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#26 GOLGO13

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Posted 05 November 2012 - 11:08 PM

I had a Televue 13mm type 6 and felt it was dim also. Ultimately I didn't really like it and sold it.

#27 RodgerHouTex

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Posted 05 November 2012 - 11:34 PM

Ditto on the Nagler type 6 13mm. But I still have it.

#28 ThreeD

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Posted 06 November 2012 - 12:48 AM


Are any of those Baader Orthos that were tested BGOs?


Yes, I tested the Baader 18 mm, 9 mm and 7 mm Ortho, see the beginging of the thread, the transmission ranges between ~ 95.7-97.8%

best regards

Thomas

Thanks. With my initial read I saw the "Ortho I" and "Ortho II" and thought maybe they were something different (and perhaps older than I've seen since I'm a relative newbie). I now realize you were just identifying two individual BGOs. Most excellent.

#29 Alvin Huey

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Posted 06 November 2012 - 01:30 AM

Good stuff...

How about the ZAO-II? ;)


Alvin,

At a guess , i would say 103% !!

Ian.


:funny:

#30 Sasa

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Posted 06 November 2012 - 04:04 AM

There must be something else what drives the eyepiece reach on faint fuzzies and stars. Not only transmission, or if transmition, then its whole spectral characteristic as BillP pointed out (especially in blue light) - see discussion in the following link. Some time ago I was reporting here surprisingly visible difference between TV15 plossl (new bought in 2011) and CZJ O-16 (old, bought used) on faint galaxies: here. Of course, this was just one session, so one must take it with care.

#31 sixela

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Posted 06 November 2012 - 08:14 AM

There's also the matter of knowing exactly what happens to the missing light. If it's absorbed it's no big deal, if it's converted to low-angle scatter or veiling glare it's quite another matter...

#32 Starman1

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Posted 06 November 2012 - 09:56 AM

Don't forget the "little secret" of eyepiece manufacture: no two samples of the same brand, model, and focal length eyepiece are identical.
I've only at three times in my life bought 3 samples of the same eyepiece and compared them (in the same scope on the same targets on the same nights).
Two of those three times I could see slight differences between the eyepieces. Subtle, yes, but I labeled them and repeated the view on another night and got the same results.
It does point out that variations in polish, assembly quality, and possibly, adherence to the design parameters exactly, may have played a role.
The third time one of the three was noticeably inferior to the other two.
The point at which you can take for granted that every sample of the same eyepiece will be the same is......where? I don't know.
Anyway, I think small variations in transmission could be due to factors related to the manufacture.
Interesting to think about.

#33 ThreeD

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Posted 06 November 2012 - 03:13 PM

Don't forget the "little secret" of eyepiece manufacture: no two samples of the same brand, model, and focal length eyepiece are identical.
...
Anyway, I think small variations in transmission could be due to factors related to the manufacture.

That's no little secret -- at least to me. Every manufacturing process has tolerances.

In fact to expand upon this notion, as is widely known and often discussed here, quite often there really are only a few manufacturers of an item and many companies source their brand name products from the same manufacturer. This type of thing happens in a lot of industries and is not limited to astronomy products.

What many people do not consider is that most of the time the brand name provides different specifications, often in the form of differing tolerances, to the manufacturer. For example, I know someone who, years ago, worked as a manager for a Kingsford Briquette manufacturing plant. The very same plant produced a few different brands, including some store brand generics, on a contract basis. The difference was that the other brands, particularly the generics, quite often had a relaxed specification and thus the batches that didn't meet the more rigorous Kingsford specification (primarily for moisture content) were used to fill the orders for the other brands so long as it still met their specs. The result being that if you buy a cheaper brand of briquettes you may be getting the same quality as the more expensive Kingsford but you might not.

I'm confident that this same type of thing occurs in the EP market. EPs within the same brand are going to vary from unit to unit -- it is impossible to make two items *exactly* the same. The question is, how much variation will one see. I strongly suspect less expensive brands see a much wider variation in quality.

Even if the OEM isn't the same, it would be very interesting to see the results of several units for each of several brand names. For example, TV vs ES vs Brandon vs you name it, etc. Such data will give an idea of how tight each brand names' tolerance specifications are.

