BST

[buzzlightyear]

Hi all,

I have now purchased the 25mm and 8mm BST starguider EP.

My question is do you unscrew the top of the EP to help with anything or should it be shut tight?

Thanks in advance.

[davedownsouth]

Winding up the rubber bit at the top of the eyepiece gives you more eye relief; if you like that sort of thing 

[John]

The top part of the eyepiece twists up and down to adjust the eye to eye lens distance. If you don't wear glasses you will probably find that towards the top end of it's travel works best. The opposite is the case if you do wear glasses when observing. 

The eye relief of the eyepiece actually stays the same during this but the adjustable top allows each person to find the correct and comfortable placement for their eye.

[davedownsouth]

I thought the distance it wound up meant you got more eye relief?  Think I am going to have to find out what eye relief means

[John]

I thought the distance it wound up meant you got more eye relief?  Think I am going to have to find out what eye relief means

Eye relief is the distance in mm that the eye needs to be from the top lens to see the full field of view of the eyepiece. It's measured from the centre of the eye (top) lens of the eyepiece. It only varies with a variable focal length eyepiece (ie: a zoom) or when you use a barlow lens with the eyepiece as the barlow changes the optical path through the eyepiece pushing the eye relief outwards a bit.

The actual optimum placement of the eye though varies with each person because the contours of their face and their glasses prescription so an adjustable eye cup is useful.

[buzzlightyear]

Thanks guys.

[Charic]

........ I have prescription glasses which I don't wear at the telescope, but for me, I find it most comfortable with the cups in their lowered position, each to their own will be the case. The actual eye relief is fixed,  as John points out above.

The twist up cups only allow stand-off, for the optimum field of view, you can adjust this to your liking  and  then rest your eye socket on the cap (be gentle or the scope will shake?) The other principle use is to offer shade, maybe  shielding your eyes from street lighting, or a neighbours window light?

[buzzlightyear]

Once the weather allows I'll have a play with them

[Caldwell14]

Once the weather allows I'll have a play with them

Nevermind the weather, its the pollution you need to watch

[buzzlightyear]

Sandblast the scope,