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Equipment Discussions >> Eyepieces

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ThomasM
sage


Reged: 04/19/09

Eypiece transmission
      #5502437 - 11/03/12 01:47 PM

There is a lot of discussion about eypiece transmission, but measurements are rare. This week I performed measurements of the transmission of several popular eyepieces using a laser diode with 532 nm wavelength and a 25 mm f=125 mm refractor and a thorlabs power meter.

Eyepiece/ Transmission in %

Baader 36 mm Asphric 94,9
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 (edited)
TV Panoptic 25 mm 95,2
TV Ethos 17 mm I 91.7
TV Ethos 17 mm II 92.4 (added)
TV Nagler 13 mm I 87,6
TV Nagler 13 mm II 87,3 (added)
Leica Aspheric Zoom with TMB Barlow 6-12 mm 93,4
Leica Aspheric Zoom 9-18 mm 94,4
Thorlabs Monocentric 10 mm fully multicaoted 93,7
No name Plössl 4 mm (MgF2) 86,5
TMB ED 1.8x Barlow > 99%


The statistical errors (standard diviation) are less than 0.5 %, systematic errors presumably less than 2 %, at least for the long focal length eyepieces.

A few things surprised me:

1. The transmission of the Leica Zoom (8 lenses) exceeds that of the Thorlabs monocentric, a three lens, single element eyepiece, although the Thorlabs is fully multicoated. Edited: After removing dust from the front lens I obtained 96.9%
2. The Transmission of the TV 13 mm Nagler is rather low compared to a previous measurement of the TV Nagler 9 mm, (http://www.amateurastronomie.com/Astronomie/tips/tips3.htm). I repated the measurement, to make sure that the transmission is indeed below 90%.
3. The two Baader 18mm ortho eyepieces differ by more than one percent, this is reproducable.

In practice these differences are probably academic, they are presumably almost invisible.
Best regards

Thomas

p.s. I repeated the measurement for the some eyepieces and added new values (Nov 5 2012)

Edited by ThomasM (11/05/12 01:42 PM)


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Eypiece transmission new [Re: ThomasM]
      #5502589 - 11/03/12 03:49 PM

Did you clean the eyepieces before testing them?

Regards,

Jim


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: jrbarnett]
      #5502595 - 11/03/12 03:55 PM

Quote:

Did you clean the eyepieces before testing them?

Regards,

Jim




Actually, the eyepieces were very clean. Anyhow, I wiped the eyelense with a microfaser fabric and removed dust with a clean brush.

best regards


Thomas

p.s. would you suggest to do additional cleaning, e.g. with alcohol or with 'optical wonder' fluid from Baader?


Edited by ThomasM (11/03/12 04:09 PM)


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Eypiece transmission new [Re: ThomasM]
      #5502607 - 11/03/12 04:07 PM

Thomas,
The 13 Nagler was an original Nagler, I presume.
That actually doesn't surprise me since my original 14mm Meade Series 4000 (smoothside, some uncoated surfaces internally) also transmitted about 85%, IIRC.
Coatings have substantially improved since then.
A fully multi-coated 4-element, 2-group, eyepiece could transmit as much as 98.0% You had one right there, at 97.9%
In theory, an Ethos could have a transmission of 94.1% Your 91.7% indicates it misses the theoretical by just a hair.

Since the highest transmission is 97.9%, you kind of want none of your eyepieces to fall below a loss of 0.1 magnitude, or 10%, which says it should be at least 87.9%

Only 2 of the eyepieces you tested missed that, and I bet the no-name Plossl was uncoated on its interior surfaces. Or the coatings were very much sub-par, as a good MgFl2 coating on all surfaces could yield as high as 94.1% transmission.

The fact that a ten inch reaches over 0.4 magnitudes deeper than an 8" shows how little effect transmission in eyepieces has. Probably of more importance are factors such as the spectrum of transmission and the polish quality on the glass.

Oh, one more thing: the transmission of 100% was equalized AFTER the refractor, I presume. What was the transmission of the refractor?

Edited by Starman1 (11/03/12 04:10 PM)


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: Starman1]
      #5502624 - 11/03/12 04:27 PM

Quote:

Thomas,
The 13 Nagler was an original Nagler, I presume.

...
Coatings have substantially improved since then.
A fully multi-coated 4-element, 2-group, eyepiece could transmit as much as 98.0% You had one right there, at 97.9%
In theory, an Ethos could have a transmission of 94.1% Your 91.7% indicates it misses the theoretical by just a hair.


...

The fact that a ten inch reaches over 0.4 magnitudes deeper than an 8" shows how little effect transmission in eyepieces has. Probably of more importance are factors such as the spectrum of transmission and the polish quality on the glass.

Oh, one more thing: the transmission of 100% was equalized AFTER the refractor, I presume. What was the transmission of the refractor?




Don,
thanks for your comments. Actually, the 13 mm Nagler is a five years old T6, that's why I am surprised that the measured transmission is 'only' 87.6%.

The transmission was measured by comparing the direct beam behind the focal spot of the fractor lens and the beam passing through the eyepiece. I have not measured the transmission of the fractor lens, but I principle I could have done that.

best regards

Thomas


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Eypiece transmission new [Re: ThomasM]
      #5502642 - 11/03/12 04:44 PM

If you have a loupe or a magnifying glass, inspeact the eye lenses of each. If they look clean, you're fine. If you see any evidence of grime, haze, oil, etc., I would give 'em a cleaning with Pursol or similar cleaning agent.

It can't hurt to check. My eyepieces tend to get pretty dirty. I'm usually rewarded with a mess whenever I do a loupe inspection.

- Jim


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robboski2004
member


Reged: 01/14/08

Re: Eypiece transmission new [Re: jrbarnett]
      #5502696 - 11/03/12 05:38 PM


Hello Thomas,

I also recently setup a 532nm laser to measure the following eyepieces.........

17.3mm Delos 96%
17mm Ethos 93.5%
32mm TV Plossl 95% ( what do you expect for $130 !!!)
41mm Panoptic 96%
32mm Meade SWA 88%
22mm Pan ( 1990's) 87%

setup : laser into optical fibre which expands the beam to 10mm entering the eyepiece, then through KG5 filter to isolate green from original diode wavelength into a newport intergrating sphere and power meter.

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 !!

Regards,
Ian.


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denis0007dl
sage
***

Reged: 04/17/12

Loc: Croatia
Re: Eypiece transmission new [Re: robboski2004]
      #5502768 - 11/03/12 06:22 PM

It would be interesting to test Explore Scientific 68" and 82" eyepieces

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Paul G
Post Laureate
*****

Reged: 05/08/03

Loc: Freedonia
Re: Eypiece transmission new [Re: ThomasM]
      #5502905 - 11/03/12 08:07 PM

Quote:

Quote:

Thomas,
The 13 Nagler was an original Nagler, I presume.

...
Coatings have substantially improved since then.
A fully multi-coated 4-element, 2-group, eyepiece could transmit as much as 98.0% You had one right there, at 97.9%
In theory, an Ethos could have a transmission of 94.1% Your 91.7% indicates it misses the theoretical by just a hair.


...

The fact that a ten inch reaches over 0.4 magnitudes deeper than an 8" shows how little effect transmission in eyepieces has. Probably of more importance are factors such as the spectrum of transmission and the polish quality on the glass.

Oh, one more thing: the transmission of 100% was equalized AFTER the refractor, I presume. What was the transmission of the refractor?




Don,
thanks for your comments. Actually, the 13 mm Nagler is a five years old T6, that's why I am surprised that the measured transmission is 'only' 87.6%.

The transmission was measured by comparing the direct beam behind the focal spot of the fractor lens and the beam passing through the eyepiece. I have not measured the transmission of the fractor lens, but I principle I could have done that.

best regards

Thomas




Interesting. I wonder how the methodology differs from this where the T6 Naglers did much better:

Eyepiece Transmission


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jtaylor996
scholastic sledgehammer


Reged: 09/02/08

Loc: North Texas
Re: Eypiece transmission new [Re: Paul G]
      #5503127 - 11/03/12 10:34 PM

I wonder if this number changes across the FOV...

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robboski2004
member


Reged: 01/14/08

Re: Eypiece transmission new [Re: jtaylor996]
      #5503146 - 11/03/12 10:51 PM


The 22mm Panoptic manufactured in the 90's has a distinct
change in coating colour on the steep eyelens and field lens curves.
When i measured the 41mm Pan, i obtained virtually the same transmission whether the 10mm circle was centered in the field lens or off to one side.

Ian.


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: Paul G]
      #5503419 - 11/04/12 05:09 AM

Quote:

Quote:

Quote:

Thomas,
The 13 Nagler was an original Nagler, I presume.

...
Coatings have substantially improved since then.
A fully multi-coated 4-element, 2-group, eyepiece could transmit as much as 98.0% You had one right there, at 97.9%
In theory, an Ethos could have a transmission of 94.1% Your 91.7% indicates it misses the theoretical by just a hair.


...

The fact that a ten inch reaches over 0.4 magnitudes deeper than an 8" shows how little effect transmission in eyepieces has. Probably of more importance are factors such as the spectrum of transmission and the polish quality on the glass.

Oh, one more thing: the transmission of 100% was equalized AFTER the refractor, I presume. What was the transmission of the refractor?




Don,
thanks for your comments. Actually, the 13 mm Nagler is a five years old T6, that's why I am surprised that the measured transmission is 'only' 87.6%.

The transmission was measured by comparing the direct beam behind the focal spot of the fractor lens and the beam passing through the eyepiece. I have not measured the transmission of the fractor lens, but I principle I could have done that.

best regards

Thomas




Interesting. I wonder how the methodology differs from this where the T6 Naglers did much better:

Eyepiece Transmission




I was surprised too that the transmission of the 13 mm Nagler T6 (I got 87.6%) is more than 4 % lower than that given in the link above. Actually, I have no idea how the measurements were performed. I own a scond Nagler 13mm T6 for binowing and could do an additional measurement.

best regards

Thomas


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: robboski2004]
      #5503421 - 11/04/12 05:15 AM

Quote:


Hello Thomas,

I also recently setup a 532nm laser to measure the following eyepieces.........

17.3mm Delos 96%
17mm Ethos 93.5%
32mm TV Plossl 95% ( what do you expect for $130 !!!)
41mm Panoptic 96%
32mm Meade SWA 88%
22mm Pan ( 1990's) 87%

setup : laser into optical fibre which expands the beam to 10mm entering the eyepiece, then through KG5 filter to isolate green from original diode wavelength into a newport intergrating sphere and power meter.

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 !!

Regards,
Ian.




Ian,

these are very intersting results. The Delos seems to be very good, 3 % higher transmission than the Ethos. Your value for the 17 mm Ethos is slightly higher than mine this is probably within the error bars. Can you estimate your error bars? Do you intend to measure the transmission of shorter focal length eyepieces, e.g. 8 or 10 mm Delos?

best regards

Thomas


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davidpitre
Post Laureate
*****

Reged: 05/10/05

Loc: Central Texas
Re: Eypiece transmission new [Re: ThomasM]
      #5503576 - 11/04/12 08:55 AM

Check out the TMB barlow. I use one, and always wondered about the cumulative effect it added in terms of light loss when viewing extremely faint objects. Question answered.

It is notable that Ian and Thomas both measured the 17 Ethos, their measurements differing by almost 2%.


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astroducky
sage


Reged: 10/02/06

Loc: South East Asia
Re: Eypiece transmission new [Re: ThomasM]
      #5503645 - 11/04/12 09:45 AM

Have you taken into account that the laser itself fluctuates a few percent over time? Unless you directly take the 'input' beam into the system and concurrently/ immediately measure the 'output' of the beam, it will not be that accurate. Also, the power meter itself has an accuracy typically of 3%. That could also answer why there are differences in results of similar eyepieces.

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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: davidpitre]
      #5503681 - 11/04/12 10:10 AM

Quote:

Check out the TMB barlow. I use one, and always wondered about the cumulative effect it added in terms of light loss when viewing extremely faint objects. Question answered.

