be between the two eyepieces (again, 6mm Ethos vs 6mm Delos).

NEVERTHELESS, if the differences Alvin claims exist (and who am I to doubt his perceptions, given his observing experience and accomplishments)... the factors outlined above invite a better explanation of why any claimed differences in transmission should exist based on the AFOV difference. Where the 37% differential advantage in input light flux for the 6mm Ethos gets internally dissipated relative to the Delos is a lot to explain.

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Chris,
The obvious answer would be based on the assumption the Delos has a smaller number of elements. But, given the high transmission of the Pentax XW eyepieces (averaging 8 elements), and the tests on-line that show that the number of elements and transmission is somewhat loosely related (some high-element count eyepieces have better transmission than some low element count eyepieces), the difference would appear to be part physical, part physiological, and part psychological:

The physical side would be in the nature of optical quality, transmission percentage, spectrum of transmission, exit pupil produced, etc. Since Ethos and Delos are both using state-of-the-art coatings, I wouldn't really expect any difference here that could be measured by anything except a machine in a lab.

The physiological side would be that there is some evidence that shielding the eye from peripheral light may improve sensitivity on the central axis. In that way, a somewhat narrower field of view might, by making a larger "blacked out" periphery, make fainter targets more detectable. I would like to see more tests in a lab on that, but it would explain why many people see fainter targets in narrower field eyepieces, for instance, when the light transmission difference is beneath the brain's ability to see it.

The psychological side of it would be in how the viewer relates to the larger eye lens, greater eye relief, and just relaxing comfort of using the eyepiece. I have often heard comments about the Pentax XWs concerning how being in a very relaxed condition, visually, allowed for easier use and more study of the target. The Delos might just be a bit more comfortable to use, leading to a longer and more comfortable examination of a target--hence, more details seen.

One thing that occurs to me is the quality of the individual sample. Though there is very little variation between eyepieces of the same brand, model, and focal length, there is some. I have seen this myself when comparing 3 of the same eyepiece in the same scope on the same night on the same target. Production quality (in all its aspects) is most certainly a bell-shaped curve. The best eyepieces have an exceedingly narrow bell, but some golden-eyed individuals can see the difference--especially when eyepieces are on opposite sides of that bell-shaped curve. Alvin may have gotten some perfect examples of the design. That that can have an effect is seen in star images for sure. But can it be seen on other targets? Maybe.

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Exactly Don. Basically light transmission per square area...not total light flux through the eyepiece...as obviously the Ethos, or better yet the "new" 13-element ES 120 degree eyepiece would have even higher light flux than the Ethos.

I've looked through three different 6mm Delos and all are of the same result.

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