I believe the saying should be "You generally get at least what you paid for." Afterall, sometimes you might be lucky and buy a cheap item and get one that matches the specs of a premium product. Just as with brand names, each observer needs to decide what guarantee of quality they need as not everyone has the same ability to discern visual details.

#34 ThomasM

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Posted 07 November 2012 - 09:38 AM

There's also the matter of knowing exactly what happens to the missing light. If it's absorbed it's no big deal, if it's converted to low-angle scatter or veiling glare it's quite another matter...


This is certainly an interesting question. Let's take a six element eyepiece with 12 air-glas surfaces and assume 0.5 % reflectivity of each surface. Then 6 % of the incoming light will be directly reflected into the direction of the objective lens or mirror. In addition we have weak reflections between two surfaces, the number of reflections scales roughly quadratically with the number of surfaces (actually 2n^2 - n reflections, if n is the number of surfaces, half of them into the direction of the eye). If we make an estimate we get roughly 12x12 weak reflections into the observers eye each with 0.005^2 times the intensity of the incoming beam, or in total 0.35 %. All in all, without any loss in the glass we have a transmission loss of 6.7 %, but only 0.35 % are undirected stray light producing some sort of glare. So we can expect 93.3 % transmission which is close to the measured transmission of complex eyepieces (Ethos, Leica Zoom). Since the intensity of scattered light due reflections between two surface scales quadratically with the number of air-glass interfaces and quadratically with the reflectivity of each surface this is only an issue of complex eyepieces with many elements or if the coatings are bad.

best regards

Thomas

#35 Sarkikos

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Posted 07 November 2012 - 09:42 AM

So eyepiece transmission might only be an appreciable problem in eyepieces with many elements or if the eyepiece has inferior coatings? I could have guessed that without all the math. But the math apparently confirms my guess.

:grin:
Mike

#36 ThomasM

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Posted 08 November 2012 - 04:09 PM

So eyepiece transmission might only be an appreciable problem in eyepieces with many elements or if the eyepiece has inferior coatings? I could have guessed that without all the math. But the math apparently confirms my guess.

:grin:
Mike


Mike,

to a large extend I would agree. Another, already mentioned aspect, is the colour tone, the transmissin can vary with wavelength. Some high refractive index glases have substantial absorption at short wavelength, between 400 and 450 nm. The eyepiece transmission survy listes a few eyepieces with less than 70% at 400 nm. Whether the low transmission at short wavelength and yellow tone results from the glas or the coating is not so clear to me.

best regards

Thomas

#37 robboski2004

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Posted 20 November 2012 - 09:40 PM


Hello Thomas,

Just received and measured a 12mm Delos........96% @ 532nm.
27mm Pan..........96.4% @ 532nm.


Will possibly order a 8mm Delos next year ?

Regards.
Ian.

#38 Alvin Huey

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Posted 21 November 2012 - 04:47 PM

Thanks for the reports all.

I really enjoy using the Delos for wide field when I can't use the ZAO-II. I'm still looking for an 8mm SPL. I wonder how it measures.

Transmission is just one piece of the puzzle along with (lack of) scatter, and sharpness...that ultimately give the best view of an object.

#39 dscarpa

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Posted 21 November 2012 - 06:04 PM

No surprize for me as to the Delos's high transmission rate. I've had a 17.3 for awhile and got a 12 a few weeks ago. The amount of M42-42 they pull in alone and using TV and Siebert barlows with my WO ZS-110 from my darkish suburban yard is a wonder. Views of clusters are also excellent. I'll give you odds XWs rate highly as well. I don't find the view in my very recent vintage LVW to be dimmer than that in the Delos or XWs. Ditto with my Ethos and WO UWAN. Not so with my 3 T6s, the difference between them and my top tier on DSOs isn't subtle. Some of that may be due to the T6s warmer tone and their lacking the clarity of the others. I noticed the same thing with the Radians I used to have. The T6s and Radians are very sharp with great contrast and scatter controll so it's not due to that. I suspect that ES eyepieces have pretty good transmission. That seems to be the case with my 14 ES 82 and 20 ES100 and they're cooler with better clairity than the T6s and Radians. Ditto with my 15 and 24 Pans. David

#40 ThomasM

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Posted 11 December 2012 - 05:49 PM


Have a 27mm Pan and 12mm Delos on order.
So my set will be 41mm / 27mm Pans 96% and 17.3mm / 12mm Delos all transmitting approx 96% half way between photopic and scotopic curves.