It is notable that Ian and Thomas both measured the 17 Ethos, their measurements differing by almost 2%.




Yes, the TMB Barlow is excellent, the coatings are darker than that of any eyepiece I own, very low scatter and the transmission is better than 99%.

Regards

Thomas

p.s. I could also check a second 17 mm Ethos and see if the transmission is the same


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: astroducky]
      #5503687 - 11/04/12 10:17 AM

Quote:

Have you taken into account that the laser itself fluctuates a few percent over time? Unless you directly take the 'input' beam into the system and concurrently/ immediately measure the 'output' of the beam, it will not be that accurate. Also, the power meter itself has an accuracy typically of 3%. That could also answer why there are differences in results of similar eyepieces.




The numbers are obtained by first measuring the direct beam, then the beam with eyepiece, this cyle is repeated 10 times. After warm up the laser is very stable, short term fluctions less than 0,5%, this includes the error of the power meter. Standard diviation is 0.2%. Therefor, as stated above, I expect statiscal errors to be less than 0.5 %, systematic errors are much more difficult to judge but I would guess less than 1-2 %.

In other words, the differences in the transmisson of similar eyepieces are real.



best regards

Thomas

Edited by ThomasM (11/04/12 03:46 PM)


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robboski2004
member


Reged: 01/14/08

Re: Eypiece transmission new [Re: ThomasM]
      #5504134 - 11/04/12 03:45 PM


Hello Thomas,

Claiming absolute values is always fraught with danger !

However, the control in my setup is eyepiece / no eyepiece.

I would be confident to claim +/- 0.5% with the measurements i supplied.
These measements were obtained over extended periods,using slightly different setups which all became very consistent.

I have a 12mm Delos on order, so will be in a position to measure it's transmission in the next 2 weeks or so ?

Regards,
Ian.


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robboski2004
member


Reged: 01/14/08

Re: Eypiece transmission new [Re: denis0007dl]
      #5504148 - 11/04/12 03:55 PM


Hello Denis,

Unfortunately, i do not have access to any ES eyepieces
at this time.

Regards,
Ian.


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ThreeD
Pooh-Bah


Reged: 12/23/08

Loc: Sacramento suburbs
Re: Eypiece transmission new [Re: robboski2004]
      #5504857 - 11/05/12 01:41 AM

Very interesting stuff.

I know that Alvin Huey, who thrives on pushing the limits of observability, has switched to using Delos for his widefield EPs based on his own experience. These results seem to validate his observations.

Edit: Alvin also swears by his TMB ED barlow. Very, very interesting.

Are any of those Baader Orthos that were tested BGOs?

Edited by ThreeD (11/05/12 01:46 AM)


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: ThreeD]
      #5505470 - 11/05/12 01:49 PM

Quote:


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


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: robboski2004]
      #5505544 - 11/05/12 02:41 PM

Quote:


Hello Thomas,

Claiming absolute values is always fraught with danger !

However, the control in my setup is eyepiece / no eyepiece.

I would be confident to claim +/- 0.5% with the measurements i supplied.
These measements were obtained over extended periods,using slightly different setups which all became very consistent.

I have a 12mm Delos on order, so will be in a position to measure it's transmission in the next 2 weeks or so ?

Regards,
Ian.




Jan,

I agree, claming absolute values can be dangerous. I got the impression that your error bars are a little bit smaller than mine, I have just started with eyepiece transmission measurements. I am pretty sure that my total error bar is less than 2 %, but presumably less than 1 %.

You got 93.5 % transmission for the 17 mm Ethos, I obtained 91.7 %. In order to check the discrapency I repeated the measurement and got 91.5 % and in addition I measured the transmission of a second Ethos 17 mm and obtained 92.4%.


Finally, the 'low' transmission of the Nagler 13 mm T6 was surprising, I got 87.6 % and now for a second Nagler 13 mm T6 I obtained 87.3 % ( compared to ~93% of the Nagler 9 mm T6 http://www.amateurastronomie.com/Astronomie/tips/tips3.htm). I should add that the eyepiece was carefully cleaned, first with with a brush to removed dust, then with a microfaser fabric and 'optical wonder' cleaning agent from Baader.

So, please let us know when you have measured transmission of further eyepieces (Delos 12 mm and shorter focal length).


best regards

Thomas


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Alvin Huey
Carpal Tunnel
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Reged: 10/18/05

Loc: NorCal
Re: Eypiece transmission new [Re: ThomasM]
      #5505622 - 11/05/12 03:49 PM

Good stuff...

How about the ZAO-II?


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5u4
super member
*****

Reged: 04/27/06

Loc: FL
Re: Eypiece transmission new [Re: Alvin Huey]
      #5505639 - 11/05/12 04:07 PM

Wonder if the lowish transmission of the 2 13T6's are representative of all 13T6's or just ones from a certain period where the coatings may have been less than perfect or whatever. I have a brand new 13T6 which makes me wonder where mine falls in the transmission dept.

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robboski2004
member


Reged: 01/14/08

Re: Eypiece transmission new [Re: Alvin Huey]
      #5506030 - 11/05/12 09:43 PM

Quote:

Good stuff...

How about the ZAO-II?




Alvin,

At a guess , i would say 103% !!

Ian.


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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Eypiece transmission new [Re: ThomasM]
      #5506146 - 11/05/12 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.

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RodgerHouTex
Pooh-Bah
*****

Reged: 06/02/09

Loc: Houston, Texas, USA
Re: Eypiece transmission new [Re: GOLGO13]
      #5506180 - 11/05/12 11:34 PM

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

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ThreeD
Pooh-Bah


Reged: 12/23/08

Loc: Sacramento suburbs
Re: Eypiece transmission new [Re: ThomasM]
      #5506231 - 11/06/12 12:48 AM

Quote:

Quote:


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.

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Alvin Huey
Carpal Tunnel
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Reged: 10/18/05

Loc: NorCal
Re: Eypiece transmission new [Re: robboski2004]
      #5506256 - 11/06/12 01:30 AM

Quote:

Quote:

Good stuff...

How about the ZAO-II?




Alvin,

At a guess , i would say 103% !!

Ian.






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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Eypiece transmission new [Re: Alvin Huey]
      #5506316 - 11/06/12 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.

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sixela
Postmaster
*****

Reged: 12/23/04

Loc: Boechout, Belgium
Re: Eypiece transmission new [Re: Sasa]
      #5506456 - 11/06/12 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...

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Eypiece transmission new [Re: sixela]
      #5506577 - 11/06/12 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.


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ThreeD
Pooh-Bah


Reged: 12/23/08

Loc: Sacramento suburbs
Re: Eypiece transmission new [Re: Starman1]
      #5507055 - 11/06/12 03:13 PM

Quote:

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.


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission new [Re: sixela]
      #5508092 - 11/07/12 09:38 AM

Quote:

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

Edited by ThomasM (11/07/12 09:45 AM)


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Re: Eypiece transmission new [Re: ThomasM]
      #5508095 - 11/07/12 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.


Mike


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Re: Eypiece transmission new [Re: Sarkikos]
      #5510186 - 11/08/12 04:09 PM

Quote:

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.


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


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Re: Eypiece transmission new [Re: ThomasM]
      #5531102 - 11/20/12 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.


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Re: Eypiece transmission new [Re: robboski2004]
      #5532629 - 11/21/12 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.


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Re: Eypiece transmission new [Re: ThomasM]
      #5532745 - 11/21/12 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

Edited by dscarpa (11/21/12 06:46 PM)


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Re: Eypiece transmission new [Re: robboski2004]
      #5566365 - 12/11/12 05:49 PM

Quote:



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 !!

Regards,
Ian.




Ian,

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


best regards

Thomas


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robboski2004
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Re: Eypiece transmission new [Re: ThomasM]
      #5566539 - 12/11/12 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.


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Re: Eypiece transmission new [Re: robboski2004]
      #5566594 - 12/11/12 09:17 PM

Ian,

Quote:

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




Thomas measured the BGO's as follows:

Quote:

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?

Mike


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Re: Eypiece transmission new [Re: Sarkikos]
      #5566660 - 12/11/12 10:14 PM

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


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Re: Eypiece transmission new [Re: Starman1]
      #5567200 - 12/12/12 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?

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


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Re: Eypiece transmission new [Re: Sarkikos]
      #5567367 - 12/12/12 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


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Re: Eypiece transmission new [Re: Starman1]
      #5567442 - 12/12/12 12:07 PM

Quote:

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.

Edited by BillP (12/12/12 12:08 PM)


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Re: Eypiece transmission new [Re: BillP]
      #5567637 - 12/12/12 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.

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Re: Eypiece transmission new [Re: BillP]
      #5567708 - 12/12/12 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.


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Re: Eypiece transmission new [Re: Paul G]
      #5567717 - 12/12/12 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


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Re: Eypiece transmission new [Re: Sarkikos]
      #5567757 - 12/12/12 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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Re: Eypiece transmission new [Re: Starman1]
      #5567808 - 12/12/12 03:13 PM

Quote:

Sorry, no way. Human vision has a logarithmic response.




I agree that the likelyhood that even the very very best observer can reliably differentiate between much less than 10% brightness variation is unlikely.

On the other hand, I think that I have to interject this. I believe that some of the discrepency is they way we look at the numbers, and we tend to do this with an "Absolute" scale of "100%" so that any eyepeice that is between 90% and 100% would appear as bright.

Quote:

Since the highest transmission is 97.9%, you kind of want none of your eyepieces to fall below a loss of 0.1 magnitude, or 10%, which says it should be at least 87.9%




But that is not the way it works. You really have to start the differential from the lowest transmission eyepeices and add 10% from the bottom.

In other words, if you started with an eyepice with 88% transmission, you would have a "Baseline" brightness as compared to the 100% absolute.

But to see a difference, you would only have to be 10% brighter than this baseline.

So, if the eyepeice started with 88% transmission, and you added 10% to that, you would add 8.8% transmission.

Now my math may not be perfect so this is more about the idea. So, this means that if I can see a difference of 10%, if I use an eyepeice with 88% + 10% of that baseline brightness, I would come up with a relative transmission of the sum of the two. So, a 10% brightness increase from the baseline would be 88% plus 10% of that (8.8%) for a total of 96.8%. So, the step between an eyepeiece with 88% transmission and one with 96.8% transmission would perhaps be at the edge of the range of detection for some individuals, but perhaps not all.

Anyway, we can't look at it as a fraction of 100%, but as the amount of light increase from the baseline eyepeice and add 10% to that number.

And using this, I could indeed see people detecting a tiny brightness difference. But these two eyepieces would have to be seperated by between 8.8% or more in "absolute" transmission.

My own experience is that the difference in brightness is so tiny and difficult to see that it is basically meaningless and no one should worry about this with modern eyepcies.

But some older eyepecies did seem dim to me. Most notably, the Meade 8.8 UWA and a Meade 6.4mm Plossl (Contamination in the cementing between the lenes on the plossl. In other words, a defective unit. I think the Meade 8.8 just didn't have modern enough coatings).

Mostly, modern wide field eyepces though seem to be on par with simpler types to me in brightness. If there is a difference, it is very, very subtle.

Anyway, this explains has at the extremes of transmission, it could be possible to see without 10% seperation on an absolute scale, but I still believe that while there may indeed be individual cases where we see an eyepeice with below 90% transmission compared to some of the eyepieces with the highest possible transmission, most eyepecies today have better than this. Not all, but most.

But using the logic above, I can see how an 88% transmission eyepeice could be detected when compared to a 96.8% transmission, and clearly some of the better eyepcies have this level of transmission.

If somone measured a T6 Nagler and it had 88.7% transmission, then yes, an eyepeie with (88.7 + 8.7) 97.4% transmission should be able to be discerned by someone doing very careful comparisons.

Will it make a difference in viewing? Maybe. I an not inclined to worry about it though. Given that every eyepiece design in production today is diffraction limited at the center of the field, to me personally, all of the meaningful difference in eyepiece performance is to be found off axis. Here, differences are titanic and easy to see, and for me personally have a huge impact on how I perceive the field. But a barely detectable change in brightness (.1 magnitude) provokes a big yawn from me personally.

