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Astro Physics 130EDT f/8 - how to really find out if air- or oilspaced?

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#1 donadani

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Posted 10 December 2017 - 07:29 AM

This question is just for curiosity as I´m a big fan of the 130EDT f8 as one of my favorite (maybe THE favorite?) scope in the arsenal and really would like to know some more background info about these great apos. 

 

So does maybe someone know for sure if Astro Physics offered their 130EDT scopes airspaced as well as oilspaced? And if so - how could the difference be seen when looking to the lenses?

 

I read a lot about this topic here and there and my actual understanding is that both options were offered early in EDT product history and changed later to oilspaced only. As some guys mentioned - they were offered to choose with their ordering if they wanna have a oil- or airspaced objective. Another one mentioned he could try an oilspaced scope at the dealer only to find it was not very promising - after that he tested an airspaced one that totaly wowwed him... 

 

When I bought my EDT second hand the preowner told me it is an oilspaced objective - but asking George directly and with reference to the SN - he came back telling me it is an early (first run) airspaced design... so I went with that.

 

Just before some weeks I was offered another 130EDT that was out for sale just for some time and seemed not to get much interest. Maybe because of some minor shortcommings (some dust on the objective, uneven focusser, dent in the dewcap and a scratch in the tube). But these was found in the price that was too good to not taking it and more important: the preowner promised a fantastic optics and was so sure about that - that he offered to take the scope back if it not meets one's expectations. Lucky me - that many people seems to prefere more buying new doublets from China instead of top notch, full apo optics that maybe need some little maintanence smile.gif

 

Of course I asked at AP too if the design is an oil or airspaced one and Christine came back telling me it is an 1996 oilspaced one.

 

So at this point I have two 130EDT proofen by AP that one is airspaced and one oilspaced and should be one of the few persons on the planet who are able to answere the question best... but it´s not that easy...

 

Meanwhile I had the chance to test both optics against each other: at the startest they are absolute identical! and I mean absolute wink.gif

 

At a high (350x) magnification (and only with going high you can see differences in quality in my view!) at Altair they show absolute concentric, nearly identical looking and clearly divided rings on both sides of the focus with only a very fine color impression on the outer ring (intrafocal a bit red / extrafocal a bit blue). Inside focus both show a nice round airy disc with a first diffraction ring, of course without any color at all - so I would call it TEXTBOOK. Surprisingly for me was that I could not see any little difference with both scopes... - I mean that speaks for the quality AP is well known for.

 

But coming back to the original question - how could be seen the difference in air- vs. oilspaced at the glas???

 

I can´t see it! Not even with a green laser shining through the objective. There could not be seen any space between the lenses of the "airspaced" apo. Both are absolutely identical. Only difference I can see is that the coating of the older scope is a bit more reddish compared to a more blue, colder tone on the "newer" one. Next to that the older one has plates from plastic instead of cork for settling the lens package - both plate types are behind the glas - not between! .

 

So finally I can not see a difference other then the mentioned between this "proofen" airspaced and oilspaced 130EDTs. Would be happy if others could add some infos - if these scopes really was offered with both spacing types? and if so how can it be detected?

 

Btw. - of course I cleaned the objective and straighten the dew cap of the second EDT. The focusser meanwhile runs smooth again like butter smile.gif

 

...and as I don´t wanna boring you with all that text - finally some pics of course too wink.gif

 

 

 

 

 

 

cs

Chris


Edited by donadani, 10 December 2017 - 12:23 PM.


#2 Wildetelescope

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Posted 10 December 2017 - 08:57 AM

Shine a green laser at the lens.  If air spaced you should see reflections at each surface,  if oil spaced, not. 

 

Jmd

  

 

Edit.  sorry! I see you tried that!  Not sure what to tell you.  Interested in what others have to say.

 

 


Edited by Wildetelescope, 10 December 2017 - 08:59 AM.


#3 otocycle

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Posted 10 December 2017 - 09:45 AM

The only way I have been able to tell the difference is to illuminate the perimeter of the objective lens group with an ultra violet (UV) light source.   If oil spaced, you will see what looks like two rings of fluorescent material around the edges with a fragmented (capillary ?) texture for the two inner mated surfaces, consistent with the mating of three lenses that form the triplet.

 

I have seen this fluoresced material in both my 1998 AP155 EDF and 2003 AP130 f/8.35 EDT.

 

None of my Takahashi doublets or Meade/Celestron/ES achromats have this property.

 

Unfortunately, I don't have an "air spaced" AP160 to play with and prove my theory !


Edited by otocycle, 10 December 2017 - 09:47 AM.


#4 donadani

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Posted 10 December 2017 - 10:07 AM

Do you mean that tape around the lenses - that is typically for AP? 

 

I think both of them have it - but looking a bit different...

 

 

First run - 130EDT probably air-spaced

 

 

 

 

1996 - 130EDT probably oil-spaced

 

 

 

 



#5 otocycle

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Posted 10 December 2017 - 10:15 AM

Do you mean that tape around the lenses - that is typically for AP? 

