Hi all. I am hoping someone out there might have some information about a 90mm / FL 900mm (f/10) refractor model that used to be sold by the now defunct company - York Optical. In 2003 I purchased the refractor which looks exactly like the current standard achromat type Skywatcher and Saxon 90mm / 900mm, from
I ask because the telescope (which came with a basic EQ mount included) does NOT have a single word, specification, brand name, or technical details anywhere on either the scope or mount. I am assuming that it is a basic chinese made refractor?? A photo is attached (I hope).
Any information appreciated, although I suspect that time and tide has buried the information. Thanks,............
Last edited by BadWolf; 17-08-2021 at 01:35 PM.
Reason: spelling
hello mate a good mate of mine used to work at york about that time here in perth
although he is not an avtive member on IIS any longer he could still answer the question
pat
Pat, if you get a chance to ask him, that would be appreciated. All I really want to know is if the 90mm lens might be perhaps an ED style rather than a basic achromatic. The reason I am curious is that the " no name" York refractor seems to be almost as sharp and as free of chromatic aberration as my Sky Watcher ED 80. Of course, being an f/10, the colour aberration should not be as pronounced as a short focal length?? Maybe?? Thanks, Stewart
A 90mm with an ED lens would have cost over a $1000 back in 2003 and I suspect that it would have also come with a better mount. It looks like an achromatic to me.
Nevertheless, the 90mm F10 achromatic had plenty of fans who said that the colour correction was good.
"Of course, being an f/10, the colour aberration should not be as pronounced as a short focal length?? Maybe?? "
From my scant reading the reduction of chromatism sufficiently is closer to F15. A F15 doublet should be just as good as a triplet of a shorter F/L, regarding achromatism/chromatism anyway. So, at F10 it should have some natural correction occurring.
Hopefully someone will confirm this or correct it.
Thanks Bob. I did not think of the pricing factor. The cost, including EQ mount from York Optical was $850 in 2003 as I recall, so that would likely rule out the lens element being any type of ED glass. Most probably just a decent achromat.
Stewart,
I have a York 80 ED from the same period.
The ED design is clearly marked on the objective outer ring.
I would have thought if your scope was an ED it would have similar markings.
Thanks for the information Ken. Unfortunately my scope has nothing written on the lens element. I have pulled the element out (although the dew shield seems to not come off) and checked, but nothing. probably it is just a cheap Chinese scope from back then/ Maybe York got a bulk deal with someone in China?? Thanks anyway, Stewart
Thanks for the information Ken. Unfortunately my scope has nothing written on the lens element. I have pulled the element out (although the dew shield seems to not come off) and checked, but nothing. probably it is just a cheap Chinese scope from back then/ Maybe York got a bulk deal with someone in China?? Thanks anyway, Stewart
Hello Stewart,
I have a 90/900 achromat myself, a Meade...
But I've only used it with an alt-azimuth, at least once, and after having blackened and flocked it throughout...
The Trapezium and its environs within the Orion nebula were absolutely stunning through it, and at 90x.
It almost meets the Sidgwick standard for colour-correction...
Good information, thanks. While using it on the moon and Jupiter/Saturn, it seems to be virtually free of CA, and apart from a dimmer image, it is nearly as good as my SW ED80 for bright double stars such as Alpha C. Perhaps I got a very good "copy" of the lens?
I was not aware of the Sidgwick / Conrady table regarding achromats and CA, so thanks for pointing me that direction. For now I plan to use it for lunar and planetary observation - probably on those nights when the moon, aided by city lights, turns the night into day! It may also be useful for double stars over the relevant Dawes limit for that aperture.