But someone saying that they can see the difference between a .92% and a .97% transmission? I for one don't believe it.

I do feel as if seeing the difference between an eyepiece with 88% transmission and 97% is indeed possible even thought they are not seperate by 10% of the total brightness because it is the relative brightness differece starting with the lower transmission unit.

Edited by Eddgie (12/12/12 03:17 PM)


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Re: Eypiece transmission new [Re: Eddgie]
      #5567860 - 12/12/12 03:47 PM

Here is an example from this thread that corresponds to the post I just made.

If the TV Nagler 13 mm II has 87.3% transmission, to be seen as 10% brighter, you would add 10% to that figure, or 8.73% in relative terms. So adding 10% of the 87.3% means that any eyepice with 96.03% transmission would be 10% brighter on a relative scale.

And I have no doubt that someone looking for it could see this difference.

But this is an old eyepeice, and modern eyepeies tend to be better than this.

I would put the cutoff at 89% though. If add 10% to this, you get 97.9%. Still possible that there are some eyepieces out there with this level of transmission difference, but for the most part, most modern eyepices will indeed have transmission that is within 10%, but you are looking for a 10% improvement in brightness over the one with the lowest transmission, and not as an absolute of the highst possible transmission.

In other words, If I started with 50% and added 20% transmission to this, I would still have only 60% of the total.

This is important for marketing because sometimes you rea that "Transmission has been improved by 8%!"

But suppose you have a Baader Mark V bino that already has 93% light transmission. If you improved it by 8%", then it would have 101% light transmission, and of course that can't happen.

But if it starts with 88% and baader improved it by 10%, then the unit passes 10% more light than it did in the past. But it is only working at 96.8% transmission.

It didn't go from 88% to 98%, but the transmission could very honestly be said to have improved by 10%.

And this was common in the great SCT coating wars. People thought that a 7% transmission inprovment meant on an absolute scale, but it was relative to the amount of light that was going through the system. From a marketing standpoint, it sounds better to say that "Transmission has improved by 10%" rather than say "we went from 70% transmission to 77% transmission. To someone not thinking about it, it would sound like 80% of the light is getting though, but that is not what a 10% increas means at all. It means 10% more from where you startetd.

Hope this example helps.

Edited by Eddgie (12/12/12 03:50 PM)


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Re: Eypiece transmission new [Re: Eddgie]
      #5567877 - 12/12/12 03:58 PM

I didn't see information about the current ES series in this thread, but regarding the Nagler T6 line (and 13mm in particular), info here may relate to my experience evaluating them against comparable focal lengths in the ES line. I have posted my observations before.

I could not claim that there were faint stars that I could not see in the T6 but did see in the ES. However, I could definitely discern faint stars more quickly in the ES than the T6.


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Re: Eypiece transmission new [Re: slack]
      #5568197 - 12/12/12 07:59 PM

I subscribe to the physiological, not psychological theory.

Talking about diffuse, threshold objects. When you observe the Flame Nebula do you look for detail and veining with Alnitak in the field? If you do you're missing a lot of detail. Move Alnitak out of the field to get rid of that "flashlight" shining in your eyes and it's a whole new object you're viewing. Perhaps an extreme example so let me continue.

Now for me a threshold subject would be Stephan's Quintet. Tackle that with a Nagler, Delos or any other wide field and there's not a prayer of detection. I know, I've tried. Drop in a 40-45 deg. ortho and they will shimmer into view. Why? Because many, many "flashlights" dispered across the wide field ep are shining in my eyes. The ortho cuts the view down to a couple dozen, maybe(I've never counted). When your eyes are fully dark adapted even a 9-10 mag star in the field will seem bright and make a difference between detection or not.

Jim


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Re: Eypiece transmission new [Re: Jim Curry]
      #5568223 - 12/12/12 08:18 PM

Jim,

Yes, exactly. The physical eye plays a larger role in visual astronomy than many observers seem to realize. Why wouldn't it? The telescope is important. The eyepiece is important. But what about the eye of the observer?

Just try to detect a faint fuzzy at the limiting magnitude of any telescope, even with an eyepiece which has the highest possible light transmission, when the eye is not optimally dark adapted. Good luck with that.

Mike


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Re: Eypiece transmission new [Re: Sarkikos]
      #5568259 - 12/12/12 08:52 PM

Since I have been getting out observing with others I have noticed a big difference among folks in what each can see (or say they can see) with their naked eye. It's interesting as there are quite a few reasons as to why that happens. One thing that bugs me is the folks that refuse to get glasses or corrective lenses.

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Re: Eypiece transmission new [Re: Jim Curry]
      #5568262 - 12/12/12 08:54 PM

Quote:

I subscribe to the physiological, not psychological theory.

Talking about diffuse, threshold objects. When you observe the Flame Nebula do you look for detail and veining with Alnitak in the field? If you do you're missing a lot of detail. Move Alnitak out of the field to get rid of that "flashlight" shining in your eyes and it's a whole new object you're viewing. Perhaps an extreme example so let me continue.

Now for me a threshold subject would be Stephan's Quintet. Tackle that with a Nagler, Delos or any other wide field and there's not a prayer of detection. I know, I've tried. Drop in a 40-45 deg. ortho and they will shimmer into view. Why? Because many, many "flashlights" dispersed across the wide field ep are shining in my eyes. The ortho cuts the view down to a couple dozen, maybe(I've never counted). When your eyes are fully dark adapted even a 9-10 mag star in the field will seem bright and make a difference between detection or not.

Jim



Well, I see the point and I agree. That's not the ONLY explanation, though it works in the case of NGC2024 or NGC404 or even the Horsehead. It also partially explains why raising power can make something more visible--it narrows the field of view.
But it doesn't explain why sometimes the reverse occurs (e.g I see fainter things with the 100 degree 13 Ethos than I did with the 82 degree 13 Nagler) or why some observers claim to see fainter in one 45 degree eyepiece than another.

But I'll grant there may be both physiological and psychological factors at work.


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Re: Eypiece transmission new [Re: Dave Ittner]
      #5568267 - 12/12/12 08:57 PM

Quote:

Since I have been getting out observing with others I have noticed a big difference among folks in what each can see (or say they can see) with their naked eye. It's interesting as there are quite a few reasons as to why that happens. One thing that bugs me is the folks that refuse to get glasses or corrective lenses.



In some cases, as my optometrist and I have discussed, it's simply impossible to correct the person's vision because there are multiple cylinders of astigmatism and variable correction needed across the retina.
But vanity, poverty, and convenience all play roles in human lives.


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Re: Eypiece transmission new [Re: Dave Ittner]
      #5568283 - 12/12/12 09:08 PM

Dave,

Quote:

Since I have been getting out observing with others I have noticed a big difference among folks in what each can see (or say they can see) with their naked eye. It's interesting as there are quite a few reasons as to why that happens. One thing that bugs me is the folks that refuse to get glasses or corrective lenses.




... or wear good sunglasses or clip-ons during the day to protect their eyes. Can folks really expect to have their eyes scoured by full sunlight over a lifetime and not have it affect their ability to see the faint stuff at night?

Mike


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Dave Ittner
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Re: Eypiece transmission new [Re: Sarkikos]
      #5568304 - 12/12/12 09:19 PM

yup, something I now try to bring to everyone's attention more often.

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Re: Eypiece transmission new [Re: Eddgie]
      #5568758 - 12/13/12 07:23 AM

Quote:

Here is an example from this thread that corresponds to the post I just made.

If the TV Nagler 13 mm II has 87.3% transmission, to be seen as 10% brighter, you would add 10% to that figure, or 8.73% in relative terms. So adding 10% of the 87.3% means that any eyepice with 96.03% transmission would be 10% brighter on a relative scale.




That's not how our visual system works. If you increase transmission 10% the difference would be barely detectable, some would see a slight difference, others wouldn't see a change. It's a physiological phenomenon called response compression. For example, for a point light source or an extended object to be seen as 100% brighter its intensity would have to be increased about 900%.


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Re: Eypiece transmission new [Re: Paul G]
      #5568791 - 12/13/12 08:12 AM

I think you guys are just looking at your eyepieces and not looking thru them. The 6mm Delos shows so much more on Jupiter than the latest ortho, the Kasai, that it is no contest. When you put the Delos in, it's like you just put your glasses on. Jupiter is sharper-clearer-more contrasty, put in any positive adjective you can think of, it is so much better, plus you have 70 degrees to play with. Ever since I bought my first Pentax XW, and now the Delos, they both are superior visually, just like the Zeiss, over anything else out there.

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Re: Eypiece transmission new [Re: tomharri]
      #5568823 - 12/13/12 08:41 AM

I don't think Jupiter - or any other bright planet - is a good test of transmission. For that you need to look at deep sky objects. IMO, the best light-transmission field test would involve detecting objects near the limiting magnitude of the telescope.

Even detecting faint moons of a bright planet is not the best test of transmission. In that case, it's too easy to confuse the effects of light scatter with light transmission. Best to keep it simple.

Mike


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Re: Eypiece transmission new [Re: ThomasM]
      #5781768 - 04/06/13 12:32 PM

A short update, here are transmissions for 532 nm:

Kasai HC Ortho 12 mm, 97.8%
Baader Classic Ortho 10 mm, 97 %
Paradigem 8 mm, 90,5 %

in addition I measured the transmission at 405 nm

Kasai HC Ortho 12 mm, 89%
Baader Classic Ortho 10 mm, 95 %
TMB ED 1.8x barlow, 94,5%

regards

Thomas


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Re: Eypiece transmission new [Re: ThomasM]
      #5781904 - 04/06/13 01:49 PM

Quote:

A short update, here are transmissions for 532 nm:

Kasai HC Ortho 12 mm, 97.8%
Baader Classic Ortho 10 mm, 97 %
Paradigm 8 mm, 90,5 %

in addition I measured the transmission at 405 nm

Kasai HC Ortho 12 mm, 89%
Baader Classic Ortho 10 mm, 95 %
TMB ED 1.8x barlow, 94,5%

regards

Thomas



What this points out is that if the eyepiece is inexpensive, the absolute state-of-the-art coatings are unlikely to be applied.
If they were, the transmissions at 532nm would have read 98%, 98%, and 96% respectively.
The very high-end brands also multi-coat the lens surfaces that are cemented to increase transmission and reduce internal scatter.

This also shows that transmission spectra differ from eyepiece to eyepiece.

One of the things I found remarkable about TeleVue's newer Ethos and Delos eyepiece types was the improved red transmission. Whether this was simply due to improved transmission over the Nagler series, or actually represented a different curve of transmission (my suspicion), I don't know, but it points out how somewhat different transmission levels at the extremes may influence one's perception of "tint" in the eyepiece.


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Re: Eypiece transmission new [Re: denis0007dl]
      #5782141 - 04/06/13 04:25 PM

Quote:

It would be interesting to test Explore Scientific 68" and 82" eyepieces



Not to mention the ES100° and 120° eyepieces...

Clears,


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Re: Eypiece transmission new [Re: Starman1]
      #5782233 - 04/06/13 05:21 PM

Quote:

Quote:

A short update, here are transmissions for 532 nm:

Kasai HC Ortho 12 mm, 97.8%
Baader Classic Ortho 10 mm, 97 %
Paradigm 8 mm, 90,5 %


Thomas



What this points out is that if the eyepiece is inexpensive, the absolute state-of-the-art coatings are unlikely to be applied.
If they were, the transmissions at 532nm would have read 98%, 98%, and 96% respectively.
The very high-end brands also multi-coat the lens surfaces that are cemented to increase transmission and reduce internal scatter.

This also shows that transmission spectra differ from eyepiece to eyepiece.

One of the things I found remarkable about TeleVue's newer Ethos and Delos eyepiece types was the improved red transmission. Whether this was simply due to improved transmission over the Nagler series, or actually represented a different curve of transmission (my suspicion), I don't know, but it points out how somewhat different transmission levels at the extremes may influence one's perception of "tint" in the eyepiece.




