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
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
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
...and as I don´t wanna boring you with all that text - finally some pics of course too
Edited by donadani, 10 December 2017 - 12:23 PM.