Explore Scientific 82 degree 11mm Eyepiece

[johnturley]

I have a full set of the 82 degree Explore Scientific eyepieces with 1.25in barrel (14mm, 11mm, 8.8mm, 6.7mm, and 4.7mm), and fairly pleased with them as a whole, I find them to be a significant step up from the 60 degree Meade Series 5000 both in terms of the wider field and sharper definition. However I find the 11mm to be a bit of an odd man out in so much, while all the the others are approximately parfocal (focusing within about 1mm of each other), the 11mm focuses about 3-4 mm further out. This causes me some problems when using it with my 14in Newtonian to which I have fitted a Baader Steeltrack Diamond focuser, which has just 40mm of travel. I have positioned the focuser such that I can just reach focus with my Canon EOS 6D camera, and all the ES eyepieces apart from the 11mm then require about 38 mm of out focus from that point, but with the 11mm requiring an extra 3-4mm, I need either to use an extension tube, or not fully insert the eyepiece into the focuser.

Is there any particular reason why the 11mm is different from the others, or have I  possibly got a rogue specimen.

John

[pregulla]

According to Ernest's measurements 14mm is the oddball one requiring 4-6mm more inward travel then the rest. So either there is some variation in production or they have changed it over the years for some reason.

Maybe you could use parfocalizing rings to solve this. Not sure how it would work with tapered barrel though.

[alan potts]

It was interesting of that range it was the one Meade never had in their UWA 5000 series, I have a feeling the 11mm was developed after the Meade range, it goes back a good few years now. I had all the Meade ones apart from the 18mm, again here is where ExSc differ from Meade in size, Meade had this as a 1.25inch eyepiece. 30mm was massive, drop it on your foot and you would not walk for a while.

Alan

[johnturley]

18 minutes ago, pregulla said:

According to Ernest's measurements 14mm is the oddball one requiring 4-6mm more inward travel then the rest. So either there is some variation in production or they have changed it over the years for some reason.

Maybe you could use parfocalizing rings to solve this. Not sure how it would work with tapered barrel though.

My 14mm does not require any significant extra inward travel, so maybe there is some variation in production

John