Actually, I think the simple rule of 1% loss per single element does not apply for short focal lenght Orthos, typially the transmission is less by 1-2%, I have no idea if it is an artefact of the measurement or if it is real, but this trend can also be seen here:

http://www.amateurastronomie.com/Astronomie/tips/tips3.htm

The transmission of a 12 mm Ortho with an excellent Barlow, such as the TMB ED is better than that of an 7 mm Orho, while at the same time it is much more comfortable to use.

Thomas

p.s. I was not aware of the high transmission of the Ethos eyepieces in the red, are there any results published?


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alancygnusx2
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Re: Eypiece transmission new [Re: ThomasM]
      #5782334 - 04/06/13 06:15 PM

Hi Thomas,

Thanks for posting your transmission measurements.

Regarding multicoatings there is a nice article by Rodger Gordon who was an optical engineer for unitron.

The article is here:

Multicoatings


Multicoatings can not only absorb some of the spectrum, but can also cause narrow angle scattering, which has already been mentioned above in this thread.

It would be interesting to shine lasers of different wavelenghts through each eyepiece and have the resulting spot projected onto a distant wall to see how much scattering there is, and to see if it varies between eyepieces.


Alan

Edited by alancygnusx2 (04/06/13 06:17 PM)


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Re: Eypiece transmission new [Re: alancygnusx2]
      #5782378 - 04/06/13 06:37 PM

Sigh.
This old canard again.
If you truly appreciate HOW a multicoating enhances transmission, then you would appreciate that IF the multicoating layers are chosen correctly (and they are in tandem with the refractive index of the glass they coat), then this so-called "narrow angle light scatter" cannot occur (or, if you will, what level of it occurs could not possibly be visible to the eye). It will be the axial ray that has the highest transmission, least reflection and scatter, and it is the more oblique rays that are more likely to scatter and/or be changed in spectrum.

Of course, it's certainly possible that inexpensive multi-coatings may not be the proper materials to produce the best transmission (leading to more reflection), and it may be that, applied to poorly-polished surfaces, they don't help enough to reduce what scatter would have been already there.

But note that all such "reports" are anecdotal, and they are usually suspect for the same reason global climate change reports from coal companies are suspect--the principals have a stake in the end result of such an "examination of evidence".

And it is interesting to note that many of the eyepieces that are the most highly-regarded eyepieces made are and were multi-coated throughout. In fact, several such eyepieces are known for having NO light scatter, either on or off axis.


As for the previous point that you can count on 1% light loss per element, this is no longer true. Some 8-element eyepieces with 10 air-to-glass surfaces transmit more than 96% and some 9-element eyepieces are in the same range. It does, however, depend on the coatings chosen, and those particular eyepieces would have lost prodigious amounts of light were it not for the use of expensive multicoatings on every glass surface. Nikon even has some professional 20-element photographic lenses that transmit somewhere in the 96-97% range. We could never afford those coatings in telescope eyepieces, but it goes to show that modern multi-coatings are a far cry from the multicoatings of yesteryear.


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Re: Eypiece transmission new [Re: Starman1]
      #5782686 - 04/06/13 09:46 PM

Quote:

As for the previous point that you can count on 1% light loss per element, this is no longer true. Some 8-element eyepieces with 10 air-to-glass surfaces transmit more than 96% and some 9-element eyepieces are in the same range. It does, however, depend on the coatings chosen, and those particular eyepieces would have lost prodigious amounts of light were it not for the use of expensive multicoatings on every glass surface. Nikon even has some professional 20-element photographic lenses that transmit somewhere in the 96-97% range. We could never afford those coatings in telescope eyepieces, but it goes to show that modern multi-coatings are a far cry from the multicoatings of yesteryear.






So true Don! In this day & age, we have a wealth of them to choose from as well.



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Re: Eypiece transmission new [Re: Starman1]
      #5782754 - 04/06/13 10:12 PM

I have no doubt that the ZAO IIs have multicoatings which cause close to zero scatter. I'd like to to see data on other eyepieces before I assumed their multicoatings were as good as the ones on the Zeiss. There's a big difference between knowing how to do it well and being able to do it well, and within price constraints that the amateur market will bear.

When I purchased a ball eyepiece from Harry Siebert, we were talking about coatings, he mentioned to me that there are eyepieces currently on the market that do not transmit evenly across the full visual spectrum due to their multicoatings. One would think that should be a thing of the past, but it isn't. Optics is a nuanced field, I wouldn't take anything for granted.

If you feel narrow angle scatter is a canard, I would appreciate a good link or a reference with data showing otherwise. My intention in making my previous post was to be helpful to Thomas. As far as I know Rodger Gordon was extremely well respected for his work.

Edited by alancygnusx2 (04/06/13 11:02 PM)


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Re: Eypiece transmission new [Re: alancygnusx2]
      #5782992 - 04/07/13 01:11 AM

very informative thread. thanks guys

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Re: Eypiece transmission new [Re: alancygnusx2]
      #5783057 - 04/07/13 02:45 AM

Quote:

I have no doubt that the ZAO IIs have multicoatings which cause close to zero scatter. I'd like to to see data on other eyepieces before I assumed their multicoatings were as good as the ones on the Zeiss. There's a big difference between knowing how to do it well and being able to do it well, and within price constraints that the amateur market will bear.

When I purchased a ball eyepiece from Harry Siebert, we were talking about coatings, he mentioned to me that there are eyepieces currently on the market that do not transmit evenly across the full visual spectrum due to their multicoatings. One would think that should be a thing of the past, but it isn't. Optics is a nuanced field, I wouldn't take anything for granted.

If you feel narrow angle scatter is a canard, I would appreciate a good link or a reference with data showing otherwise. My intention in making my previous post was to be helpful to Thomas. As far as I know Rodger Gordon was extremely well respected for his work.



Follow this thread:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3457819/Main...
and this one:
http://tech.groups.yahoo.com/group/tec-scopes/message/14857
There is no agreement among very respected sources.
I mentioned this once to a friend of mine who designs lenses for the military and he mentioned he'd heard of it but that the effect was "irrelevant" when "coating materials were properly chosen for the index of refraction".
And the conversation I had one afternoon with the Nikon engineers who design coatings on lenses to maximize transmission only mentioned the positive effects of superior coatings for transmission, reduction of scatter ,and improved contrast.

As for Siebert's comments, he's right. Also, uncoated eyepieces don't transmit flat across the visible band, either. And neither do simple MgFl2 coatings. or aluminum coatings on mirrors, etc. I have done literally thousands of hours of observing through hundreds of scopes and hundreds of different eyepieces over 50 years. And the only "narrow angle light scatter" I've ever seen was color in refractors (aka chromatic aberration).
Oh, I've seen scatter all right--that caused by haze in the atmosphere, dew on the optics or lenses, rough optical surfaces, light reflection internal to the scope and eyepiece, uncoated lenses, dust on optical surfaces, spherical aberration, uncorrected fields, aberrations of multiple kinds, etc. etc.

I side with Roland Christen on this one. Superior multi-coatings make possible superior contrast, not poorer contrast.


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Re: Eypiece transmission new [Re: Starman1]
      #5783082 - 04/07/13 04:22 AM

Quote:

Quote:

I have no doubt that the ZAO IIs have multicoatings which cause close to zero scatter. I'd like to to see data on other eyepieces before I assumed their multicoatings were as good as the ones on the Zeiss. There's a big difference between knowing how to do it well and being able to do it well, and within price constraints that the amateur market will bear.

When I purchased a ball eyepiece from Harry Siebert, we were talking about coatings, he mentioned to me that there are eyepieces currently on the market that do not transmit evenly across the full visual spectrum due to their multicoatings. One would think that should be a thing of the past, but it isn't. Optics is a nuanced field, I wouldn't take anything for granted.

If you feel narrow angle scatter is a canard, I would appreciate a good link or a reference with data showing otherwise. My intention in making my previous post was to be helpful to Thomas. As far as I know Rodger Gordon was extremely well respected for his work.



Follow this thread:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3457819/Main...
and this one:
http://tech.groups.yahoo.com/group/tec-scopes/message/14857
There is no agreement among very respected sources.
I mentioned this once to a friend of mine who designs lenses for the military and he mentioned he'd heard of it but that the effect was "irrelevant" when "coating materials were properly chosen for the index of refraction".
And the conversation I had one afternoon with the Nikon engineers who design coatings on lenses to maximize transmission only mentioned the positive effects of superior coatings for transmission, reduction of scatter ,and improved contrast.

As for Siebert's comments, he's right. Also, uncoated eyepieces don't transmit flat across the visible band, either. And neither do simple MgFl2 coatings. or aluminum coatings on mirrors, etc. I have done literally thousands of hours of observing through hundreds of scopes and hundreds of different eyepieces over 50 years. And the only "narrow angle light scatter" I've ever seen was color in refractors (aka chromatic aberration).
Oh, I've seen scatter all right--that caused by haze in the atmosphere, dew on the optics or lenses, rough optical surfaces, light reflection internal to the scope and eyepiece, uncoated lenses, dust on optical surfaces, spherical aberration, uncorrected fields, aberrations of multiple kinds, etc. etc.

I side with Roland Christen on this one. Superior multi-coatings make possible superior contrast, not poorer contrast.





As BillP lists in the thread, there are many scientific papers explaining the phenomenon of low angle scatter. A canard is a false and baseless story, it doesn't seem like that word should be used to describe a phenomenon that has backing from scientific publications as well as some serious experts in optics.

Thomas Back specifically mentioned he measured low angle scatter on his coatings for his monocentrics and thought they were the lowest scatter he had seen on multicoated eyepieces.

You mention you haven't seen any scatter, but Chris Lord reports that the effect would be a reduction in contrast between contrast boundaries.

How is it that a simple uncoated bk7 ball lens performs as well on the planets on axis as the best planetary eyepieces available?

At the very highest levels of performance, I will guess that unless significant expense in getting multicoatings applied using the best technology, there is the potential for degradation of the image.

Our problem as amateurs is that we don't have the equipment to objectively measure things like narrow angle scatter for ourselves.

Edited by alancygnusx2 (04/07/13 04:24 AM)


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Re: Eypiece transmission new [Re: Starman1]
      #5783639 - 04/07/13 11:52 AM

Quote:

I side with Roland Christen on this one. Superior multi-coatings make possible superior contrast, not poorer contrast.




Indeed, doing a search on the Yahoo AP turns up many postings by Roland Christen on eyepiece coatings, contrast, and performance from the point of a optician and purist. Coatings of course being only one element of eyepiece performance. Extrapolating from "superior coating" to "superior eyepiece" would be a logical error. But it's certainly a good place to start.

It would appear that RC was of the opinion that while a few commercial eyepieces might do it well, only Zeiss was doing it correctly.


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Re: Eypiece transmission new [Re: alancygnusx2]
      #5783673 - 04/07/13 12:12 PM

Quote:

Our problem as amateurs is that we don't have the equipment to objectively measure things like narrow angle scatter for ourselves.




Indeed, that is the crux of the problem.

I have seen first-hand how the 13 Ethos had better transmission than my T4 Naglers. And I am definitely a Delos enthusiast with three of them in my eyepiece case. But on the planets and double stars, I love the performance of my MgFL coated Brandons. With my only test equipment being the Mk-I eyeball there is no way of telling if it is because of the coatings, or in spite of the coatings. The only clue is that Don Yier did trial multi-coatings and elected not to do them on a performance basis.

I do know the end result, which keeps repeating itself across nights and telescopes. If it weren't the case I would be Astromarting those Brandons in a heartbeat for other eyepieces.


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alancygnusx2
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Re: Eypiece transmission new [Re: Jeff Morgan]
      #5783928 - 04/07/13 02:29 PM

Hi Jeff,

Thank you for your comments, and also including a link to Roland's post,

I see he indicates quite clearly that eyepiece multicoatings do not automatically mean high contrast and high transmission, and suboptimal adjustment of the coatings to each glass type in the elements is the cause.


