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Old 17-06-2018, 11:56 AM
SkyWatch (Dean)
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SkyWatch is offline
 
Join Date: Jan 2013
Location: Adelaide
Posts: 361
Hi Gordon,
They come in 15, 20, 30, 42 and 50mm fl's. The 15 is a 4-element design, and the rest are 5-element.
I have the 42mm version, and it works well in long FL scopes like yours. It is not entirely sharp to the edge, but the longer the FL the better it gets.
One issue to be aware of is that depending which site you read they have a claimed AFOV of 65-68, apart from the 50mm which is claimed 60. However, my 42mm doesn't have a true field stop: the lens retaining ring effectively acts as a field stop, and is around 41.5mm in diameter, but because this is inside the focal plane of the eyepiece it provides a fuzzy edge, and there is no clear field stop when you look through the eyepiece. (The field stop determines the true FOV: TFOV=field stop/focal length x 57.3) This corresponds to an AFOV of around 57, not 65-68 as advertised...
I can't speak for the other focal lengths, but I believe they are generally good value for money in a scope like yours.
My only concern is whether you can move your scope to the vertical with a 2" diagonal. I believe others have said that it hits the base of the mount on the LX90 when trying to go above around 70 or so. This is something to check before you commit to extra eyepieces.
All the best, and happy viewing.

- Dean
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