Eye relieve of BST explorer ED eyepieces?

[YKSE]

On Ebay, the ER is given as 13mm for all the EPs when stated, but I've seen somewhere mentioned as 18mm. This 5mm difference can be of importance of a glass-wearer. Anyone would like to clarify it for me?

[ronin]

At a guess 13mm is from the top of the last glass surface and 18mm is from the optical centre of the last optical lens.

Assuming the diagram StL have displayed is correct and representative and that the last lens is the right hand side one, with it being a doublet and looking as if the edges are substantial then the optical centre could be 5mm below the upper surface.

Unfortunately both are correct, similar the focal length of a telescope is not from the front face or the rear face it is from the optical centre, not of much concern generally on an objective but if building a scope from a lens it is relevant to the tube length for the focuser position.

As an edit: I always thought they were 15mm eye relief when I bought mine. :rolleyes:

[Mark in Macc]

I have the12mm and it has generous eye relief. They are relaxing EPs to use. I think that is one of the reasons they are so popular. Alan at Sky's the Limit might lend you one as a try before you buy.

[ronl]

It does say 13mm ER, I wear glasses myself and I have 4 BST Starguiders and find them

to be very good, and easy and the eye, but that is my personal view of them, others my differ.

[YKSE]

Thanks all for the clarifying info, really appreciate it.

[Stargazer_00]

I'm very surprised if that's all they have as stated eye relief. I'd expect them all to be 18mm+. Second only to Delos in my experience in terms of comfort although I haven't looked through every sort of eyepiece by a long stretch..

More comfortable than ES82/BGO/Plossls for sure.