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Re: Eypiece transmission new [Re: alancygnusx2]
      #5784208 - 04/07/13 04:16 PM

Quote:

Hi Jeff,

Thank you for your comments, and also including a link to Roland's post,

I see he indicates quite clearly that eyepiece multicoatings do not automatically mean high contrast and high transmission, and suboptimal adjustment of the coatings to each glass type in the elements is the cause.




Yes, reading Roland's posts are like a graduate-level course. The more of his posts you read the more you realize that all this focus on coatings is barking up the wrong tree.

The big issues are the glass count (since glass scatters light by it's very nature), dirt between the elements, pits (polish), and dirt on the eye and field lens.

Of these, it appears he views contaminants between the lenses as the worst offender. The best contrast comes from the cleanest internals, which means lenses individually hand-assembled by a very picky craftsman. Three manufacturers come to mind in this regard: Zeiss, Astro-Physics (the short lived SPL line), and Brandon.


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Re: Eypiece transmission new [Re: Jeff Morgan]
      #5784319 - 04/07/13 05:07 PM

Quote:

Quote:

Hi Jeff,

Thank you for your comments, and also including a link to Roland's post,

I see he indicates quite clearly that eyepiece multicoatings do not automatically mean high contrast and high transmission, and suboptimal adjustment of the coatings to each glass type in the elements is the cause.




Yes, reading Roland's posts are like a graduate-level course. The more of his posts you read the more you realize that all this focus on coatings is barking up the wrong tree.

The big issues are the glass count (since glass scatters light by it's very nature), dirt between the elements, pits (polish), and dirt on the eye and field lens.

Of these, it appears he views contaminants between the lenses as the worst offender. The best contrast comes from the cleanest internals, which means lenses individually hand-assembled by a very picky craftsman. Three manufacturers come to mind in this regard: Zeiss, Astro-Physics (the short lived SPL line), and Brandon.



And TeleVue, for both cleanliness and coatings. Lens count can't explain everything or the 9 element Ethos wouldn't beat the 7 element Naglers, but they do.
Dirt on or near the focal plane of the eyepiece is the worst place to see it. External dirt can be cleaned off (I recommend ROR).


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Re: Eypiece transmission new [Re: Starman1]
      #5785175 - 04/08/13 01:25 AM

Quote:


And TeleVue, for both cleanliness and coatings. Lens count can't explain everything or the 9 element Ethos wouldn't beat the 7 element Naglers, but they do.
Dirt on or near the focal plane of the eyepiece is the worst place to see it. External dirt can be cleaned off (I recommend ROR).




And so they do, I've seen it myself. Extra effort (money) can largely overcome inherent handicaps. In the end it's results with the Mk-I eyeball that pays the bills. (Or more accurately, creates new credit card bills.) I'm quite happy with my Delos and Brandons. Different approaches, excellent results in both cases. There certainly is more than one way to skin the cat.

With any luck Tele Vue is leveraging the Delos experience and diligently working on focal lengths above 22 mm, perhaps a Panoptic Type 2 or Nagler Type 7.

Thanks for bringing RC up, I enjoyed re-reading his views on eyepieces. One tends to forget fundamentals over time. Perhaps the best quote was (to paraphrase): you can buy $9 worth of eyepieces from the Far East, but that does not mean you get $9 worth of glass.


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Re: Eypiece transmission new [Re: Starman1]
      #5785855 - 04/08/13 12:24 PM

Actually I own three type 6s - a 3.5mm, 7mm, and a 13mm - all of which came new with dirt and dust internally. Sent them back to TV, payed to have them cleaned, and they only cleaned the exterior surfaces of the eye and field lenses. Even though I told them that the dirt was internal.

When it comes to light throughput, they also suck. When comparing them to similar BGOs, I can easily see Rhea (Saturn's moon) with my EON 80 and the BGOs. With the Nagler type 6s, Rhea is not visible, even with averted vision.


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Re: Eypiece transmission new [Re: Shneor]
      #5788773 - 04/09/13 05:34 PM

Quote:

Quote:

It would be interesting to test Explore Scientific 68" and 82" eyepieces



Not to mention the ES100° and 120° eyepieces...

Clears,




I am aware of only one report on the ES 9 mm 100 degree eyepiece at a German website giving a transmission of 91 %
http://www.blackskynet.de/okulartransmission.html, the error bar is around 5%. The same website gives transmission of Ethos eyepieces of almost 100 % at 532nm, so the measured transmission seems to me a little bit too high.


Thomas


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Re: Eypiece transmission new [Re: RodgerHouTex]
      #5788780 - 04/09/13 05:38 PM

Quote:



When it comes to light throughput, they also suck. When comparing them to similar BGOs, I can easily see Rhea (Saturn's moon) with my EON 80 and the BGOs. With the Nagler type 6s, Rhea is not visible, even with averted vision.




The transmission ot the nagler 7 and 13 mm T6 eyepieces is not top notch, I got values of 87%, almost 10% less transmission than that of Baader orthos in line with your findings.

Thomas


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Re: Eypiece transmission new [Re: Starman1]
      #5802214 - 04/16/13 09:47 AM

Quote:

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




Don, I read this again (and again and ) and this is the best rationale for the tiny glass eyepiece/less glass debate I've read. You suggest several times that it is only psychological while at the same time acknowledging that it is really seen. However, could it not end up being a REAL physiological effect, caused by decreasing the fov upon the eye itself, darkening the sky background and creating a real benefit? How are we so sure, that it is only psychological in nature?


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Re: Eypiece transmission new [Re: t.r.]
      #5802371 - 04/16/13 11:24 AM

The idea I got from Don's post is that this is a physiological effect, not a psychological one. At one point Don calls it "psycho-physiological." Maybe he just mispoke when he says it is "psychologicial"?

If the eye is able to become more deeply dark adapted due to a smaller AFOV, this could be explained by the fact that there is less light coming into the eye, similar to how an iris can let less light into a camera. Pretty straight-forward to my way of thinking.

After all, don't we see grosser examples of the same idea when observers suggest that we use a narrower AFOV eyepiece to see the Horsehead Nebula so we can keep Alnitak (Zeta Orionis) out of the field of view?

In that case, though, I noticed that eyepieces with similar AFOV's did not show me the Horsehead equally well. IME, the coatings were one of the best determinants of which eyepiece showed B33 with the most contrast and structure. Sterling Plossl 25mm with FMC was better than UO VT 25 with MC or Brandon 24 with FC.

But of course there are bound to be other determinants of overall light transmission. These can include degree of scatter, polish, cleanliness of the lenses, baffling, as well as quality and appropriateness of the coatings (besides just FMC, FC, MC or C) and AFOV.

Mike


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Re: Eypiece transmission new [Re: t.r.]
      #5802386 - 04/16/13 11:35 AM

Well, we don't. It could be physiological, and unrelated to what everyone thinks it must be caused by.
In which case, it isn't less glass, or transmission, or even wavefront accuracy, but a matter of field size.

There might be multiple factors at work. Because it's also possible that reducing lens count does impact the visibility of low-contrast features on planets (and there might be more than one reason for that), while having little relevance for the appearance of a faint nebula at the very limit of vision.

Since experienced observers know the visible/invisible dichotomy is really more of a slope than a cliff (objects at the limit become visible a slightly lower % of the time with decreasing brightness--it is easy to say something isn't visible at all, but it's hard to say something is visible only 10% or 20% of the time). And something may not be seen at first, yet seen later. Example: many times I've looked at an object in my 12.5" and barely seen it at all, then walked over to look at the object through a 28", and seen details, then walked back to my 12.5" to see those same details, only a lot fainter. Why didn't I see them the first time? If I'd said they were invisible, I'd have been wrong. And just exactly where IS the transition between seen 5% of the time and not seen at all?

Old time observers always said it took a bigger scope to discover something than it took to see it afterwards. That wasn't physiological, it was psychological.

So it is with eyepieces. If I don't see something in one eyepiece, but do in a second eyepiece, then go back to the first eyepiece, I can now see it in the first eyepiece. What does that mean? Is it merely transmission? Or the spectrum of the transmission? Or is there some other phenomenon at work?
Because if there is a field size difference, there might be other factors at work--'psycho-physiological', if you will.

It certainly is worthy of exploring, experimentally.


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Re: Eypiece transmission new [Re: Sarkikos]
      #5802402 - 04/16/13 11:48 AM

Quote:

The idea I got from Don's post is that this is a physiological effect, not a psychological one. At one point Don calls it "psycho-physiological." Maybe he just mispoke when he says it is "psychologicial"?

If the eye is able to become more deeply dark adapted due to a smaller AFOV, this could be explained by the fact that there is less light coming into the eye, similar to how an iris can let less light into a camera. Pretty straight-forward to my way of thinking.

After all, don't we see grosser examples of the same idea when observers suggest that we use a narrower AFOV eyepiece to see the Horsehead Nebula so we can keep Alnitak (Zeta Orionis) out of the field of view?

In that case, though, I noticed that eyepieces with similar AFOV's did not show me the Horsehead equally well. IME, the coatings were one of the best determinants of which eyepiece showed B33 with the most contrast and structure. Sterling Plossl 25mm with FMC was better than UO VT 25 with MC or Brandon 24 with FC.

But of course there are bound to be other determinants of overall light transmission. These can include degree of scatter, polish, cleanliness of the lenses, baffling, as well as quality and appropriateness of the coatings (besides just FMC, FC, MC or C) and AFOV.

Mike




When I was in school, psychology studies in labs investigated not only our reactions but how our responses were tempered by factors other than pure physiology. A study of, for instance, how our mind adds color to faint grays at the very limits of our vision would have been a psychology experiment. If the brain incorrectly interprets stimuli from outside, it is a psychological phenomenon. For clarity, I called it 'psycho-physiological'. Trompe-l'oeil phenomena are a good example of psychological phenomena.
It is in that sense I used the word psychological.

Our physiology sees it, but HOW we see it, or interpret what we see, is psychological.

If we start getting into the source of contrast in eyepieces, we have to explore both psychological as well as physical and physiological aspects. Contrast is a synergistic interaction of a whole laundry list of factors, not just one thing, and it is just possible that field size may be one of them.
And our response wouldn't be a physical, measurable, aspect of eyepieces, either, however real.

Edited by Starman1 (04/16/13 11:52 AM)


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Re: Eypiece transmission new [Re: Starman1]
      #5802443 - 04/16/13 12:08 PM

Don,

Quote:

Old time observers always said it took a bigger scope to discover something than it took to see it afterwards. That wasn't physiological, it was psychological.

So it is with eyepieces. If I don't see something in one eyepiece, but do in a second eyepiece, then go back to the first eyepiece, I can now see it in the first eyepiece. What does that mean? Is it merely transmission? Or the spectrum of the transmission? Or is there some other phenomenon at work?
Because if there is a field size difference, there might be other factors at work--'psycho-physiological', if you will.




IMO, it's best to call these phenomena psycho-physiological rather than psychological. Whether warranted or not, psychological can have the connotations "imaginary," "not real," "a result of suggestion." If the observer did not "see" something in one eyepiece or telescope but saw it later the same night in another, it may have been very near the threshold of seeing in the first eyepiece/telescope.

So now the observer knows the location, general shape and other attributes of the object. When he goes back to the first eyepiece/telescope, he suddenly sees the object. This is not psychological, in the sense of "imaginary" or "suggested." The observer is actually seeing the object now. He knew what to look for and where to look for it.

Even so, obviously the object was more easily seen in the eyepiece/telescope in which the observer saw it first. This would still be the case if he now switched back and forth between the eyepieces/telescopes.

Mike


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Re: Eypiece transmission new [Re: Starman1]
      #5802464 - 04/16/13 12:20 PM

Don,

Quote:

When I was in school, psychology studies in labs investigated not only our reactions but how our responses were tempered by factors other than pure physiology. A study of, for instance, how our mind adds color to faint grays at the very limits of our vision would have been a psychology experiment. If the brain incorrectly interprets stimuli from outside, it is a psychological phenomenon. For clarity, I called it 'psycho-physiological'. Trompe-l'oeil phenomena are a good example of psychological phenomena.
It is in that sense I used the word psychological.