 

I think both of them have it - but looking a bit different...

 

No, not the tape.  Shining a UV light at the edges of the inner glasses will fluoresce "residue" around the perimeter.  You can get an idea of the fluorescence by also shining the UV light on the adhesive used to affix cork spacers on later production EDFs.



#6 Jon Isaacs

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Posted 10 December 2017 - 11:35 AM

The easiest way to tell an oil spaced objective from an air spaced objective:

 

Inspect the outside of the objective cell.  An oil spaced objective will have a dip stick..  :)

 

( Sorry but I just couldn't resist the temptation.) 

 

Jon



#7 Jeff B

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Posted 10 December 2017 - 11:36 AM

Most of the oil spaced objectives were wrapped in Kapton tape to hold them together, seal the edges and act as an additional buffer to the cell inner wall.   Looking at the lens edges, they display a distinct reddish-yellow-brown color.  The tape may or may not span the entire edge thickness of the lens.  If not, I see two brownish stripes separated by distinct white stripes (which are the portions of the edges that do not have tape).  This is what I see in your last picture and with my AP oiled triplets.  So I'll guess that in your first pictures, the oil spaced lens in on the right.

 

Nice scopes Chris!!!  

 

Jeff

 

Edit, added a picture

Attached Thumbnails

  • Objective Lens.jpg

Edited by Jeff B, 10 December 2017 - 11:40 AM.


#8 donadani

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Posted 10 December 2017 - 11:53 AM

@otocycle - unfortunately I have no UV light here  - but maybe will organize one if that works... (and if they´re not too expensive!)  - thanks for the hint!

 

 

The easiest way to tell an oil spaced objective from an air spaced objective:

 

Inspect the outside of the objective cell.  An oil spaced objective will have a dip stick..  smile.gif

 

( Sorry but I just couldn't resist the temptation.) 

 

Jon

 

again what learned (dip stick)... wink.gif thanks!

 

Reading your last sentence first I though you suggest to simply dissassemble the objective wink.gif


Edited by donadani, 10 December 2017 - 12:12 PM.


#9 donadani

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Posted 10 December 2017 - 12:02 PM

Nice scopes Chris!!!  

thanks! smile.gif - maybe I should grab one of Matts connection clamps and start to build a bino ;)

 

 

This is what I see in your last picture and with my AP oiled triplets.  So I'll guess that in your first pictures, the oil spaced lens in on the right.

you´re right

 

 

But as you can see in the pic before the other objective seems to have a kind of brownish whatever around the lens too... It´s not as bright shining in the flashlight as the one in the oil filled scope but I thought it´s maybe just a variation of the tape?

 

Your lens looks just a "little" bit bigger - what is it? smile.gif

 

cs

Chris


Edited by donadani, 10 December 2017 - 12:04 PM.


#10 vahe

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Posted 10 December 2017 - 01:43 PM

 

I read a lot about this topic here and there and my actual understanding is that both options were offered early in EDT product history and changed later to oilspaced only. As some guys mentioned - they were offered to choose with their ordering if they wanna have a oil- or airspaced objective. 

 

I can´t see it! Not even with a green laser shining through the objective. There could not be seen any space between the lenses of the "airspaced" apo. Both are absolutely identical. Only difference I can see is that the coating of the older scope is a bit more reddish compared to a more blue, colder tone on the "newer" one. Next to that the older one has plates from plastic instead of cork for settling the lens package - both plate types are behind the glas - not between! .

 

 

A little background information, I have a 155 f/9 EDT, circa 1992 design and was received in January of 1993.

.
Prior to the shipment I received a letter from AP giving me the option of completing the triplet in air space or oil spaced configuration, AP’s recommendation was to go with oil spaced as it was superior to air spaced version for many reasons including 6% more light efficiency due to inevitable internal reflections in the air space design, I decided to go with oil spaced lens.

.
To me the option of going oil vs air space in a single triplet is puzzling, if a lens is optimized for oil spacing separating the lenses with an air space will definitely affect the overall correction of the triplet, I asked for an explanation but never got an answer.

.
In a true air spaced design the interior surfaces of lenses are not identical and therefore can not be converted to oil spaced design so what I am thinking in those early days AP decided to make their lenses with the same internal radiuses allowing them to do either oil or air spaced, if my assumption is correct then the air space must be very very small and invisible, and next to impossible to detect with green laser.

.

Vahe



#11 donadani

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Posted 10 December 2017 - 02:44 PM

vahe thanks for your input! 

 

Had the same thoughts about how AP could offer both designs as option for the enduser?!? normaly airspaced designs use the four further surfaces for an optimized color correction against the cost of slower cooldown and a more labourios manufacturing but this would require another calculation of the design compared with that of the oilspaced one.

 

But just if AP used the same design for both options with a really small gap between the lenses - I would guess it should be possible to see it if a laser beam passes. As I could not see anything like that I just doubt a little bit if the "airspaced" one really is airspaced... but on the other side I can´t see any reason why AP should claim it if it´s not true. Could be an error in the recordings too maybe?