Tough time to be an amateur observer :jump:!!

Regards,
Ian.


Ian,

any news from the 12 mm Delos? Did you had a chance measuring the transmission?


best regards

Thomas

#41 robboski2004

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Posted 11 December 2012 - 08:24 PM

Hello Thomas,

Just received and measured a 12mm Delos........96% @ 532nm.
27mm Pan..........96.4% @ 532nm.


Will possibly order a 8mm Delos next year ?

Regards.
Ian.

#42 Sarkikos

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Posted 11 December 2012 - 09:17 PM

Ian,

Just received and measured a 12mm Delos........96% @ 532nm.
27mm Pan..........96.4% @ 532nm.


Thomas measured the BGO's as follows:

Baader 18 mm Ortho I 96,3
Baader 18 mm Ortho II 97.9
Baader 9 mm Ortho 95,7
Baader 7 mm Ortho 95.8


So it appears the BGO's have very similar transmission to the 12mm Delos and 27mm Pan. I think I'll hang onto my BGO's, or are at least most of them. They are good for faint fuzzies as well as planets / lunar. I do carry some with me when I go to my dark site.

Now, I wonder how the transmission of my XW's would compare to all these? :thinking:

Mike

#43 Starman1

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Posted 11 December 2012 - 10:14 PM

Asked and answered:
http://pentaxplus.jp...h/xo-xw/63.html

#44 Sarkikos

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Posted 12 December 2012 - 09:22 AM

Thanks, Don!

It looks like 96% transmission for the XW's at 550 nm. Judging from the graph, the transmission at 532 nm should be not much less than that, certainly no less than 95%. According to focal length, the XW's vary between about 95% and 96% transmission. So the XW's transmission is closely comparable to the Delos and BGO's.

A reasonable deduction from this - assuming all the measurements are correct - is that for deep sky light-transmission, there is no advantage to any of the three eyepiece lines over the others. XW's, Delos and BGO's are approximately equal in transmission.

So does this mean I should leave my BGO's home for planet / lunar and instead use my XW's at the dark site? :thinking:

Up to now I haven't really had a chance to compare the BGO's against the XW's for faint fuzzies. But I have gotten the impression that the BGO's let me go deeper than my ES eyepieces and my Baader Zoom.

Mike

#45 Starman1

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Posted 12 December 2012 - 11:21 AM

Mike,
We've talked about this before on the forums. It seems that there is a psychological phenomenon at work here. It's long been known that no human is capable of seeing a transmission or brightness difference of just a few percent, yet people see a difference in what they can see when comparing narrowfield eyepieces to widefields on deep sky objects.
Alvin Huey reports he can see more in the Delos than the Ethos, and more in his ZAOs than in the Delos. If the transmission of those eyepieces is within a few percent, and it appears to be, he should physiologically not be able to see a difference.
But if a psycho-physiological phenomenon is at work, then what he reports could be reality.

Here is the speculation, and it deserves a lab study somewhere:
narrowing the field of view results in an overall blacker field seen by the eye. The total amount of light entering the eye is reduced, and more of the peripheral field is seen as black. After all, a normally functioning eye has between 120 and 150 degrees of vision. If the eyepiece has a 40 degree field, then 80 to 110 degrees of that field will be black.
This may allow the dark adaptation of the eye to proceed to its maximum degree (I stare at the ground to accomplish the same thing), even though there is still light in the central 40 degrees of vision.
Or, the contrast between the black of the peripheral field and the illuminated image in the center causes an enhanced contrast in the center.
One would predict, therefore, that increasing the size of the apparent field would reduce the ability to see the faintest targets in the field, and so it seems, from anecdotal evidence.

We can test the hypothesis by using some widefield eyepieces with high transmission and some excellent narrowfield eyepieces of high transmission. IF we can legitimately see some fainter targets in the narrowfield eyepieces, then we know the psychological phenomenon is real because transmission cannot be the reason.