Our physiology sees it, but HOW we see it, or interpret what we see, is psychological.

If we start getting into the source of contrast in eyepieces, we have to explore both psychological as well as physical and physiological aspects. Contrast is a synergistic interaction of a whole laundry list of factors, not just one thing, and it is just possible that field size may be one of them.
And our response wouldn't be a physical, measurable, aspect of eyepieces, either, however real.




Yes, I know these concepts and addressed them in my last post. I just don't want to confuse the more scientific meaning of "psychological" with the everyday connotations of "imaginary," "not real," "suggested," etc. Even in scientific terms, psychophysics is a subset of psychology.

Mike


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t.r.
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Re: Eypiece transmission new [Re: Sarkikos]
      #5802517 - 04/16/13 12:37 PM

I still say that potentially there is more at work here. Pilots become very familiar with illusions and perception problems. Once the academic knowledge is understood and they have learning through experience...illusions can be realized and ignored or perceived in their true context. I do see real differences at the eyepiece knowing full well these illusions and matters of perception exist. This particular issue doesn't go away with knowledge and experience leading me to believe it is not simply psychological.

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Re: Eypiece transmission new [Re: t.r.]
      #5803515 - 04/16/13 08:50 PM

Quote:

I still say that potentially there is more at work here. Pilots become very familiar with illusions and perception problems. Once the academic knowledge is understood and they have learning through experience...illusions can be realized and ignored or perceived in their true context. I do see real differences at the eyepiece knowing full well these illusions and matters of perception exist. This particular issue doesn't go away with knowledge and experience leading me to believe it is not simply psychological.



I am using the term 'psychological' in its scientific context to mean "how the brain interprets the physiological sensation of seeing", not to mean something that doesn't exist. If we all see it, it is real to humans, regardless of whether it is an illusion or not.

The trick is to figure out WHY we see what we do when physiological analysis says we shouldn't see it. I gave the example of not seeing something in a smaller scope, then seeing it in a larger scope, then going back to the smaller scope and seeing it. Nothing changed physiologically, but something obviously changed psychologically.

THAT we see something different in eyepiece A than in eyepiece B is not the issue. It's WHY we see something different. Especially if light transmission differences are too small to account for the differences seen. The example of seeing something in one eyepiece and then discovering you could see it in the other after all is similar to my scope analogy. WHY didn't you see it in the first eyepiece initially? WHY did it show up in the second eyepiece? And WHY could you now see it in the first when it was overlooked the first time?
These would seem to be psychological interactions between the eyepieces and the brain interpreting the images as opposed to physical differences in the eyepieces or perhaps the interaction of a particular characteristic of the physical eyepiece and the brain of the observer.

Real, nonetheless. So is it the elusive term we call contrast? If so, we only have to look at 20 parameters of the eyepiece and how the eyepiece interacts with the scope to pin down the actual reason why something might be more visible in one eyepiece than in another.

One thing I can assert with confidence, though: it doesn't depend on the number of elements of glass between your eye and the scope. I have too many personal examples of seeing things in a 9 element eyepiece that I could not in a 6 element eyepiece to think that it has anything to do with element count.

But if not, on what does it depend? The spectrum of transmission? The sensitivity of the viewer's eye and how that corresponds to the maximum transmission point of the eyepiece? Anecdotal evidence, however, seems to be weighted in favor of chaos, with some individuals NOT seeing what other observers see as obvious.

If there is a uniformity to opinion, it seems to be that narrower field (mostly with fewer elements, but not all) eyepieces seem to produce better contrast than wider field eyepieces. It was addressing why that may be that I posted what I posted. It could be a host of other factors at work, but I suspect the psychological factor, although because there is confusion about the meaning of that term, I used "psycho-physiological".


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Re: Eypiece transmission new [Re: Starman1]
      #5803605 - 04/16/13 10:04 PM

Psychological, psycho-physiological, physical ... as long as we define what we mean in context, and what we mean is conveyed to the reader, it's best to avoid potentially-confusing labels. We really shouldn't assume that every reader of this blog took that course in psychophysiology/psychophysics or has even read anything about the subject. For better or worse, most people understand words by their most common meanings, not necessarily the ones taught in university courses.

But I could say the same thing about many posts that get into the weeds about mathematics, optical theory, etc., etc. Nothing new, no big deal.

So I guess we should add "psychological" to the growing list of other terms that cause confusion because their common meanings are not the same as their more technical ones. Psychological, contrast, distortion, glare ... I'm sure there are others by now.

Mike


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Re: Eypiece transmission new [Re: Starman1]
      #5803655 - 04/16/13 10:33 PM

Don,

Quote:

The trick is to figure out WHY we see what we do when physiological analysis says we shouldn't see it. I gave the example of not seeing something in a smaller scope, then seeing it in a larger scope, then going back to the smaller scope and seeing it. Nothing changed physiologically, but something obviously changed psychologically.




Can we be so sure that physiological analysis says we can't see it? What does this "physiological analysis" entail? Merely looking in a small scope, then a big scope, then the small scope again? I don't see any physiological analysis here, only raw experiential phenomena which we need to try to understand.

Quote:

THAT we see something different in eyepiece A than in eyepiece B is not the issue. It's WHY we see something different. Especially if light transmission differences are too small to account for the differences seen.




I don't think that a difference in light transmission is telling the whole story. If this is the sole "physiological analysis" in this case, I think it disregards other factors.

Let's look at your example of eyepieces with narrow AFOVs versus those with wider AFOVs. If an eyepiece with a narrower AFOV allows an observer to perceive dimmer objects than an eyepiece with a wider AFOV, even though the difference in light transmission between the two eyepieces is too small to account for the differences seen in the eyepieces, something else must be at work than merely a difference in light transmission. I think that the eyepiece with a narrow AFOV is allowing less light to enter the eye, which allows the eye to attain a deeper level of dark adaptation. Other things being equal - including light transmission - an eye that is more deeply dark adapted will see dimmer objects. And one factor that might allow that eye to go deeper is a narrower AFOV.

Should we really call the eye going through dark adaptation a psychological process? I suppose technically we could, but I think that for the vast majority of people this would be a misleading and confusing use of the term "psychological." Better to avoid it.

Mike


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Re: Eypiece transmission new [Re: Starman1]
      #5803661 - 04/16/13 10:38 PM

Quote:


If there is a uniformity to opinion, it seems to be that narrower field (mostly with fewer elements, but not all) eyepieces seem to produce better contrast than wider field eyepieces. It was addressing why that may be that I posted what I posted. It could be a host of other factors at work, but I suspect the psychological factor, although because there is confusion about the meaning of that term, I used "psycho-physiological".




I used to wonder if that was the reason myself. Then I decided to stop wondering and do an experiment to determine if it was a driver myself. So I took a wide field, which I judged to have less transmission and less contrast than a min glass eyepiece, and put in a new field stop so it had the same afov as the min glass unit. I did observation tests both indoors and outdoors before and after the new field stop that leveled the afovs.

Results? Min glass unit had more contrast and more transmission than the wide field regardless of the wide fields afov. Both eyepieces were from the same manufacturer as well. So my experiment went counter to my expectations, and it was NOT a perception issue at work with afov size.


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Re: Eypiece transmission new [Re: BillP]
      #5803701 - 04/16/13 11:07 PM

Bill,

Very good experiment and interesting results.

FWIW, I've never thought that AFOV per se had any effect on my perception of objects, in terms of better or worse contrast or otherwise. I've always thought that any effect was due to better light transmission of the glass, better (or different) coatings, better polishing, better baffling.

However, I do think it is possible that a narrower AFOV might cause the eye to better dark adapt than a larger AFOV. But beyond that possibility, I really don't think AFOV has any effect on perception, at least not mine.

Mike


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Re: Eypiece transmission new [Re: Starman1]
      #5803793 - 04/17/13 12:39 AM

Quote:


One thing I can assert with confidence, though: it doesn't depend on the number of elements of glass between your eye and the scope. I have too many personal examples of seeing things in a 9 element eyepiece that I could not in a 6 element eyepiece to think that it has anything to do with element count.




As a blanket statement that would be questionable.

Quality of manufacture and assembly is a big factor and can account for your 9 element eyepieces superior to various 6 element eyepieces. I have seen this myself with Ethos besting T4 Naglers in a small but quite noticeable fashion. I suspect that Ethos represents a superior effort and specification on the part of the manufacturer rather than a contravention of the laws of physics.

Certainly the latest Tele Vue offerings (Ethos and Delos) do have the high standard. Most observers seem to rate them above the cheaper clone brand with the same glass count (I do), and they would probably be better than a cheaply made six (or four) element bargain eyepiece.

Don't get me wrong on this - I am not downing 9 element eyepieces, my three Delos have a very secure place in the eyepiece case (I may even add a fourth). They offer things the simple glass does not such as eye relief, wider fields, and fast scope performance. But if you're limiting the playing field to transmission you unwittingly stacked the deck against the complex designs. Comparing premium 9 to premium 4 - I'll go with Roland Christen and Alvin Huey on this one.


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Re: Eypiece transmission new [Re: Jeff Morgan]
      #5803945 - 04/17/13 05:08 AM

I think both phenomenon are at work :
Physical : Premium 4 element ep give more data to our eyes than a 9 element ep,
Psychological : We see with the brain more than with the eye.

You certainly know this kind of illusion :


Which square is grayer ? A or B ?

Edited by Smithfr2000 (04/17/13 05:08 AM)


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Re: Eypiece transmission new [Re: BillP]
      #5804072 - 04/17/13 08:08 AM

Quote:

Quote:


If there is a uniformity to opinion, it seems to be that narrower field (mostly with fewer elements, but not all) eyepieces seem to produce better contrast than wider field eyepieces. It was addressing why that may be that I posted what I posted. It could be a host of other factors at work, but I suspect the psychological factor, although because there is confusion about the meaning of that term, I used "psycho-physiological".




I used to wonder if that was the reason myself. Then I decided to stop wondering and do an experiment to determine if it was a driver myself. So I took a wide field, which I judged to have less transmission and less contrast than a min glass eyepiece, and put in a new field stop so it had the same afov as the min glass unit. I did observation tests both indoors and outdoors before and after the new field stop that leveled the afovs.

Results? Min glass unit had more contrast and more transmission than the wide field regardless of the wide fields afov. Both eyepieces were from the same manufacturer as well. So my experiment went counter to my expectations, and it was NOT a perception issue at work with afov size.




Excellent experiment...and repeatable!!! Now, we should all have a dual set of these eyepieces and take them into the field at star parties and gather some data! Then, we could prove or disprove the hypothesis!


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Re: Eypiece transmission new [Re: t.r.]
      #5804084 - 04/17/13 08:15 AM

Some observers have said that a narrower AFOV can help concentrate the attention and thereby produce an enhanced perception of detail and contrast. Again, FWIW, I have never noticed that effect in my own perception. Never, no way, not at all.

For me, the most obvious effect from a narrower AFOV is that I need to nudge the Dob more often. The only other possible effect is perhaps a somewhat deeper dark adaptation, depending on what is in the field of view, and what is blocked by the field stop. Other than these effects ... nothing. Really, how could there be any other effect? Or maybe I just don't need any external artifice to focus my attention.

Mike


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Re: Eypiece transmission new [Re: Smithfr2000]
      #5804104 - 04/17/13 08:35 AM

Quote:

I think both phenomenon are at work :
Physical : Premium 4 element ep give more data to our eyes than a 9 element ep,
Psychological : We see with the brain more than with the eye.

You certainly know this kind of illusion :


Which square is grayer ? A or B ?




But would an illusion of this type matter when comparing two different eyepieces used to observe the same object? I don't think so.

Mike


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Re: Eypiece transmission new [Re: Sarkikos]
      #5804344 - 04/17/13 11:05 AM

This picture just shows that our brain renders what he receives from the eyes with background algorithm we do not control. And our brain analysis takes into account the target environment. In this picture, our perception of the square A and B's color is influenced by the green pipe's shadow.
I think the same phenomenon can be at work on the ep, and field of view is not a detail for our brain analysis (big gap between 30° or 100°).
Anyway, a rational analysis is required to confirm this thinking.