#12 Kent10

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Posted 10 December 2017 - 02:55 PM

Chris, I wonder if you asked this question on the AP Yahoo group https://groups.yahoo...ations/messages  if Roland himself would give you an answer.


#13 donadani

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Posted 10 December 2017 - 03:05 PM

Hi Kent - I have no account there yet and I don´t really like the format (find it a bit confusing...) - hoped the relevant infos will apear here too. But maybe I will later on as I´m really interested in - thanks for the link!

 

cs

Chris


Edited by donadani, 10 December 2017 - 03:05 PM.


#14 Kent10

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Posted 10 December 2017 - 03:08 PM

Roland participates a lot on that yahoo site (I don't like the format either) but not here unfortunately as you know.


#15 Kent10

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Posted 10 December 2017 - 03:09 PM

On the yahoo site, I have it set to send me emails when someone posts so that is pretty convenient as long as you don't mind getting the emails.



#16 Kent10

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Posted 10 December 2017 - 03:12 PM

If you decide you don't want to join, maybe later I can ask the question if someone else hasn't done it already.



#17 donadani

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Posted 10 December 2017 - 03:19 PM

THAT would be too great!!! flowerred.gif



#18 donadani

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Posted 10 December 2017 - 03:33 PM

Just to give you an impression of how I got the scope wink.gif

 

 

how it was offered:

 

 

 

 

how it looked when using a good camera

 

 

 

 

after a (really slight) cleaning

 

 

 

cs

Chris


Edited by donadani, 10 December 2017 - 03:35 PM.


#19 Kent10

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Posted 10 December 2017 - 03:57 PM

Hi Chris,
 
I asked the question on yahoo.  I'll let you know what I find out.  I hope you don't mind me calling you a friend smile.gif.
 
 
Here it is.
 

How to Tell if a Scope is Oil-Spaced or Air-Spaced?

 

Hi all,

 

A friend of mine has two AP 130mm triplets.  From what the sellers have told him, he believes one is oil-spaced and the other air-spaced.  Without taking them apart to check, is there a way to tell for certain which is oil-spaced and which is air-spaced?

 

Thanks very much, Kent



#20 donadani

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Posted 10 December 2017 - 04:05 PM

 

...I hope you don't mind me calling you a friend smile.gif.

you really are!!! :) Great!!! waytogo.gif thank you very much Kent! 

 

Looking forward to any new info.

 

If it´s allowed you could maybe post a link to this thread...  but just an idea.

 

cs

Chris 



#21 vahe

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Posted 10 December 2017 - 09:49 PM

Just a comment, since you did not mention the green laser test I bet everyone reading the post is going to recommend that.

 

Vahe



#22 Jeff B

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Posted 10 December 2017 - 10:02 PM

 

Nice scopes Chris!!!  

thanks! smile.gif - maybe I should grab one of Matts connection clamps and start to build a bino wink.gif

 

 

This is what I see in your last picture and with my AP oiled triplets.  So I'll guess that in your first pictures, the oil spaced lens in on the right.

you´re right

 

 

But as you can see in the pic before the other objective seems to have a kind of brownish whatever around the lens too... It´s not as bright shining in the flashlight as the one in the oil filled scope but I thought it´s maybe just a variation of the tape?

 

Your lens looks just a "little" bit bigger - what is it? smile.gif

 

cs

Chris

 

Chris, a special 152mm F10.

 

Jeff



#23 Kunama

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Posted 10 December 2017 - 10:15 PM

Oh what a lovely pair of binoculars you have there Chris.... bow.gif  after my First Light with the Bino-TSA last night I would throughly recommend turning those into a Binoscope.... 



#24 donadani

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Posted 11 December 2017 - 12:26 AM

Hi Matt - really thought about it when I saw you building your great TSA bino. waytogo.gif  

 

But unfortunately there will not be much improvement for me beause I have a strong "leading" eye. So if looking through a bino there is just only the picture of one eye availible until I willful "switch" to the other eye... but again only one picture then I´m really aware of then. 

 

Before some weeks I curiously tried a 102mm Binoptic Bino of a starfriend - only to find out I prefere the mono version tongue2.gif

 

But if... these scopes would be my first choice for sure! wink.gif



#25 Kunama

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Posted 11 December 2017 - 01:49 AM

Hi Matt - really thought about it when I saw you building your great TSA bino. waytogo.gif  

 

But unfortunately there will not be much improvement for me beause I have a strong "leading" eye. So if looking through a bino there is just only the picture of one eye availible until I willful "switch" to the other eye... but again only one picture then I´m really aware of then. 

 

Before some weeks I curiously tried a 102mm Binoptic Bino of a starfriend - only to find out I prefere the mono version tongue2.gif

 

But if... these scopes would be my first choice for sure! wink.gif

I guess you could send them here to Australia, I don't mind looking after them for you even though they are not Takahashis .... cool.gif




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