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Equipment Discussions >> Eyepieces

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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
*****

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
*****

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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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Suburban Maryland, USA
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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ThomasM
sage


Reged: 04/19/09

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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robboski2004
member


Reged: 01/14/08

Re: Eypiece transmission [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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Alvin Huey
Carpal Tunnel
*****

Reged: 10/18/05

Loc: NorCal
Re: Eypiece transmission [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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dscarpa
Post Laureate
*****

Reged: 03/15/08

Loc: San Diego Ca.
Re: Eypiece transmission [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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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission [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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