Edited by Smithfr2000 (04/17/13 11:07 AM)


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Re: Eypiece transmission new [Re: Smithfr2000]
      #5804357 - 04/17/13 11:14 AM

I agree that a lot of rational analysis is needed and also a lot of field experiments and a lot of bench testing! The more data - and the more analysis of the data - the better.

Mike


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Jeff Morgan
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Re: Eypiece transmission new [Re: BillP]
      #5804359 - 04/17/13 11:15 AM

I recall that Roland Christen mentioned another eyepiece test for scatter. I'll have to search for the details, but here is the general outline of the Blue Sky Test: Place two eyepieces side-by-side on the ground on a blue sky day with the eye lens facing the sky. Photograph the two. The more scatter an eyepiece has, the brighter the eye lens appears.

This method has the advantage of isolating the variable human factor (physiological/psychological) from the equation. All of the answer lies in the digital image. The only variables would be manufacturing variance (likely quite small, at least for premium makes) and cleanliness of the eyepieces (quite controllable by the experimenter).

I suppose one could even use Photoshop to sample the RGB values of the pixels that compose the eye lens and come up with a relative quantitative measure. It would probably not be valid from day to day due to sun and camera angles, but it would be valid between the two eyepieces in the single photo.


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Re: Eypiece transmission new [Re: Sarkikos]
      #5804368 - 04/17/13 11:21 AM

Here is the explanation for the Checkershadow illusion:

Why does the illusion work?

Mike


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Re: Eypiece transmission new [Re: Sarkikos]
      #5804386 - 04/17/13 11:34 AM

When would an instance similar in principal to the Checkershadow illusion ever occur in observational amateur astronomy? On Earth, under our atmosphere, light is diffused and there are no sharp deep black shadows as in space. Our eyes have evolved to deal with images common to our Earth environments, not those in space.

Certainly all shadows in lunar landscapes are sharp and black. AFAIK, shadows cast by the Galilean moons of Jupiter are jet black. Would there ever be any image similar to the Checkershadow illusion for amateur astronomers? I'm not sure if a comparison between a wide field and narrow field eyepiece looking at the same object could qualify.

Mike


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Re: Eypiece transmission new [Re: Sarkikos]
      #5804484 - 04/17/13 12:35 PM

Well, we are back to the factors that influence the visibility of objects in the field of one eyepiece that make details more visible in one than the other.
Since a 4-element 20mm eyepiece will have the same exit pupil as a 9-element 20mm eyepiece, and measurements show some multi-element eyepieces have higher light transmissions than some small-lens-count eyepieces, and since multiple sources show the inability to discriminate brightness levels below a difference of 8-10% (this has been hashed out before and the evidence shows this time after time), the differences between eyepieces do not seem to be related to lens count in specific examples (though they could be in other examples).

So we are left with contrast as a deciding factor. And contrast is improved by reducing scatter and concentrating the light in specific places.
Some factors influencing contrast and our ability to see small differences therein (and not all are often though of as "contrast" parameters):
--improved polish will reduce light scatter and increase light concentration in the correct places. This may be one of the most important factors of all.
--manufacturing tolerances. The eyepiece has to be as close as possible to the design or negative effects can occur, like SA or astigmatism. This factor rolls assembly quality and adherence to proper curves and coatings into one factor.
--choice of the correct coatings for the glass types used will improve transmission and reduce scatter.
--lack of internal reflections in the eyepiece from lens edges, spacers, filter threads, etc. The best eyepieces have NO visible reflections from any internals.
--wavefront accuracy AFTER passage through the lenses. Though some cancellation of errors can occur, it seems obvious that reducing surfaces, with all other factors equal, is more likely to result in less damage to the wavefront.
--the quality of the design. If the eyepiece has chromatic aberration or aberrations induced by the f/ratio of the scope, then the eyepiece will have reduced image quality.
--the shape of the observer's cornea. Bright images can bounce off the cornea and reflect from the lens below it. Certain shapes of eye lenses are more prone to this than others, as are some corneas. The interaction of these factors can deleteriously affect the image quality by increasing glow and ghosting and reducing contrast.
--obstruction in the telescope. Whether in the form of a secondary or spider vanes, light scatter and a loss of contrast accompany obstruction and this can have an effect on the evaluation of an eyepiece. Many times it's difficult to know exactly when to attribute a loss of contrast to the eyepiece and when to the scope.
--exit pupil and size of image. If the size of the object or detail desired to be seen happens to be large when the exit pupil is also large, you have the best of both worlds. But, most of the time, seeing details requires magnification, and that means smaller exit pupils. It's why the Contrast Threshold is better in larger scopes: higher magnifications at the same exit pupil. It's also the reason exit pupil has to be exactly the same size to compare two eyepieces in one scope.
Another way to say this is that larger aperture improves contrast.
--spectrum of transmission. If the eyepiece rolls off the blues and the eye is most sensitive to those wavelengths at night, bluish features may become harder to see. As we age, out eye's lens also yellows and we lose the blues. A younger viewer may see bluish details better than an older observer. If the spiral galaxy's arms are bluer than the core, it would seem that the spiral arms would be more visible to a younger viewer or an eyepiece that had a flatter spectrum of transmission in the blue. We don't know, and the manufacturers don't advertise, the spectrum of transmission in our eyepieces, but this could influence a comparison of "contrast" for certain features. One published example: the Pentax XW eyepieces reach a transmission level of 96% at 550nm, but are below 80% transmission at 400nm.
--match of spectrum with object. This is obvious. If you want to see something faint, the spectrum of transmission should be high at the appropriate wavelengths. This could influence the visibility of an object in one eyepiece and not another.
--the difference factor. If the scope is small, the resolution of the scope may not be sufficient to identify differences between two eyepieces, whereas if the scope is large the differences might become quite apparent.

I could go on, but I think it's obvious that evaluating eyepieces is a difficult thing when so many factors influence what we see. But I think the on-axis differences between two non-defective eyepieces are always going to be very hard to see. At best they are going to be subtle, and observing experience will trump what small differences may be there. That doesn't mean we shouldn't do what we can to maximize what gets through or to improve contrast as much as we can given the constraints of aperture.

But it does mean that we tend to debate these issues as if they were a matter of great importance. And they are not. Keep the object on axis, and pretty much one well-designed and well-made eyepiece equals another. The differences are all off-axis.

I've said before, and I will say again, if the eyepiece isn't defective, your ability or inability to see something isn't going to be related to the eyepiece. I have never, in 50 years, been held back by the axial image quality in my eyepieces, except for 3 defects. Variations in seeing, collimation, thermal issues, etc. are so large compared to the differences in eyepieces, that the eyepieces essentially don't matter. When we discuss these on-axis differences in eyepieces, we are arguing over the penny and ignoring the other 99 cents in the dollar.

I guess it's what we do when we're not observing.

Now, talk about off-axis images and the story changes radically. There, the differences equal the other factors and eyepieces are all different, often impressively so.


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Re: Eypiece transmission new [Re: Starman1]
      #5804524 - 04/17/13 01:01 PM

That Roland experiment seems flawed to me. Aren't you only getting the reflected sky light off the outer surface element? Simply, a reflection? If the light doesn't pass through all the elements in the eyepiece, how is this experiment showing scatter of each element(assuming not a cemented stack like a mono)? Or is the light being reflected off the white paper below and then coming back up through? Also, the coating type would play a role, no? It may be a good test of the outer surface scatter, but I'm not so sure it can be conclusive for the eyepiece as a whole.

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Re: Eypiece transmission new [Re: t.r.]
      #5804533 - 04/17/13 01:07 PM

I have heard of shining laser light through an eyepiece to test for scatter. That might be a better test than Roland's.

Mike


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Re: Eypiece transmission new [Re: t.r.]
      #5804543 - 04/17/13 01:19 PM

Quote:

That Roland experiment seems flawed to me.




I agree. Multicoatings vary greatly on their efficiency once you depart from 90 degrees on-axis. So if you have them lined up like he did you are actually viewing into each eye lens at a slightly different angle, and the multicoating efficiency will therefore vary with the different angles. Would be better to have the eye lens be at a fixed hight and offset from the camera, and the camera using a fixed focus, aperture, shutter, ISO. Then take individual pics of each eyepiece in the exact same orientation at the exact same exposure setting, stitch them all together into one photo and do the visual compare.


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Re: Eypiece transmission new [Re: Starman1]
      #5804548 - 04/17/13 01:23 PM

Quote:

...I could go on, but I think it's obvious that evaluating eyepieces is a difficult thing when so many factors influence what we see.




I agree that it is difficult, especially if the evaluation is trying to determine the root cause. Heck, probably impossible actually. However, comparing two eyepieces is an easy thing when the goal is to determine which is doing the best job in one's own gear, under one's own skies, with their own eyes. And this is, afterall, where the rubber hits the road and is all that truely matters


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Re: Eypiece transmission new [Re: BillP]
      #5804551 - 04/17/13 01:27 PM

THAT's the FACT, JACK!

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Re: Eypiece transmission new [Re: Sarkikos]
      #5804607 - 04/17/13 02:00 PM

Well, what the Checkershadow illusion shows is how strongly what our brain expects to see affects what we think we see. Even if you sample the two boxes in Photoshop to prove to yourself that they are exactly the same, your visual system still sees what it expects to see, not what is really there.

The smaller the real difference between eyepieces, the greater the effect of our biases and expectations. One needn't go far in astronomy to find famous experienced observers using state of the are equipment describe in exquisite detail features that don't exist.


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Re: Eypiece transmission new [Re: Paul G]
      #5804724 - 04/17/13 03:04 PM

Quote:

Well, what the Checkershadow illusion shows is how strongly what our brain expects to see affects what we think we see. Even if you sample the two boxes in Photoshop to prove to yourself that they are exactly the same, your visual system still sees what it expects to see, not what is really there.

The smaller the real difference between eyepieces, the greater the effect of our biases and expectations. One needn't go far in astronomy to find famous experienced observers using state of the are equipment describe in exquisite detail features that don't exist.



Well, that's one of the points, isn't it?

Even if we KNOW that seeing a faint red tint on such and such a nebula is impossible and likely the result of our visual system, we still see it.
We cannot interpret, in many cases, the things we see so that we can pin down the cause. In that sense, Bill is right.

A good example: the background in eyepiece A is darker than eyepiece B (they are both the same focal length). Does A have less scatter, or lower transmission? Could you tell on a planet? No, too bright and too much light to spare. Could you tell on a faint star? No, probably not unless you can tell the difference between being visible 10% of the time and 5% of the time.
Could you tell on a faint galaxy? Again, probably not because of transparency variations that occur on the time frame of moments.

It's probably going to boil down to which you prefer, whether or not that corresponds to the most accurate rendition of the image coming through the scope. What's the goal of a view through the scope? To please the observer? To most accurately represent reality? To show features and details not seen in another eyepiece?

If the first, then you have a good explanation for the popularity of those mult-element ultrawide field eyepieces, don't you? If it's the 2nd, then we want the best polish, flattest transmission, and least distorted eyepiece we can find. If it's the 3rd, then you just might prefer a tint to the image, or the highest transmission possible, or the best coatings possible.

And if you want all three? It may be possible, and those eyepieces may already be out there. There just is no consensus of opinion, though. Or maybe there is. I can't tell.


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Re: Eypiece transmission new [Re: t.r.]
      #5804860 - 04/17/13 04:35 PM

I don't think it was RC's test although he has posted photos of it. As you might have guessed, the Astro-Physics SPL eyepiece did exceptionally well.

I was trying to track down the origin and details on the test but ran out of time at lunch. If you're on the Yahoo Astro-Physics group do a search for "sidewalk test" or "whitewall test". A few people posted results, the planetary-oriented eps (Tak LE, Brandon, etc.) seem to have done pretty well.