A good test field would be the center of Abell 426 where the number of galaxies visible rises almost exponentially with aperture. Small differences in light grasp can make a big change in the number of galaxies seen. One night we saw 8 galaxies in an 8", 18 in a 16", and 51 in a 28", and the 28" field was slightly smaller than the smaller scopes.

There is also the possibility the psychological phenomenon is not universal, i.e. it might make a difference to some observers but not all. I've often said that, other than for 3 defective eyepieces, no eyepiece I've owned (out of 300+) has ever prevented me from seeing an object visible in the aperture I was using at the time. I've seen essentially zero on-axis differences among various eyepieces, where seeing a faint target is concerned, regardless of apparent field or the number of elements. But my experience is not scientific, because I did not compare them all on the same night and same targets. And memory is unreliable.

That does not relate to the personal preferences end of the equation, where an observer's reaction to the apparent field plays a role in determining whether or not an observer would actually use a particular eyepiece. As an example, even finding that the Delos eyepieces were superior to the Ethos eyepieces would not prompt me to go out and buy a set of Delos eyepieces because, for me, the apparent field of the Delos is unacceptably narrow. My personal passage to wider fields is permanent, and one way.

But this test of a variety of high transmission eyepieces with differing apparent fields could be quite informative. And, in a club or group of observers, it might be possible to put together the necessary eyepieces

#46 BillP

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Posted 12 December 2012 - 12:07 PM

It seems that there is a psychological phenomenon at work here. It's long been known that no human is capable of seeing a transmission or brightness difference of just a few percent, yet people see a difference in what they can see when comparing narrowfield eyepieces to widefields on deep sky objects.

Alvin Huey reports he can see more in the Delos than the Ethos, and more in his ZAOs than in the Delos. If the transmission of those eyepieces is within a few percent, and it appears to be, he should physiologically not be able to see a difference. But if a psycho-physiological phenomenon is at work, then what he reports could be reality.


Don,

I see your point of conjecture, but do not agree (having abouit the same eyepiece quantity history). Yes you could be true, but there are other possibilites just as plausable IMO.

First off, I would say the premise of your 1st statement is too generalized and therefore incorrect. I have not seen any research indicating that humans cannot see differences of a few percent. I have seen studies where as little as 9 extra photons can be picked up by our perceptions though FYI! On studies where there is the 8-10% reporting, I have seen a multitude of them where people were shown point sources and with direct vision could not tell easily when the point source was dimmed on a second look. However I have never seen a study where it was conducted using adverted vision, in which the eye is more sensitive, nor a study were it was done with areas instead of point sources...especially when the area image was only partially illumintated with a gradual decreasing illimination. So all the studys really do not in any way model astronomical observing circumstances. It is actually very easy to logic through how a dim star can be just a few photons below the eye's threshold to perceive, then with an added 1% transmission in the eyepiece or scope have that threshold crossed so it is perceived. This is the circumstance that Alvin is explaining. I have read no study properly modeling astronomical situations. The onces I have read can only be extrapolated to things like if one can tell a sub-magnitude difference between two stars if that difference is less than 5%. So not what Alvin was conveying in his observing circumstance.

I do believe that there can also be in the mix a psycho-physiological phenomenon as you suggest. Actually it is probably present there for all of us biasing our perceptions based on expectations. However, to suggest that it would only cut one way I would say makes no sense. So would posit that it is just as likely that for those observers who do not see these differences, on-axis or otherwise, that they could just as likely have a psycho-physiological phenomenon happening to them preventing their seeing.

FWIW, I can tease out on-axis differences rather easily. Not on all targets, but on subsets of targets where the smallest contrast or brightness level does move things past a threshold. based on how I do some of mu larger scale comparisons, I would say that the likelihood of an expectations bias is many times eliminated as the many eyepieces are on a platform in the dark and ordered and reordered based on what is observed through them...and after a few minutes really have no idea what the eyepiece is that I am viewing through as it is just a poistion in the lineup at this point. When done, need to bring the table insode to see who's 1st and who's last as all I have is audio notes describing the differences between the slot positions. And there are differences to be seen in some way shape or form many times.

Anyway, food for thought. In the end though, I am alwaysof the opinion that the root cause why a difference is seen is really not important. All that is important is knowing that one eyepiece shows better or more for a particular observer with their optical chain.

