Eyecup diameter, Zeiss pockets (1 Viewer)

[Gijs van Ginkel]

Ignatius, post 20,
The Ramsden dynameter is not sitting on the rim of the eycup, but it fits into the eyecup, so it rests directly on the lens with the exit pupil and the eyerelief is measured immediately from the surface of the exit lens of the eyepiece. John Roberts has given a very good image of the Ramsden dynameter found on wikipedia see his post 18 in which he refers to wikipedia and these figures seem crystal clear to me.
Gijs van Ginkel

 

[Ignatius]

Ignatius, post 20,
The Ramsden dynameter is not sitting on the rim of the eycup, but it fits into the eyecup, so it rests directly on the lens with the exit pupil and the eyerelief is measured immediately from the surface of the exit lens of the eyepiece. John Roberts has given a very good image of the Ramsden dynameter found on wikipedia see his post 18 in which he refers to wikipedia and these figures seem crystal clear to me.
Gijs van Ginkel

According to this diagramm from the Wikipedia article referred to the dynameter does indeed sit on top of the eyepiece/eyecup and not on top of the lens. There is nothing in the dynameter that fits into the eyecup. It is flat at both ends.



But obviously I am a bit obtuse, so thank you for your instruction.

 

[henry link]

I'd love to have a dynameter, but they seem to be rare items and expensive I think. For many years I've made do with this simple method of measuring eye relief using only household items. The main difficulty is getting everything leveled and squared up well.

I point the binocular out a window into bright light and line up the eyepiece on a ruler placed on a table top. Then I slide a small white box along the ruler until the exit pupil comes to focus on the flat surface of the box. Then I just measure the distance on the ruler between the back of eyepiece and the box. The last step is to determine how far the eye lens is recessed from the back of the eyepiece and add that to arrive at the total distance between the eye lens surface and the focused exit pupil. I used a tire tread depth gauge for that last step today when measuring the eye relief of the Swarovski 8x30 Habicht in the photo. The result was 12mm (11mm + 1mm recess), the same as Swarovski's spec. If I want to know the "usable" eye relief for eyeglass wearers I just measure from the eyecup at minimum extension and leave out the last step.

 

[Canip]

they seem to be rare items and expensive

Indeed, Henry (mine cost as much as an NL), and in the end, for practical reasons, other methods like yours are absolutely fine, the dynameter is just more convenient to use, but not significantly more precise in the end result.

 

[tenex]

These measurements of yours may exceed actual ER on average because (Western?) eye sockets are typically recessed by a few mm.

Thanks for playing. Actually my measurements undercut the manufacturers'.

Oops, I should have looked back. Let me deftly flip my remark: your measurements may fall short of actual ER on average because eyecups often seem too short now for the increasing ER of eyepieces. I tend to have this problem myself lately.