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Re: Eypiece transmission new [Re: Jeff Morgan]
      #5804924 - 04/17/13 05:11 PM

Quote:

I don't think it was RC's test although he has posted photos of it. As you might have guessed, the Astro-Physics SPL eyepiece did exceptionally well.

I was trying to track down the origin and details on the test but ran out of time at lunch. If you're on the Yahoo Astro-Physics group do a search for "sidewalk test" or "whitewall test". A few people posted results, the planetary-oriented eps (Tak LE, Brandon, etc.) seem to have done pretty well.




Sidewalk test


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Re: Eypiece transmission new [Re: Starman1]
      #5805348 - 04/17/13 07:51 PM

Quote:

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.




Interesting hypothesis. I saw a crisp up on Jupiter and slightly better stellar points on the Trapezium when comparing a 5mm Pentax XW to a 5 XO. Smaller AFOV = better contrast? Very interesting!


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Re: Eypiece transmission new [Re: Sarkikos]
      #5805361 - 04/17/13 07:59 PM

Quote:

The telescope is important. The eyepiece is important. But what about the eye of the observer?




Amen!


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Re: Eypiece transmission new [Re: ThomasM]
      #5805383 - 04/17/13 08:15 PM

What about the University Optics HDs (or did you discuss them under a different name?)

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Re: Eypiece transmission new [Re: ThomasM]
      #5805386 - 04/17/13 08:16 PM

A most interesting discussion. However, my brain is now totally dead.

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Re: Eypiece transmission new [Re: Starman1]
      #5811375 - 04/20/13 04:54 PM

Quote:


A good example: the background in eyepiece A is darker than eyepiece B (they are both the same focal length). Does A have less scatter, or lower transmission? Could you tell on a planet? No, too bright and too much light to spare. Could you tell on a faint star? No, probably not unless you can tell the difference between being visible 10% of the time and 5% of the time.
Could you tell on a faint galaxy? Again, probably not because of transparency variations that occur on the time frame of moments.




Don. I have to diffe3r with you on this last point. If you are looking at an faint galaxy, contrast matters. Last autumn, I was looking for the 4 galaxies of the Burbridge Chain, the faintest one is mag 18.1. It did now show in my 6mm Ethos (and if I remember correctly, not even in Alvin Huey's 6mm Delos). but it did in Alvin's 6mm ZAOII. which does show more contrast (darker background). I can't give you a percentage difference. But for trying to observe the faintest fuzzy your telescope and the observing conditions allow, possible, even a small difference in contrast can be the difference in seeing it or not.
Clears,


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Re: Eypiece transmission new [Re: Shneor]
      #5811448 - 04/20/13 05:44 PM

Shneor,
Visible what % of the time? Winking in 5% of the time and invisible 95% of the time versus invisible 100% of the time?
Or visible 100% of the time versus 0% of the time?
If the former, it might be possible. If the latter, I'm sorry, I don't buy it. I've never seen this in any scope of any size all the way up to 32".
After spotting the galaxy in the 6mm ZAO did you go back to the 6mm Delos and try again?
I can't tell you how many times I've not seen some detail in the 12.5", walked over to a 28", seen the detail, then returned to the 12.5" to now be able to see the detail I couldn't before.
But I'll grant you that there are slight differences in contrast in eyepieces. How important that is is a matter for the observer to decide.


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Re: Eypiece transmission new [Re: Starman1]
      #5811462 - 04/20/13 05:53 PM

Burbidge's Chain:
http://www.astronomy-mall.com/Adventures.In.Deep.Space/burbidge.htm
2 are easy in the 12.5". The 3rd I picked up on a near perfect night. Nearby ESO 540-19 is brighter.

The 4th is invisible in the 12.5" but we picked it up in a nearby 22".
It's brighter than you mentioned, but still very very faint.


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Re: Eypiece transmission new [Re: Jeff Morgan]
      #5811509 - 04/20/13 06:31 PM

Quote:

I don't think it was RC's test although he has posted photos of it. As you might have guessed, the Astro-Physics SPL eyepiece did exceptionally well.

I was trying to track down the origin and details on the test but ran out of time at lunch. If you're on the Yahoo Astro-Physics group do a search for "sidewalk test" or "whitewall test". A few people posted results, the planetary-oriented eps (Tak LE, Brandon, etc.) seem to have done pretty well.




Here is a site with Roland's coating test.

http://geogdata.csun.edu/~voltaire/roland/coating.html

The eyepieces need to be in the shade to avoid direct reflections. Also a black cap on the bottom to avoid reflections internally off the sidewalk.

Mike


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Re: Eypiece transmission new [Re: MikeRatcliff]
      #5812097 - 04/20/13 11:52 PM

Thanks for the link with the correct procedure. This should be an easy and fun test. But hopefully not too illuminating, if you know what I mean.

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Re: Eypiece transmission new [Re: Sarkikos]
      #5814261 - 04/21/13 10:13 PM

Quote:

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




The problem is that objects at the limit of detection are not constantly at the limit of detection. When the seeing disperses the light a little bit they fall below the threshold detection level and when the seeing comes back they are there again.

So if you are comparing say a 90% transmission eyepiece and a 95% transmission eyepiece what you have is two overlapping gaussian distributions with slightly different means.

That said, I do think there was a very noticeable difference between the Meade 14 UWA "classic" that I had once upon a time and the 14XW which blew it away in every respect, IMO.

I do find it noteworthy that Pentax sees fit to post its technical specs: light transmission, astigmatism, field curvature, etc. I think you do that when you're not afraid of what anyone else is putting on the market.

I did finally purchase a Delos 17.3 on the 'mart to fill the XW gap between 14 and 20mm. Currently I have a Zeiss 16.8 and will be testing them against one another.

Greg N


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Re: Eypiece transmission new [Re: gnowellsct]
      #5814305 - 04/21/13 10:23 PM

I took apart one of those Series 4000 Meade 14mm UWA Japanese eyepieces. Several internal surfaces were uncoated (yes, not even MgFl2).
High transmission did not accompany the superior polish. Too bad, that.


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Re: Eypiece transmission new [Re: Sarkikos]
      #5814311 - 04/21/13 10:27 PM

Quote:

Don,

Quote:

The trick is to figure out WHY we see what we do when physiological analysis says we shouldn't see it. I gave the example of not seeing something in a smaller scope, then seeing it in a larger scope, then going back to the smaller scope and seeing it. Nothing changed physiologically, but something obviously changed psychologically.




Can we be so sure that physiological analysis says we can't see it? What does this "physiological analysis" entail? Merely looking in a small scope, then a big scope, then the small scope again? I don't see any physiological analysis here, only raw experiential phenomena which we need to try to understand.

Quote:

THAT we see something different in eyepiece A than in eyepiece B is not the issue. It's WHY we see something different. Especially if light transmission differences are too small to account for the differences seen.




I don't think that a difference in light transmission is telling the whole story. If this is the sole "physiological analysis" in this case, I think it disregards other factors.

Let's look at your example of eyepieces with narrow AFOVs versus those with wider AFOVs. If an eyepiece with a narrower AFOV allows an observer to perceive dimmer objects than an eyepiece with a wider AFOV, even though the difference in light transmission between the two eyepieces is too small to account for the differences seen in the eyepieces, something else must be at work than merely a difference in light transmission. I think that the eyepiece with a narrow AFOV is allowing less light to enter the eye, which allows the eye to attain a deeper level of dark adaptation. Other things being equal - including light transmission - an eye that is more deeply dark adapted will see dimmer objects. And one factor that might allow that eye to go deeper is a narrower AFOV.

Should we really call the eye going through dark adaptation a psychological process? I suppose technically we could, but I think that for the vast majority of people this would be a misleading and confusing use of the term "psychological." Better to avoid it.

Mike





Well ya know, I have a different perspective on this question. I do sometimes chase dim things for sport. My tiny glass options are the both the XOs and the ZAO II set.

I have never ever seen something in the tiny glass that I could not also see in the XWs.

In fact I disagree with the notion of a detection advantage with the narrow fov tiny glass.

To my mind, when you are looking for something at-the-limit, you are looking for a "disturbance in the force" of the general sky background. When you are really homing in on a tiny field, there are all sorts of irregular slight this's and thats's, who knows what they are, they move when you move the scope, they're not on the charts, maybe they're small clouds, maybe they're random universe junk.

But back to my point. You're looking for something. You need a *background pattern*. The larger FOV gives you a *background pattern* so that when you tap the tube or give slight touches on the paddle you can evaluate whether you are seeing a very dim something relative to other things.

In a narrow field you have less to compare with and, I think, object detection is actually a bit harder. A wider field gives a better context so you can say, ah, that's it, that smudge there....(and then rotate the eyepiece to make sure it isn't on your lens).

I guess I would add that the main advantage of my tiny glass ZAO IIs and XOs is that they permit me to join discussions such as these with the benefit of experience. Aside from that if the evil fairy turned my XOs and ZAO IIs into $15 budget plossls it probably wouldn't affect my observing much but if she went after my XWs it would be like gouging out my eyes. So to speak.

Greg N


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Re: Eypiece transmission new [Re: Starman1]
      #5814330 - 04/21/13 10:36 PM

Quote:

Variations in seeing, collimation, thermal issues, etc. are so large compared to the differences in eyepieces, that the eyepieces essentially don't matter. When we discuss these on-axis differences in eyepieces, we are arguing over the penny and ignoring the other 99 cents in the dollar.






I suspect mainly we're discussing which eyepiece is *clean*. Greg N


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Re: Eypiece transmission new [Re: Starman1]
      #5822674 - 04/25/13 05:30 PM

Quote:

Shneor,
Visible what % of the time? Winking in 5% of the time and invisible 95% of the time versus invisible 100% of the time?
Or visible 100% of the time versus 0% of the time?
If the former, it might be possible. If the latter, I'm sorry, I don't buy it. I've never seen this in any scope of any size all the way up to 32".
After spotting the galaxy in the 6mm ZAO did you go back to the 6mm Delos and try again?
I can't tell you how many times I've not seen some detail in the 12.5", walked over to a 28", seen the detail, then returned to the 12.5" to now be able to see the detail I couldn't before.
But I'll grant you that there are slight differences in contrast in eyepieces. How important that is is a matter for the observer to decide.





Don,

It is the former. We didn't see it 100% of the time with the Ethos and at least 25% of the time with the ZAO-II.

At OSP (NELM 7.5+). I saw Hickson 99E 100% with ZAO-II, 75% with Delos and 50% with Ethos.
http://www.faintfuzzies.com/OR-Sept022011-OSP.html

I never saw something 100% of the time with the ZAO-II, which I could not see at all with the Ethos nor Delos. I


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Shneor
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Reged: 03/01/05

Loc: Northern California
Re: Eypiece transmission new [Re: Starman1]
      #5824416 - 04/26/13 01:22 PM

Quote:

Burbidge's Chain:
http://www.astronomy-mall.com/Adventures.In.Deep.Space/burbidge.htm
2 are easy in the 12.5". The 3rd I picked up on a near perfect night. Nearby ESO 540-19 is brighter.

The 4th is invisible in the 12.5" but we picked it up in a nearby 22".
It's brighter than you mentioned, but still very very faint.



You are right about being visible for some percentage of the time vs. not at all, for the mosgt part. But also, you (or at least I) won't see it at all until someone tells me where it is, vs. not seeing it at all. Burbridge's chain, seeing all 4 galaxies, is a good test of transparency and darkness for a 22".
Clears,


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BillP
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Reged: 11/26/06

Loc: Vienna, VA
Re: Eypiece transmission new [Re: gnowellsct]
      #5824484 - 04/26/13 01:53 PM

Quote:

I have never ever seen something in the tiny glass that I could not also see in the XWs.




I have quite often seen things in my tiny glass that I could not see in my fat glass. It also goes without saying that sometimes things can be seen in both but it is much more difficult to see in the fat glass. These differences primarly show themselves on Globs and Planets for me, and is quite repeatable most any evening. Of course though, these differences may also be on other targets but I primarily only observe planets and globs and am not much of celestial smudge guy.

Tiny glass is good, fat glass is good, neither replaces the other. At least this is my experience.


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