#47 Paul G

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Posted 12 December 2012 - 01:51 PM

AAVSO has crunched large numbers of observations and came up with the same 8-10% difference needed to perceive a difference in brightness. That's directly applicable. This is not surprising given that for one light source to be perceived as twice as bright as another it has to be 9 times as bright (response compression). It's also important to distinguish between absolute threshold and difference threshold.

#48 Starman1

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Posted 12 December 2012 - 02:24 PM

In long conversations with AAVSO people, it has been noted that even the best observers cannot reliably detect a magnitude difference less than 0.1 magnitudes, which represents a 10% difference in brightness. Only by getting a large number of reports can they statistically narrow that to about 0.05 magnitude.

Lab studies I've read show that brightness differences of less than 10% fall into the "random chance" range of accuracy, with a "floor" of about 8%. That doesn't mean no observer could see a difference smaller than 8%, but it implies there is a floor to human perception as a statistical thing.

When we are talking the visibility of a faint star at the limit of averted vision, it's fair to ask, "With what percentage seen?". The limiting magnitude calculators seem to settle on 10% visible/90% invisible as a standard for determining visibility, but that is sort of arbitrary. Why not 5% or 15%? And I think the interpretation of "visible" varies from person to person. What difference is present between "invisible" and "visible with averted vision 10% of the time"? I've never read anything on that, ever.

One thing I've experienced over and over again through the years is the "you need a large scope to discover X, but not a large scope to see X after it's discovered". What I mean by that is that I may have difficulty seeing something in, say, my 12.5". I walk over and easily view it in a 28". Then I walk back and discover I CAN see it in the 12.5", only it's dimmer--but still there.

So what I distrust is the "now I see it, now I don't" type of statements concerning eyepieces. Nothing is simply visible or simply invisible; it's visible a certain percentage of the time, and that percentage varies, perhaps. But if it's invisible in a particular scope, I simply don't believe that changing eyepieces can make that "visible/invisible" difference. I've never seen it and every time I've thought I've seen it, looking longer proved me wrong.

So when talking about visibility of certain things at the limit, I believe that extreme differences reported between eyepieces of similar transmission are psychological. That doesn't mean they're not real. I don't think we really know the causes. Which is why I think a test of a number of individuals with a number of eyepieces of differing apparent field on the same target in the same scope on the same night could be interesting. And it might illustrate some psychological phenomenon worth studying in a more controlled environment.

I should also state that measured differences in transmission between eyepieces can exceed the 8-10% threshold. I've seen transmission percentages in the low 80s and the high 90s, and that difference is noticeable to nearly all observers.
But when the differences are 95-98%? Sorry, no way. Human vision has a logarithmic response. Or should I say no statistically significant way because random chance might score correctly for a particular individual and only indicate true randomness in a large sample.

#49 Sarkikos

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Posted 12 December 2012 - 02:26 PM

Gus,

I was thinking in terms of mere detection of a faint object - star, galaxy, BN, whatever - rather than comparative brightness. But if that 8-10% differential is toward the LM of a particular optical train - absolute rather than difference threshold - it should still be important.

Mike

#50 Sarkikos

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Posted 12 December 2012 - 02:43 PM

If two eyepieces have virtually the same transmission - let's say an XW and a BGO - and an object near the LM of an optical train can be seen in the BGO but not in XW, I'd say the difference is in the eye of the beholder ... literally.

As Don suggested, it makes sense that this detection difference is due to a difference in the level of light adaptation of the eye when looking through the two eyepieces. An eyepiece with a narrower AFOV will shield more of the surrounding background light from the observer's eye. I think that this alone could make a barely detectable object detectable in the BGO but not in the XW.

I have seen variations in my own level of dark adaptation produced by globular clusters and moderately bright stars when I've been trying to detect faint galaxies and nebulae. If a narrow-field Ortho keeps us from seeing these brighter objects, it makes sense to me that it could help us to see a very dim object - even if the transmission of the Ortho is no better than that of the wide-field eyepiece.

Of course, the observer could keep a bright star or glob just beyond the edge of an 82 or 100 degree eyepiece. But then the object we want to detect would probably not be near on-axis, where we would want it to be for optimally aberration-free viewing. Besides, the natural compulsion - at least mine - is to place the object we want to observe toward the center of the FOV.

Mike






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